8 files changed, 1252 insertions, 11 deletions

diff --git a/crates/assists/src/handlers/auto_import.rs b/crates/assists/src/handlers/auto_import.rs
index 4a7059c83..e49e641b3 100644
--- a/crates/assists/src/handlers/auto_import.rs
+++ b/crates/assists/src/handlers/auto_import.rs
@@ -6,7 +6,7 @@ use crate::{
     AssistContext, AssistId, AssistKind, Assists, GroupLabel,
 };
 
-// Feature: Import Insertion
+// Feature: Auto Import
 //
 // Using the `auto-import` assist it is possible to insert missing imports for unresolved items.
 // When inserting an import it will do so in a structured manner by keeping imports grouped,
@@ -100,7 +100,7 @@ pub(crate) fn auto_import(acc: &mut Assists, ctx: &AssistContext) -> Option<()>
     let group = import_group_message(import_assets.import_candidate());
     let scope = ImportScope::find_insert_use_container(import_assets.syntax_under_caret(), ctx)?;
     let syntax = scope.as_syntax_node();
-    for import in proposed_imports {
+    for (import, _) in proposed_imports {
         acc.add_group(
             &group,
             AssistId("auto_import", AssistKind::QuickFix),
diff --git a/crates/assists/src/handlers/change_visibility.rs b/crates/assists/src/handlers/change_visibility.rs
index 32dc05378..22d7c95d9 100644
--- a/crates/assists/src/handlers/change_visibility.rs
+++ b/crates/assists/src/handlers/change_visibility.rs
@@ -1,7 +1,7 @@
 use syntax::{
     ast::{self, NameOwner, VisibilityOwner},
     AstNode,
-    SyntaxKind::{CONST, ENUM, FN, MODULE, STATIC, STRUCT, TRAIT, VISIBILITY},
+    SyntaxKind::{CONST, ENUM, FN, MODULE, STATIC, STRUCT, TRAIT, TYPE_ALIAS, VISIBILITY},
     T,
 };
 use test_utils::mark;
@@ -30,13 +30,20 @@ fn add_vis(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let item_keyword = ctx.token_at_offset().find(|leaf| {
         matches!(
             leaf.kind(),
-            T![const] | T![static] | T![fn] | T![mod] | T![struct] | T![enum] | T![trait]
+            T![const]
+                | T![static]
+                | T![fn]
+                | T![mod]
+                | T![struct]
+                | T![enum]
+                | T![trait]
+                | T![type]
         )
     });
 
     let (offset, target) = if let Some(keyword) = item_keyword {
         let parent = keyword.parent();
-        let def_kws = vec![CONST, STATIC, FN, MODULE, STRUCT, ENUM, TRAIT];
+        let def_kws = vec![CONST, STATIC, TYPE_ALIAS, FN, MODULE, STRUCT, ENUM, TRAIT];
         // Parent is not a definition, can't add visibility
         if !def_kws.iter().any(|&def_kw| def_kw == parent.kind()) {
             return None;
@@ -160,6 +167,11 @@ mod tests {
     }
 
     #[test]
+    fn change_visibility_type_alias() {
+        check_assist(change_visibility, "<|>type T = ();", "pub(crate) type T = ();");
+    }
+
+    #[test]
     fn change_visibility_handles_comment_attrs() {
         check_assist(
             change_visibility,
diff --git a/crates/assists/src/handlers/fill_match_arms.rs b/crates/assists/src/handlers/fill_match_arms.rs
index 676f5ad92..eda45f5b3 100644
--- a/crates/assists/src/handlers/fill_match_arms.rs
+++ b/crates/assists/src/handlers/fill_match_arms.rs
@@ -59,7 +59,7 @@ pub(crate) fn fill_match_arms(acc: &mut Assists, ctx: &AssistContext) -> Option<
             .filter(|variant_pat| is_variant_missing(&mut arms, variant_pat))
             .map(|pat| make::match_arm(iter::once(pat), make::expr_empty_block()))
             .collect::<Vec<_>>();
-        if Some(enum_def) == FamousDefs(&ctx.sema, module.krate()).core_option_Option() {
+        if Some(enum_def) == FamousDefs(&ctx.sema, Some(module.krate())).core_option_Option() {
             // Match `Some` variant first.
