4 files changed, 365 insertions, 67 deletions

diff --git a/crates/ra_assists/Cargo.toml b/crates/ra_assists/Cargo.toml
index 434e6656c..50be8d9bc 100644
--- a/crates/ra_assists/Cargo.toml
+++ b/crates/ra_assists/Cargo.toml
@@ -10,6 +10,7 @@ doctest = false
 [dependencies]
 format-buf = "1.0.0"
 join_to_string = "0.1.3"
+rustc-hash = "1.0"
 itertools = "0.8.0"
 
 ra_syntax = { path = "../ra_syntax" }
diff --git a/crates/ra_assists/src/assists/add_missing_impl_members.rs b/crates/ra_assists/src/assists/add_missing_impl_members.rs
index bc49e71fe..bf1136193 100644
--- a/crates/ra_assists/src/assists/add_missing_impl_members.rs
+++ b/crates/ra_assists/src/assists/add_missing_impl_members.rs
@@ -1,12 +1,13 @@
-use std::collections::HashMap;
-
-use hir::{db::HirDatabase, HasSource};
+use hir::{db::HirDatabase, HasSource, InFile};
 use ra_syntax::{
     ast::{self, edit, make, AstNode, NameOwner},
     SmolStr,
 };
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{
+    ast_transform::{self, AstTransform, QualifyPaths, SubstituteTypeParams},
+    Assist, AssistCtx, AssistId,
+};
 
 #[derive(PartialEq)]
 enum AddMissingImplMembersMode {
@@ -134,25 +135,23 @@ fn add_missing_impl_members_inner(
         return None;
     }
 
-    let file_id = ctx.frange.file_id;
     let db = ctx.db;
+    let file_id = ctx.frange.file_id;
+    let trait_file_id = trait_.source(db).file_id;
 
     ctx.add_assist(AssistId(assist_id), label, |edit| {
         let n_existing_items = impl_item_list.impl_items().count();
-        let substs = get_syntactic_substs(impl_node).unwrap_or_default();
-        let generic_def: hir::GenericDef = trait_.into();
-        let substs_by_param: HashMap<_, _> = generic_def
-            .params(db)
-            .into_iter()
-            // this is a trait impl, so we need to skip the first type parameter -- this is a bit hacky
-            .skip(1)
-            .zip(substs.into_iter())
-            .collect();
+        let module = hir::SourceAnalyzer::new(
+            db,
+            hir::InFile::new(file_id.into(), impl_node.syntax()),
+            None,
+        )
+        .module();
+        let ast_transform = QualifyPaths::new(db, module)
+            .or(SubstituteTypeParams::for_trait_impl(db, trait_, impl_node));
         let items = missing_items
             .into_iter()
-            .map(|it| {
-                substitute_type_params(db, hir::InFile::new(file_id.into(), it), &substs_by_param)
-            })
+            .map(|it| ast_transform::apply(&*ast_transform, InFile::new(trait_file_id, it)))
             .map(|it| match it {
                 ast::ImplItem::FnDef(def) => ast::ImplItem::FnDef(add_body(def)),
                 _ => it,
@@ -177,56 +176,6 @@ fn add_body(fn_def: ast::FnDef) -> ast::FnDef {
     }
 }
 
-// FIXME: It would probably be nicer if we could get this via HIR (i.e. get the
-// trait ref, and then go from the types in the substs back to the syntax)
-// FIXME: This should be a general utility (not even just for assists)
-fn get_syntactic_substs(impl_block: ast::ImplBlock) -> Option<Vec<ast::TypeRef>> {
-    let target_trait = impl_block.target_trait()?;
-    let path_type = match target_trait {
-        ast::TypeRef::PathType(path) => path,
-        _ => return None,
-    };
-    let type_arg_list = path_type.path()?.segment()?.type_arg_list()?;
-    let mut result = Vec::new();
-    for type_arg in type_arg_list.type_args() {
-        let type_arg: ast::TypeArg = type_arg;
-        result.push(type_arg.type_ref()?);
-    }
-    Some(result)
-}
-
-// FIXME: This should be a general utility (not even just for assists)
-fn substitute_type_params<N: AstNode>(
-    db: &impl HirDatabase,
-    node: hir::InFile<N>,
-    substs: &HashMap<hir::TypeParam, ast::TypeRef>,
-) -> N {
-    let type_param_replacements = node
-        .value
-        .syntax()
-        .descendants()
-        .filter_map(ast::TypeRef::cast)
-        .filter_map(|n| {
-            let path = match &n {
-                ast::TypeRef::PathType(path_type) => path_type.path()?,
-                _ => return None,
-            };
-            let analyzer = hir::SourceAnalyzer::new(db, node.with_value(n.syntax()), None);
-            let resolution = analyzer.resolve_path(db, &path)?;
-            match resolution {
-                hir::PathResolution::TypeParam(tp) => Some((n, substs.get(&tp)?.clone())),
-                _ => None,
-            }
-        })
-        .collect::<Vec<_>>();
-
-    if type_param_replacements.is_empty() {
-        node.value
-    } else {
-        edit::replace_descendants(&node.value, type_param_replacements.into_iter())
-    }
-}
-
 /// Given an `ast::ImplBlock`, resolves the target trait (the one being
 /// implemented) to a `ast::TraitDef`.
 fn resolve_target_trait_def(
@@ -401,6 +350,174 @@ impl Foo for S {
     }
 
