use hir::{
    Adt, AsAssocItem, HasSource, HirDisplay, Module, PathResolution, Semantics, StructKind, Type,
    TypeInfo,
};
use ide_db::{
    FileId, FxHashMap, FxHashSet, RootDatabase, SnippetCap,
    defs::{Definition, NameRefClass},
    famous_defs::FamousDefs,
    helpers::is_editable_crate,
    path_transform::PathTransform,
    source_change::SourceChangeBuilder,
};
use itertools::Itertools;
use stdx::to_lower_snake_case;
use syntax::{
    Edition, SyntaxKind, SyntaxNode, T, TextRange,
    ast::{
        self, AstNode, BlockExpr, CallExpr, HasArgList, HasGenericParams, HasModuleItem,
        HasTypeBounds,
        edit::{AstNodeEdit, IndentLevel},
        syntax_factory::SyntaxFactory,
    },
    syntax_editor::{Position, SyntaxEditor},
};

use crate::{
    AssistContext, AssistId, Assists,
    utils::{convert_reference_type, expr_fill_default, find_struct_impl},
};

// Assist: generate_function
//
// Adds a stub function with a signature matching the function under the cursor.
//
// ```
// struct Baz;
// fn baz() -> Baz { Baz }
// fn foo() {
//     bar$0("", baz());
// }
//
// ```
// ->
// ```
// struct Baz;
// fn baz() -> Baz { Baz }
// fn foo() {
//     bar("", baz());
// }
//
// fn bar(arg: &'static str, baz: Baz) ${0:-> _} {
//     todo!()
// }
//
// ```
pub(crate) fn generate_function(acc: &mut Assists, ctx: &AssistContext<'_, '_>) -> Option<()> {
    gen_fn(acc, ctx).or_else(|| gen_method(acc, ctx))
}

fn gen_fn(acc: &mut Assists, ctx: &AssistContext<'_, '_>) -> Option<()> {
    let path_expr: ast::PathExpr = ctx.find_node_at_offset()?;
    let call = path_expr.syntax().parent().and_then(ast::CallExpr::cast)?;
    let path = path_expr.path()?;
    let name_ref = path.segment()?.name_ref()?;
    if ctx.sema.resolve_path(&path).is_some() {
        // The function call already resolves, no need to add a function
        return None;
    }

    let fn_name = &*name_ref.text();
    let TargetInfo { target_module, adt_info, target, file } =
        fn_target_info(ctx, path, &call, fn_name)?;

    if let Some(m) = target_module
        && !is_editable_crate(m.krate(ctx.db()), ctx.db())
    {
        return None;
    }
    let make = SyntaxFactory::without_mappings();

    let function_builder =
        FunctionBuilder::from_call(&make, ctx, &call, fn_name, target_module, target, &adt_info)?;
    let text_range = call.syntax().text_range();
    let label = format!("Generate {} function", function_builder.fn_name);
    add_func_to_accumulator(acc, ctx, text_range, function_builder, file, adt_info, label)
}

struct TargetInfo {
    target_module: Option<Module>,
    adt_info: Option<AdtInfo>,
    target: GeneratedFunctionTarget,
    file: FileId,
}

impl TargetInfo {
    fn new(
        target_module: Option<Module>,
        adt_info: Option<AdtInfo>,
        target: GeneratedFunctionTarget,
        file: FileId,
    ) -> Self {
        Self { target_module, adt_info, target, file }
    }
}

fn fn_target_info(
    ctx: &AssistContext<'_, '_>,
    path: ast::Path,
    call: &CallExpr,
    fn_name: &str,
) -> Option<TargetInfo> {
    match path.qualifier() {
        Some(qualifier) => match ctx.sema.resolve_path(&qualifier) {
            Some(hir::PathResolution::Def(hir::ModuleDef::Module(module))) => {
                get_fn_target_info(ctx, Some(module), call.clone())
            }
            Some(hir::PathResolution::Def(hir::ModuleDef::Adt(adt))) => {
                if let hir::Adt::Enum(_) = adt {
                    // Don't suggest generating function if the name starts with an uppercase letter
                    if fn_name.starts_with(char::is_uppercase) {
                        return None;
                    }
                }

                assoc_fn_target_info(ctx, call, adt, fn_name)
            }
            Some(hir::PathResolution::SelfType(impl_)) => {
                let adt = impl_.self_ty(ctx.db()).as_adt()?;
                assoc_fn_target_info(ctx, call, adt, fn_name)
            }
            _ => None,
        },
        _ => get_fn_target_info(ctx, None, call.clone()),
    }
}

fn gen_method(acc: &mut Assists, ctx: &AssistContext<'_, '_>) -> Option<()> {
    let call: ast::MethodCallExpr = ctx.find_node_at_offset()?;
    if ctx.sema.resolve_method_call(&call).is_some() {
        return None;
    }

    let fn_name = call.name_ref()?;
    let receiver_ty = ctx.sema.type_of_expr(&call.receiver()?)?.original().strip_references();
    let adt = receiver_ty.as_adt()?;

    let target_module = adt.module(ctx.sema.db);
    if !is_editable_crate(target_module.krate(ctx.db()), ctx.db()) {
        return None;
    }

    let enclosing_impl = ctx.find_node_at_offset::<ast::Impl>();
    let cursor_impl = enclosing_impl.filter(|impl_| {
        ctx.sema.to_def(impl_).is_some_and(|def| {
            def.self_ty(ctx.sema.db).as_adt() == Some(adt) && def.trait_(ctx.sema.db).is_none()
        })
    });

    let (impl_, file) = if let Some(impl_) = cursor_impl {
        (Some(impl_), ctx.vfs_file_id())
    } else {
        get_adt_source(ctx, &adt, fn_name.text().as_str())?
    };
    let target = get_method_target(ctx, &impl_, &adt)?;

    let make = SyntaxFactory::without_mappings();

    let function_builder = FunctionBuilder::from_method_call(
        &make,
        ctx,
        &call,
        &fn_name,
        receiver_ty,
        target_module,
        target,
    )?;
    let text_range = call.syntax().text_range();
    let adt_info = AdtInfo::new(adt, impl_.is_some());
    let label = format!("Generate {} method", function_builder.fn_name);
    add_func_to_accumulator(acc, ctx, text_range, function_builder, file, Some(adt_info), label)
}

fn add_func_to_accumulator(
    acc: &mut Assists,
    ctx: &AssistContext<'_, '_>,
    text_range: TextRange,
    function_builder: FunctionBuilder,
    file: FileId,
    adt_info: Option<AdtInfo>,
    label: String,
) -> Option<()> {
    acc.add(AssistId::generate("generate_function"), label, text_range, |edit| {
        let target = function_builder.target.clone();
        let snippet_cap = ctx.config.snippet_cap;

        if let Some(adt) = adt_info
            .and_then(|adt_info| if adt_info.impl_exists { None } else { Some(adt_info.adt) })
        {
            target.insert_impl_at(edit, file, ctx, &function_builder, adt, snippet_cap);
        } else {
            target.insert_fn_at(edit, file, &function_builder, snippet_cap);
        }
    })
}

fn get_adt_source(
    ctx: &AssistContext<'_, '_>,
    adt: &hir::Adt,
    fn_name: &str,
) -> Option<(Option<ast::Impl>, FileId)> {
    let range = adt.source(ctx.sema.db)?.syntax().original_file_range_rooted(ctx.sema.db);

    let file = ctx.sema.parse(range.file_id);
    let adt_source =
        ctx.sema.find_node_at_offset_with_macros(file.syntax(), range.range.start())?;
    find_struct_impl(ctx, &adt_source, &[fn_name.to_owned()])
        .map(|impl_| (impl_, range.file_id.file_id(ctx.db())))
}

struct FunctionBuilder {
    target: GeneratedFunctionTarget,
    fn_name: ast::Name,
    generic_param_list: Option<ast::GenericParamList>,
    where_clause: Option<ast::WhereClause>,
    params: ast::ParamList,
    fn_body: BlockExpr,
    ret_type: Option<ast::RetType>,
    should_focus_return_type: bool,
    visibility: Visibility,
    is_async: bool,
    target_edition: Edition,
}

impl FunctionBuilder {
    /// Prepares a generated function that matches `call`.
    /// The function is generated in `target_module` or next to `call`
    fn from_call(
        make: &SyntaxFactory,
        ctx: &AssistContext<'_, '_>,
        call: &ast::CallExpr,
        fn_name: &str,
        target_module: Option<Module>,
        target: GeneratedFunctionTarget,
        adt_info: &Option<AdtInfo>,
    ) -> Option<Self> {
        let target_module =
            target_module.or_else(|| ctx.sema.scope(target.syntax()).map(|it| it.module()))?;
        let target_edition = target_module.krate(ctx.db()).edition(ctx.db());

        let current_module = ctx.sema.scope(call.syntax())?.module();
        let visibility = calculate_necessary_visibility(current_module, target_module, ctx);
        let fn_name = make.name(fn_name);
        let mut necessary_generic_params = FxHashSet::default();
        let params = fn_args(
            make,
            ctx,
            target_module,
            ast::CallableExpr::Call(call.clone()),
            &mut necessary_generic_params,
        )?;

        let await_expr = call.syntax().parent().and_then(ast::AwaitExpr::cast);
        let is_async = await_expr.is_some();

        let ret_type;
        let should_focus_return_type;
        let fn_body;

        // If generated function has the name "new" and is an associated function, we generate fn body
        // as a constructor and assume a "Self" return type.
        if let Some(body) =
            make_fn_body_as_new_function(make, ctx, &fn_name.text(), adt_info, target_edition)
        {
            ret_type = Some(make.ret_type(make.ty_path(make.ident_path("Self")).into()));
            should_focus_return_type = false;
            fn_body = body;
        } else {
            let expr_for_ret_ty = await_expr.map_or_else(|| call.clone().into(), |it| it.into());
            (ret_type, should_focus_return_type) = make_return_type(
                make,
                ctx,
                &expr_for_ret_ty,
                target_module,
                &mut necessary_generic_params,
            );
            let placeholder_expr = expr_fill_default(ctx.config);
            fn_body = make.block_expr(vec![], Some(placeholder_expr));
        };

        let (generic_param_list, where_clause) =
            fn_generic_params(make, ctx, necessary_generic_params, &target)?;

