17 files changed, 900 insertions, 98 deletions

diff --git a/crates/ide/src/completion.rs b/crates/ide/src/completion.rs
index 33bed6991..daea2aa95 100644
--- a/crates/ide/src/completion.rs
+++ b/crates/ide/src/completion.rs
@@ -19,6 +19,7 @@ mod complete_unqualified_path;
 mod complete_postfix;
 mod complete_macro_in_item_position;
 mod complete_trait_impl;
+mod complete_mod;
 
 use ide_db::RootDatabase;
 
@@ -124,6 +125,7 @@ pub(crate) fn completions(
     complete_postfix::complete_postfix(&mut acc, &ctx);
     complete_macro_in_item_position::complete_macro_in_item_position(&mut acc, &ctx);
     complete_trait_impl::complete_trait_impl(&mut acc, &ctx);
+    complete_mod::complete_mod(&mut acc, &ctx);
 
     Some(acc)
 }
diff --git a/crates/ide/src/completion/complete_attribute.rs b/crates/ide/src/completion/complete_attribute.rs
index 0abfaebcb..f4a9864d1 100644
--- a/crates/ide/src/completion/complete_attribute.rs
+++ b/crates/ide/src/completion/complete_attribute.rs
@@ -13,6 +13,10 @@ use crate::completion::{
 };
 
 pub(super) fn complete_attribute(acc: &mut Completions, ctx: &CompletionContext) -> Option<()> {
+    if ctx.mod_declaration_under_caret.is_some() {
+        return None;
+    }
+
     let attribute = ctx.attribute_under_caret.as_ref()?;
     match (attribute.path(), attribute.token_tree()) {
         (Some(path), Some(token_tree)) if path.to_string() == "derive" => {
diff --git a/crates/ide/src/completion/complete_keyword.rs b/crates/ide/src/completion/complete_keyword.rs
index 53ba76e0e..5645b41fa 100644
--- a/crates/ide/src/completion/complete_keyword.rs
+++ b/crates/ide/src/completion/complete_keyword.rs
@@ -510,6 +510,28 @@ pub mod future {
             expect![[r#"
                 kw await expr.await
             "#]],
+        );
+
+        check(
+            r#"
+//- /main.rs
+use std::future::*;
+fn foo() {
+    let a = async {};
+    a.<|>
+}
+
+//- /std/lib.rs
+pub mod future {
+    #[lang = "future_trait"]
+    pub trait Future {
+        type Output;
+    }
+}
+"#,
+            expect![[r#"
+                kw await expr.await
+            "#]],
         )
     }
 
