//! Completion for associated items in a trait implementation.
//!
//! This module adds the completion items related to implementing associated
//! items within an `impl Trait for Struct` block. The current context node
//! must be within either a `FN`, `TYPE_ALIAS`, or `CONST` node
//! and an direct child of an `IMPL`.
//!
//! # Examples
//!
//! Considering the following trait `impl`:
//!
//! ```ignore
//! trait SomeTrait {
//!     fn foo();
//! }
//!
//! impl SomeTrait for () {
//!     fn f$0
//! }
//! ```
//!
//! may result in the completion of the following method:
//!
//! ```ignore
//! # trait SomeTrait {
//! #    fn foo();
//! # }
//!
//! impl SomeTrait for () {
//!     fn foo() {}$0
//! }
//! ```

use hir::{MacroCallId, Name, db::ExpandDatabase};
use ide_db::text_edit::TextEdit;
use ide_db::{
    SymbolKind, documentation::HasDocs, path_transform::PathTransform,
    syntax_helpers::prettify_macro_expansion, traits::get_missing_assoc_items,
};
use syntax::ast::HasGenericParams;
use syntax::syntax_editor::{Position, SyntaxEditor};
use syntax::{
    AstNode, SmolStr, SyntaxElement, SyntaxKind, T, TextRange, ToSmolStr,
    ast::{
        self, HasGenericArgs, HasTypeBounds,
        edit::{AstNodeEdit, AttrsOwnerEdit},
    },
    format_smolstr,
};

use crate::{
    CompletionContext, CompletionItem, CompletionItemKind, CompletionRelevance, Completions,
    context::PathCompletionCtx,
};

#[derive(Copy, Clone, Debug, PartialEq, Eq)]
enum ImplCompletionKind {
    All,
    Fn,
    TypeAlias,
    Const,
}

pub(crate) fn complete_trait_impl_const(
    acc: &mut Completions,
    ctx: &CompletionContext<'_, '_>,
    name: &Option<ast::Name>,
) -> Option<()> {
    complete_trait_impl_name(acc, ctx, name, ImplCompletionKind::Const)
}

pub(crate) fn complete_trait_impl_type_alias(
    acc: &mut Completions,
    ctx: &CompletionContext<'_, '_>,
    name: &Option<ast::Name>,
) -> Option<()> {
    complete_trait_impl_name(acc, ctx, name, ImplCompletionKind::TypeAlias)
}

pub(crate) fn complete_trait_impl_fn(
    acc: &mut Completions,
    ctx: &CompletionContext<'_, '_>,
    name: &Option<ast::Name>,
) -> Option<()> {
    complete_trait_impl_name(acc, ctx, name, ImplCompletionKind::Fn)
}

fn complete_trait_impl_name(
    acc: &mut Completions,
    ctx: &CompletionContext<'_, '_>,
    name: &Option<ast::Name>,
    kind: ImplCompletionKind,
) -> Option<()> {
    let macro_file_item = match name {
        Some(name) => name.syntax().parent(),
        None => {
            let token = &ctx.token;
            match token.kind() {
                SyntaxKind::WHITESPACE => token.prev_token()?,
                _ => token.clone(),
            }
            .parent()
        }
    }?;
    let real_file_item = ctx.sema.original_syntax_node_rooted(&macro_file_item)?;
    // item -> ASSOC_ITEM_LIST -> IMPL
    let impl_def = ast::Impl::cast(macro_file_item.parent()?.parent()?)?;
    let replacement_range = {
        // ctx.sema.original_ast_node(item)?;
        let first_child = real_file_item
            .children_with_tokens()
            .find(|child| {
                !matches!(
                    child.kind(),
                    SyntaxKind::COMMENT | SyntaxKind::WHITESPACE | SyntaxKind::ATTR
                )
            })
            .unwrap_or_else(|| SyntaxElement::Node(real_file_item.clone()));

        TextRange::new(first_child.text_range().start(), ctx.source_range().end())
    };

    complete_trait_impl(acc, ctx, kind, replacement_range, &impl_def);
    Some(())
}

pub(crate) fn complete_trait_impl_item_by_name(
    acc: &mut Completions,
    ctx: &CompletionContext<'_, '_>,
    path_ctx: &PathCompletionCtx<'_>,
    name_ref: &Option<ast::NameRef>,
    impl_: &Option<ast::Impl>,
) {
    if !path_ctx.is_trivial_path() {
        return;
    }
    if let Some(impl_) = impl_ {
        complete_trait_impl(
            acc,
            ctx,
            ImplCompletionKind::All,
            match name_ref
                .as_ref()
                .and_then(|name| ctx.sema.original_syntax_node_rooted(name.syntax()))
            {
                Some(name) => name.text_range(),
                None => ctx.source_range(),
            },
            impl_,
        );
    }
}