        Some(Self {
            target,
            fn_name,
            generic_param_list,
            where_clause,
            params,
            fn_body,
            ret_type,
            should_focus_return_type,
            visibility,
            is_async,
            target_edition,
        })
    }

    fn from_method_call(
        make: &SyntaxFactory,
        ctx: &AssistContext<'_, '_>,
        call: &ast::MethodCallExpr,
        name: &ast::NameRef,
        receiver_ty: Type<'_>,
        target_module: Module,
        target: GeneratedFunctionTarget,
    ) -> Option<Self> {
        let target_edition = target_module.krate(ctx.db()).edition(ctx.db());

        let current_module = ctx.sema.scope(call.syntax())?.module();
        let visibility = calculate_necessary_visibility(current_module, target_module, ctx);

        let fn_name = make.name(name.ident_token()?.text());
        let mut necessary_generic_params = FxHashSet::default();
        necessary_generic_params.extend(receiver_ty.generic_params(ctx.db()));
        let params = fn_args(
            make,
            ctx,
            target_module,
            ast::CallableExpr::MethodCall(call.clone()),
            &mut necessary_generic_params,
        )?;

        let await_expr = call.syntax().parent().and_then(ast::AwaitExpr::cast);
        let is_async = await_expr.is_some();

        let expr_for_ret_ty = await_expr.map_or_else(|| call.clone().into(), |it| it.into());
        let (ret_type, should_focus_return_type) = make_return_type(
            make,
            ctx,
            &expr_for_ret_ty,
            target_module,
            &mut necessary_generic_params,
        );

        let (generic_param_list, where_clause) =
            fn_generic_params(make, ctx, necessary_generic_params, &target)?;

        let placeholder_expr = expr_fill_default(ctx.config);
        let fn_body = make.block_expr(vec![], Some(placeholder_expr));

        Some(Self {
            target,
            fn_name,
            generic_param_list,
            where_clause,
            params,
            fn_body,
            ret_type,
            should_focus_return_type,
            visibility,
            is_async,
            target_edition,
        })
    }

    fn render(&self, make: &SyntaxFactory) -> ast::Fn {
        let visibility = match self.visibility {
            Visibility::None => None,
            Visibility::Crate => Some(make.visibility_pub_crate()),
            Visibility::Pub => Some(make.visibility_pub()),
        };
        let type_params =
            self.generic_param_list.clone().filter(|list| list.generic_params().next().is_some());
        make.fn_(
            None,
            visibility,
            self.fn_name.clone(),
            type_params,
            self.where_clause.clone(),
            self.params.clone(),
            self.fn_body.clone(),
            self.ret_type.clone(),
            self.is_async,
            false, // FIXME : const and unsafe are not handled yet.
            false,
            false,
        )
    }
}

/// Makes an optional return type along with whether the return type should be focused by the cursor.
/// If we cannot infer what the return type should be, we create a placeholder type.
///
/// The rule for whether we focus a return type or not (and thus focus the function body),
/// is rather simple:
/// * If we could *not* infer what the return type should be, focus it (so the user can fill-in
///   the correct return type).
/// * If we could infer the return type, don't focus it (and thus focus the function body) so the
///   user can change the `todo!` function body.
fn make_return_type(
    make: &SyntaxFactory,
    ctx: &AssistContext<'_, '_>,
    expr: &ast::Expr,
    target_module: Module,
    necessary_generic_params: &mut FxHashSet<hir::GenericParam>,
) -> (Option<ast::RetType>, bool) {
    let (ret_ty, should_focus_return_type) =
        match ctx.sema.type_of_expr(expr).map(TypeInfo::original) {
            Some(ty) if ty.is_unknown() => (Some(make.ty_placeholder()), true),
            None => (Some(make.ty_placeholder()), true),
            Some(ty) if ty.is_unit() => (None, false),
            Some(ty) => {
                necessary_generic_params.extend(ty.generic_params(ctx.db()));
                let rendered = ty.display_source_code(ctx.db(), target_module.into(), true);
                match rendered {
                    Ok(rendered) => (Some(make.ty(&rendered)), false),
                    Err(_) => (Some(make.ty_placeholder()), true),
                }
            }
        };
    let ret_type = ret_ty.map(|ty| make.ret_type(ty));
    (ret_type, should_focus_return_type)
}

fn make_fn_body_as_new_function(
    make: &SyntaxFactory,
    ctx: &AssistContext<'_, '_>,
    fn_name: &str,
    adt_info: &Option<AdtInfo>,
    edition: Edition,
) -> Option<ast::BlockExpr> {
    if fn_name != "new" {
        return None;
    };
    let adt_info = adt_info.as_ref()?;

    let path_self = make.ident_path("Self");
    let placeholder_expr = expr_fill_default(ctx.config);
    let tail_expr = if let Some(strukt) = adt_info.adt.as_struct() {
        match strukt.kind(ctx.db()) {
            StructKind::Record => {
                let fields = strukt
                    .fields(ctx.db())
                    .iter()
                    .map(|field| {
                        make.record_expr_field(
                            make.name_ref(&format!(
                                "{}",
                                field.name(ctx.db()).display(ctx.db(), edition)
                            )),
                            Some(placeholder_expr.clone()),
                        )
                    })
                    .collect::<Vec<_>>();

                make.record_expr(path_self, make.record_expr_field_list(fields)).into()
            }
            StructKind::Tuple => {
                let args = strukt
                    .fields(ctx.db())
                    .iter()
                    .map(|_| placeholder_expr.clone())
                    .collect::<Vec<_>>();

                make.expr_call(make.expr_path(path_self), make.arg_list(args)).into()
            }
            StructKind::Unit => make.expr_path(path_self),
        }
    } else {
        placeholder_expr
    };

    let fn_body = make.block_expr(vec![], Some(tail_expr));
    Some(fn_body)
}

fn get_fn_target_info(
    ctx: &AssistContext<'_, '_>,
    target_module: Option<Module>,
    call: CallExpr,
) -> Option<TargetInfo> {
    let (target, file) = get_fn_target(ctx, target_module, call)?;
    Some(TargetInfo::new(target_module, None, target, file))
}

fn get_fn_target(
    ctx: &AssistContext<'_, '_>,
    target_module: Option<Module>,
    call: CallExpr,
) -> Option<(GeneratedFunctionTarget, FileId)> {
    let mut file = ctx.vfs_file_id();
    let target = match target_module {
        Some(target_module) => {
            let (in_file, target) = next_space_for_fn_in_module(ctx.db(), target_module);
            file = in_file;
            target
        }
        None => next_space_for_fn_after_call_site(ast::CallableExpr::Call(call))?,
    };
    Some((target, file))
}

fn get_method_target(
    ctx: &AssistContext<'_, '_>,
    impl_: &Option<ast::Impl>,
    adt: &Adt,
) -> Option<GeneratedFunctionTarget> {
    let target = match impl_ {
        Some(impl_) => GeneratedFunctionTarget::InImpl(impl_.clone()),
        None => GeneratedFunctionTarget::AfterItem(adt.source(ctx.sema.db)?.syntax().value.clone()),
    };
    Some(target)
}

fn assoc_fn_target_info(
    ctx: &AssistContext<'_, '_>,
    call: &CallExpr,
    adt: hir::Adt,
    fn_name: &str,
) -> Option<TargetInfo> {
    let current_module = ctx.sema.scope(call.syntax())?.module();
    let module = adt.module(ctx.sema.db);
    let target_module = if current_module == module { None } else { Some(module) };
    if current_module.krate(ctx.db()) != module.krate(ctx.db()) {
        return None;
    }
    let (impl_, file) = get_adt_source(ctx, &adt, fn_name)?;
    let target = get_method_target(ctx, &impl_, &adt)?;
    let adt_info = AdtInfo::new(adt, impl_.is_some());
    Some(TargetInfo::new(target_module, Some(adt_info), target, file))
}

#[derive(Clone)]
enum GeneratedFunctionTarget {
    AfterItem(SyntaxNode),
    InEmptyItemList(SyntaxNode),
    InImpl(ast::Impl),
}

impl GeneratedFunctionTarget {
    fn syntax(&self) -> &SyntaxNode {
        match self {
            GeneratedFunctionTarget::AfterItem(it) => it,
            GeneratedFunctionTarget::InEmptyItemList(it) => it,
            GeneratedFunctionTarget::InImpl(it) => it.syntax(),
        }
    }

    fn parent(&self) -> SyntaxNode {
        match self {
            GeneratedFunctionTarget::AfterItem(it) => it.parent().expect("item without parent"),
            GeneratedFunctionTarget::InEmptyItemList(it) => it.clone(),
            GeneratedFunctionTarget::InImpl(it) => it.syntax().clone(),
        }
    }

    fn insert_impl_at(
        &self,
        edit: &mut SourceChangeBuilder,
        file: FileId,
        ctx: &AssistContext<'_, '_>,
        function_builder: &FunctionBuilder,
        adt: Adt,
        cap: Option<SnippetCap>,
    ) {
        let editor = edit.make_editor(self.syntax());

        match self {
            GeneratedFunctionTarget::AfterItem(item) => {
                let position = if item.parent().is_some() {
                    Position::after(item)
                } else {
                    Position::first_child_of(item)
                };

                let indent = IndentLevel::from_node(item);
                insert_rendered_impl(
                    &editor,
                    edit,
                    ctx,
                    function_builder,
                    adt,
                    position,
                    indent,
                    indent,
                    cap,
                );
            }
            GeneratedFunctionTarget::InEmptyItemList(item_list) => {
                let insert_after =
                    item_list.children_with_tokens().find_or_first(|child| child.kind() == T!['{']);
                let position = match insert_after {
                    Some(child) => Position::after(child),
                    None => Position::first_child_of(item_list),
                };

                let indent = IndentLevel::from_node(item_list);
                let leading_indent = indent + 1;
                insert_rendered_impl(
                    &editor,
                    edit,
                    ctx,
                    function_builder,
                    adt,
                    position,
                    indent,
                    leading_indent,
                    cap,
                );
            }
            GeneratedFunctionTarget::InImpl(_) => {
                unreachable!("can't insert an impl inside an impl")
            }
        }
        edit.add_file_edits(file, editor);
    }

    fn insert_fn_at(
        &self,
        edit: &mut SourceChangeBuilder,
        file: FileId,
        function_builder: &FunctionBuilder,
        cap: Option<SnippetCap>,
    ) {
        let editor = edit.make_editor(self.syntax());
        let make = editor.make();