diff --git a/crates/ide/src/completion/complete_mod.rs b/crates/ide/src/completion/complete_mod.rs
new file mode 100644
index 000000000..3cfc2e131
--- /dev/null
+++ b/crates/ide/src/completion/complete_mod.rs
@@ -0,0 +1,324 @@
+//! Completes mod declarations.
+
+use base_db::{SourceDatabaseExt, VfsPath};
+use hir::{Module, ModuleSource};
+use ide_db::RootDatabase;
+use rustc_hash::FxHashSet;
+
+use crate::{CompletionItem, CompletionItemKind};
+
+use super::{
+    completion_context::CompletionContext, completion_item::CompletionKind,
+    completion_item::Completions,
+};
+
+/// Complete mod declaration, i.e. `mod <|> ;`
+pub(super) fn complete_mod(acc: &mut Completions, ctx: &CompletionContext) -> Option<()> {
+    let mod_under_caret = match &ctx.mod_declaration_under_caret {
+        Some(mod_under_caret) if mod_under_caret.item_list().is_some() => return None,
+        Some(mod_under_caret) => mod_under_caret,
+        None => return None,
+    };
+
+    let _p = profile::span("completion::complete_mod");
+
+    let current_module = ctx.scope.module()?;
+
+    let module_definition_file =
+        current_module.definition_source(ctx.db).file_id.original_file(ctx.db);
+    let source_root = ctx.db.source_root(ctx.db.file_source_root(module_definition_file));
+    let directory_to_look_for_submodules = directory_to_look_for_submodules(
+        current_module,
+        ctx.db,
+        source_root.path_for_file(&module_definition_file)?,
+    )?;
+
+    let existing_mod_declarations = current_module
+        .children(ctx.db)
+        .filter_map(|module| Some(module.name(ctx.db)?.to_string()))
+        .collect::<FxHashSet<_>>();
+
+    let module_declaration_file =
+        current_module.declaration_source(ctx.db).map(|module_declaration_source_file| {
+            module_declaration_source_file.file_id.original_file(ctx.db)
+        });
+
+    source_root
+        .iter()
+        .filter(|submodule_candidate_file| submodule_candidate_file != &module_definition_file)
+        .filter(|submodule_candidate_file| {
+            Some(submodule_candidate_file) != module_declaration_file.as_ref()
+        })
+        .filter_map(|submodule_file| {
+            let submodule_path = source_root.path_for_file(&submodule_file)?;
+            let directory_with_submodule = submodule_path.parent()?;
+            match submodule_path.name_and_extension()? {
+                ("lib", Some("rs")) | ("main", Some("rs")) => None,
+                ("mod", Some("rs")) => {
+                    if directory_with_submodule.parent()? == directory_to_look_for_submodules {
+                        match directory_with_submodule.name_and_extension()? {
+                            (directory_name, None) => Some(directory_name.to_owned()),
+                            _ => None,
+                        }
+                    } else {
+                        None
+                    }
+                }
+                (file_name, Some("rs"))
+                    if directory_with_submodule == directory_to_look_for_submodules =>
+                {
+                    Some(file_name.to_owned())
+                }
+                _ => None,
+            }
+        })
+        .filter(|name| !existing_mod_declarations.contains(name))
+        .for_each(|submodule_name| {
+            let mut label = submodule_name;
+            if mod_under_caret.semicolon_token().is_none() {
+                label.push(';')
+            }
+            acc.add(
+                CompletionItem::new(CompletionKind::Magic, ctx.source_range(), &label)
+                    .kind(CompletionItemKind::Module),
+            )
+        });
+
+    Some(())
+}
+
+fn directory_to_look_for_submodules(
+    module: Module,
+    db: &RootDatabase,
+    module_file_path: &VfsPath,
+) -> Option<VfsPath> {
+    let directory_with_module_path = module_file_path.parent()?;
+    let base_directory = match module_file_path.name_and_extension()? {
+        ("mod", Some("rs")) | ("lib", Some("rs")) | ("main", Some("rs")) => {
+            Some(directory_with_module_path)
+        }
+        (regular_rust_file_name, Some("rs")) => {
+            if matches!(
+                (
+                    directory_with_module_path
+                        .parent()
+                        .as_ref()
+                        .and_then(|path| path.name_and_extension()),
+                    directory_with_module_path.name_and_extension(),
+                ),
+                (Some(("src", None)), Some(("bin", None)))
+            ) {
+                // files in /src/bin/ can import each other directly
+                Some(directory_with_module_path)
+            } else {
+                directory_with_module_path.join(regular_rust_file_name)
+            }
+        }
+        _ => None,
+    }?;
+
+    let mut resulting_path = base_directory;
+    for module in module_chain_to_containing_module_file(module, db) {
+        if let Some(name) = module.name(db) {
+            resulting_path = resulting_path.join(&name.to_string())?;
+        }
+    }
+
+    Some(resulting_path)
+}
+
+fn module_chain_to_containing_module_file(
+    current_module: Module,
+    db: &RootDatabase,
+) -> Vec<Module> {
+    let mut path = Vec::new();
+
+    let mut current_module = Some(current_module);
+    while let Some(ModuleSource::Module(_)) =
+        current_module.map(|module| module.definition_source(db).value)
+    {
+        if let Some(module) = current_module {
+            path.insert(0, module);
+            current_module = module.parent(db);
+        } else {
+            current_module = None;
+        }
+    }
+
+    path
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::completion::{test_utils::completion_list, CompletionKind};
+    use expect_test::{expect, Expect};
+
+    fn check(ra_fixture: &str, expect: Expect) {
+        let actual = completion_list(ra_fixture, CompletionKind::Magic);
+        expect.assert_eq(&actual);
+    }
+
+    #[test]
+    fn lib_module_completion() {
+        check(
+            r#"
+            //- /lib.rs
+            mod <|>
+            //- /foo.rs
+            fn foo() {}
+            //- /foo/ignored_foo.rs
+            fn ignored_foo() {}
+            //- /bar/mod.rs
+            fn bar() {}
+            //- /bar/ignored_bar.rs
+            fn ignored_bar() {}
+        "#,
+            expect![[r#"
+                md bar;
+                md foo;
+            "#]],
+        );
+    }
+
+    #[test]
+    fn no_module_completion_with_module_body() {
+        check(
+            r#"
+            //- /lib.rs
+            mod <|> {
+
+            }
+            //- /foo.rs
+            fn foo() {}
+        "#,
+            expect![[r#""#]],
+        );
+    }
+
+    #[test]
+    fn main_module_completion() {
+        check(
+            r#"
+            //- /main.rs
+            mod <|>
+            //- /foo.rs
+            fn foo() {}
+            //- /foo/ignored_foo.rs
+            fn ignored_foo() {}
+            //- /bar/mod.rs
+            fn bar() {}
+            //- /bar/ignored_bar.rs
+            fn ignored_bar() {}
+        "#,
+            expect![[r#"
+                md bar;
+                md foo;
+            "#]],
+        );
+    }
+
+    #[test]
+    fn main_test_module_completion() {
+        check(
+            r#"
+            //- /main.rs
+            mod tests {
+                mod <|>;
+            }
+            //- /tests/foo.rs
+            fn foo() {}
+        "#,
+            expect![[r#"
+                md foo
+            "#]],
+        );
+    }
+
+    #[test]
+    fn directly_nested_module_completion() {
+        check(
+            r#"
+            //- /lib.rs
+            mod foo;
+            //- /foo.rs
+            mod <|>;
+            //- /foo/bar.rs
+            fn bar() {}
+            //- /foo/bar/ignored_bar.rs
+            fn ignored_bar() {}
+            //- /foo/baz/mod.rs
+            fn baz() {}
+            //- /foo/moar/ignored_moar.rs
+            fn ignored_moar() {}
+        "#,
+            expect![[r#"
+                md bar
+                md baz
+            "#]],
+        );
+    }
+
+    #[test]
+    fn nested_in_source_module_completion() {
+        check(
+            r#"
+            //- /lib.rs
+            mod foo;
+            //- /foo.rs
+            mod bar {
+                mod <|>
+            }
+            //- /foo/bar/baz.rs
+            fn baz() {}
+        "#,
+            expect![[r#"
+                md baz;
+            "#]],
+        );
+    }
+
+    // FIXME binary modules are not supported in tests properly
+    // Binary modules are a bit special, they allow importing the modules from `/src/bin`
+    // and that's why are good to test two things:
+    // * no cycles are allowed in mod declarations
+    // * no modules from the parent directory are proposed
+    // Unfortunately, binary modules support is in cargo not rustc,
+    // hence the test does not work now
+    //
+    // #[test]
+    // fn regular_bin_module_completion() {
+    //     check(
+    //         r#"
+    //         //- /src/bin.rs
+    //         fn main() {}
+    //         //- /src/bin/foo.rs
+    //         mod <|>
+    //         //- /src/bin/bar.rs
+    //         fn bar() {}
+    //         //- /src/bin/bar/bar_ignored.rs
+    //         fn bar_ignored() {}
+    //     "#,
+    //         expect![[r#"
+    //             md bar;
+    //         "#]],
+    //     );
+    // }
+
+    #[test]
+    fn already_declared_bin_module_completion_omitted() {
+        check(
+            r#"
+            //- /src/bin.rs
+            fn main() {}
+            //- /src/bin/foo.rs
+            mod <|>
+            //- /src/bin/bar.rs
+            mod foo;
+            fn bar() {}
+            //- /src/bin/bar/bar_ignored.rs
+            fn bar_ignored() {}
+        "#,
+            expect![[r#""#]],
+        );
+    }
+}
diff --git a/crates/ide/src/completion/complete_qualified_path.rs b/crates/ide/src/completion/complete_qualified_path.rs
index accb09f7e..00e89f0fd 100644
--- a/crates/ide/src/completion/complete_qualified_path.rs
+++ b/crates/ide/src/completion/complete_qualified_path.rs
@@ -13,7 +13,7 @@ pub(super) fn complete_qualified_path(acc: &mut Completions, ctx: &CompletionCon
         None => return,
     };
 