fn complete_trait_impl(
    acc: &mut Completions,
    ctx: &CompletionContext<'_, '_>,
    kind: ImplCompletionKind,
    replacement_range: TextRange,
    impl_def: &ast::Impl,
) {
    if let Some(hir_impl) = ctx.sema.to_def(impl_def) {
        get_missing_assoc_items(&ctx.sema, impl_def)
            .into_iter()
            .filter(|item| ctx.check_stability_and_hidden(*item))
            .for_each(|item| {
                use self::ImplCompletionKind::*;
                match (item, kind) {
                    (hir::AssocItem::Function(func), All | Fn) => {
                        add_function_impl(acc, ctx, replacement_range, func, hir_impl)
                    }
                    (hir::AssocItem::TypeAlias(type_alias), All | TypeAlias) => {
                        add_type_alias_impl(acc, ctx, replacement_range, type_alias, hir_impl)
                    }
                    (hir::AssocItem::Const(const_), All | Const) => {
                        add_const_impl(acc, ctx, replacement_range, const_, hir_impl)
                    }
                    _ => {}
                }
            });
    }
}

fn add_function_impl(
    acc: &mut Completions,
    ctx: &CompletionContext<'_, '_>,
    replacement_range: TextRange,
    func: hir::Function,
    impl_def: hir::Impl,
) {
    let fn_name = &func.name(ctx.db);
    let sugar: &[_] = if func.is_async(ctx.db) {
        &[AsyncSugaring::Async, AsyncSugaring::Desugar]
    } else if func.returns_impl_future(ctx.db) {
        &[AsyncSugaring::Plain, AsyncSugaring::Resugar]
    } else {
        &[AsyncSugaring::Plain]
    };
    for &sugaring in sugar {
        add_function_impl_(acc, ctx, replacement_range, func, impl_def, fn_name, sugaring);
    }
}

fn add_function_impl_(
    acc: &mut Completions,
    ctx: &CompletionContext<'_, '_>,
    replacement_range: TextRange,
    func: hir::Function,
    impl_def: hir::Impl,
    fn_name: &Name,
    async_sugaring: AsyncSugaring,
) {
    let async_ = if let AsyncSugaring::Async | AsyncSugaring::Resugar = async_sugaring {
        "async "
    } else {
        ""
    };
    let label = format_smolstr!(
        "{}fn {}({})",
        async_,
        fn_name.display(ctx.db, ctx.edition),
        if func.assoc_fn_params(ctx.db).is_empty() { "" } else { ".." }
    );

    let completion_kind = CompletionItemKind::SymbolKind(if func.has_self_param(ctx.db) {
        SymbolKind::Method
    } else {
        SymbolKind::Function
    });

    let mut item = CompletionItem::new(completion_kind, replacement_range, label, ctx.edition);
    item.lookup_by(format!("{}fn {}", async_, fn_name.display(ctx.db, ctx.edition)))
        .set_documentation(func.docs(ctx.db))
        .set_relevance(CompletionRelevance { exact_name_match: true, ..Default::default() });

    if let Some(source) = ctx.sema.source(func)
        && let Some(transformed_fn) =
            get_transformed_fn(ctx, source.value, impl_def, async_sugaring)
    {
        let function_decl = function_declaration(ctx, &transformed_fn, source.file_id.macro_file());
        let ws = if function_decl.contains('\n') { "\n" } else { " " };
        match ctx.config.snippet_cap {
            Some(cap) => {
                let snippet = format!("{function_decl}{ws}{{\n    $0\n}}");
                item.snippet_edit(cap, TextEdit::replace(replacement_range, snippet));
            }
            None => {
                let header = format!("{function_decl}{ws}{{");
                item.text_edit(TextEdit::replace(replacement_range, header));
            }
        };
        item.add_to(acc, ctx.db);
    }
}

#[derive(Copy, Clone)]
enum AsyncSugaring {
    Desugar,
    Resugar,
    Async,
    Plain,
}

/// Transform a relevant associated item to inline generics from the impl, remove attrs and docs, etc.
fn get_transformed_assoc_item(
    ctx: &CompletionContext<'_, '_>,
    assoc_item: ast::AssocItem,
    impl_def: hir::Impl,
) -> Option<ast::AssocItem> {
    let trait_ = impl_def.trait_(ctx.db)?;
    let source_scope = &ctx.sema.scope(assoc_item.syntax())?;
    let impl_source = ctx.sema.source(impl_def)?;
    let target_scope = &ctx.sema.scope(impl_source.syntax().value)?;
    let transform =
        PathTransform::trait_impl(target_scope, source_scope, trait_, impl_source.value);

    // FIXME: Paths in nested macros are not handled well. See
    // `macro_generated_assoc_item2` test.
    let assoc_item = ast::AssocItem::cast(transform.apply(assoc_item.syntax()))?;
    let (editor, assoc_item) = SyntaxEditor::with_ast_node(&assoc_item);
    assoc_item.remove_attrs_and_docs(&editor);
    ast::AssocItem::cast(editor.finish().new_root().clone())
}