        match self {
            GeneratedFunctionTarget::AfterItem(item) => {
                let position = if item.parent().is_some() {
                    Position::after(item)
                } else {
                    Position::first_child_of(item)
                };

                let indent = IndentLevel::from_node(item);
                insert_rendered_fn(
                    &editor,
                    edit,
                    function_builder,
                    position,
                    indent,
                    format!("\n\n{indent}"),
                    None,
                    cap,
                );
            }
            GeneratedFunctionTarget::InEmptyItemList(item_list) => {
                let insert_after =
                    item_list.children_with_tokens().find_or_first(|child| child.kind() == T!['{']);
                let position = match insert_after {
                    Some(child) => Position::after(child),
                    None => Position::first_child_of(item_list),
                };

                let indent = IndentLevel::from_node(item_list);
                let leading_indent = indent + 1;
                insert_rendered_fn(
                    &editor,
                    edit,
                    function_builder,
                    position,
                    leading_indent,
                    format!("\n{leading_indent}"),
                    Some(format!("\n{indent}")),
                    cap,
                );
            }
            GeneratedFunctionTarget::InImpl(impl_) => {
                let leading_indent = impl_.indent_level() + 1;

                if let Some(item_list) = impl_.assoc_item_list() {
                    let insert_after_item = item_list.assoc_items().last();
                    let insert_after = item_list
                        .assoc_items()
                        .last()
                        .map(|it| it.syntax().clone().into())
                        .or_else(|| {
                            item_list
                                .syntax()
                                .children_with_tokens()
                                .find_or_first(|child| child.kind() == T!['{'])
                        });
                    let position = match insert_after {
                        Some(child) => Position::after(child),
                        None => Position::first_child_of(item_list.syntax()),
                    };
                    let indent = impl_.indent_level();
                    let leading_ws = if insert_after_item.is_some() {
                        format!("\n\n{leading_indent}")
                    } else {
                        format!("\n{leading_indent}")
                    };
                    let trailing_ws = insert_after_item.is_none().then(|| format!("\n{indent}"));
                    insert_rendered_fn(
                        &editor,
                        edit,
                        function_builder,
                        position,
                        leading_indent,
                        leading_ws,
                        trailing_ws,
                        cap,
                    );
                } else {
                    let func = function_builder.render(make).indent(leading_indent);
                    let item_list = make.assoc_item_list([func.into()]);
                    if let Some(fn_) = item_list.syntax().descendants().find_map(ast::Fn::cast) {
                        add_generated_fn_annotation(&editor, edit, function_builder, &fn_, cap);
                    }
                    editor.insert(Position::last_child_of(impl_.syntax()), item_list.syntax());
                }
            }
        }
        edit.add_file_edits(file, editor);
    }
}

fn insert_rendered_impl(
    editor: &SyntaxEditor,
    edit: &mut SourceChangeBuilder,
    ctx: &AssistContext<'_, '_>,
    function_builder: &FunctionBuilder,
    adt: Adt,
    position: Position,
    impl_indent: IndentLevel,
    leading_ws_indent: IndentLevel,
    cap: Option<SnippetCap>,
) {
    let make = editor.make();
    let leading_ws = make.whitespace(&format!("\n{leading_ws_indent}"));
    let name = make.ty_path(make.ident_path(&format!(
        "{}",
        adt.name(ctx.db()).display(ctx.db(), function_builder.target_edition)
    )));

    // FIXME: adt may have generic params.
    let fn_ = function_builder.render(make).indent(IndentLevel(1));
    let impl_ =
        make.impl_(None, None, None, name.into(), None, Some(make.assoc_item_list([fn_.into()])));
    let impl_ = impl_.indent(impl_indent);
    if let Some(fn_) = impl_.syntax().descendants().find_map(ast::Fn::cast) {
        add_generated_fn_annotation(editor, edit, function_builder, &fn_, cap);
    }

    editor.insert_all(position, vec![leading_ws.into(), impl_.syntax().clone().into()]);
}

fn insert_rendered_fn(
    editor: &SyntaxEditor,
    edit: &mut SourceChangeBuilder,
    function_builder: &FunctionBuilder,
    position: Position,
    indent: IndentLevel,
    leading_ws: String,
    trailing_ws: Option<String>,
    cap: Option<SnippetCap>,
) {
    let make = editor.make();
    let leading_ws = make.whitespace(&leading_ws);
    let func = function_builder.render(make).indent(indent);
    add_generated_fn_annotation(editor, edit, function_builder, &func, cap);

    let mut elements = vec![leading_ws.into(), func.syntax().clone().into()];
    if let Some(trailing_ws) = trailing_ws {
        elements.push(make.whitespace(&trailing_ws).into());
    }
    editor.insert_all(position, elements);
}

fn add_generated_fn_annotation(
    editor: &SyntaxEditor,
    edit: &mut SourceChangeBuilder,
    function_builder: &FunctionBuilder,
    fn_: &ast::Fn,
    cap: Option<SnippetCap>,
) {
    let Some(cap) = cap else { return };

    let annotation = edit.make_placeholder_snippet(cap);
    if function_builder.should_focus_return_type
        && let Some(ret_type) = fn_.ret_type()
    {
        editor.add_annotation(ret_type.syntax(), annotation);
    } else if let Some(tail_expr) = fn_.body().and_then(|body| body.tail_expr()) {
        editor.add_annotation(tail_expr.syntax(), annotation);
    }
}

struct AdtInfo {
    adt: hir::Adt,
    impl_exists: bool,
}

impl AdtInfo {
    fn new(adt: Adt, impl_exists: bool) -> Self {
        Self { adt, impl_exists }
    }
}

/// Computes parameter list for the generated function.
fn fn_args(
    make: &SyntaxFactory,
    ctx: &AssistContext<'_, '_>,
    target_module: Module,
    call: ast::CallableExpr,
    necessary_generic_params: &mut FxHashSet<hir::GenericParam>,
) -> Option<ast::ParamList> {
    let mut arg_names = Vec::new();
    let mut arg_types = Vec::new();
    for arg in call.arg_list()?.args() {
        arg_names.push(fn_arg_name(&ctx.sema, &arg));
        arg_types.push(fn_arg_type(ctx, target_module, &arg, necessary_generic_params));
    }
    deduplicate_arg_names(&mut arg_names);
    let params = arg_names
        .into_iter()
        .zip(arg_types)
        .map(|(name, ty)| make.param(make.simple_ident_pat(make.name(&name)).into(), make.ty(&ty)));

    Some(make.param_list(
        match call {
            ast::CallableExpr::Call(_) => None,
            ast::CallableExpr::MethodCall(_) => Some(make.self_param()),
        },
        params,
    ))
}

/// Gets parameter bounds and where predicates in scope and filters out irrelevant ones. Returns
/// `None` when it fails to get scope information.
///
/// See comment on `filter_unnecessary_bounds()` for what bounds we consider relevant.
///
/// NOTE: Generic parameters returned from this function may cause name clash at `target`. We don't
/// currently do anything about it because it's actually easy to resolve it after the assist: just
/// use the Rename functionality.
fn fn_generic_params(
    make: &SyntaxFactory,
    ctx: &AssistContext<'_, '_>,
    necessary_params: FxHashSet<hir::GenericParam>,
    target: &GeneratedFunctionTarget,
) -> Option<(Option<ast::GenericParamList>, Option<ast::WhereClause>)> {
    if necessary_params.is_empty() {
        // Not really needed but fast path.
        return Some((None, None));
    }

    // 1. Get generic parameters (with bounds) and where predicates in scope.
    let (generic_params, where_preds) = params_and_where_preds_in_scope(ctx);

    // 2. Extract type parameters included in each bound.
    let mut generic_params = generic_params
        .into_iter()
        .filter_map(|it| compute_contained_params_in_generic_param(ctx, it))
        .collect();
    let mut where_preds = where_preds
        .into_iter()
        .filter_map(|it| compute_contained_params_in_where_pred(ctx, it))
        .collect();

    // 3. Filter out unnecessary bounds.
    filter_unnecessary_bounds(&mut generic_params, &mut where_preds, necessary_params);
    filter_bounds_in_scope(&mut generic_params, &mut where_preds, ctx, target);

    let source_scope = generic_params.first().and_then(|param| ctx.sema.scope(param.node.syntax()));
    let target_scope = source_scope.as_ref().and_then(|_| ctx.sema.scope(&target.parent()));

    let generic_params: Vec<ast::GenericParam> =
        generic_params.into_iter().map(|it| it.node).collect();
    let where_preds: Vec<ast::WherePred> = where_preds.into_iter().map(|it| it.node).collect();

    let (generic_params, where_preds) = if let Some(source_scope) = source_scope
        && let Some(target_scope) = target_scope
        && source_scope.module() != target_scope.module()
    {
        // 4. Rewrite paths
        let transform = PathTransform::generic_transformation(&target_scope, &source_scope);
        let generic_params = generic_params.iter().map(|it| it.syntax());
        let where_preds = where_preds.iter().map(|it| it.syntax());
        transform
            .apply_all(generic_params.chain(where_preds))
            .into_iter()
            .filter_map(|it| {
                if let Some(it) = ast::GenericParam::cast(it.clone()) {
                    Some(either::Either::Left(it))
                } else {
                    ast::WherePred::cast(it).map(either::Either::Right)
                }
            })
            .partition_map(|it| it)
    } else {
        (generic_params, where_preds)
    };

    let generic_param_list = make.generic_param_list(generic_params);
    let where_clause =
        if where_preds.is_empty() { None } else { Some(make.where_clause(where_preds)) };

    Some((Some(generic_param_list), where_clause))
}

fn params_and_where_preds_in_scope(
    ctx: &AssistContext<'_, '_>,
) -> (Vec<ast::GenericParam>, Vec<ast::WherePred>) {
    let Some(body) = containing_body(ctx) else {
        return Default::default();
    };

    let mut generic_params = Vec::new();
    let mut where_clauses = Vec::new();