-    if ctx.attribute_under_caret.is_some() {
+    if ctx.attribute_under_caret.is_some() || ctx.mod_declaration_under_caret.is_some() {
         return;
     }
 
@@ -730,4 +730,26 @@ fn f() {}
             expect![[""]],
         );
     }
+
+    #[test]
+    fn completes_function() {
+        check(
+            r#"
+fn foo(
+    a: i32,
+    b: i32
+) {
+
+}
+
+fn main() {
+    fo<|>
+}
+"#,
+            expect![[r#"
+                fn foo(…) fn foo(a: i32, b: i32)
+                fn main() fn main()
+            "#]],
+        );
+    }
 }
diff --git a/crates/ide/src/completion/complete_trait_impl.rs b/crates/ide/src/completion/complete_trait_impl.rs
index 26f268bd1..ff115df92 100644
--- a/crates/ide/src/completion/complete_trait_impl.rs
+++ b/crates/ide/src/completion/complete_trait_impl.rs
@@ -46,76 +46,86 @@ use crate::{
     display::function_declaration,
 };
 
+#[derive(Debug, PartialEq, Eq)]
+enum ImplCompletionKind {
+    All,
+    Fn,
+    TypeAlias,
+    Const,
+}
+
 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);
-                }
+    if let Some((kind, trigger, impl_def)) = completion_match(ctx) {
+        get_missing_assoc_items(&ctx.sema, &impl_def).into_iter().for_each(|item| match item {
+            hir::AssocItem::Function(fn_item)
+                if kind == ImplCompletionKind::All || kind == ImplCompletionKind::Fn =>
+            {
+                add_function_impl(&trigger, acc, ctx, fn_item)
             }
-
-            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);
-                }
+            hir::AssocItem::TypeAlias(type_item)
+                if kind == ImplCompletionKind::All || kind == ImplCompletionKind::TypeAlias =>
+            {
+                add_type_alias_impl(&trigger, acc, ctx, type_item)
             }
-
-            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);
-                }
+            hir::AssocItem::Const(const_item)
+                if kind == ImplCompletionKind::All || kind == ImplCompletionKind::Const =>
+            {
+                add_const_impl(&trigger, acc, ctx, const_item)
             }
-
             _ => {}
-        }
+        });
     }
 }
 