/// Transform a relevant associated item to inline generics from the impl, remove attrs and docs, etc.
fn get_transformed_fn(
    ctx: &CompletionContext<'_, '_>,
    fn_: ast::Fn,
    impl_def: hir::Impl,
    async_: AsyncSugaring,
) -> Option<ast::Fn> {
    let trait_ = impl_def.trait_(ctx.db)?;
    let source_scope = &ctx.sema.scope(fn_.syntax())?;
    let impl_source = ctx.sema.source(impl_def)?;
    let target_scope = &ctx.sema.scope(impl_source.syntax().value)?;
    let transform =
        PathTransform::trait_impl(target_scope, source_scope, trait_, impl_source.value);

    let fn_ = fn_.reset_indent();
    // FIXME: Paths in nested macros are not handled well. See
    // `macro_generated_assoc_item2` test.
    let fn_ = ast::Fn::cast(transform.apply(fn_.syntax()))?;
    let (editor, fn_) = SyntaxEditor::with_ast_node(&fn_);
    let factory = editor.make();
    fn_.remove_attrs_and_docs(&editor);
    match async_ {
        AsyncSugaring::Desugar => {
            match fn_.ret_type() {
                Some(ret_ty) => {
                    let ty = ret_ty.ty()?;
                    editor.replace(
                        ty.syntax(),
                        factory.ty(&format!("impl Future<Output = {ty}>")).syntax(),
                    );
                }
                None => {
                    let ret_type = factory.ret_type(factory.ty("impl Future<Output = ()>"));
                    editor.insert_with_whitespace(
                        Position::after(fn_.param_list()?.syntax()),
                        ret_type.syntax(),
                    );
                }
            }
            editor.delete(fn_.async_token()?);
        }
        AsyncSugaring::Resugar => {
            let ty = fn_.ret_type()?.ty()?;
            match &ty {
                // best effort guessing here
                ast::Type::ImplTraitType(t) => {
                    let output = t.type_bound_list()?.bounds().find_map(|b| match b.ty()? {
                        ast::Type::PathType(p) => {
                            let p = p.path()?.segment()?;
                            if p.name_ref()?.text() != "Future" {
                                return None;
                            }
                            match p.generic_arg_list()?.generic_args().next()? {
                                ast::GenericArg::AssocTypeArg(a)
                                    if a.name_ref()?.text() == "Output" =>
                                {
                                    a.ty()
                                }
                                _ => None,
                            }
                        }
                        _ => None,
                    })?;
                    if let ast::Type::TupleType(ty) = &output
                        && ty.fields().next().is_none()
                    {
                        editor.delete(fn_.ret_type()?.syntax());
                    } else {
                        editor.replace(ty.syntax(), output.syntax());
                    }
                }
                _ => (),
            }
            editor.insert_with_whitespace(
                Position::first_child_of(fn_.syntax()),
                factory.token(T![async]),
            );
        }
        AsyncSugaring::Async | AsyncSugaring::Plain => (),
    }
    ast::Fn::cast(editor.finish().new_root().clone())
}

fn add_type_alias_impl(
    acc: &mut Completions,
    ctx: &CompletionContext<'_, '_>,
    replacement_range: TextRange,
    type_alias: hir::TypeAlias,
    impl_def: hir::Impl,
) {
    let alias_name = type_alias.name(ctx.db).as_str().to_smolstr();

    let label = format_smolstr!("type {alias_name} =");

    let mut item =
        CompletionItem::new(SymbolKind::TypeAlias, replacement_range, label, ctx.edition);
    item.lookup_by(format!("type {alias_name}"))
        .set_documentation(type_alias.docs(ctx.db))
        .set_relevance(CompletionRelevance { exact_name_match: true, ..Default::default() });

    if let Some(source) = ctx.sema.source(type_alias) {
        let assoc_item = ast::AssocItem::TypeAlias(source.value);
        if let Some(transformed_item) = get_transformed_assoc_item(ctx, assoc_item, impl_def) {
            let transformed_ty = match transformed_item {
                ast::AssocItem::TypeAlias(ty) => ty,
                _ => unreachable!(),
            };

            let start = transformed_ty.syntax().text_range().start();

            let end = if let Some(end) =
                transformed_ty.colon_token().map(|tok| tok.text_range().start())
            {
                end
            } else if let Some(end) = transformed_ty.eq_token().map(|tok| tok.text_range().start())
            {
                end
            } else if let Some(end) = transformed_ty
                .where_clause()
                .and_then(|wc| wc.where_token())
                .map(|tok| tok.text_range().start())
            {
                end
            } else if let Some(end) =
                transformed_ty.semicolon_token().map(|tok| tok.text_range().start())
            {
                end
            } else {
                return;
            };

            let len = end - start;
            let mut decl = transformed_ty.syntax().text().slice(..len).to_string();
            decl.truncate(decl.trim_end().len());
            decl.push_str(" = ");

            let wc = transformed_ty
                .where_clause()
                .map(|wc| {
                    let ws = wc
                        .where_token()
                        .and_then(|it| it.prev_token())
                        .filter(|token| token.kind() == SyntaxKind::WHITESPACE)
                        .map(|token| token.to_string())
                        .unwrap_or_else(|| " ".into());
                    format!("{ws}{wc}")
                })
                .unwrap_or_default();