             mark::hit!(option_order);
             variants.reverse()
diff --git a/crates/assists/src/handlers/fix_visibility.rs b/crates/assists/src/handlers/fix_visibility.rs
index d505e9444..66f74150c 100644
--- a/crates/assists/src/handlers/fix_visibility.rs
+++ b/crates/assists/src/handlers/fix_visibility.rs
@@ -1,9 +1,11 @@
 use base_db::FileId;
 use hir::{db::HirDatabase, HasSource, HasVisibility, PathResolution};
-use syntax::{ast, AstNode, TextRange, TextSize};
+use syntax::{
+    ast::{self, VisibilityOwner},
+    AstNode, TextRange, TextSize,
+};
 
 use crate::{utils::vis_offset, AssistContext, AssistId, AssistKind, Assists};
-use ast::VisibilityOwner;
 
 // FIXME: this really should be a fix for diagnostic, rather than an assist.
 
diff --git a/crates/assists/src/handlers/generate_from_impl_for_enum.rs b/crates/assists/src/handlers/generate_from_impl_for_enum.rs
index 7f04b9572..674e5a175 100644
--- a/crates/assists/src/handlers/generate_from_impl_for_enum.rs
+++ b/crates/assists/src/handlers/generate_from_impl_for_enum.rs
@@ -75,7 +75,7 @@ fn existing_from_impl(
     let enum_ = variant.parent_enum(sema.db);
     let krate = enum_.module(sema.db).krate();
 
-    let from_trait = FamousDefs(sema, krate).core_convert_From()?;
+    let from_trait = FamousDefs(sema, Some(krate)).core_convert_From()?;
 
     let enum_type = enum_.ty(sema.db);
 
diff --git a/crates/assists/src/handlers/generate_impl.rs b/crates/assists/src/handlers/generate_impl.rs
index 9989109b5..114974465 100644
--- a/crates/assists/src/handlers/generate_impl.rs
+++ b/crates/assists/src/handlers/generate_impl.rs
@@ -1,6 +1,6 @@
 use itertools::Itertools;
 use stdx::format_to;
-use syntax::ast::{self, AstNode, GenericParamsOwner, NameOwner};
+use syntax::ast::{self, AstNode, AttrsOwner, GenericParamsOwner, NameOwner};
 
 use crate::{AssistContext, AssistId, AssistKind, Assists};
 
@@ -27,6 +27,7 @@ pub(crate) fn generate_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<()
     let nominal = ctx.find_node_at_offset::<ast::AdtDef>()?;
     let name = nominal.name()?;
     let target = nominal.syntax().text_range();
+
     acc.add(
         AssistId("generate_impl", AssistKind::Generate),
         format!("Generate impl for `{}`", name),
@@ -35,7 +36,15 @@ pub(crate) fn generate_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<()
             let type_params = nominal.generic_param_list();
             let start_offset = nominal.syntax().text_range().end();
             let mut buf = String::new();
-            buf.push_str("\n\nimpl");
+            buf.push_str("\n\n");
+            nominal
+                .attrs()
+                .filter(|attr| {
+                    attr.as_simple_call().map(|(name, _arg)| name == "cfg").unwrap_or(false)
+                })
+                .for_each(|attr| buf.push_str(format!("{}\n", attr.to_string()).as_str()));
+
+            buf.push_str("impl");
             if let Some(type_params) = &type_params {
                 format_to!(buf, "{}", type_params.syntax());
             }
@@ -91,6 +100,35 @@ mod tests {
             "struct Foo<'a, T: Foo<'a>> {<|>}",
             "struct Foo<'a, T: Foo<'a>> {}\n\nimpl<'a, T: Foo<'a>> Foo<'a, T> {\n    $0\n}",
         );
+        check_assist(
+            generate_impl,
+            r#"
+            #[cfg(feature = "foo")]
+            struct Foo<'a, T: Foo<'a>> {<|>}"#,
+            r#"
+            #[cfg(feature = "foo")]
+            struct Foo<'a, T: Foo<'a>> {}
+
+            #[cfg(feature = "foo")]
+            impl<'a, T: Foo<'a>> Foo<'a, T> {
+                $0
+            }"#,
+        );
+
+        check_assist(
+            generate_impl,
+            r#"
+            #[cfg(not(feature = "foo"))]
+            struct Foo<'a, T: Foo<'a>> {<|>}"#,
+            r#"
+            #[cfg(not(feature = "foo"))]
+            struct Foo<'a, T: Foo<'a>> {}
+
+            #[cfg(not(feature = "foo"))]
+            impl<'a, T: Foo<'a>> Foo<'a, T> {
+                $0
+            }"#,
+        );
     }
 
     #[test]
diff --git a/crates/assists/src/handlers/qualify_path.rs b/crates/assists/src/handlers/qualify_path.rs
new file mode 100644
index 000000000..f436bdbbf
--- /dev/null
+++ b/crates/assists/src/handlers/qualify_path.rs
@@ -0,0 +1,1048 @@
+use std::iter;
+
+use hir::AsName;
+use ide_db::RootDatabase;
+use syntax::{
+    ast,
+    ast::{make, ArgListOwner},
+    AstNode,
+};
+use test_utils::mark;