-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 completion_match(ctx: &CompletionContext) -> Option<(ImplCompletionKind, SyntaxNode, Impl)> {
+    let mut token = ctx.token.clone();
+    // For keywork without name like `impl .. { fn <|> }`, the current position is inside
+    // the whitespace token, which is outside `FN` syntax node.
+    // We need to follow the previous token in this case.
+    if token.kind() == SyntaxKind::WHITESPACE {
+        token = token.prev_token()?;
+    }
+
+    let impl_item_offset = match token.kind() {
+        // `impl .. { const <|> }`
+        // ERROR      0
+        //   CONST_KW <- *
+        SyntaxKind::CONST_KW => 0,
+        // `impl .. { fn/type <|> }`
+        // FN/TYPE_ALIAS  0
+        //   FN_KW        <- *
+        SyntaxKind::FN_KW | SyntaxKind::TYPE_KW => 0,
+        // `impl .. { fn/type/const foo<|> }`
+        // FN/TYPE_ALIAS/CONST  1
+        //  NAME                0
+        //    IDENT             <- *
+        SyntaxKind::IDENT if token.parent().kind() == SyntaxKind::NAME => 1,
+        // `impl .. { foo<|> }`
+        // MACRO_CALL       3
+        //  PATH            2
+        //    PATH_SEGMENT  1
+        //      NAME_REF    0
+        //        IDENT     <- *
+        SyntaxKind::IDENT if token.parent().kind() == SyntaxKind::NAME_REF => 3,
+        _ => return None,
+    };
+
+    let impl_item = token.ancestors().nth(impl_item_offset)?;
+    // Must directly belong to an impl block.
+    // IMPL
+    //   ASSOC_ITEM_LIST
+    //     <item>
+    let impl_def = ast::Impl::cast(impl_item.parent()?.parent()?)?;
+    let kind = match impl_item.kind() {
+        // `impl ... { const <|> fn/type/const }`
+        _ if token.kind() == SyntaxKind::CONST_KW => ImplCompletionKind::Const,
+        SyntaxKind::CONST | SyntaxKind::ERROR => ImplCompletionKind::Const,
+        SyntaxKind::TYPE_ALIAS => ImplCompletionKind::TypeAlias,
+        SyntaxKind::FN => ImplCompletionKind::Fn,
+        SyntaxKind::MACRO_CALL => ImplCompletionKind::All,
+        _ => return None,
+    };
+    Some((kind, impl_item, impl_def))
 }
 
 fn add_function_impl(
@@ -261,19 +271,191 @@ ta type TestType = \n\
     }
 
     #[test]
-    fn no_nested_fn_completions() {
+    fn no_completion_inside_fn() {
         check(
             r"
-trait Test {
-    fn test();
-    fn test2();
+trait Test { fn test(); fn test2(); }
+struct T;
+
+impl Test for T {
+    fn test() {
+        t<|>
+    }
+}
+",
+            expect![[""]],
+        );
+
+        check(
+            r"
+trait Test { fn test(); fn test2(); }
+struct T;
+
+impl Test for T {
+    fn test() {
+        fn t<|>
+    }
+}
+",
+            expect![[""]],
+        );
+
+        check(
+            r"
+trait Test { fn test(); fn test2(); }
+struct T;
+
+impl Test for T {
+    fn test() {
+        fn <|>
+    }
 }
+",
+            expect![[""]],
+        );
+
+        // https://github.com/rust-analyzer/rust-analyzer/pull/5976#issuecomment-692332191
+        check(
+            r"
+trait Test { fn test(); fn test2(); }
 struct T;
 
