1 files changed, 488 insertions, 0 deletions

diff --git a/crates/ide/src/completion/complete_trait_impl.rs b/crates/ide/src/completion/complete_trait_impl.rs
new file mode 100644
index 000000000..478e31262
--- /dev/null
+++ b/crates/ide/src/completion/complete_trait_impl.rs
@@ -0,0 +1,488 @@
+//! Completion for associated items in a trait implementation.
+//!
+//! This module adds the completion items related to implementing associated
+//! items within a `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<|>
+//! }
+//! ```
+//!
+//! may result in the completion of the following method:
+//!
+//! ```ignore
+//! # trait SomeTrait {
+//! #    fn foo();
+//! # }
+//!
+//! impl SomeTrait for () {
+//!     fn foo() {}<|>
+//! }
+//! ```
+
+use assists::utils::get_missing_assoc_items;
+use hir::{self, Docs, HasSource};
+use syntax::{
+    ast::{self, edit, Impl},
+    AstNode, SyntaxKind, SyntaxNode, TextRange, T,
+};
+use text_edit::TextEdit;
+
+use crate::{
+    completion::{
+        CompletionContext, CompletionItem, CompletionItemKind, CompletionKind, Completions,
+    },
+    display::function_declaration,
+};
+
+pub(crate) fn complete_trait_impl(acc: &mut Completions, ctx: &CompletionContext) {
+    if let Some((trigger, impl_def)) = completion_match(ctx) {
+        match trigger.kind() {
+            SyntaxKind::NAME_REF => get_missing_assoc_items(&ctx.sema, &impl_def)
+                .into_iter()
+                .for_each(|item| match item {
+                    hir::AssocItem::Function(fn_item) => {
+                        add_function_impl(&trigger, acc, ctx, fn_item)
+                    }
+                    hir::AssocItem::TypeAlias(type_item) => {
+                        add_type_alias_impl(&trigger, acc, ctx, type_item)
+                    }
+                    hir::AssocItem::Const(const_item) => {
+                        add_const_impl(&trigger, acc, ctx, const_item)
+                    }
+                }),
+
+            SyntaxKind::FN => {
+                for missing_fn in get_missing_assoc_items(&ctx.sema, &impl_def)
+                    .into_iter()
+                    .filter_map(|item| match item {
+                        hir::AssocItem::Function(fn_item) => Some(fn_item),
+                        _ => None,
+                    })
+                {
+                    add_function_impl(&trigger, acc, ctx, missing_fn);
+                }
+            }
+
+            SyntaxKind::TYPE_ALIAS => {
+                for missing_fn in get_missing_assoc_items(&ctx.sema, &impl_def)
+                    .into_iter()
+                    .filter_map(|item| match item {
+                        hir::AssocItem::TypeAlias(type_item) => Some(type_item),
+                        _ => None,
+                    })
+                {
+                    add_type_alias_impl(&trigger, acc, ctx, missing_fn);
+                }
+            }
+
+            SyntaxKind::CONST => {
+                for missing_fn in get_missing_assoc_items(&ctx.sema, &impl_def)
+                    .into_iter()
+                    .filter_map(|item| match item {
+                        hir::AssocItem::Const(const_item) => Some(const_item),
+                        _ => None,
+                    })
+                {
+                    add_const_impl(&trigger, acc, ctx, missing_fn);
+                }
+            }
+
+            _ => {}
+        }
+    }
+}
+
+fn completion_match(ctx: &CompletionContext) -> Option<(SyntaxNode, Impl)> {