    // There are two items where generic parameters currently in scope may be declared: the item
    // the cursor is at, and its parent (if any).
    //
    // We handle parent first so that their generic parameters appear first in the generic
    // parameter list of the function we're generating.
    let db = ctx.db();
    if let Some(parent) = body.as_assoc_item(db).map(|it| it.container(db)) {
        match parent {
            hir::AssocItemContainer::Impl(it) => {
                let (params, clauses) = get_bounds_in_scope(ctx, it);
                generic_params.extend(params);
                where_clauses.extend(clauses);
            }
            hir::AssocItemContainer::Trait(it) => {
                let (params, clauses) = get_bounds_in_scope(ctx, it);
                generic_params.extend(params);
                where_clauses.extend(clauses);
            }
        }
    }

    // Other defs with body may inherit generic parameters from its parent, but never have their
    // own generic parameters.
    if let hir::DefWithBody::Function(it) = body {
        let (params, clauses) = get_bounds_in_scope(ctx, it);
        generic_params.extend(params);
        where_clauses.extend(clauses);
    }

    (generic_params, where_clauses)
}

fn containing_body(ctx: &AssistContext<'_, '_>) -> Option<hir::DefWithBody> {
    let item: ast::Item = ctx.find_node_at_offset()?;
    let def = match item {
        ast::Item::Fn(it) => ctx.sema.to_def(&it)?.into(),
        ast::Item::Const(it) => ctx.sema.to_def(&it)?.into(),
        ast::Item::Static(it) => ctx.sema.to_def(&it)?.into(),
        _ => return None,
    };
    Some(def)
}

fn get_bounds_in_scope<D>(
    ctx: &AssistContext<'_, '_>,
    def: D,
) -> (impl Iterator<Item = ast::GenericParam>, impl Iterator<Item = ast::WherePred>)
where
    D: HasSource,
    D::Ast: HasGenericParams,
{
    // This function should be only called with `Impl`, `Trait`, or `Function`, for which it's
    // infallible to get source ast.
    let node = ctx.sema.source(def).expect("definition's source couldn't be found").value;
    let generic_params = node.generic_param_list().into_iter().flat_map(|it| it.generic_params());
    let where_clauses = node.where_clause().into_iter().flat_map(|it| it.predicates());
    (generic_params, where_clauses)
}

#[derive(Debug)]
struct ParamBoundWithParams {
    node: ast::GenericParam,
    /// Generic parameter `node` introduces.
    ///
    /// ```text
    /// impl<T> S<T> {
    ///     fn f<U: Trait<T>>() {}
    ///          ^ this
    /// }
    /// ```
    ///
    /// `U` in this example.
    self_ty_param: hir::GenericParam,
    /// Generic parameters contained in the trait reference of this bound.
    ///
    /// ```text
    /// impl<T> S<T> {
    ///     fn f<U: Trait<T>>() {}
    ///             ^^^^^^^^ params in this part
    /// }
    /// ```
    ///
    /// `T` in this example.
    other_params: FxHashSet<hir::GenericParam>,
}

#[derive(Debug)]
struct WherePredWithParams {
    node: ast::WherePred,
    /// Generic parameters contained in the "self type" of this where predicate.
    ///
    /// ```text
    /// Struct<T, U>: Trait<T, Assoc = V>,
    /// ^^^^^^^^^^^^ params in this part
    /// ```
    ///
    /// `T` and `U` in this example.
    self_ty_params: FxHashSet<hir::GenericParam>,
    /// Generic parameters contained in the trait reference of this where predicate.
    ///
    /// ```text
    /// Struct<T, U>: Trait<T, Assoc = V>,
    ///               ^^^^^^^^^^^^^^^^^^^ params in this part
    /// ```
    ///
    /// `T` and `V` in this example.
    other_params: FxHashSet<hir::GenericParam>,
}

fn compute_contained_params_in_generic_param(
    ctx: &AssistContext<'_, '_>,
    node: ast::GenericParam,
) -> Option<ParamBoundWithParams> {
    match &node {
        ast::GenericParam::TypeParam(ty) => {
            let self_ty_param = ctx.sema.to_def(ty)?.into();

            let other_params = ty
                .type_bound_list()
                .into_iter()
                .flat_map(|it| it.bounds())
                .flat_map(|bound| bound.syntax().descendants())
                .filter_map(|node| filter_generic_params(ctx, node))
                .collect();

            Some(ParamBoundWithParams { node, self_ty_param, other_params })
        }
        ast::GenericParam::ConstParam(ct) => {
            let self_ty_param = ctx.sema.to_def(ct)?.into();
            Some(ParamBoundWithParams { node, self_ty_param, other_params: FxHashSet::default() })
        }
        ast::GenericParam::LifetimeParam(_) => {
            // FIXME: It might be a good idea to handle lifetime parameters too.
            None
        }
    }
}

fn compute_contained_params_in_where_pred(
    ctx: &AssistContext<'_, '_>,
    node: ast::WherePred,
) -> Option<WherePredWithParams> {
    let self_ty = node.ty()?;
    let bound_list = node.type_bound_list()?;

    let self_ty_params = self_ty
        .syntax()
        .descendants()
        .filter_map(|node| filter_generic_params(ctx, node))
        .collect();

    let other_params = bound_list
        .bounds()
        .flat_map(|bound| bound.syntax().descendants())
        .filter_map(|node| filter_generic_params(ctx, node))
        .collect();

    Some(WherePredWithParams { node, self_ty_params, other_params })
}

fn filter_generic_params(
    ctx: &AssistContext<'_, '_>,
    node: SyntaxNode,
) -> Option<hir::GenericParam> {
    let path = ast::Path::cast(node)?;
    match ctx.sema.resolve_path(&path)? {
        PathResolution::TypeParam(it) => Some(it.into()),
        PathResolution::ConstParam(it) => Some(it.into()),
        _ => None,
    }
}

/// Filters out irrelevant bounds from `generic_params` and `where_preds`.
///
/// Say we have a trait bound `Struct<T>: Trait<U>`. Given `necessary_params`, when is it relevant
/// and when not? Some observations:
/// - When `necessary_params` contains `T`, it's likely that we want this bound, but now we have
///   an extra param to consider: `U`.
/// - On the other hand, when `necessary_params` contains `U` (but not `T`), then it's unlikely
///   that we want this bound because it doesn't really constrain `U`.
///
/// (FIXME?: The latter clause might be overstating. We may want to include the bound if the self
/// type does *not* include generic params at all - like `Option<i32>: From<U>`)
///
/// Can we make this a bit more formal? Let's define "dependency" between generic parameters and
/// trait bounds:
/// - A generic parameter `T` depends on a trait bound if `T` appears in the self type (i.e. left
///   part) of the bound.
/// - A trait bound depends on a generic parameter `T` if `T` appears in the bound.
///
/// Using the notion, what we want is all the bounds that params in `necessary_params`
/// *transitively* depend on!
///
/// Now it's not hard to solve: we build a dependency graph and compute all reachable nodes from
/// nodes that represent params in `necessary_params` by usual and boring DFS.
///
/// The time complexity is O(|generic_params| + |where_preds| + |necessary_params|).
fn filter_unnecessary_bounds(
    generic_params: &mut Vec<ParamBoundWithParams>,
    where_preds: &mut Vec<WherePredWithParams>,
    necessary_params: FxHashSet<hir::GenericParam>,
) {
    // All `self_ty_param` should be unique as they were collected from `ast::GenericParamList`s.
    let param_map: FxHashMap<hir::GenericParam, usize> =
        generic_params.iter().map(|it| it.self_ty_param).zip(0..).collect();
    let param_count = param_map.len();
    let generic_params_upper_bound = param_count + generic_params.len();
    let node_count = generic_params_upper_bound + where_preds.len();

    // | node index range                        | what the node represents |
    // |-----------------------------------------|--------------------------|
    // | 0..param_count                          | generic parameter        |
    // | param_count..generic_params_upper_bound | `ast::GenericParam`      |
    // | generic_params_upper_bound..node_count  | `ast::WherePred`         |
    let mut graph = Graph::new(node_count);
    for (pred, pred_idx) in generic_params.iter().zip(param_count..) {
        let param_idx = param_map[&pred.self_ty_param];
        graph.add_edge(param_idx, pred_idx);
        graph.add_edge(pred_idx, param_idx);

        for param in &pred.other_params {
            let param_idx = param_map[param];
            graph.add_edge(pred_idx, param_idx);
        }
    }
    for (pred, pred_idx) in where_preds.iter().zip(generic_params_upper_bound..) {
        for param in &pred.self_ty_params {
            let param_idx = param_map[param];
            graph.add_edge(param_idx, pred_idx);
            graph.add_edge(pred_idx, param_idx);
        }
        for param in &pred.other_params {
            let param_idx = param_map[param];
            graph.add_edge(pred_idx, param_idx);
        }
    }

    let starting_nodes = necessary_params.iter().flat_map(|param| param_map.get(param).copied());
    let reachable = graph.compute_reachable_nodes(starting_nodes);

    // Not pretty, but effective. If only there were `Vec::retain_index()`...
    let mut idx = param_count;
    generic_params.retain(|_| {
        idx += 1;
        reachable[idx - 1]
    });
    stdx::always!(idx == generic_params_upper_bound, "inconsistent index");
    where_preds.retain(|_| {
        idx += 1;
        reachable[idx - 1]
    });
}

/// Filters out bounds from impl if we're generating the function into the same impl we're
/// generating from.
fn filter_bounds_in_scope(
    generic_params: &mut Vec<ParamBoundWithParams>,
    where_preds: &mut Vec<WherePredWithParams>,
    ctx: &AssistContext<'_, '_>,
    target: &GeneratedFunctionTarget,
) -> Option<()> {
    let target_impl = target.parent().ancestors().find_map(ast::Impl::cast)?;
    let target_impl = ctx.sema.to_def(&target_impl)?;
    // It's sufficient to test only the first element of `generic_params` because of the order of
    // insertion (see `params_and_where_preds_in_scope()`).
    let def = generic_params.first()?.self_ty_param.parent();
    if def != hir::GenericDef::Impl(target_impl) {
        return None;
    }

    // Now we know every element that belongs to an impl would be in scope at `target`, we can
    // filter them out just by looking at their parent.
    generic_params.retain(|it| !matches!(it.self_ty_param.parent(), hir::GenericDef::Impl(_)));
    where_preds.retain(|it| {
        it.node.syntax().parent().and_then(|it| it.parent()).and_then(ast::Impl::cast).is_none()
    });