 impl Test for T {
     fn test() {
+        foo.<|>
+    }
+}
+",
+            expect![[""]],
+        );
+
+        check(
+            r"
+trait Test { fn test(_: i32); fn test2(); }
+struct T;
+
+impl Test for T {
+    fn test(t<|>)
+}
+",
+            expect![[""]],
+        );
+
+        check(
+            r"
+trait Test { fn test(_: fn()); fn test2(); }
+struct T;
+
+impl Test for T {
+    fn test(f: fn <|>)
+}
+",
+            expect![[""]],
+        );
+    }
+
+    #[test]
+    fn no_completion_inside_const() {
+        check(
+            r"
+trait Test { const TEST: fn(); const TEST2: u32; type Test; fn test(); }
+struct T;
+
+impl Test for T {
+    const TEST: fn <|>
+}
+",
+            expect![[""]],
+        );
+
+        check(
+            r"
+trait Test { const TEST: u32; const TEST2: u32; type Test; fn test(); }
+struct T;
+
+impl Test for T {
+    const TEST: T<|>
+}
+",
+            expect![[""]],
+        );
+
+        check(
+            r"
+trait Test { const TEST: u32; const TEST2: u32; type Test; fn test(); }
+struct T;
+
+impl Test for T {
+    const TEST: u32 = f<|>
+}
+",
+            expect![[""]],
+        );
+
+        check(
+            r"
+trait Test { const TEST: u32; const TEST2: u32; type Test; fn test(); }
+struct T;
+
+impl Test for T {
+    const TEST: u32 = {
         t<|>
+    };
+}
+",
+            expect![[""]],
+        );
+
+        check(
+            r"
+trait Test { const TEST: u32; const TEST2: u32; type Test; fn test(); }
+struct T;
+
+impl Test for T {
+    const TEST: u32 = {
+        fn <|>
+    };
+}
+",
+            expect![[""]],
+        );
+
+        check(
+            r"
+trait Test { const TEST: u32; const TEST2: u32; type Test; fn test(); }
+struct T;
+
+impl Test for T {
+    const TEST: u32 = {
+        fn t<|>
+    };
+}
+",
+            expect![[""]],
+        );
     }
+
+    #[test]
+    fn no_completion_inside_type() {
+        check(
+            r"
+trait Test { type Test; type Test2; fn test(); }
+struct T;
+
+impl Test for T {
+    type Test = T<|>;
+}
+",
+            expect![[""]],
+        );
+
+        check(
+            r"
+trait Test { type Test; type Test2; fn test(); }
+struct T;
+
+impl Test for T {
+    type Test = fn <|>;
 }
 ",
             expect![[""]],
@@ -485,4 +667,67 @@ impl Test for () {
 ",
         );
     }
+
+    #[test]
+    fn complete_without_name() {
+        let test = |completion: &str, hint: &str, completed: &str, next_sibling: &str| {
+            println!(
+                "completion='{}', hint='{}', next_sibling='{}'",
+                completion, hint, next_sibling
+            );
+
+            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 <|> 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("bar", "fn <|>", "fn bar() {\n    $0\n}", next_sibling);
+            test("Foo", "type <|>", "type Foo = ", next_sibling);
+            test("CONST", "const <|>", "const CONST: u16 = ", next_sibling);
+        }
+    }
 }
diff --git a/crates/ide/src/completion/complete_unqualified_path.rs b/crates/ide/src/completion/complete_unqualified_path.rs
index 1f1b682a7..8eda4b64d 100644
--- a/crates/ide/src/completion/complete_unqualified_path.rs
+++ b/crates/ide/src/completion/complete_unqualified_path.rs
@@ -13,6 +13,7 @@ pub(super) fn complete_unqualified_path(acc: &mut Completions, ctx: &CompletionC
     if ctx.record_lit_syntax.is_some()
         || ctx.record_pat_syntax.is_some()
         || ctx.attribute_under_caret.is_some()
+        || ctx.mod_declaration_under_caret.is_some()
     {
         return;
     }
diff --git a/crates/ide/src/completion/completion_context.rs b/crates/ide/src/completion/completion_context.rs
index 3ef1b97cf..671b13328 100644
--- a/crates/ide/src/completion/completion_context.rs
+++ b/crates/ide/src/completion/completion_context.rs
@@ -77,6 +77,7 @@ pub(crate) struct CompletionContext<'a> {
     pub(super) is_path_type: bool,
     pub(super) has_type_args: bool,
     pub(super) attribute_under_caret: Option<ast::Attr>,
+    pub(super) mod_declaration_under_caret: Option<ast::Module>,
     pub(super) unsafe_is_prev: bool,
     pub(super) if_is_prev: bool,
     pub(super) block_expr_parent: bool,
@@ -159,6 +160,7 @@ impl<'a> CompletionContext<'a> {
             has_type_args: false,
             dot_receiver_is_ambiguous_float_literal: false,
             attribute_under_caret: None,
+            mod_declaration_under_caret: None,
             unsafe_is_prev: false,
             in_loop_body: false,
             ref_pat_parent: false,
@@ -246,7 +248,10 @@ impl<'a> CompletionContext<'a> {
         self.trait_as_prev_sibling = has_trait_as_prev_sibling(syntax_element.clone());
         self.is_match_arm = is_match_arm(syntax_element.clone());
         self.has_item_list_or_source_file_parent =
-            has_item_list_or_source_file_parent(syntax_element);
+            has_item_list_or_source_file_parent(syntax_element.clone());
+        self.mod_declaration_under_caret =
+            find_node_at_offset::<ast::Module>(&file_with_fake_ident, offset)
+                .filter(|module| module.item_list().is_none());
     }
 
     fn fill(
diff --git a/crates/ide/src/completion/patterns.rs b/crates/ide/src/completion/patterns.rs
index c6ae589db..b17ddf133 100644
--- a/crates/ide/src/completion/patterns.rs
+++ b/crates/ide/src/completion/patterns.rs
@@ -115,6 +115,7 @@ pub(crate) fn if_is_prev(element: SyntaxElement) -> bool {
         .filter(|it| it.kind() == IF_KW)
         .is_some()
 }
+
 #[test]
 fn test_if_is_prev() {
     check_pattern_is_applicable(r"if l<|>", if_is_prev);
diff --git a/crates/ide/src/diagnostics.rs b/crates/ide/src/diagnostics.rs
index b2b972b02..dc815a483 100644
--- a/crates/ide/src/diagnostics.rs
+++ b/crates/ide/src/diagnostics.rs
@@ -622,13 +622,65 @@ pub struct Foo { pub a: i32, pub b: i32 }
             r#"
 use a;
 use a::{c, d::e};
+
+mod a {
+    mod c {}
+    mod d {
+        mod e {}
+    }
+}
 "#,
         );
-        check_fix(r#"use {<|>b};"#, r#"use b;"#);
-        check_fix(r#"use {b<|>};"#, r#"use b;"#);
-        check_fix(r#"use a::{c<|>};"#, r#"use a::c;"#);
-        check_fix(r#"use a::{self<|>};"#, r#"use a;"#);
-        check_fix(r#"use a::{c, d::{e<|>}};"#, r#"use a::{c, d::e};"#);
+        check_fix(
+            r"
+            mod b {}
+            use {<|>b};
+            ",
+            r"
+            mod b {}
+            use b;
+            ",
+        );
+        check_fix(
+            r"
+            mod b {}
+            use {b<|>};
+            ",
+            r"
+            mod b {}
+            use b;
+            ",
+        );
+        check_fix(
+            r"
+            mod a { mod c {} }
+            use a::{c<|>};
+            ",
+            r"
+            mod a { mod c {} }
+            use a::c;
+            ",
+        );
+        check_fix(
+            r"
+            mod a {}
+            use a::{self<|>};
+            ",
+            r"
+            mod a {}
+            use a;
+            ",
+        );
+        check_fix(
+            r"
+            mod a { mod c {} mod d { mod e {} } }
+            use a::{c, d::{e<|>}};
+            ",
+            r"
+            mod a { mod c {} mod d { mod e {} } }
+            use a::{c, d::e};
+            ",
+        );
     }
 