     #[test]
+    fn test_qualify_path_1() {
+        check_assist(
+            add_missing_impl_members,
+            "
+mod foo {
+    pub struct Bar;
+    trait Foo { fn foo(&self, bar: Bar); }
+}
+struct S;
+impl foo::Foo for S { <|> }",
+            "
+mod foo {
+    pub struct Bar;
+    trait Foo { fn foo(&self, bar: Bar); }
+}
+struct S;
+impl foo::Foo for S {
+    <|>fn foo(&self, bar: foo::Bar) { unimplemented!() }
+}",
+        );
+    }
+
+    #[test]
+    fn test_qualify_path_generic() {
+        check_assist(
+            add_missing_impl_members,
+            "
+mod foo {
+    pub struct Bar<T>;
+    trait Foo { fn foo(&self, bar: Bar<u32>); }
+}
+struct S;
+impl foo::Foo for S { <|> }",
+            "
+mod foo {
+    pub struct Bar<T>;
+    trait Foo { fn foo(&self, bar: Bar<u32>); }
+}
+struct S;
+impl foo::Foo for S {
+    <|>fn foo(&self, bar: foo::Bar<u32>) { unimplemented!() }
+}",
+        );
+    }
+
+    #[test]
+    fn test_qualify_path_and_substitute_param() {
+        check_assist(
+            add_missing_impl_members,
+            "
+mod foo {
+    pub struct Bar<T>;
+    trait Foo<T> { fn foo(&self, bar: Bar<T>); }
+}
+struct S;
+impl foo::Foo<u32> for S { <|> }",
+            "
+mod foo {
+    pub struct Bar<T>;
+    trait Foo<T> { fn foo(&self, bar: Bar<T>); }
+}
+struct S;
+impl foo::Foo<u32> for S {
+    <|>fn foo(&self, bar: foo::Bar<u32>) { unimplemented!() }
+}",
+        );
+    }
+
+    #[test]
+    fn test_substitute_param_no_qualify() {
+        // when substituting params, the substituted param should not be qualified!
+        check_assist(
+            add_missing_impl_members,
+            "
+mod foo {
+    trait Foo<T> { fn foo(&self, bar: T); }
+    pub struct Param;
+}
+struct Param;
+struct S;
+impl foo::Foo<Param> for S { <|> }",
+            "
+mod foo {
+    trait Foo<T> { fn foo(&self, bar: T); }
+    pub struct Param;
+}
+struct Param;
+struct S;
+impl foo::Foo<Param> for S {
+    <|>fn foo(&self, bar: Param) { unimplemented!() }
+}",
+        );
+    }
+
+    #[test]
+    fn test_qualify_path_associated_item() {
+        check_assist(
+            add_missing_impl_members,
+            "
+mod foo {
+    pub struct Bar<T>;
+    impl Bar<T> { type Assoc = u32; }
+    trait Foo { fn foo(&self, bar: Bar<u32>::Assoc); }
+}
+struct S;
+impl foo::Foo for S { <|> }",
+            "
+mod foo {
+    pub struct Bar<T>;
+    impl Bar<T> { type Assoc = u32; }
+    trait Foo { fn foo(&self, bar: Bar<u32>::Assoc); }
+}
+struct S;
+impl foo::Foo for S {
+    <|>fn foo(&self, bar: foo::Bar<u32>::Assoc) { unimplemented!() }
+}",
+        );
+    }
+
+    #[test]
+    fn test_qualify_path_nested() {
+        check_assist(
+            add_missing_impl_members,
+            "
+mod foo {
+    pub struct Bar<T>;
+    pub struct Baz;
+    trait Foo { fn foo(&self, bar: Bar<Baz>); }
+}
+struct S;
+impl foo::Foo for S { <|> }",
+            "
+mod foo {
+    pub struct Bar<T>;
+    pub struct Baz;
+    trait Foo { fn foo(&self, bar: Bar<Baz>); }
+}
+struct S;
+impl foo::Foo for S {
+    <|>fn foo(&self, bar: foo::Bar<foo::Baz>) { unimplemented!() }
+}",
+        );
+    }
+
+    #[test]
+    fn test_qualify_path_fn_trait_notation() {
+        check_assist(
+            add_missing_impl_members,
+            "
+mod foo {
+    pub trait Fn<Args> { type Output; }
+    trait Foo { fn foo(&self, bar: dyn Fn(u32) -> i32); }
+}