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    utils::import_assets::{ImportAssets, ImportCandidate},
+    utils::mod_path_to_ast,
+    AssistId, AssistKind, GroupLabel,
+};
+
+// Assist: qualify_path
+//
+// If the name is unresolved, provides all possible qualified paths for it.
+//
+// ```
+// fn main() {
+//     let map = HashMap<|>::new();
+// }
+// # pub mod std { pub mod collections { pub struct HashMap { } } }
+// ```
+// ->
+// ```
+// fn main() {
+//     let map = std::collections::HashMap::new();
+// }
+// # pub mod std { pub mod collections { pub struct HashMap { } } }
+// ```
+pub(crate) fn qualify_path(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let import_assets =
+        if let Some(path_under_caret) = ctx.find_node_at_offset_with_descend::<ast::Path>() {
+            ImportAssets::for_regular_path(path_under_caret, &ctx.sema)
+        } else if let Some(method_under_caret) =
+            ctx.find_node_at_offset_with_descend::<ast::MethodCallExpr>()
+        {
+            ImportAssets::for_method_call(method_under_caret, &ctx.sema)
+        } else {
+            None
+        }?;
+    let proposed_imports = import_assets.search_for_relative_paths(&ctx.sema);
+    if proposed_imports.is_empty() {
+        return None;
+    }
+
+    let candidate = import_assets.import_candidate();
+    let range = ctx.sema.original_range(import_assets.syntax_under_caret()).range;
+
+    let qualify_candidate = match candidate {
+        ImportCandidate::QualifierStart(_) => {
+            mark::hit!(qualify_path_qualifier_start);
+            let path = ast::Path::cast(import_assets.syntax_under_caret().clone())?;
+            let segment = path.segment()?;
+            QualifyCandidate::QualifierStart(segment)
+        }
+        ImportCandidate::UnqualifiedName(_) => {
+            mark::hit!(qualify_path_unqualified_name);
+            QualifyCandidate::UnqualifiedName
+        }
+        ImportCandidate::TraitAssocItem(_) => {
+            mark::hit!(qualify_path_trait_assoc_item);
+            let path = ast::Path::cast(import_assets.syntax_under_caret().clone())?;
+            let (qualifier, segment) = (path.qualifier()?, path.segment()?);
+            QualifyCandidate::TraitAssocItem(qualifier, segment)
+        }
+        ImportCandidate::TraitMethod(_) => {
+            mark::hit!(qualify_path_trait_method);
+            let mcall_expr = ast::MethodCallExpr::cast(import_assets.syntax_under_caret().clone())?;
+            QualifyCandidate::TraitMethod(ctx.sema.db, mcall_expr)
+        }
+    };
+
+    let group_label = group_label(candidate);
+    for (import, item) in proposed_imports {
+        acc.add_group(
+            &group_label,
+            AssistId("qualify_path", AssistKind::QuickFix),
+            label(candidate, &import),
+            range,
+            |builder| {
+                qualify_candidate.qualify(
+                    |replace_with: String| builder.replace(range, replace_with),
+                    import,
+                    item,
+                )
+            },
+        );
+    }
+    Some(())
+}
+
+enum QualifyCandidate<'db> {
+    QualifierStart(ast::PathSegment),
+    UnqualifiedName,
+    TraitAssocItem(ast::Path, ast::PathSegment),
+    TraitMethod(&'db RootDatabase, ast::MethodCallExpr),
+}
+
+impl QualifyCandidate<'_> {
+    fn qualify(&self, mut replacer: impl FnMut(String), import: hir::ModPath, item: hir::ItemInNs) {
+        match self {
+            QualifyCandidate::QualifierStart(segment) => {
+                let import = mod_path_to_ast(&import);
+                replacer(format!("{}::{}", import, segment));
+            }
+            QualifyCandidate::UnqualifiedName => replacer(mod_path_to_ast(&import).to_string()),
+            QualifyCandidate::TraitAssocItem(qualifier, segment) => {
+                let import = mod_path_to_ast(&import);
+                replacer(format!("<{} as {}>::{}", qualifier, import, segment));
+            }
+            &QualifyCandidate::TraitMethod(db, ref mcall_expr) => {
+                Self::qualify_trait_method(db, mcall_expr, replacer, import, item);
+            }
+        }
+    }
+
+    fn qualify_trait_method(
+        db: &RootDatabase,
+        mcall_expr: &ast::MethodCallExpr,
+        mut replacer: impl FnMut(String),
+        import: hir::ModPath,
+        item: hir::ItemInNs,
+    ) -> Option<()> {
+        let receiver = mcall_expr.receiver()?;