     #[test]
diff --git a/crates/ide/src/display.rs b/crates/ide/src/display.rs
index 41b5bdc49..2484dbbf1 100644
--- a/crates/ide/src/display.rs
+++ b/crates/ide/src/display.rs
@@ -41,7 +41,14 @@ pub(crate) fn function_declaration(node: &ast::Fn) -> String {
         format_to!(buf, "{}", type_params);
     }
     if let Some(param_list) = node.param_list() {
-        format_to!(buf, "{}", param_list);
+        let params: Vec<String> = param_list
+            .self_param()
+            .into_iter()
+            .map(|self_param| self_param.to_string())
+            .chain(param_list.params().map(|param| param.to_string()))
+            .collect();
+        // Useful to inline parameters
+        format_to!(buf, "({})", params.join(", "));
     }
     if let Some(ret_type) = node.ret_type() {
         if ret_type.ty().is_some() {
diff --git a/crates/ide/src/hover.rs b/crates/ide/src/hover.rs
index efec0184e..37171cbef 100644
--- a/crates/ide/src/hover.rs
+++ b/crates/ide/src/hover.rs
@@ -2647,6 +2647,70 @@ fn foo(ar<|>g: &impl Foo + Bar<S>) {}
     }
 
     #[test]
+    fn test_hover_async_block_impl_trait_has_goto_type_action() {
+        check_actions(
+            r#"
+struct S;
+fn foo() {
+    let fo<|>o = async { S };
+}
+
+#[prelude_import] use future::*;
+mod future {
+    #[lang = "future_trait"]
+    pub trait Future { type Output; }
+}
+"#,
+            expect![[r#"
+                [
+                    GoToType(
+                        [
+                            HoverGotoTypeData {
+                                mod_path: "test::future::Future",
+                                nav: NavigationTarget {
+                                    file_id: FileId(
+                                        1,
+                                    ),
+                                    full_range: 101..163,
+                                    focus_range: Some(
+                                        140..146,
+                                    ),
+                                    name: "Future",
+                                    kind: TRAIT,
+                                    container_name: None,
+                                    description: Some(
+                                        "pub trait Future",
+                                    ),
+                                    docs: None,
+                                },
+                            },
+                            HoverGotoTypeData {
+                                mod_path: "test::S",
+                                nav: NavigationTarget {
+                                    file_id: FileId(
+                                        1,
+                                    ),
+                                    full_range: 0..9,
+                                    focus_range: Some(
+                                        7..8,
+                                    ),
+                                    name: "S",
+                                    kind: STRUCT,
+                                    container_name: None,
+                                    description: Some(
+                                        "struct S",
+                                    ),
+                                    docs: None,
+                                },
+                            },
+                        ],
+                    ),
+                ]
+            "#]],
+        );
+    }
+
+    #[test]
     fn test_hover_arg_generic_impl_trait_has_goto_type_action() {
         check_actions(
             r#"
diff --git a/crates/ide/src/lib.rs b/crates/ide/src/lib.rs
index 570790384..3b97e087f 100644
--- a/crates/ide/src/lib.rs
+++ b/crates/ide/src/lib.rs
@@ -81,7 +81,9 @@ pub use crate::{
     },
 };
 
-pub use assists::{Assist, AssistConfig, AssistId, AssistKind, ResolvedAssist};
+pub use assists::{
+    utils::MergeBehaviour, Assist, AssistConfig, AssistId, AssistKind, ResolvedAssist,
+};
 pub use base_db::{
     Canceled, CrateGraph, CrateId, Edition, FileId, FilePosition, FileRange, SourceRoot,
     SourceRootId,
diff --git a/crates/ide/src/syntax_highlighting.rs b/crates/ide/src/syntax_highlighting.rs
index 25d6f7abd..d9fc25d88 100644
--- a/crates/ide/src/syntax_highlighting.rs
+++ b/crates/ide/src/syntax_highlighting.rs
@@ -4,7 +4,7 @@ mod injection;
 #[cfg(test)]
 mod tests;
 
-use hir::{Name, Semantics, VariantDef};
+use hir::{Local, Name, Semantics, VariantDef};
 use ide_db::{
     defs::{classify_name, classify_name_ref, Definition, NameClass, NameRefClass},
     RootDatabase,
@@ -13,8 +13,8 @@ use rustc_hash::FxHashMap;
 use syntax::{
     ast::{self, HasFormatSpecifier},
     AstNode, AstToken, Direction, NodeOrToken, SyntaxElement,
-    SyntaxKind::*,
-    TextRange, WalkEvent, T,
+    SyntaxKind::{self, *},
+    SyntaxNode, SyntaxToken, TextRange, WalkEvent, T,
 };
 
 use crate::FileId;
@@ -454,6 +454,32 @@ fn macro_call_range(macro_call: &ast::MacroCall) -> Option<TextRange> {
     Some(TextRange::new(range_start, range_end))
 }
 