    Some(())
}

/// Makes duplicate argument names unique by appending incrementing numbers.
///
/// ```ignore
/// let mut names: Vec<String> =
///     vec!["foo".into(), "foo".into(), "bar".into(), "baz".into(), "bar".into()];
/// deduplicate_arg_names(&mut names);
/// let expected: Vec<String> =
///     vec!["foo_1".into(), "foo_2".into(), "bar_1".into(), "baz".into(), "bar_2".into()];
/// assert_eq!(names, expected);
/// ```
fn deduplicate_arg_names(arg_names: &mut [String]) {
    let mut arg_name_counts = FxHashMap::default();
    for name in arg_names.iter() {
        *arg_name_counts.entry(name).or_insert(0) += 1;
    }
    let duplicate_arg_names: FxHashSet<String> = arg_name_counts
        .into_iter()
        .filter(|(_, count)| *count >= 2)
        .map(|(name, _)| name.clone())
        .collect();

    let mut counter_per_name = FxHashMap::default();
    for arg_name in arg_names.iter_mut() {
        if duplicate_arg_names.contains(arg_name) {
            let counter = counter_per_name.entry(arg_name.clone()).or_insert(1);
            arg_name.push('_');
            arg_name.push_str(&counter.to_string());
            *counter += 1;
        }
    }
}

fn fn_arg_name(sema: &Semantics<'_, RootDatabase>, arg_expr: &ast::Expr) -> String {
    let name = (|| match arg_expr {
        ast::Expr::CastExpr(cast_expr) => Some(fn_arg_name(sema, &cast_expr.expr()?)),
        expr => {
            let name_ref = expr
                .syntax()
                .descendants()
                .filter_map(ast::NameRef::cast)
                .filter(|name| name.ident_token().is_some())
                .last()?;
            if let Some(NameRefClass::Definition(Definition::Const(_) | Definition::Static(_), _)) =
                NameRefClass::classify(sema, &name_ref)
            {
                return Some(name_ref.to_string().to_lowercase());
            };
            Some(to_lower_snake_case(&name_ref.to_string()))
        }
    })();
    match name {
        Some(mut name) if name.starts_with(|c: char| c.is_ascii_digit()) => {
            name.insert_str(0, "arg");
            name
        }
        Some(name) => name,
        None => "arg".to_owned(),
    }
}

fn fn_arg_type(
    ctx: &AssistContext<'_, '_>,
    target_module: Module,
    fn_arg: &ast::Expr,
    generic_params: &mut FxHashSet<hir::GenericParam>,
) -> String {
    fn maybe_displayed_type(
        ctx: &AssistContext<'_, '_>,
        target_module: Module,
        fn_arg: &ast::Expr,
        generic_params: &mut FxHashSet<hir::GenericParam>,
    ) -> Option<String> {
        let ty = ctx.sema.type_of_expr(fn_arg)?.adjusted();
        if ty.is_unknown() {
            return None;
        }

        generic_params.extend(ty.generic_params(ctx.db()));

        if ty.is_reference() || ty.is_mutable_reference() {
            let famous_defs = &FamousDefs(&ctx.sema, ctx.sema.scope(fn_arg.syntax())?.krate());
            convert_reference_type(ty.strip_references(), ctx.db(), famous_defs)
                .map(|conversion| conversion.convert_type(ctx.db(), target_module).to_string())
                .or_else(|| ty.display_source_code(ctx.db(), target_module.into(), true).ok())
        } else {
            ty.display_source_code(ctx.db(), target_module.into(), true).ok()
        }
    }

    maybe_displayed_type(ctx, target_module, fn_arg, generic_params)
        .unwrap_or_else(|| String::from("_"))
}

/// Returns the position inside the current mod or file
/// directly after the current block
/// We want to write the generated function directly after
/// fns, impls or macro calls, but inside mods
fn next_space_for_fn_after_call_site(expr: ast::CallableExpr) -> Option<GeneratedFunctionTarget> {
    let mut ancestors = expr.syntax().ancestors().peekable();
    let mut last_ancestor: Option<SyntaxNode> = None;
    while let Some(next_ancestor) = ancestors.next() {
        match next_ancestor.kind() {
            SyntaxKind::SOURCE_FILE => {
                break;
            }
            SyntaxKind::ITEM_LIST
                if ancestors.peek().map(|a| a.kind()) == Some(SyntaxKind::MODULE) =>
            {
                break;
            }
            _ => {}
        }
        last_ancestor = Some(next_ancestor);
    }
    last_ancestor.map(GeneratedFunctionTarget::AfterItem)
}

fn next_space_for_fn_in_module(
    db: &dyn hir::db::HirDatabase,
    target_module: hir::Module,
) -> (FileId, GeneratedFunctionTarget) {
    let module_source = target_module.definition_source(db);
    let file = module_source.file_id.original_file(db);
    let assist_item = match &module_source.value {
        hir::ModuleSource::SourceFile(it) => match it.items().last() {
            Some(last_item) => GeneratedFunctionTarget::AfterItem(last_item.syntax().clone()),
            None => GeneratedFunctionTarget::AfterItem(it.syntax().clone()),
        },
        hir::ModuleSource::Module(it) => match it.item_list().and_then(|it| it.items().last()) {
            Some(last_item) => GeneratedFunctionTarget::AfterItem(last_item.syntax().clone()),
            None => {
                let item_list =
                    it.item_list().expect("module definition source should have an item list");
                GeneratedFunctionTarget::InEmptyItemList(item_list.syntax().clone())
            }
        },
        hir::ModuleSource::BlockExpr(it) => {
            if let Some(last_item) =
                it.statements().take_while(|stmt| matches!(stmt, ast::Stmt::Item(_))).last()
            {
                GeneratedFunctionTarget::AfterItem(last_item.syntax().clone())
            } else {
                GeneratedFunctionTarget::InEmptyItemList(it.syntax().clone())
            }
        }
    };

    (file.file_id(db), assist_item)
}

#[derive(Clone, Copy)]
enum Visibility {
    None,
    Crate,
    Pub,
}

fn calculate_necessary_visibility(
    current_module: Module,
    target_module: Module,
    ctx: &AssistContext<'_, '_>,
) -> Visibility {
    let db = ctx.db();
    let current_module = current_module.nearest_non_block_module(db);
    let target_module = target_module.nearest_non_block_module(db);

    if target_module.krate(ctx.db()) != current_module.krate(ctx.db()) {
        Visibility::Pub
    } else if current_module.path_to_root(db).contains(&target_module) {
        Visibility::None
    } else {
        Visibility::Crate
    }
}

// This is never intended to be used as a generic graph structure. If there's ever another need of
// graph algorithm, consider adding a library for that (and replace the following).
/// Minimally implemented directed graph structure represented by adjacency list.
struct Graph {
    edges: Vec<Vec<usize>>,
}

impl Graph {
    fn new(node_count: usize) -> Self {
        Self { edges: vec![Vec::new(); node_count] }
    }

    fn add_edge(&mut self, from: usize, to: usize) {
        self.edges[from].push(to);
    }

    fn edges_for(&self, node_idx: usize) -> &[usize] {
        &self.edges[node_idx]
    }

    fn len(&self) -> usize {
        self.edges.len()
    }

    fn compute_reachable_nodes(
        &self,
        starting_nodes: impl IntoIterator<Item = usize>,
    ) -> Vec<bool> {
        let mut visitor = Visitor::new(self);
        for idx in starting_nodes {
            visitor.mark_reachable(idx);
        }
        visitor.visited
    }
}

struct Visitor<'g> {
    graph: &'g Graph,
    visited: Vec<bool>,
    // Stack is held in this struct so we can reuse its buffer.
    stack: Vec<usize>,
}

impl<'g> Visitor<'g> {
    fn new(graph: &'g Graph) -> Self {
        let visited = vec![false; graph.len()];
        Self { graph, visited, stack: Vec::new() }
    }

    fn mark_reachable(&mut self, start_idx: usize) {
        // non-recursive DFS
        stdx::always!(self.stack.is_empty());

        self.stack.push(start_idx);
        while let Some(idx) = self.stack.pop() {
            if !self.visited[idx] {
                self.visited[idx] = true;
                for &neighbor in self.graph.edges_for(idx) {
                    if !self.visited[neighbor] {
                        self.stack.push(neighbor);
                    }
                }
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::tests::{check_assist, check_assist_not_applicable};

    use super::*;

    #[test]
    fn add_function_with_no_args() {
        check_assist(
            generate_function,
            r"
fn foo() {
    bar$0();
}
",
            r"
fn foo() {
    bar();
}

fn bar() ${0:-> _} {
    todo!()
}
",
        )
    }

    #[test]
    fn add_function_from_method() {
        // This ensures that the function is correctly generated
        // in the next outer mod or file
        check_assist(
            generate_function,
            r"
impl Foo {
    fn foo() {
        bar$0();
    }
}
",
            r"
impl Foo {
    fn foo() {
        bar();
    }
}

fn bar() ${0:-> _} {
    todo!()
}
",
        )
    }

    #[test]
    fn add_function_directly_after_current_block() {
        // The new fn should not be created at the end of the file or module
        check_assist(
            generate_function,
            r"
fn foo1() {
    bar$0();
}

fn foo2() {}
",
            r"
fn foo1() {
    bar();
}

fn bar() ${0:-> _} {
    todo!()
}

fn foo2() {}
",
        )
    }

    #[test]
    fn add_function_with_no_args_in_same_module() {
        check_assist(
            generate_function,
            r"
mod baz {
    fn foo() {
        bar$0();
    }
}
",
            r"
mod baz {
    fn foo() {
        bar();
    }

    fn bar() ${0:-> _} {
        todo!()
    }
}
",
        )
    }

    #[test]
    fn add_function_with_upper_camel_case_arg() {
        check_assist(
            generate_function,
            r"
struct BazBaz;
fn foo() {
    bar$0(BazBaz);
}
",
            r"
struct BazBaz;
fn foo() {
    bar(BazBaz);
}

fn bar(baz_baz: BazBaz) ${0:-> _} {
    todo!()
}
",
        );
    }

    #[test]
    fn add_function_with_upper_camel_case_arg_as_cast() {
        check_assist(
            generate_function,
            r"
struct BazBaz;
fn foo() {
    bar$0(&BazBaz as *const BazBaz);
}
",
            r"
struct BazBaz;
fn foo() {
    bar(&BazBaz as *const BazBaz);
}