+        let trait_method_name = mcall_expr.name_ref()?;
+        let arg_list = mcall_expr.arg_list().map(|arg_list| arg_list.args());
+        let trait_ = item_as_trait(item)?;
+        let method = find_trait_method(db, trait_, &trait_method_name)?;
+        if let Some(self_access) = method.self_param(db).map(|sp| sp.access(db)) {
+            let import = mod_path_to_ast(&import);
+            let receiver = match self_access {
+                hir::Access::Shared => make::expr_ref(receiver, false),
+                hir::Access::Exclusive => make::expr_ref(receiver, true),
+                hir::Access::Owned => receiver,
+            };
+            replacer(format!(
+                "{}::{}{}",
+                import,
+                trait_method_name,
+                match arg_list.clone() {
+                    Some(args) => make::arg_list(iter::once(receiver).chain(args)),
+                    None => make::arg_list(iter::once(receiver)),
+                }
+            ));
+        }
+        Some(())
+    }
+}
+
+fn find_trait_method(
+    db: &RootDatabase,
+    trait_: hir::Trait,
+    trait_method_name: &ast::NameRef,
+) -> Option<hir::Function> {
+    if let Some(hir::AssocItem::Function(method)) =
+        trait_.items(db).into_iter().find(|item: &hir::AssocItem| {
+            item.name(db).map(|name| name == trait_method_name.as_name()).unwrap_or(false)
+        })
+    {
+        Some(method)
+    } else {
+        None
+    }
+}
+
+fn item_as_trait(item: hir::ItemInNs) -> Option<hir::Trait> {
+    if let hir::ModuleDef::Trait(trait_) = hir::ModuleDef::from(item.as_module_def_id()?) {
+        Some(trait_)
+    } else {
+        None
+    }
+}
+
+fn group_label(candidate: &ImportCandidate) -> GroupLabel {
+    let name = match candidate {
+        ImportCandidate::UnqualifiedName(it) | ImportCandidate::QualifierStart(it) => &it.name,
+        ImportCandidate::TraitAssocItem(it) | ImportCandidate::TraitMethod(it) => &it.name,
+    };
+    GroupLabel(format!("Qualify {}", name))
+}
+
+fn label(candidate: &ImportCandidate, import: &hir::ModPath) -> String {
+    match candidate {
+        ImportCandidate::UnqualifiedName(_) => format!("Qualify as `{}`", &import),
+        ImportCandidate::QualifierStart(_) => format!("Qualify with `{}`", &import),
+        ImportCandidate::TraitAssocItem(_) => format!("Qualify `{}`", &import),
+        ImportCandidate::TraitMethod(_) => format!("Qualify with cast as `{}`", &import),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn applicable_when_found_an_import_partial() {
+        mark::check!(qualify_path_unqualified_name);
+        check_assist(
+            qualify_path,
+            r"
+            mod std {
+                pub mod fmt {
+                    pub struct Formatter;
+                }
+            }
+
+            use std::fmt;
+
+            <|>Formatter
+            ",
+            r"
+            mod std {
+                pub mod fmt {
+                    pub struct Formatter;
+                }
+            }
+
+            use std::fmt;
+
+            fmt::Formatter
+            ",
+        );
+    }
+
+    #[test]
+    fn applicable_when_found_an_import() {
+        check_assist(
+            qualify_path,
+            r"
+            <|>PubStruct
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+            r"
+            PubMod::PubStruct
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn applicable_in_macros() {
+        check_assist(
+            qualify_path,
+            r"
+            macro_rules! foo {
+                ($i:ident) => { fn foo(a: $i) {} }
+            }
+            foo!(Pub<|>Struct);
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+            r"
+            macro_rules! foo {
+                ($i:ident) => { fn foo(a: $i) {} }
+            }
+            foo!(PubMod::PubStruct);
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn applicable_when_found_multiple_imports() {
+        check_assist(
+            qualify_path,
+            r"
+            PubSt<|>ruct
+
+            pub mod PubMod1 {
+                pub struct PubStruct;
+            }
+            pub mod PubMod2 {
+                pub struct PubStruct;
+            }
+            pub mod PubMod3 {
+                pub struct PubStruct;
+            }
+            ",
+            r"
+            PubMod3::PubStruct
+
+            pub mod PubMod1 {
+                pub struct PubStruct;
+            }
+            pub mod PubMod2 {