            match ctx.config.snippet_cap {
                Some(cap) => {
                    let snippet = format!("{decl}$0{wc};");
                    item.snippet_edit(cap, TextEdit::replace(replacement_range, snippet));
                }
                None => {
                    decl.push_str(&wc);
                    item.text_edit(TextEdit::replace(replacement_range, decl));
                }
            };
            item.add_to(acc, ctx.db);
        }
    }
}

fn add_const_impl(
    acc: &mut Completions,
    ctx: &CompletionContext<'_, '_>,
    replacement_range: TextRange,
    const_: hir::Const,
    impl_def: hir::Impl,
) {
    let const_name = const_.name(ctx.db).map(|n| n.display_no_db(ctx.edition).to_smolstr());

    if let Some(const_name) = const_name
        && let Some(source) = ctx.sema.source(const_)
    {
        let assoc_item = ast::AssocItem::Const(source.value);
        if let Some(transformed_item) = get_transformed_assoc_item(ctx, assoc_item, impl_def) {
            let transformed_const = match transformed_item {
                ast::AssocItem::Const(const_) => const_,
                _ => unreachable!(),
            };

            let label =
                make_const_compl_syntax(ctx, &transformed_const, source.file_id.macro_file());
            let replacement = format!("{label} ");

            let mut item =
                CompletionItem::new(SymbolKind::Const, replacement_range, label, ctx.edition);
            item.lookup_by(format_smolstr!("const {const_name}"))
                .set_documentation(const_.docs(ctx.db))
                .set_relevance(CompletionRelevance {
                    exact_name_match: true,
                    ..Default::default()
                });
            match ctx.config.snippet_cap {
                Some(cap) => item.snippet_edit(
                    cap,
                    TextEdit::replace(replacement_range, format!("{replacement}$0;")),
                ),
                None => item.text_edit(TextEdit::replace(replacement_range, replacement)),
            };
            item.add_to(acc, ctx.db);
        }
    }
}

fn make_const_compl_syntax(
    ctx: &CompletionContext<'_, '_>,
    const_: &ast::Const,
    macro_file: Option<MacroCallId>,
) -> SmolStr {
    let const_ = if let Some(macro_file) = macro_file {
        let span_map = ctx.db.expansion_span_map(macro_file);
        prettify_macro_expansion(ctx.db, const_.syntax().clone(), span_map, ctx.krate.into())
    } else {
        const_.syntax().clone()
    };

    let start = const_.text_range().start();
    let const_end = const_.text_range().end();

    let end = const_
        .children_with_tokens()
        .find(|s| s.kind() == T![;] || s.kind() == T![=])
        .map_or(const_end, |f| f.text_range().start());

    let len = end - start;
    let range = TextRange::new(0.into(), len);

    let syntax = const_.text().slice(range).to_string();

    format_smolstr!("{} =", syntax.trim_end())
}

fn function_declaration(
    ctx: &CompletionContext<'_, '_>,
    node: &ast::Fn,
    macro_file: Option<MacroCallId>,
) -> String {
    let node = if let Some(macro_file) = macro_file {
        let span_map = ctx.db.expansion_span_map(macro_file);
        prettify_macro_expansion(ctx.db, node.syntax().clone(), span_map, ctx.krate.into())
    } else {
        node.syntax().clone()
    };

    let start = node.text_range().start();
    let end = node.text_range().end();

    let end = node
        .last_child_or_token()
        .filter(|s| s.kind() == T![;] || s.kind() == SyntaxKind::BLOCK_EXPR)
        .map_or(end, |f| f.text_range().start());

    let len = end - start;
    let syntax = node.text().slice(..len).to_string();

    syntax.trim_end().to_owned()
}

#[cfg(test)]
mod tests {
    use expect_test::expect;

    use crate::tests::{check, check_edit, check_no_kw};

    #[test]
    fn no_completion_inside_fn() {
        check_no_kw(
            r"
trait Test { fn test(); fn test2(); }
struct T;

impl Test for T {
    fn test() {
        t$0
    }
}
",
            expect![[r#"
                sp Self  T
                st T     T
                tt Test
                bt u32 u32
            "#]],
        );

        check_no_kw(
            r"
trait Test { fn test(); fn test2(); }
struct T;

impl Test for T {
    fn test() {
        fn t$0
    }
}
",
            expect![[""]],
        );

        check_no_kw(
            r"
trait Test { fn test(); fn test2(); }
struct T;

impl Test for T {
    fn test() {
        fn $0
    }
}
",
            expect![[""]],
        );

        // https://github.com/rust-lang/rust-analyzer/pull/5976#issuecomment-692332191
        check_no_kw(
            r"
trait Test { fn test(); fn test2(); }
struct T;

impl Test for T {
    fn test() {
        foo.$0
    }
}
",
            expect![[r#""#]],
        );

        check_no_kw(
            r"
trait Test { fn test(_: i32); fn test2(); }
struct T;

impl Test for T {
    fn test(t$0)
}
",
            expect![[r#"
                sp Self
                st T
                bn &mut self
                bn &self
                bn mut self
                bn self
            "#]],
        );

        check_no_kw(
            r"
trait Test { fn test(_: fn()); fn test2(); }
struct T;

impl Test for T {
    fn test(f: fn $0)
}
",
            expect![[r#"
                sp Self
                st T
            "#]],
        );
    }