fn bar(baz_baz: *const BazBaz) ${0:-> _} {
    todo!()
}
",
        );
    }

    #[test]
    fn add_function_with_function_call_arg() {
        check_assist(
            generate_function,
            r"
struct Baz;
fn baz() -> Baz { todo!() }
fn foo() {
    bar$0(baz());
}
",
            r"
struct Baz;
fn baz() -> Baz { todo!() }
fn foo() {
    bar(baz());
}

fn bar(baz: Baz) ${0:-> _} {
    todo!()
}
",
        );
    }

    #[test]
    fn add_function_with_method_call_arg() {
        check_assist(
            generate_function,
            r"
struct Baz;
impl Baz {
    fn foo(&self) -> Baz {
        ba$0r(self.baz())
    }
    fn baz(&self) -> Baz {
        Baz
    }
}
",
            r"
struct Baz;
impl Baz {
    fn foo(&self) -> Baz {
        bar(self.baz())
    }
    fn baz(&self) -> Baz {
        Baz
    }
}

fn bar(baz: Baz) -> Baz {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn add_function_with_string_literal_arg() {
        check_assist(
            generate_function,
            r#"
fn foo() {
    $0bar("bar")
}
"#,
            r#"
fn foo() {
    bar("bar")
}

fn bar(arg: &'static str) {
    ${0:todo!()}
}
"#,
        )
    }

    #[test]
    fn add_function_with_char_literal_arg() {
        check_assist(
            generate_function,
            r#"
fn foo() {
    $0bar('x')
}
"#,
            r#"
fn foo() {
    bar('x')
}

fn bar(arg: char) {
    ${0:todo!()}
}
"#,
        )
    }

    #[test]
    fn add_function_with_int_literal_arg() {
        check_assist(
            generate_function,
            r"
fn foo() {
    $0bar(42)
}
",
            r"
fn foo() {
    bar(42)
}

fn bar(arg: i32) {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn add_function_with_cast_int_literal_arg() {
        check_assist(
            generate_function,
            r"
fn foo() {
    $0bar(42 as u8)
}
",
            r"
fn foo() {
    bar(42 as u8)
}

fn bar(arg: u8) {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn name_of_cast_variable_is_used() {
        // Ensures that the name of the cast type isn't used
        // in the generated function signature.
        check_assist(
            generate_function,
            r"
fn foo() {
    let x = 42;
    bar$0(x as u8)
}
",
            r"
fn foo() {
    let x = 42;
    bar(x as u8)
}

fn bar(x: u8) {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn add_function_with_variable_arg() {
        check_assist(
            generate_function,
            r"
fn foo() {
    let worble = ();
    $0bar(worble)
}
",
            r"
fn foo() {
    let worble = ();
    bar(worble)
}

fn bar(worble: ()) {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn add_function_with_impl_trait_arg() {
        check_assist(
            generate_function,
            r#"
//- minicore: sized
trait Foo {}
fn foo() -> impl Foo {
    todo!()
}
fn baz() {
    $0bar(foo())
}
"#,
            r#"
trait Foo {}
fn foo() -> impl Foo {
    todo!()
}
fn baz() {
    bar(foo())
}

fn bar(foo: impl Foo) {
    ${0:todo!()}
}
"#,
        )
    }

    #[test]
    fn borrowed_arg() {
        check_assist(
            generate_function,
            r"
struct Baz;
fn baz() -> Baz { todo!() }

fn foo() {
    bar$0(&baz())
}
",
            r"
struct Baz;
fn baz() -> Baz { todo!() }

fn foo() {
    bar(&baz())
}

fn bar(baz: &Baz) {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn add_function_with_qualified_path_arg() {
        check_assist(
            generate_function,
            r"
mod Baz {
    pub struct Bof;
    pub fn baz() -> Bof { Bof }
}
fn foo() {
    $0bar(Baz::baz())
}
",
            r"
mod Baz {
    pub struct Bof;
    pub fn baz() -> Bof { Bof }
}
fn foo() {
    bar(Baz::baz())
}

fn bar(baz: Baz::Bof) {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn generate_function_with_generic_param() {
        check_assist(
            generate_function,
            r"
fn foo<T, const N: usize>(t: [T; N]) { $0bar(t) }
",
            r"
fn foo<T, const N: usize>(t: [T; N]) { bar(t) }

fn bar<T, const N: usize>(t: [T; N]) {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn generate_function_with_parent_generic_param() {
        check_assist(
            generate_function,
            r"
struct S<T>(T);
impl<T> S<T> {
    fn foo<U>(t: T, u: U) { $0bar(t, u) }
}
",
            r"
struct S<T>(T);
impl<T> S<T> {
    fn foo<U>(t: T, u: U) { bar(t, u) }
}

fn bar<T, U>(t: T, u: U) {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn generic_param_in_receiver_type() {
        // FIXME: Generic parameter `T` should be part of impl, not method.
        check_assist(
            generate_function,
            r"
struct S<T>(T);
fn foo<T, U>(s: S<T>, u: U) { s.$0foo(u) }
",
            r"
struct S<T>(T);
impl S {
    fn foo<T, U>(&self, u: U) {
        ${0:todo!()}
    }
}
fn foo<T, U>(s: S<T>, u: U) { s.foo(u) }
",
        )
    }

    #[test]
    fn generic_param_in_return_type() {
        check_assist(
            generate_function,
            r"
fn foo<T, const N: usize>() -> [T; N] { $0bar() }
",
            r"
fn foo<T, const N: usize>() -> [T; N] { bar() }

fn bar<T, const N: usize>() -> [T; N] {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn generate_fn_with_bounds() {
        // FIXME: where predicates should be on next lines.
        check_assist(
            generate_function,
            r"
trait A<T> {}
struct S<T>(T);
impl<T: A<i32>> S<T>
where
    T: A<i64>,
{
    fn foo<U>(t: T, u: U)
    where
        T: A<()>,
        U: A<i32> + A<i64>,
    {
        $0bar(t, u)
    }
}
",
            r"
trait A<T> {}
struct S<T>(T);
impl<T: A<i32>> S<T>
where
    T: A<i64>,
{
    fn foo<U>(t: T, u: U)
    where
        T: A<()>,
        U: A<i32> + A<i64>,
    {
        bar(t, u)
    }
}

fn bar<T: A<i32>, U>(t: T, u: U) where T: A<i64>, T: A<()>, U: A<i32> + A<i64> {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn include_transitive_param_dependency() {
        // FIXME: where predicates should be on next lines.
        check_assist(
            generate_function,
            r"
trait A<T> { type Assoc; }
trait B { type Item; }
struct S<T>(T);
impl<T, U, V: B, W> S<(T, U, V, W)>
where
    T: A<U, Assoc = V>,
    S<V::Item>: A<U, Assoc = W>,
{
    fn foo<I>(t: T, u: U)
    where
        U: A<T, Assoc = I>,
    {
        $0bar(u)
    }
}
",
            r"
trait A<T> { type Assoc; }
trait B { type Item; }
struct S<T>(T);
impl<T, U, V: B, W> S<(T, U, V, W)>
where
    T: A<U, Assoc = V>,
    S<V::Item>: A<U, Assoc = W>,
{
    fn foo<I>(t: T, u: U)
    where
        U: A<T, Assoc = I>,
    {
        bar(u)
    }
}

fn bar<T, U, V: B, W, I>(u: U) where T: A<U, Assoc = V>, S<V::Item>: A<U, Assoc = W>, U: A<T, Assoc = I> {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn irrelevant_bounds_are_filtered_out() {
        check_assist(
            generate_function,
            r"
trait A<T> {}
struct S<T>(T);
impl<T, U, V, W> S<(T, U, V, W)>
where
    T: A<U>,
    V: A<W>,
{
    fn foo<I>(t: T, u: U)
    where
        U: A<T> + A<I>,
    {
        $0bar(u)
    }
}
",
            r"
trait A<T> {}
struct S<T>(T);
impl<T, U, V, W> S<(T, U, V, W)>
where
    T: A<U>,
    V: A<W>,
{
    fn foo<I>(t: T, u: U)
    where
        U: A<T> + A<I>,
    {
        bar(u)
    }
}

fn bar<T, U, I>(u: U) where T: A<U>, U: A<T> + A<I> {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn params_in_trait_arg_are_not_dependency() {
        // Even though `bar` depends on `U` and `I`, we don't have to copy these bounds:
        // `T: A<I>` and `T: A<U>`.
        check_assist(
            generate_function,
            r"
trait A<T> {}
struct S<T>(T);
impl<T, U> S<(T, U)>
where
    T: A<U>,
{
    fn foo<I>(t: T, u: U)
    where
        T: A<I>,
        U: A<I>,
    {
        $0bar(u)
    }
}
",
            r"
trait A<T> {}
struct S<T>(T);
impl<T, U> S<(T, U)>
where
    T: A<U>,
{
    fn foo<I>(t: T, u: U)
    where
        T: A<I>,
        U: A<I>,
    {
        bar(u)
    }
}

fn bar<U, I>(u: U) where U: A<I> {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn dont_copy_bounds_already_in_scope() {
        check_assist(
            generate_function,
            r"
trait A<T> {}
struct S<T>(T);
impl<T: A<i32>> S<T>
where
    T: A<usize>,
{
    fn foo<U: A<()>>(t: T, u: U)
    where
        T: A<S<i32>>,
    {
        Self::$0bar(t, u);
    }
}
",
            r"
trait A<T> {}
struct S<T>(T);
impl<T: A<i32>> S<T>
where
    T: A<usize>,
{
    fn foo<U: A<()>>(t: T, u: U)
    where
        T: A<S<i32>>,
    {
        Self::bar(t, u);
    }

    fn bar<U: A<()>>(t: T, u: U) ${0:-> _} where T: A<S<i32>> {
        todo!()
    }
}
",
        )
    }