+                pub struct PubStruct;
+            }
+            pub mod PubMod3 {
+                pub struct PubStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_already_imported_types() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            use PubMod::PubStruct;
+
+            PubStruct<|>
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_types_with_private_paths() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            PrivateStruct<|>
+
+            pub mod PubMod {
+                struct PrivateStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_when_no_imports_found() {
+        check_assist_not_applicable(
+            qualify_path,
+            "
+            PubStruct<|>",
+        );
+    }
+
+    #[test]
+    fn not_applicable_in_import_statements() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            use PubStruct<|>;
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }",
+        );
+    }
+
+    #[test]
+    fn qualify_function() {
+        check_assist(
+            qualify_path,
+            r"
+            test_function<|>
+
+            pub mod PubMod {
+                pub fn test_function() {};
+            }
+            ",
+            r"
+            PubMod::test_function
+
+            pub mod PubMod {
+                pub fn test_function() {};
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn qualify_macro() {
+        check_assist(
+            qualify_path,
+            r"
+//- /lib.rs crate:crate_with_macro
+#[macro_export]
+macro_rules! foo {
+    () => ()
+}
+
+//- /main.rs crate:main deps:crate_with_macro
+fn main() {
+    foo<|>
+}
+",
+            r"
+fn main() {
+    crate_with_macro::foo
+}
+",
+        );
+    }
+
+    #[test]
+    fn qualify_path_target() {
+        check_assist_target(
+            qualify_path,
+            r"
+            struct AssistInfo {
+                group_label: Option<<|>GroupLabel>,
+            }
+
+            mod m { pub struct GroupLabel; }
+            ",
+            "GroupLabel",
+        )
+    }
+
+    #[test]
+    fn not_applicable_when_path_start_is_imported() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            pub mod mod1 {
+                pub mod mod2 {
+                    pub mod mod3 {
+                        pub struct TestStruct;
+                    }
+                }
+            }
+
+            use mod1::mod2;
+            fn main() {
+                mod2::mod3::TestStruct<|>
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_imported_function() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            pub mod test_mod {
+                pub fn test_function() {}
+            }
+
+            use test_mod::test_function;
+            fn main() {
+                test_function<|>
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn associated_struct_function() {
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub struct TestStruct {}
+                impl TestStruct {
+                    pub fn test_function() {}
+                }
+            }
+
+            fn main() {
+                TestStruct::test_function<|>
+            }
+            ",
+            r"
+            mod test_mod {
+                pub struct TestStruct {}
+                impl TestStruct {
+                    pub fn test_function() {}
+                }
+            }
+
+            fn main() {
+                test_mod::TestStruct::test_function
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn associated_struct_const() {
+        mark::check!(qualify_path_qualifier_start);
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub struct TestStruct {}
+                impl TestStruct {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            fn main() {
+                TestStruct::TEST_CONST<|>
+            }
+            ",
+            r"
+            mod test_mod {
+                pub struct TestStruct {}
+                impl TestStruct {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            fn main() {
+                test_mod::TestStruct::TEST_CONST
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn associated_trait_function() {
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_function();
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_function() {}
+                }
+            }
+
+            fn main() {
+                test_mod::TestStruct::test_function<|>
+            }