    #[test]
    fn no_completion_inside_const() {
        check_no_kw(
            r"
trait Test { const TEST: fn(); const TEST2: u32; type Test; fn test(); }
struct T;

impl Test for T {
    const TEST: fn $0
}
",
            expect![[r#""#]],
        );

        check_no_kw(
            r"
trait Test { const TEST: u32; const TEST2: u32; type Test; fn test(); }
struct T;

impl Test for T {
    const TEST: T$0
}
",
            expect![[r#"
                sp Self  T
                st T     T
                tt Test
                bt u32 u32
            "#]],
        );

        check_no_kw(
            r"
trait Test { const TEST: u32; const TEST2: u32; type Test; fn test(); }
struct T;

impl Test for T {
    const TEST: u32 = f$0
}
",
            expect![[r#"
                sp Self  T
                st T     T
                tt Test
                bt u32 u32
            "#]],
        );

        check_no_kw(
            r"
trait Test { const TEST: u32; const TEST2: u32; type Test; fn test(); }
struct T;

impl Test for T {
    const TEST: u32 = {
        t$0
    };
}
",
            expect![[r#"
                sp Self  T
                st T     T
                tt Test
                bt u32 u32
            "#]],
        );

        check_no_kw(
            r"
trait Test { const TEST: u32; const TEST2: u32; type Test; fn test(); }
struct T;

impl Test for T {
    const TEST: u32 = {
        fn $0
    };
}
",
            expect![[""]],
        );

        check_no_kw(
            r"
trait Test { const TEST: u32; const TEST2: u32; type Test; fn test(); }
struct T;

impl Test for T {
    const TEST: u32 = {
        fn t$0
    };
}
",
            expect![[""]],
        );
    }

    #[test]
    fn no_completion_inside_type() {
        check_no_kw(
            r"
trait Test { type Test; type Test2; fn test(); }
struct T;

impl Test for T {
    type Test = T$0;
}
",
            expect![[r#"
                sp Self  T
                st T     T
                tt Test
                bt u32 u32
            "#]],
        );

        check_no_kw(
            r"
trait Test { type Test; type Test2; fn test(); }
struct T;

impl Test for T {
    type Test = fn $0;
}
",
            expect![[r#""#]],
        );
    }

    #[test]
    fn name_ref_single_function() {
        check_edit(
            "fn test",
            r#"
trait Test {
    fn test();
}
struct T;

impl Test for T {
    t$0
}
"#,
            r#"
trait Test {
    fn test();
}
struct T;

impl Test for T {
    fn test() {
    $0
}
}
"#,
        );
    }

    #[test]
    fn single_function() {
        check_edit(
            "fn test",
            r#"
trait Test {
    fn test();
}
struct T;

impl Test for T {
    fn t$0
}
"#,
            r#"
trait Test {
    fn test();
}
struct T;

impl Test for T {
    fn test() {
    $0
}
}
"#,
        );
    }

    #[test]
    fn generic_fn() {
        check_edit(
            "fn foo",
            r#"
trait Test {
    fn foo<T>();
}
struct T;

impl Test for T {
    fn f$0
}
"#,
            r#"
trait Test {
    fn foo<T>();
}
struct T;

impl Test for T {
    fn foo<T>() {
    $0
}
}
"#,
        );
        check_edit(
            "fn foo",
            r#"
trait Test {
    fn foo<T>() where T: Into<String>;
}
struct T;

impl Test for T {
    fn f$0
}
"#,
            r#"
trait Test {
    fn foo<T>() where T: Into<String>;
}
struct T;

impl Test for T {
    fn foo<T>() where T: Into<String> {
    $0
}
}
"#,
        );
    }

    #[test]
    fn associated_type() {
        check_edit(
            "type SomeType",
            r#"
trait Test {
    type SomeType;
}

impl Test for () {
    type S$0
}
"#,
            "
trait Test {
    type SomeType;
}

impl Test for () {
    type SomeType = $0;\n\
}
",
        );
        check_edit(
            "type SomeType",
            r#"
trait Test {
    type SomeType;
}

impl Test for () {
    type$0
}
"#,
            "
trait Test {
    type SomeType;
}

impl Test for () {
    type SomeType = $0;\n\
}
",
        );
    }

    #[test]
    fn associated_const() {
        check_edit(
            "const SOME_CONST",
            r#"
trait Test {
    const SOME_CONST: u16;
}

impl Test for () {
    const S$0
}
"#,
            "
trait Test {
    const SOME_CONST: u16;
}

impl Test for () {
    const SOME_CONST: u16 = $0;\n\
}
",
        );

        check_edit(
            "const SOME_CONST",
            r#"
trait Test {
    const SOME_CONST: u16 = 92;
}

impl Test for () {
    const S$0
}
"#,
            "
trait Test {
    const SOME_CONST: u16 = 92;
}

impl Test for () {
    const SOME_CONST: u16 = $0;\n\
}
",
        );
    }

    #[test]
    fn fn_with_lifetimes() {
        check_edit(
            "fn foo",
            r#"
trait Test<'a, 'b, T> {
    fn foo(&self, a: &'a T, b: &'b T) -> &'a T;
}

impl<'x, 'y, A> Test<'x, 'y, A> for () {
    t$0
}
"#,
            r#"
trait Test<'a, 'b, T> {
    fn foo(&self, a: &'a T, b: &'b T) -> &'a T;
}

impl<'x, 'y, A> Test<'x, 'y, A> for () {
    fn foo(&self, a: &'x A, b: &'y A) -> &'x A {
    $0
}
}
"#,
        );
    }