    #[test]
    fn add_function_with_fn_arg() {
        check_assist(
            generate_function,
            r"
struct Baz;
impl Baz {
    fn new() -> Self { Baz }
}
fn foo() {
    $0bar(Baz::new);
}
",
            r"
struct Baz;
impl Baz {
    fn new() -> Self { Baz }
}
fn foo() {
    bar(Baz::new);
}

fn bar(new: fn() -> Baz) ${0:-> _} {
    todo!()
}
",
        )
    }

    #[test]
    fn add_function_with_closure_arg() {
        check_assist(
            generate_function,
            r"
fn foo() {
    let closure = |x: i64| x - 1;
    $0bar(closure)
}
",
            r"
fn foo() {
    let closure = |x: i64| x - 1;
    bar(closure)
}

fn bar(closure: impl Fn(i64) -> i64) {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn unresolvable_types_default_to_placeholder() {
        check_assist(
            generate_function,
            r"
fn foo() {
    $0bar(baz)
}
",
            r"
fn foo() {
    bar(baz)
}

fn bar(baz: _) {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn arg_names_dont_overlap() {
        check_assist(
            generate_function,
            r"
struct Baz;
fn baz() -> Baz { Baz }
fn foo() {
    $0bar(baz(), baz())
}
",
            r"
struct Baz;
fn baz() -> Baz { Baz }
fn foo() {
    bar(baz(), baz())
}

fn bar(baz_1: Baz, baz_2: Baz) {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn arg_name_counters_start_at_1_per_name() {
        check_assist(
            generate_function,
            r#"
struct Baz;
fn baz() -> Baz { Baz }
fn foo() {
    $0bar(baz(), baz(), "foo", "bar")
}
"#,
            r#"
struct Baz;
fn baz() -> Baz { Baz }
fn foo() {
    bar(baz(), baz(), "foo", "bar")
}

fn bar(baz_1: Baz, baz_2: Baz, arg_1: &'static str, arg_2: &'static str) {
    ${0:todo!()}
}
"#,
        )
    }

    #[test]
    fn add_function_in_module() {
        check_assist(
            generate_function,
            r"
mod bar {}

fn foo() {
    bar::my_fn$0()
}
",
            r"
mod bar {
    pub(crate) fn my_fn() {
        ${0:todo!()}
    }
}

fn foo() {
    bar::my_fn()
}
",
        )
    }

    #[test]
    fn qualified_path_uses_correct_scope() {
        check_assist(
            generate_function,
            r#"
mod foo {
    pub struct Foo;
}
fn bar() {
    use foo::Foo;
    let foo = Foo;
    baz$0(foo)
}
"#,
            r#"
mod foo {
    pub struct Foo;
}
fn bar() {
    use foo::Foo;
    let foo = Foo;
    baz(foo)
}

fn baz(foo: foo::Foo) {
    ${0:todo!()}
}
"#,
        )
    }

    #[test]
    fn qualified_path_in_generic_bounds_uses_correct_scope() {
        check_assist(
            generate_function,
            r"
mod a {
    pub trait A {};
}
pub mod b {
    pub struct S<T>(T);
}
struct S<T>(T);
impl<T> S<T>
where
    T: a::A,
{
    fn foo<U: a::A>(t: b::S<T>, u: S<U>) {
        a::$0bar(t, u);
    }
}
",
            r"
mod a {
    pub trait A {}

    pub(crate) fn bar<T, U: self::A>(t: crate::b::S<T>, u: crate::S<U>) ${0:-> _} where T: self::A {
        todo!()
    };
}
pub mod b {
    pub struct S<T>(T);
}
struct S<T>(T);
impl<T> S<T>
where
    T: a::A,
{
    fn foo<U: a::A>(t: b::S<T>, u: S<U>) {
        a::bar(t, u);
    }
}
",
        )
    }
    #[test]
    fn add_function_in_module_containing_other_items() {
        check_assist(
            generate_function,
            r"
mod bar {
    fn something_else() {}
}

fn foo() {
    bar::my_fn$0()
}
",
            r"
mod bar {
    fn something_else() {}

    pub(crate) fn my_fn() {
        ${0:todo!()}
    }
}

fn foo() {
    bar::my_fn()
}
",
        )
    }

    #[test]
    fn add_function_in_nested_module() {
        check_assist(
            generate_function,
            r"
mod bar {
    pub mod baz {}
}

fn foo() {
    bar::baz::my_fn$0()
}
",
            r"
mod bar {
    pub mod baz {
        pub(crate) fn my_fn() {
            ${0:todo!()}
        }
    }
}

fn foo() {
    bar::baz::my_fn()
}
",
        )
    }

    #[test]
    fn add_function_in_another_file() {
        check_assist(
            generate_function,
            r"
//- /main.rs
mod foo;

fn main() {
    foo::bar$0()
}
//- /foo.rs
",
            r"


pub(crate) fn bar() {
    ${0:todo!()}
}",
        )
    }

    #[test]
    fn add_function_with_return_type() {
        check_assist(
            generate_function,
            r"
fn main() {
    let x: u32 = foo$0();
}
",
            r"
fn main() {
    let x: u32 = foo();
}

fn foo() -> u32 {
    ${0:todo!()}
}
",
        )
    }

    #[test]
    fn add_function_not_applicable_if_function_already_exists() {
        check_assist_not_applicable(
            generate_function,
            r"
fn foo() {
    bar$0();
}

fn bar() {}
",
        )
    }

    #[test]
    fn add_function_not_applicable_if_unresolved_variable_in_call_is_selected() {
        check_assist_not_applicable(
            // bar is resolved, but baz isn't.
            // The assist is only active if the cursor is on an unresolved path,
            // but the assist should only be offered if the path is a function call.
            generate_function,
            r#"
fn foo() {
    bar(b$0az);
}

fn bar(baz: ()) {}
"#,
        )
    }

    #[test]
    fn create_method_with_no_args() {
        check_assist(
            generate_function,
            r#"
struct Foo;
impl Foo {
    fn foo(&self) {
        self.bar()$0;
    }
}
"#,
            r#"
struct Foo;
impl Foo {
    fn foo(&self) {
        self.bar();
    }

    fn bar(&self) ${0:-> _} {
        todo!()
    }
}
"#,
        )
    }

    #[test]
    fn create_method_with_unused_generics() {
        check_assist(
            generate_function,
            r#"
struct Foo<S>(S);
impl<S> Foo<S> {
    fn foo(&self) {
        self.bar()$0;
    }
}
"#,
            r#"
struct Foo<S>(S);
impl<S> Foo<S> {
    fn foo(&self) {
        self.bar();
    }

    fn bar(&self) ${0:-> _} {
        todo!()
    }
}
"#,
        )
    }

    #[test]
    fn create_function_with_async() {
        check_assist(
            generate_function,
            r"
async fn foo() {
    $0bar(42).await;
}
",
            r"
async fn foo() {
    bar(42).await;
}

async fn bar(arg: i32) ${0:-> _} {
    todo!()
}
",
        )
    }

    #[test]
    fn return_type_for_async_fn() {
        check_assist(
            generate_function,
            r"
//- minicore: result
async fn foo() {
    if Err(()) = $0bar(42).await {}
}
",
            r"
async fn foo() {
    if Err(()) = bar(42).await {}
}

async fn bar(arg: i32) -> Result<_, ()> {
    ${0:todo!()}
}
",
        );
    }

    #[test]
    fn create_method() {
        check_assist(
            generate_function,
            r"
struct S;
fn foo() {S.bar$0();}
",
            r"
struct S;
impl S {
    fn bar(&self) ${0:-> _} {
        todo!()
    }
}
fn foo() {S.bar();}
",
        )
    }

    #[test]
    fn create_method_within_an_impl() {
        check_assist(
            generate_function,
            r"
struct S;
fn foo() {S.bar$0();}
impl S {}

",
            r"
struct S;
fn foo() {S.bar();}
impl S {
    fn bar(&self) ${0:-> _} {
        todo!()
    }
}

",
        )
    }

    #[test]
    fn create_method_from_different_module() {
        check_assist(
            generate_function,
            r"
mod s {
    pub struct S;
}
fn foo() {s::S.bar$0();}
",
            r"
mod s {
    pub struct S;
    impl S {
        pub(crate) fn bar(&self) ${0:-> _} {
            todo!()
        }
    }
}
fn foo() {s::S.bar();}
",
        )
    }

    #[test]
    fn create_method_from_descendant_module() {
        check_assist(
            generate_function,
            r"
struct S;
mod s {
    fn foo() {
        super::S.bar$0();
    }
}

",
            r"
struct S;
impl S {
    fn bar(&self) ${0:-> _} {
        todo!()
    }
}
mod s {
    fn foo() {
        super::S.bar();
    }
}

",
        )
    }

    #[test]
    fn create_method_with_cursor_anywhere_on_call_expression() {
        check_assist(
            generate_function,
            r"
struct S;
fn foo() {$0S.bar();}
",
            r"
struct S;
impl S {
    fn bar(&self) ${0:-> _} {
        todo!()
    }
}
fn foo() {S.bar();}
",
        )
    }

    #[test]
    fn create_async_method() {
        check_assist(
            generate_function,
            r"
//- minicore: result
struct S;
async fn foo() {
    if let Err(()) = S.$0bar(42).await {}
}
",
            r"
struct S;
impl S {
    async fn bar(&self, arg: i32) -> Result<_, ()> {
        ${0:todo!()}
    }
}
async fn foo() {
    if let Err(()) = S.bar(42).await {}
}
",
        )
    }

    #[test]
    fn create_static_method() {
        check_assist(
            generate_function,
            r"
struct S;
fn foo() {S::bar$0();}
",
            r"
struct S;
impl S {
    fn bar() ${0:-> _} {
        todo!()
    }
}
fn foo() {S::bar();}
",
        )
    }

    #[test]
    fn create_async_static_method() {
        check_assist(
            generate_function,
            r"
//- minicore: result
struct S;
async fn foo() {
    if let Err(()) = S::$0bar(42).await {}
}
",
            r"
struct S;
impl S {
    async fn bar(arg: i32) -> Result<_, ()> {
        ${0:todo!()}
    }
}
async fn foo() {
    if let Err(()) = S::bar(42).await {}
}
",
        )
    }

    #[test]
    fn create_generic_static_method() {
        check_assist(
            generate_function,
            r"
struct S;
fn foo<T, const N: usize>(t: [T; N]) { S::bar$0(t); }
",
            r"
struct S;
impl S {
    fn bar<T, const N: usize>(t: [T; N]) ${0:-> _} {
        todo!()
    }
}
fn foo<T, const N: usize>(t: [T; N]) { S::bar(t); }
",
        )
    }

    #[test]
    fn create_static_method_within_an_impl() {
        check_assist(
            generate_function,
            r"
struct S;
fn foo() {S::bar$0();}
impl S {}