+/// Returns true if the parent nodes of `node` all match the `SyntaxKind`s in `kinds` exactly.
+fn parents_match(mut node: NodeOrToken<SyntaxNode, SyntaxToken>, mut kinds: &[SyntaxKind]) -> bool {
+    while let (Some(parent), [kind, rest @ ..]) = (&node.parent(), kinds) {
+        if parent.kind() != *kind {
+            return false;
+        }
+
+        // FIXME: Would be nice to get parent out of the match, but binding by-move and by-value
+        // in the same pattern is unstable: rust-lang/rust#68354.
+        node = node.parent().unwrap().into();
+        kinds = rest;
+    }
+
+    // Only true if we matched all expected kinds
+    kinds.len() == 0
+}
+
+fn is_consumed_lvalue(
+    node: NodeOrToken<SyntaxNode, SyntaxToken>,
+    local: &Local,
+    db: &RootDatabase,
+) -> bool {
+    // When lvalues are passed as arguments and they're not Copy, then mark them as Consuming.
+    parents_match(node, &[PATH_SEGMENT, PATH, PATH_EXPR, ARG_LIST]) && !local.ty(db).is_copy(db)
+}
+
 fn highlight_element(
     sema: &Semantics<RootDatabase>,
     bindings_shadow_count: &mut FxHashMap<Name, u32>,
@@ -522,6 +548,12 @@ fn highlight_element(
 
                             let mut h = highlight_def(db, def);
 
+                            if let Definition::Local(local) = &def {
+                                if is_consumed_lvalue(name_ref.syntax().clone().into(), local, db) {
+                                    h |= HighlightModifier::Consuming;
+                                }
+                            }
+
                             if let Some(parent) = name_ref.syntax().parent() {
                                 if matches!(parent.kind(), FIELD_EXPR | RECORD_PAT_FIELD) {
                                     if let Definition::Field(field) = def {
@@ -645,21 +677,30 @@ fn highlight_element(
                         .and_then(ast::SelfParam::cast)
                         .and_then(|p| p.mut_token())
                         .is_some();
-                    // closure to enforce lazyness
-                    let self_path = || {
-                        sema.resolve_path(&element.parent()?.parent().and_then(ast::Path::cast)?)
-                    };
+                    let self_path = &element
+                        .parent()
+                        .as_ref()
+                        .and_then(SyntaxNode::parent)
+                        .and_then(ast::Path::cast)
+                        .and_then(|p| sema.resolve_path(&p));
+                    let mut h = HighlightTag::SelfKeyword.into();
                     if self_param_is_mut
-                        || matches!(self_path(),
+                        || matches!(self_path,
                             Some(hir::PathResolution::Local(local))
                                 if local.is_self(db)
                                     && (local.is_mut(db) || local.ty(db).is_mutable_reference())
                         )
                     {
-                        HighlightTag::SelfKeyword | HighlightModifier::Mutable
-                    } else {
-                        HighlightTag::SelfKeyword.into()
+                        h |= HighlightModifier::Mutable
                     }
+
+                    if let Some(hir::PathResolution::Local(local)) = self_path {
+                        if is_consumed_lvalue(element, &local, db) {
+                            h |= HighlightModifier::Consuming;
+                        }
+                    }
+
+                    h
                 }
                 T![ref] => element
                     .parent()
diff --git a/crates/ide/src/syntax_highlighting/test_data/highlighting.html b/crates/ide/src/syntax_highlighting/test_data/highlighting.html
index d0df2e0ec..cde42024c 100644
--- a/crates/ide/src/syntax_highlighting/test_data/highlighting.html
+++ b/crates/ide/src/syntax_highlighting/test_data/highlighting.html
@@ -61,8 +61,8 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
 <span class="punctuation">}</span>
 
 <span class="keyword">impl</span> <span class="struct">Foo</span> <span class="punctuation">{</span>
-    <span class="keyword">fn</span> <span class="function declaration">baz</span><span class="punctuation">(</span><span class="keyword">mut</span> <span class="self_keyword mutable">self</span><span class="punctuation">)</span> <span class="operator">-&gt;</span> <span class="builtin_type">i32</span> <span class="punctuation">{</span>
-        <span class="self_keyword">self</span><span class="punctuation">.</span><span class="field">x</span>
+    <span class="keyword">fn</span> <span class="function declaration">baz</span><span class="punctuation">(</span><span class="keyword">mut</span> <span class="self_keyword mutable">self</span><span class="punctuation">,</span> <span class="value_param declaration">f</span><span class="punctuation">:</span> <span class="struct">Foo</span><span class="punctuation">)</span> <span class="operator">-&gt;</span> <span class="builtin_type">i32</span> <span class="punctuation">{</span>
+        <span class="value_param">f</span><span class="punctuation">.</span><span class="function consuming">baz</span><span class="punctuation">(</span><span class="self_keyword consuming">self</span><span class="punctuation">)</span>
     <span class="punctuation">}</span>
 
     <span class="keyword">fn</span> <span class="function declaration">qux</span><span class="punctuation">(</span><span class="operator">&</span><span class="keyword">mut</span> <span class="self_keyword mutable">self</span><span class="punctuation">)</span> <span class="punctuation">{</span>
@@ -80,8 +80,8 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
 <span class="punctuation">}</span>
 