+            ",
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_function();
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_function() {}
+                }
+            }
+
+            fn main() {
+                <test_mod::TestStruct as test_mod::TestTrait>::test_function
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_imported_trait_for_function() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_function();
+                }
+                pub trait TestTrait2 {
+                    fn test_function();
+                }
+                pub enum TestEnum {
+                    One,
+                    Two,
+                }
+                impl TestTrait2 for TestEnum {
+                    fn test_function() {}
+                }
+                impl TestTrait for TestEnum {
+                    fn test_function() {}
+                }
+            }
+
+            use test_mod::TestTrait2;
+            fn main() {
+                test_mod::TestEnum::test_function<|>;
+            }
+            ",
+        )
+    }
+
+    #[test]
+    fn associated_trait_const() {
+        mark::check!(qualify_path_trait_assoc_item);
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    const TEST_CONST: u8;
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            fn main() {
+                test_mod::TestStruct::TEST_CONST<|>
+            }
+            ",
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    const TEST_CONST: u8;
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            fn main() {
+                <test_mod::TestStruct as test_mod::TestTrait>::TEST_CONST
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_imported_trait_for_const() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    const TEST_CONST: u8;
+                }
+                pub trait TestTrait2 {
+                    const TEST_CONST: f64;
+                }
+                pub enum TestEnum {
+                    One,
+                    Two,
+                }
+                impl TestTrait2 for TestEnum {
+                    const TEST_CONST: f64 = 42.0;
+                }
+                impl TestTrait for TestEnum {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            use test_mod::TestTrait2;
+            fn main() {
+                test_mod::TestEnum::TEST_CONST<|>;
+            }
+            ",
+        )
+    }
+
+    #[test]
+    fn trait_method() {
+        mark::check!(qualify_path_trait_method);
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(&self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(&self) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_struct.test_meth<|>od()
+            }
+            ",
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(&self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(&self) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_mod::TestTrait::test_method(&test_struct)
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn trait_method_multi_params() {
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(&self, test: i32);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(&self, test: i32) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_struct.test_meth<|>od(42)
+            }
+            ",
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(&self, test: i32);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(&self, test: i32) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_mod::TestTrait::test_method(&test_struct, 42)
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn trait_method_consume() {
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(self) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_struct.test_meth<|>od()
+            }
+            ",
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(self) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_mod::TestTrait::test_method(test_struct)
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn trait_method_cross_crate() {
+        check_assist(
+            qualify_path,
+            r"
+            //- /main.rs crate:main deps:dep
+            fn main() {
+                let test_struct = dep::test_mod::TestStruct {};
+                test_struct.test_meth<|>od()
+            }
+            //- /dep.rs crate:dep
+            pub mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(&self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(&self) {}