",
            r"
struct S;
fn foo() {S::bar();}
impl S {
    fn bar() ${0:-> _} {
        todo!()
    }
}

",
        )
    }

    #[test]
    fn create_static_method_from_different_module() {
        check_assist(
            generate_function,
            r"
mod s {
    pub struct S;
}
fn foo() {s::S::bar$0();}
",
            r"
mod s {
    pub struct S;
    impl S {
        pub(crate) fn bar() ${0:-> _} {
            todo!()
        }
    }
}
fn foo() {s::S::bar();}
",
        )
    }

    #[test]
    fn create_static_method_with_cursor_anywhere_on_call_expression() {
        check_assist(
            generate_function,
            r"
struct S;
fn foo() {$0S::bar();}
",
            r"
struct S;
impl S {
    fn bar() ${0:-> _} {
        todo!()
    }
}
fn foo() {S::bar();}
",
        )
    }

    #[test]
    fn create_static_method_within_an_impl_with_self_syntax() {
        check_assist(
            generate_function,
            r"
struct S;
impl S {
    fn foo(&self) {
        Self::bar$0();
    }
}
",
            r"
struct S;
impl S {
    fn foo(&self) {
        Self::bar();
    }

    fn bar() ${0:-> _} {
        todo!()
    }
}
",
        )
    }

    #[test]
    fn no_panic_on_invalid_global_path() {
        check_assist(
            generate_function,
            r"
fn main() {
    ::foo$0();
}
",
            r"
fn main() {
    ::foo();
}

fn foo() ${0:-> _} {
    todo!()
}
",
        )
    }

    #[test]
    fn handle_tuple_indexing() {
        check_assist(
            generate_function,
            r"
fn main() {
    let a = ((),);
    foo$0(a.0);
}
",
            r"
fn main() {
    let a = ((),);
    foo(a.0);
}

fn foo(a: ()) ${0:-> _} {
    todo!()
}
",
        )
    }

    #[test]
    fn add_function_with_const_arg() {
        check_assist(
            generate_function,
            r"
const VALUE: usize = 0;
fn main() {
    foo$0(VALUE);
}
",
            r"
const VALUE: usize = 0;
fn main() {
    foo(VALUE);
}

fn foo(value: usize) ${0:-> _} {
    todo!()
}
",
        )
    }

    #[test]
    fn add_function_with_static_arg() {
        check_assist(
            generate_function,
            r"
static VALUE: usize = 0;
fn main() {
    foo$0(VALUE);
}
",
            r"
static VALUE: usize = 0;
fn main() {
    foo(VALUE);
}

fn foo(value: usize) ${0:-> _} {
    todo!()
}
",
        )
    }

    #[test]
    fn add_function_with_static_mut_arg() {
        check_assist(
            generate_function,
            r"
static mut VALUE: usize = 0;
fn main() {
    foo$0(VALUE);
}
",
            r"
static mut VALUE: usize = 0;
fn main() {
    foo(VALUE);
}

fn foo(value: usize) ${0:-> _} {
    todo!()
}
",
        )
    }

    #[test]
    fn not_applicable_for_enum_variant() {
        check_assist_not_applicable(
            generate_function,
            r"
enum Foo {}
fn main() {
    Foo::Bar$0(true)
}
",
        );
    }

    #[test]
    fn applicable_for_enum_method() {
        check_assist(
            generate_function,
            r"
enum Foo {}
fn main() {
    Foo::bar$0();
}
",
            r"
enum Foo {}
impl Foo {
    fn bar() ${0:-> _} {
        todo!()
    }
}
fn main() {
    Foo::bar();
}
",
        )
    }

    #[test]
    fn applicable_in_different_local_crate() {
        check_assist(
            generate_function,
            r"
//- /lib.rs crate:lib new_source_root:local
fn dummy() {}
//- /main.rs crate:main deps:lib new_source_root:local
fn main() {
    lib::foo$0();
}
",
            r"
fn dummy() {}

pub fn foo() ${0:-> _} {
    todo!()
}
",
        );
    }

    #[test]
    fn applicable_in_different_local_crate_method() {
        check_assist(
            generate_function,
            r"
//- /lib.rs crate:lib new_source_root:local
pub struct S;
//- /main.rs crate:main deps:lib new_source_root:local
fn main() {
    lib::S.foo$0();
}
",
            r"
pub struct S;
impl S {
    pub fn foo(&self) ${0:-> _} {
        todo!()
    }
}
",
        );
    }

    #[test]
    fn not_applicable_in_different_library_crate() {
        check_assist_not_applicable(
            generate_function,
            r"
//- /lib.rs crate:lib new_source_root:library
fn dummy() {}
//- /main.rs crate:main deps:lib new_source_root:local
fn main() {
    lib::foo$0();
}
",
        );
    }

    #[test]
    fn not_applicable_in_different_library_crate_method() {
        check_assist_not_applicable(
            generate_function,
            r"
//- /lib.rs crate:lib new_source_root:library
pub struct S;
//- /main.rs crate:main deps:lib new_source_root:local
fn main() {
    lib::S.foo$0();
}
",
        );
    }

    #[test]
    fn new_function_assume_self_type() {
        check_assist(
            generate_function,
            r"
pub struct Foo {
    field_1: usize,
    field_2: String,
}

fn main() {
    let foo = Foo::new$0();
}
        ",
            r"
pub struct Foo {
    field_1: usize,
    field_2: String,
}
impl Foo {
    fn new() -> Self {
        ${0:Self { field_1: todo!(), field_2: todo!() }}
    }
}

fn main() {
    let foo = Foo::new();
}
        ",
        )
    }

    #[test]
    fn new_function_assume_self_type_for_tuple_struct() {
        check_assist(
            generate_function,
            r"
pub struct Foo (usize, String);

fn main() {
    let foo = Foo::new$0();
}
        ",
            r"
pub struct Foo (usize, String);
impl Foo {
    fn new() -> Self {
        ${0:Self(todo!(), todo!())}
    }
}

fn main() {
    let foo = Foo::new();
}
        ",
        )
    }

    #[test]
    fn new_function_assume_self_type_for_unit_struct() {
        check_assist(
            generate_function,
            r"
pub struct Foo;

fn main() {
    let foo = Foo::new$0();
}
        ",
            r"
pub struct Foo;
impl Foo {
    fn new() -> Self {
        ${0:Self}
    }
}

fn main() {
    let foo = Foo::new();
}
        ",
        )
    }

    #[test]
    fn new_function_assume_self_type_for_enum() {
        check_assist(
            generate_function,
            r"
pub enum Foo {}

fn main() {
    let foo = Foo::new$0();
}
        ",
            r"
pub enum Foo {}
impl Foo {
    fn new() -> Self {
        ${0:todo!()}
    }
}

fn main() {
    let foo = Foo::new();
}
        ",
        )
    }

    #[test]
    fn new_function_assume_self_type_with_args() {
        check_assist(
            generate_function,
            r#"
pub struct Foo {
    field_1: usize,
    field_2: String,
}

struct Baz;
fn baz() -> Baz { Baz }

fn main() {
    let foo = Foo::new$0(baz(), baz(), "foo", "bar");
}
        "#,
            r#"
pub struct Foo {
    field_1: usize,
    field_2: String,
}
impl Foo {
    fn new(baz_1: Baz, baz_2: Baz, arg_1: &'static str, arg_2: &'static str) -> Self {
        ${0:Self { field_1: todo!(), field_2: todo!() }}
    }
}

struct Baz;
fn baz() -> Baz { Baz }

fn main() {
    let foo = Foo::new(baz(), baz(), "foo", "bar");
}
        "#,
        )
    }

    #[test]
    fn no_generate_method_by_keyword() {
        check_assist_not_applicable(
            generate_function,
            r#"
fn main() {
    s.super$0();
}
        "#,
        );
        check_assist_not_applicable(
            generate_function,
            r#"
fn main() {
    s.Self$0();
}
        "#,
        );
        check_assist_not_applicable(
            generate_function,
            r#"
fn main() {
    s.self$0();
}
        "#,
        );
    }

    #[test]
    fn regression_21288() {
        check_assist(
            generate_function,
            r#"
//- minicore: copy
fn foo() {
    $0bar(&|x| true)
}
        "#,
            r#"
fn foo() {
    bar(&|x| true)
}

fn bar(arg: impl Fn(_) -> bool) {
    ${0:todo!()}
}
        "#,
        );
    }
    #[test]
    fn generate_method_uses_current_impl_block() {
        check_assist(
            generate_function,
            r"
struct Foo;

impl Foo {
    fn new() -> Self {
        Foo
    }
}

impl Foo {
    fn method1(&self) {
        self.method2$0(42)
    }
}
",
            r"
struct Foo;

impl Foo {
    fn new() -> Self {
        Foo
    }
}

impl Foo {
    fn method1(&self) {
        self.method2(42)
    }

    fn method2(&self, arg: i32) {
        ${0:todo!()}
    }
}
",
        )
    }

    #[test]
    fn generate_method_skips_trait_impl_for_inherent() {
        // regression: rust-lang/rust-analyzer#22123
        check_assist(
            generate_function,
            r"
struct Bar;

impl Bar {
    fn func1() {}
}

trait Foo { fn foo(&self); }

impl Foo for Bar {
    fn foo(&self) {
        self.func2$0();
    }
}
",
            r"
struct Bar;

impl Bar {
    fn func1() {}

    fn func2(&self) ${0:-> _} {
        todo!()
    }
}

trait Foo { fn foo(&self); }

impl Foo for Bar {
    fn foo(&self) {
        self.func2();
    }
}
",
        )
    }

    #[test]
    fn generate_method_from_trait_impl_creates_new_inherent_impl() {
        // #22123: no inherent impl exists, so the assist must synthesize one
        // instead of inserting into the trait impl.
        check_assist(
            generate_function,
            r"
struct Bar;

trait Foo { fn foo(&self); }

impl Foo for Bar {
    fn foo(&self) {
        self.func2$0();
    }
}
",
            r"
struct Bar;
impl Bar {
    fn func2(&self) ${0:-> _} {
        todo!()
    }
}

trait Foo { fn foo(&self); }

impl Foo for Bar {
    fn foo(&self) {
        self.func2();
    }
}
",
        )
    }
}