+    let (trigger, impl_def_offset) = ctx.token.ancestors().find_map(|p| match p.kind() {
+        SyntaxKind::FN | SyntaxKind::TYPE_ALIAS | SyntaxKind::CONST | SyntaxKind::BLOCK_EXPR => {
+            Some((p, 2))
+        }
+        SyntaxKind::NAME_REF => Some((p, 5)),
+        _ => None,
+    })?;
+    let impl_def = (0..impl_def_offset - 1)
+        .try_fold(trigger.parent()?, |t, _| t.parent())
+        .and_then(ast::Impl::cast)?;
+    Some((trigger, impl_def))
+}
+
+fn add_function_impl(
+    fn_def_node: &SyntaxNode,
+    acc: &mut Completions,
+    ctx: &CompletionContext,
+    func: hir::Function,
+) {
+    let fn_name = func.name(ctx.db).to_string();
+
+    let label = if !func.params(ctx.db).is_empty() {
+        format!("fn {}(..)", fn_name)
+    } else {
+        format!("fn {}()", fn_name)
+    };
+
+    let builder = CompletionItem::new(CompletionKind::Magic, ctx.source_range(), label)
+        .lookup_by(fn_name)
+        .set_documentation(func.docs(ctx.db));
+
+    let completion_kind = if func.has_self_param(ctx.db) {
+        CompletionItemKind::Method
+    } else {
+        CompletionItemKind::Function
+    };
+    let range = TextRange::new(fn_def_node.text_range().start(), ctx.source_range().end());
+
+    let function_decl = function_declaration(&func.source(ctx.db).value);
+    match ctx.config.snippet_cap {
+        Some(cap) => {
+            let snippet = format!("{} {{\n    $0\n}}", function_decl);
+            builder.snippet_edit(cap, TextEdit::replace(range, snippet))
+        }
+        None => {
+            let header = format!("{} {{", function_decl);
+            builder.text_edit(TextEdit::replace(range, header))
+        }
+    }
+    .kind(completion_kind)
+    .add_to(acc);
+}
+
+fn add_type_alias_impl(
+    type_def_node: &SyntaxNode,
+    acc: &mut Completions,
+    ctx: &CompletionContext,
+    type_alias: hir::TypeAlias,
+) {
+    let alias_name = type_alias.name(ctx.db).to_string();
+
+    let snippet = format!("type {} = ", alias_name);
+
+    let range = TextRange::new(type_def_node.text_range().start(), ctx.source_range().end());
+
+    CompletionItem::new(CompletionKind::Magic, ctx.source_range(), snippet.clone())
+        .text_edit(TextEdit::replace(range, snippet))
+        .lookup_by(alias_name)
+        .kind(CompletionItemKind::TypeAlias)
+        .set_documentation(type_alias.docs(ctx.db))
+        .add_to(acc);
+}
+
+fn add_const_impl(
+    const_def_node: &SyntaxNode,
+    acc: &mut Completions,
+    ctx: &CompletionContext,
+    const_: hir::Const,
+) {
+    let const_name = const_.name(ctx.db).map(|n| n.to_string());
+
+    if let Some(const_name) = const_name {
+        let snippet = make_const_compl_syntax(&const_.source(ctx.db).value);
+
+        let range = TextRange::new(const_def_node.text_range().start(), ctx.source_range().end());
+
+        CompletionItem::new(CompletionKind::Magic, ctx.source_range(), snippet.clone())
+            .text_edit(TextEdit::replace(range, snippet))
+            .lookup_by(const_name)
+            .kind(CompletionItemKind::Const)
+            .set_documentation(const_.docs(ctx.db))
+            .add_to(acc);
+    }
+}
+
+fn make_const_compl_syntax(const_: &ast::Const) -> String {
+    let const_ = edit::remove_attrs_and_docs(const_);
+
+    let const_start = const_.syntax().text_range().start();
+    let const_end = const_.syntax().text_range().end();
+
+    let start =
+        const_.syntax().first_child_or_token().map_or(const_start, |f| f.text_range().start());
+
+    let end = const_