+                }
+            }
+            ",
+            r"
+            fn main() {
+                let test_struct = dep::test_mod::TestStruct {};
+                dep::test_mod::TestTrait::test_method(&test_struct)
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn assoc_fn_cross_crate() {
+        check_assist(
+            qualify_path,
+            r"
+            //- /main.rs crate:main deps:dep
+            fn main() {
+                dep::test_mod::TestStruct::test_func<|>tion
+            }
+            //- /dep.rs crate:dep
+            pub mod test_mod {
+                pub trait TestTrait {
+                    fn test_function();
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_function() {}
+                }
+            }
+            ",
+            r"
+            fn main() {
+                <dep::test_mod::TestStruct as dep::test_mod::TestTrait>::test_function
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn assoc_const_cross_crate() {
+        check_assist(
+            qualify_path,
+            r"
+            //- /main.rs crate:main deps:dep
+            fn main() {
+                dep::test_mod::TestStruct::CONST<|>
+            }
+            //- /dep.rs crate:dep
+            pub mod test_mod {
+                pub trait TestTrait {
+                    const CONST: bool;
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    const CONST: bool = true;
+                }
+            }
+            ",
+            r"
+            fn main() {
+                <dep::test_mod::TestStruct as dep::test_mod::TestTrait>::CONST
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn assoc_fn_as_method_cross_crate() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            //- /main.rs crate:main deps:dep
+            fn main() {
+                let test_struct = dep::test_mod::TestStruct {};
+                test_struct.test_func<|>tion()
+            }
+            //- /dep.rs crate:dep
+            pub mod test_mod {
+                pub trait TestTrait {
+                    fn test_function();
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_function() {}
+                }
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn private_trait_cross_crate() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            //- /main.rs crate:main deps:dep
+            fn main() {
+                let test_struct = dep::test_mod::TestStruct {};
+                test_struct.test_meth<|>od()
+            }
+            //- /dep.rs crate:dep
+            pub mod test_mod {
+                trait TestTrait {
+                    fn test_method(&self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method(&self) {}
+                }
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_imported_trait_for_method() {
+        check_assist_not_applicable(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method(&self);
+                }
+                pub trait TestTrait2 {
+                    fn test_method(&self);
+                }
+                pub enum TestEnum {
+                    One,
+                    Two,
+                }
+                impl TestTrait2 for TestEnum {
+                    fn test_method(&self) {}
+                }
+                impl TestTrait for TestEnum {
+                    fn test_method(&self) {}
+                }
+            }
+
+            use test_mod::TestTrait2;
+            fn main() {
+                let one = test_mod::TestEnum::One;
+                one.test<|>_method();
+            }
+            ",
+        )
+    }
+
+    #[test]
+    fn dep_import() {
+        check_assist(
+            qualify_path,
+            r"
+//- /lib.rs crate:dep
+pub struct Struct;
+
+//- /main.rs crate:main deps:dep
+fn main() {
+    Struct<|>
+}
+",
+            r"
+fn main() {
+    dep::Struct
+}
+",
+        );
+    }
+
+    #[test]
+    fn whole_segment() {
+        // Tests that only imports whose last segment matches the identifier get suggested.
+        check_assist(
+            qualify_path,
+            r"
+//- /lib.rs crate:dep
+pub mod fmt {
+    pub trait Display {}
+}
+
+pub fn panic_fmt() {}
+
+//- /main.rs crate:main deps:dep
+struct S;
+
+impl f<|>mt::Display for S {}
+",
+            r"
+struct S;
+
+impl dep::fmt::Display for S {}
+",
+        );
+    }
+
+    #[test]
+    fn macro_generated() {
+        // Tests that macro-generated items are suggested from external crates.