 <span class="keyword">impl</span> <span class="struct">FooCopy</span> <span class="punctuation">{</span>
-    <span class="keyword">fn</span> <span class="function declaration">baz</span><span class="punctuation">(</span><span class="self_keyword">self</span><span class="punctuation">)</span> <span class="operator">-&gt;</span> <span class="builtin_type">u32</span> <span class="punctuation">{</span>
-        <span class="self_keyword">self</span><span class="punctuation">.</span><span class="field">x</span>
+    <span class="keyword">fn</span> <span class="function declaration">baz</span><span class="punctuation">(</span><span class="self_keyword">self</span><span class="punctuation">,</span> <span class="value_param declaration">f</span><span class="punctuation">:</span> <span class="struct">FooCopy</span><span class="punctuation">)</span> <span class="operator">-&gt;</span> <span class="builtin_type">u32</span> <span class="punctuation">{</span>
+        <span class="value_param">f</span><span class="punctuation">.</span><span class="function">baz</span><span class="punctuation">(</span><span class="self_keyword">self</span><span class="punctuation">)</span>
     <span class="punctuation">}</span>
 
     <span class="keyword">fn</span> <span class="function declaration">qux</span><span class="punctuation">(</span><span class="operator">&</span><span class="keyword">mut</span> <span class="self_keyword mutable">self</span><span class="punctuation">)</span> <span class="punctuation">{</span>
@@ -144,14 +144,15 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
     <span class="variable">y</span><span class="punctuation">;</span>
 
     <span class="keyword">let</span> <span class="keyword">mut</span> <span class="variable declaration mutable">foo</span> <span class="operator">=</span> <span class="struct">Foo</span> <span class="punctuation">{</span> <span class="field">x</span><span class="punctuation">,</span> <span class="field">y</span><span class="punctuation">:</span> <span class="variable mutable">x</span> <span class="punctuation">}</span><span class="punctuation">;</span>
+    <span class="keyword">let</span> <span class="variable declaration">foo2</span> <span class="operator">=</span> <span class="variable mutable">foo</span><span class="punctuation">.</span><span class="unresolved_reference">clone</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
     <span class="variable mutable">foo</span><span class="punctuation">.</span><span class="function">quop</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
     <span class="variable mutable">foo</span><span class="punctuation">.</span><span class="function mutable">qux</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
-    <span class="variable mutable">foo</span><span class="punctuation">.</span><span class="function consuming">baz</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
+    <span class="variable mutable">foo</span><span class="punctuation">.</span><span class="function consuming">baz</span><span class="punctuation">(</span><span class="variable consuming">foo2</span><span class="punctuation">)</span><span class="punctuation">;</span>
 
     <span class="keyword">let</span> <span class="keyword">mut</span> <span class="variable declaration mutable">copy</span> <span class="operator">=</span> <span class="struct">FooCopy</span> <span class="punctuation">{</span> <span class="field">x</span> <span class="punctuation">}</span><span class="punctuation">;</span>
     <span class="variable mutable">copy</span><span class="punctuation">.</span><span class="function">quop</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
     <span class="variable mutable">copy</span><span class="punctuation">.</span><span class="function mutable">qux</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
-    <span class="variable mutable">copy</span><span class="punctuation">.</span><span class="function">baz</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
+    <span class="variable mutable">copy</span><span class="punctuation">.</span><span class="function">baz</span><span class="punctuation">(</span><span class="variable mutable">copy</span><span class="punctuation">)</span><span class="punctuation">;</span>
 <span class="punctuation">}</span>
 
 <span class="keyword">enum</span> <span class="enum declaration">Option</span><span class="punctuation">&lt;</span><span class="type_param declaration">T</span><span class="punctuation">&gt;</span> <span class="punctuation">{</span>
diff --git a/crates/ide/src/syntax_highlighting/tests.rs b/crates/ide/src/syntax_highlighting/tests.rs
index 6f72a29bd..57d4e1252 100644
--- a/crates/ide/src/syntax_highlighting/tests.rs
+++ b/crates/ide/src/syntax_highlighting/tests.rs
@@ -35,8 +35,8 @@ impl Bar for Foo {
 }
 
 impl Foo {
-    fn baz(mut self) -> i32 {
-        self.x
+    fn baz(mut self, f: Foo) -> i32 {
+        f.baz(self)
     }
 
     fn qux(&mut self) {
@@ -54,8 +54,8 @@ struct FooCopy {
 }
 
 impl FooCopy {
-    fn baz(self) -> u32 {
-        self.x
+    fn baz(self, f: FooCopy) -> u32 {
+        f.baz(self)
     }
 
     fn qux(&mut self) {
@@ -118,14 +118,15 @@ fn main() {
     y;
 
     let mut foo = Foo { x, y: x };
+    let foo2 = foo.clone();
     foo.quop();
     foo.qux();
-    foo.baz();
+    foo.baz(foo2);
 
     let mut copy = FooCopy { x };
     copy.quop();
     copy.qux();
-    copy.baz();
+    copy.baz(copy);
 }
 
 enum Option<T> {
diff --git a/crates/ide/src/typing.rs b/crates/ide/src/typing.rs
index 899ce5f26..94b91f049 100644
--- a/crates/ide/src/typing.rs
+++ b/crates/ide/src/typing.rs
@@ -39,6 +39,14 @@ pub(crate) const TRIGGER_CHARS: &str = ".=>";
 //
 // - typing `let =` tries to smartly add `;` if `=` is followed by an existing expression
 // - typing `.` in a chain method call auto-indents
+//
+// VS Code::
+//
+// Add the following to `settings.json`:
+// [source,json]
+// ----
+// "editor.formatOnType": true,
+// ----
 pub(crate) fn on_char_typed(
     db: &RootDatabase,
     position: FilePosition,