+struct S;
+impl foo::Foo for S { <|> }",
+            "
+mod foo {
+    pub trait Fn<Args> { type Output; }
+    trait Foo { fn foo(&self, bar: dyn Fn(u32) -> i32); }
+}
+struct S;
+impl foo::Foo for S {
+    <|>fn foo(&self, bar: dyn Fn(u32) -> i32) { unimplemented!() }
+}",
+        );
+    }
+
+    #[test]
     fn test_empty_trait() {
         check_assist_not_applicable(
             add_missing_impl_members,
diff --git a/crates/ra_assists/src/ast_transform.rs b/crates/ra_assists/src/ast_transform.rs
new file mode 100644
index 000000000..cbddc50ac
--- /dev/null
+++ b/crates/ra_assists/src/ast_transform.rs
@@ -0,0 +1,179 @@
+//! `AstTransformer`s are functions that replace nodes in an AST and can be easily combined.
+use rustc_hash::FxHashMap;
+
+use hir::{db::HirDatabase, InFile, PathResolution};
+use ra_syntax::ast::{self, make, AstNode};
+
+pub trait AstTransform<'a> {
+    fn get_substitution(
+        &self,
+        node: InFile<&ra_syntax::SyntaxNode>,
+    ) -> Option<ra_syntax::SyntaxNode>;
+
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a>;
+    fn or<T: AstTransform<'a> + 'a>(self, other: T) -> Box<dyn AstTransform<'a> + 'a>
+    where
+        Self: Sized + 'a,
+    {
+        self.chain_before(Box::new(other))
+    }
+}
+
+struct NullTransformer;
+
+impl<'a> AstTransform<'a> for NullTransformer {
+    fn get_substitution(
+        &self,
+        _node: InFile<&ra_syntax::SyntaxNode>,
+    ) -> Option<ra_syntax::SyntaxNode> {
+        None
+    }
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
+        other
+    }
+}
+
+pub struct SubstituteTypeParams<'a, DB: HirDatabase> {
+    db: &'a DB,
+    substs: FxHashMap<hir::TypeParam, ast::TypeRef>,
+    previous: Box<dyn AstTransform<'a> + 'a>,
+}
+
+impl<'a, DB: HirDatabase> SubstituteTypeParams<'a, DB> {
+    pub fn for_trait_impl(
+        db: &'a DB,
+        trait_: hir::Trait,
+        impl_block: ast::ImplBlock,
+    ) -> SubstituteTypeParams<'a, DB> {
+        let substs = get_syntactic_substs(impl_block).unwrap_or_default();
+        let generic_def: hir::GenericDef = trait_.into();
+        let substs_by_param: FxHashMap<_, _> = generic_def
+            .params(db)
+            .into_iter()
+            // this is a trait impl, so we need to skip the first type parameter -- this is a bit hacky
+            .skip(1)
+            .zip(substs.into_iter())
+            .collect();
+        return SubstituteTypeParams {
+            db,
+            substs: substs_by_param,
+            previous: Box::new(NullTransformer),
+        };
+
+        // FIXME: It would probably be nicer if we could get this via HIR (i.e. get the
+        // trait ref, and then go from the types in the substs back to the syntax)
+        fn get_syntactic_substs(impl_block: ast::ImplBlock) -> Option<Vec<ast::TypeRef>> {
+            let target_trait = impl_block.target_trait()?;
+            let path_type = match target_trait {
+                ast::TypeRef::PathType(path) => path,
+                _ => return None,
+            };
+            let type_arg_list = path_type.path()?.segment()?.type_arg_list()?;
+            let mut result = Vec::new();
+            for type_arg in type_arg_list.type_args() {
+                let type_arg: ast::TypeArg = type_arg;
+                result.push(type_arg.type_ref()?);
+            }
+            Some(result)
+        }
+    }
+    fn get_substitution_inner(