    #[test]
    fn complete_without_name() {
        let test = |completion: &str, hint: &str, completed: &str, next_sibling: &str| {
            check_edit(
                completion,
                &format!(
                    r#"
trait Test {{
    type Foo;
    const CONST: u16;
    fn bar();
}}
struct T;

impl Test for T {{
    {hint}
    {next_sibling}
}}
"#
                ),
                &format!(
                    r#"
trait Test {{
    type Foo;
    const CONST: u16;
    fn bar();
}}
struct T;

impl Test for T {{
    {completed}
    {next_sibling}
}}
"#
                ),
            )
        };

        // Enumerate some possible next siblings.
        for next_sibling in [
            "",
            "fn other_fn() {}", // `const $0 fn` -> `const fn`
            "type OtherType = i32;",
            "const OTHER_CONST: i32 = 0;",
            "async fn other_fn() {}",
            "unsafe fn other_fn() {}",
            "default fn other_fn() {}",
            "default type OtherType = i32;",
            "default const OTHER_CONST: i32 = 0;",
        ] {
            test("fn bar", "fn $0", "fn bar() {\n    $0\n}", next_sibling);
            test("type Foo", "type $0", "type Foo = $0;", next_sibling);
            test("const CONST", "const $0", "const CONST: u16 = $0;", next_sibling);
        }
    }

    #[test]
    fn snippet_does_not_overwrite_comment_or_attr() {
        let test = |completion: &str, hint: &str, completed: &str| {
            check_edit(
                completion,
                &format!(
                    r#"
trait Foo {{
    type Type;
    fn function();
    const CONST: i32 = 0;
}}
struct T;

impl Foo for T {{
    // Comment
    #[bar]
    {hint}
}}
"#
                ),
                &format!(
                    r#"
trait Foo {{
    type Type;
    fn function();
    const CONST: i32 = 0;
}}
struct T;

impl Foo for T {{
    // Comment
    #[bar]
    {completed}
}}
"#
                ),
            )
        };
        test("fn function", "fn f$0", "fn function() {\n    $0\n}");
        test("type Type", "type T$0", "type Type = $0;");
        test("const CONST", "const C$0", "const CONST: i32 = $0;");
    }

    #[test]
    fn generics_are_inlined_in_return_type() {
        check_edit(
            "fn function",
            r#"
trait Foo<T> {
    fn function() -> T;
}
struct Bar;

impl Foo<u32> for Bar {
    fn f$0
}
"#,
            r#"
trait Foo<T> {
    fn function() -> T;
}
struct Bar;

impl Foo<u32> for Bar {
    fn function() -> u32 {
    $0
}
}
"#,
        )
    }

    #[test]
    fn generics_are_inlined_in_parameter() {
        check_edit(
            "fn function",
            r#"
trait Foo<T> {
    fn function(bar: T);
}
struct Bar;

impl Foo<u32> for Bar {
    fn f$0
}
"#,
            r#"
trait Foo<T> {
    fn function(bar: T);
}
struct Bar;

impl Foo<u32> for Bar {
    fn function(bar: u32) {
    $0
}
}
"#,
        )
    }

    #[test]
    fn generics_are_inlined_when_part_of_other_types() {
        check_edit(
            "fn function",
            r#"
trait Foo<T> {
    fn function(bar: Vec<T>);
}
struct Bar;

impl Foo<u32> for Bar {
    fn f$0
}
"#,
            r#"
trait Foo<T> {
    fn function(bar: Vec<T>);
}
struct Bar;

impl Foo<u32> for Bar {
    fn function(bar: Vec<u32>) {
    $0
}
}
"#,
        )
    }

    #[test]
    fn generics_are_inlined_complex() {
        check_edit(
            "fn function",
            r#"
trait Foo<T, U, V> {
    fn function(bar: Vec<T>, baz: U) -> Arc<Vec<V>>;
}
struct Bar;

impl Foo<u32, Vec<usize>, u8> for Bar {
    fn f$0
}
"#,
            r#"
trait Foo<T, U, V> {
    fn function(bar: Vec<T>, baz: U) -> Arc<Vec<V>>;
}
struct Bar;

impl Foo<u32, Vec<usize>, u8> for Bar {
    fn function(bar: Vec<u32>, baz: Vec<usize>) -> Arc<Vec<u8>> {
    $0
}
}
"#,
        )
    }