+        .syntax()
+        .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_.syntax().text().slice(range).to_string();
+
+    format!("{} = ", syntax.trim_end())
+}
+
+#[cfg(test)]
+mod tests {
+    use expect::{expect, Expect};
+
+    use crate::completion::{
+        test_utils::{check_edit, completion_list},
+        CompletionKind,
+    };
+
+    fn check(ra_fixture: &str, expect: Expect) {
+        let actual = completion_list(ra_fixture, CompletionKind::Magic);
+        expect.assert_eq(&actual)
+    }
+
+    #[test]
+    fn name_ref_function_type_const() {
+        check(
+            r#"
+trait Test {
+    type TestType;
+    const TEST_CONST: u16;
+    fn test();
+}
+struct T;
+
+impl Test for T {
+    t<|>
+}
+"#,
+            expect![["
+ct const TEST_CONST: u16 = \n\
+fn fn test()
+ta type TestType = \n\
+            "]],
+        );
+    }
+
+    #[test]
+    fn no_nested_fn_completions() {
+        check(
+            r"
+trait Test {
+    fn test();
+    fn test2();
+}
+struct T;
+
+impl Test for T {
+    fn test() {
+        t<|>
+    }
+}
+",
+            expect![[""]],
+        );
+    }
+
+    #[test]
+    fn name_ref_single_function() {
+        check_edit(
+            "test",
+            r#"
+trait Test {
+    fn test();
+}
+struct T;
+
+impl Test for T {
+    t<|>
+}
+"#,
+            r#"
+trait Test {
+    fn test();
+}
+struct T;
+
+impl Test for T {
+    fn test() {
+    $0
+}
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn single_function() {
+        check_edit(
+            "test",
+            r#"
+trait Test {
+    fn test();
+}
+struct T;
+
+impl Test for T {
+    fn t<|>
+}
+"#,
+            r#"
+trait Test {
+    fn test();
+}
+struct T;
+
+impl Test for T {
+    fn test() {
+    $0
+}
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn hide_implemented_fn() {
+        check(
+            r#"
+trait Test {
+    fn foo();
+    fn foo_bar();
+}
+struct T;
+
+impl Test for T {
+    fn foo() {}
+    fn f<|>
+}
+"#,
+            expect![[r#"
+                fn fn foo_bar()
+            "#]],
+        );
+    }
+
+    #[test]
+    fn generic_fn() {
+        check_edit(
+            "foo",
+            r#"
+trait Test {
+    fn foo<T>();
+}
+struct T;
+
+impl Test for T {
+    fn f<|>
+}
+"#,
+            r#"
+trait Test {
+    fn foo<T>();
+}
+struct T;
+
+impl Test for T {
+    fn foo<T>() {
+    $0
+}
+}
+"#,
+        );
+        check_edit(
+            "foo",
+            r#"
+trait Test {
+    fn foo<T>() where T: Into<String>;
+}
+struct T;
+
+impl Test for T {
+    fn f<|>
+}
+"#,
+            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(
+            "SomeType",
+            r#"
+trait Test {
+    type SomeType;
+}
+
+impl Test for () {
+    type S<|>
+}
+"#,
+            "
+trait Test {
+    type SomeType;
+}
+
+impl Test for () {
+    type SomeType = \n\
+}
+",
+        );
+    }
+
+    #[test]
+    fn associated_const() {
+        check_edit(
+            "SOME_CONST",
+            r#"
+trait Test {
+    const SOME_CONST: u16;
+}
+
+impl Test for () {
+    const S<|>
+}
+"#,
+            "
+trait Test {
+    const SOME_CONST: u16;
+}
+
+impl Test for () {
+    const SOME_CONST: u16 = \n\
+}
+",
+        );
+
+        check_edit(
+            "SOME_CONST",
+            r#"
+trait Test {
+    const SOME_CONST: u16 = 92;
+}
+
+impl Test for () {
+    const S<|>
+}
+"#,
+            "
+trait Test {
+    const SOME_CONST: u16 = 92;
+}
+
+impl Test for () {
+    const SOME_CONST: u16 = \n\
+}
+",
+        );
+    }
+}