+        check_assist(
+            qualify_path,
+            r"
+//- /lib.rs crate:dep
+macro_rules! mac {
+    () => {
+        pub struct Cheese;
+    };
+}
+
+mac!();
+
+//- /main.rs crate:main deps:dep
+fn main() {
+    Cheese<|>;
+}
+",
+            r"
+fn main() {
+    dep::Cheese;
+}
+",
+        );
+    }
+
+    #[test]
+    fn casing() {
+        // Tests that differently cased names don't interfere and we only suggest the matching one.
+        check_assist(
+            qualify_path,
+            r"
+//- /lib.rs crate:dep
+pub struct FMT;
+pub struct fmt;
+
+//- /main.rs crate:main deps:dep
+fn main() {
+    FMT<|>;
+}
+",
+            r"
+fn main() {
+    dep::FMT;
+}
+",
+        );
+    }
+}
diff --git a/crates/assists/src/handlers/replace_string_with_char.rs b/crates/assists/src/handlers/replace_string_with_char.rs
new file mode 100644
index 000000000..4ca87a8ec
--- /dev/null
+++ b/crates/assists/src/handlers/replace_string_with_char.rs
@@ -0,0 +1,141 @@
+use syntax::{
+    ast::{self, HasStringValue},
+    AstToken,
+    SyntaxKind::STRING,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: replace_string_with_char
+//
+// Replace string with char.
+//
+// ```
+// fn main() {
+//     find("{<|>");
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     find('{');
+// }
+// ```
+pub(crate) fn replace_string_with_char(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let token = ctx.find_token_at_offset(STRING).and_then(ast::String::cast)?;
+    let value = token.value()?;
+    let target = token.syntax().text_range();
+
+    if value.chars().take(2).count() != 1 {
+        return None;
+    }
+
+    acc.add(
+        AssistId("replace_string_with_char", AssistKind::RefactorRewrite),
+        "Replace string with char",
+        target,
+        |edit| {
+            edit.replace(token.syntax().text_range(), format!("'{}'", value));
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn replace_string_with_char_target() {
+        check_assist_target(
+            replace_string_with_char,
+            r#"
+            fn f() {
+                let s = "<|>c";
+            }
+            "#,
+            r#""c""#,
+        );
+    }
+
+    #[test]
+    fn replace_string_with_char_assist() {
+        check_assist(
+            replace_string_with_char,
+            r#"
+    fn f() {
+        let s = "<|>c";
+    }
+    "#,
+            r##"
+    fn f() {
+        let s = 'c';
+    }
+    "##,
+        )
+    }
+
+    #[test]
+    fn replace_string_with_char_assist_with_emoji() {
+        check_assist(
+            replace_string_with_char,
+            r#"
+    fn f() {
+        let s = "<|>😀";
+    }
+    "#,
+            r##"
+    fn f() {
+        let s = '😀';
+    }
+    "##,
+        )
+    }
+
+    #[test]
+    fn replace_string_with_char_assist_not_applicable() {
+        check_assist_not_applicable(
+            replace_string_with_char,
+            r#"
+    fn f() {
+        let s = "<|>test";
+    }
+    "#,
+        )
+    }
+
+    #[test]
+    fn replace_string_with_char_works_inside_macros() {
+        check_assist(
+            replace_string_with_char,
+            r#"
+                fn f() {
+                    format!(<|>"x", 92)
+                }
+                "#,
+            r##"
+                fn f() {
+                    format!('x', 92)
+                }
+                "##,
+        )
+    }
+
+    #[test]
+    fn replace_string_with_char_works_func_args() {
+        check_assist(
+            replace_string_with_char,
+            r#"
+                fn f() {
+                    find(<|>"x");
+                }
+                "#,
+            r##"
+                fn f() {
+                    find('x');
+                }
+                "##,
+        )
+    }
+}