    #[test]
    fn generics_are_inlined_in_associated_const() {
        check_edit(
            "const BAR",
            r#"
trait Foo<T> {
    const BAR: T;
}
struct Bar;

impl Foo<u32> for Bar {
    const B$0
}
"#,
            r#"
trait Foo<T> {
    const BAR: T;
}
struct Bar;

impl Foo<u32> for Bar {
    const BAR: u32 = $0;
}
"#,
        )
    }

    #[test]
    fn generics_are_inlined_in_where_clause() {
        check_edit(
            "fn function",
            r#"
trait SomeTrait<T> {}

trait Foo<T> {
    fn function()
    where Self: SomeTrait<T>;
}
struct Bar;

impl Foo<u32> for Bar {
    fn f$0
}
"#,
            r#"
trait SomeTrait<T> {}

trait Foo<T> {
    fn function()
    where Self: SomeTrait<T>;
}
struct Bar;

impl Foo<u32> for Bar {
    fn function()
where Self: SomeTrait<u32>
{
    $0
}
}
"#,
        )
    }

    #[test]
    fn works_directly_in_impl() {
        check_no_kw(
            r#"
trait Tr {
    fn required();
}

impl Tr for () {
    $0
}
"#,
            expect![[r#"
            fn fn required()
        "#]],
        );
        check_no_kw(
            r#"
trait Tr {
    fn provided() {}
    fn required();
}

impl Tr for () {
    fn provided() {}
    $0
}
"#,
            expect![[r#"
            fn fn required()
        "#]],
        );
    }

    #[test]
    fn fixes_up_macro_generated() {
        check_edit(
            "fn foo",
            r#"
macro_rules! noop {
    ($($item: item)*) => {
        $($item)*
    }
}

noop! {
    trait Foo {
        fn foo(&mut self, bar: i64, baz: &mut u32) -> Result<(), u32>;
    }
}

struct Test;

impl Foo for Test {
    $0
}
"#,
            r#"
macro_rules! noop {
    ($($item: item)*) => {
        $($item)*
    }
}

noop! {
    trait Foo {
        fn foo(&mut self, bar: i64, baz: &mut u32) -> Result<(), u32>;
    }
}

struct Test;

impl Foo for Test {
    fn foo(&mut self,bar: i64,baz: &mut u32) -> Result<(),u32> {
    $0
}
}
"#,
        );
    }

    #[test]
    fn macro_generated_assoc_item() {
        check_edit(
            "fn method",
            r#"
macro_rules! ty { () => { i32 } }
trait SomeTrait { type Output; }
impl SomeTrait for i32 { type Output = i64; }
macro_rules! define_method {
    () => {
        fn method(&mut self, params: <ty!() as SomeTrait>::Output);
    };
}
trait AnotherTrait { define_method!(); }
impl AnotherTrait for () {
    $0
}
"#,
            r#"
macro_rules! ty { () => { i32 } }
trait SomeTrait { type Output; }
impl SomeTrait for i32 { type Output = i64; }
macro_rules! define_method {
    () => {
        fn method(&mut self, params: <ty!() as SomeTrait>::Output);
    };
}
trait AnotherTrait { define_method!(); }
impl AnotherTrait for () {
    fn method(&mut self,params: <ty!()as SomeTrait>::Output) {
    $0
}
}
"#,
        );
    }

    // FIXME: `T` in `ty!(T)` should be replaced by `PathTransform`.
    #[test]
    fn macro_generated_assoc_item2() {
        check_edit(
            "fn method",
            r#"
macro_rules! ty { ($me:ty) => { $me } }
trait SomeTrait { type Output; }
impl SomeTrait for i32 { type Output = i64; }
macro_rules! define_method {
    ($t:ty) => {
        fn method(&mut self, params: <ty!($t) as SomeTrait>::Output);
    };
}
trait AnotherTrait<T: SomeTrait> { define_method!(T); }
impl AnotherTrait<i32> for () {
    $0
}
"#,
            r#"
macro_rules! ty { ($me:ty) => { $me } }
trait SomeTrait { type Output; }
impl SomeTrait for i32 { type Output = i64; }
macro_rules! define_method {
    ($t:ty) => {
        fn method(&mut self, params: <ty!($t) as SomeTrait>::Output);
    };
}
trait AnotherTrait<T: SomeTrait> { define_method!(T); }
impl AnotherTrait<i32> for () {
    fn method(&mut self,params: <ty!(T)as SomeTrait>::Output) {
    $0
}
}
"#,
        );
    }

    #[test]
    fn includes_gat_generics() {
        check_edit(
            "type Ty",
            r#"
trait Tr<'b> {
    type Ty<'a: 'b, T: Copy, const C: usize>;
}

impl<'b> Tr<'b> for () {
    $0
}
"#,
            r#"
trait Tr<'b> {
    type Ty<'a: 'b, T: Copy, const C: usize>;
}

impl<'b> Tr<'b> for () {
    type Ty<'a: 'b, T: Copy, const C: usize> = $0;
}
"#,
        );
    }
    #[test]
    fn includes_where_clause() {
        check_edit(
            "type Ty",
            r#"
trait Tr {
    type Ty where Self: Copy;
}

impl Tr for () {
    $0
}
"#,
            r#"
trait Tr {
    type Ty where Self: Copy;
}

impl Tr for () {
    type Ty = $0 where Self: Copy;
}
"#,
        );
    }

    #[test]
    fn strips_comments() {
        check_edit(
            "fn func",
            r#"
trait Tr {
    /// docs
    #[attr]
    fn func();
}
impl Tr for () {
    $0
}
"#,
            r#"
trait Tr {
    /// docs
    #[attr]
    fn func();
}
impl Tr for () {
    fn func() {
    $0
}
}
"#,
        );
        check_edit(
            "const C",
            r#"
trait Tr {
    /// docs
    #[attr]
    const C: usize;
}
impl Tr for () {
    $0
}
"#,
            r#"
trait Tr {
    /// docs
    #[attr]
    const C: usize;
}
impl Tr for () {
    const C: usize = $0;
}
"#,
        );
        check_edit(
            "type Item",
            r#"
trait Tr {
    /// docs
    #[attr]
    type Item;
}
impl Tr for () {
    $0
}
"#,
            r#"
trait Tr {
    /// docs
    #[attr]
    type Item;
}
impl Tr for () {
    type Item = $0;
}
"#,
        );
    }

    #[test]
    fn impl_fut() {
        check_edit(
            "fn foo",
            r#"
//- minicore: future, send, sized
use core::future::Future;

trait DesugaredAsyncTrait {
    fn foo(&self) -> impl Future<Output = usize> + Send;
}

impl DesugaredAsyncTrait for () {
    $0
}
"#,
            r#"
use core::future::Future;

trait DesugaredAsyncTrait {
    fn foo(&self) -> impl Future<Output = usize> + Send;
}

impl DesugaredAsyncTrait for () {
    fn foo(&self) -> impl Future<Output = usize> + Send {
    $0
}
}
"#,
        );
    }

    #[test]
    fn impl_fut_resugared() {
        check_edit(
            "async fn foo",
            r#"
//- minicore: future, send, sized
use core::future::Future;

trait DesugaredAsyncTrait {
    fn foo(&self) -> impl Future<Output = usize> + Send;
}

impl DesugaredAsyncTrait for () {
    $0
}
"#,
            r#"
use core::future::Future;

trait DesugaredAsyncTrait {
    fn foo(&self) -> impl Future<Output = usize> + Send;
}

impl DesugaredAsyncTrait for () {
    async fn foo(&self) -> usize {
    $0
}
}
"#,
        );

        check_edit(
            "async fn foo",
            r#"
//- minicore: future, send, sized
use core::future::Future;

trait DesugaredAsyncTrait {
    fn foo(&self) -> impl Future<Output = ()> + Send;
}

impl DesugaredAsyncTrait for () {
    $0
}
"#,
            r#"
use core::future::Future;

trait DesugaredAsyncTrait {
    fn foo(&self) -> impl Future<Output = ()> + Send;
}

impl DesugaredAsyncTrait for () {
    async fn foo(&self) {
    $0
}
}
"#,
        );
    }

    #[test]
    fn async_desugared() {
        check_edit(
            "fn foo",
            r#"
//- minicore: future, send, sized
use core::future::Future;

trait DesugaredAsyncTrait {
    async fn foo(&self) -> usize;
}

impl DesugaredAsyncTrait for () {
    $0
}
"#,
            r#"
use core::future::Future;

trait DesugaredAsyncTrait {
    async fn foo(&self) -> usize;
}

impl DesugaredAsyncTrait for () {
     fn foo(&self) -> impl Future<Output = usize> {
    $0
}
}
"#,
        );
    }

    #[test]
    fn async_() {
        check_edit(
            "async fn foo",
            r#"
//- minicore: future, send, sized
use core::future::Future;

trait DesugaredAsyncTrait {
    async fn foo(&self) -> usize;
}

impl DesugaredAsyncTrait for () {
    $0
}
"#,
            r#"
use core::future::Future;

trait DesugaredAsyncTrait {
    async fn foo(&self) -> usize;
}

impl DesugaredAsyncTrait for () {
    async fn foo(&self) -> usize {
    $0
}
}
"#,
        );
    }

    #[test]
    fn within_attr_macro() {
        check(
            r#"
//- proc_macros: identity
trait Trait {
    fn foo(&self) {}
    fn bar(&self) {}
    fn baz(&self) {}
}

#[proc_macros::identity]
impl Trait for () {
    f$0
}
                "#,
            expect![[r#"
                me fn bar(..)
                me fn baz(..)
                me fn foo(..)
                md proc_macros::
                kw crate::
                kw self::
            "#]],
        );
        check(
            r#"
//- proc_macros: identity
trait Trait {
    fn foo(&self) {}
    fn bar(&self) {}
    fn baz(&self) {}
}

#[proc_macros::identity]
impl Trait for () {
    fn $0
}
        "#,
            expect![[r#"
                me fn bar(..)
                me fn baz(..)
                me fn foo(..)
            "#]],
        );
    }
}