+        &self,
+        node: InFile<&ra_syntax::SyntaxNode>,
+    ) -> Option<ra_syntax::SyntaxNode> {
+        let type_ref = ast::TypeRef::cast(node.value.clone())?;
+        let path = match &type_ref {
+            ast::TypeRef::PathType(path_type) => path_type.path()?,
+            _ => return None,
+        };
+        let analyzer = hir::SourceAnalyzer::new(self.db, node, None);
+        let resolution = analyzer.resolve_path(self.db, &path)?;
+        match resolution {
+            hir::PathResolution::TypeParam(tp) => Some(self.substs.get(&tp)?.syntax().clone()),
+            _ => None,
+        }
+    }
+}
+
+impl<'a, DB: HirDatabase> AstTransform<'a> for SubstituteTypeParams<'a, DB> {
+    fn get_substitution(
+        &self,
+        node: InFile<&ra_syntax::SyntaxNode>,
+    ) -> Option<ra_syntax::SyntaxNode> {
+        self.get_substitution_inner(node).or_else(|| self.previous.get_substitution(node))
+    }
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
+        Box::new(SubstituteTypeParams { previous: other, ..self })
+    }
+}
+
+pub struct QualifyPaths<'a, DB: HirDatabase> {
+    db: &'a DB,
+    from: Option<hir::Module>,
+    previous: Box<dyn AstTransform<'a> + 'a>,
+}
+
+impl<'a, DB: HirDatabase> QualifyPaths<'a, DB> {
+    pub fn new(db: &'a DB, from: Option<hir::Module>) -> Self {
+        Self { db, from, previous: Box::new(NullTransformer) }
+    }
+
+    fn get_substitution_inner(
+        &self,
+        node: InFile<&ra_syntax::SyntaxNode>,
+    ) -> Option<ra_syntax::SyntaxNode> {
+        // FIXME handle value ns?
+        let from = self.from?;
+        let p = ast::Path::cast(node.value.clone())?;
+        if p.segment().and_then(|s| s.param_list()).is_some() {
+            // don't try to qualify `Fn(Foo) -> Bar` paths, they are in prelude anyway
+            return None;
+        }
+        let analyzer = hir::SourceAnalyzer::new(self.db, node, None);
+        let resolution = analyzer.resolve_path(self.db, &p)?;
+        match resolution {
+            PathResolution::Def(def) => {
+                let found_path = from.find_use_path(self.db, def)?;
+                let args = p
+                    .segment()
+                    .and_then(|s| s.type_arg_list())
+                    .map(|arg_list| apply(self, node.with_value(arg_list)));
+                Some(make::path_with_type_arg_list(path_to_ast(found_path), args).syntax().clone())
+            }
+            PathResolution::Local(_)
+            | PathResolution::TypeParam(_)
+            | PathResolution::SelfType(_) => None,
+            PathResolution::Macro(_) => None,
+            PathResolution::AssocItem(_) => None,
+        }
+    }
+}
+
+pub fn apply<'a, N: AstNode>(transformer: &dyn AstTransform<'a>, node: InFile<N>) -> N {
+    let syntax = node.value.syntax();
+    let result = ra_syntax::algo::replace_descendants(syntax, &|element| match element {
+        ra_syntax::SyntaxElement::Node(n) => {
+            let replacement = transformer.get_substitution(node.with_value(&n))?;
+            Some(replacement.into())
+        }
+        _ => None,
+    });
+    N::cast(result).unwrap()
+}
+
+impl<'a, DB: HirDatabase> AstTransform<'a> for QualifyPaths<'a, DB> {
+    fn get_substitution(
+        &self,
+        node: InFile<&ra_syntax::SyntaxNode>,
+    ) -> Option<ra_syntax::SyntaxNode> {
+        self.get_substitution_inner(node).or_else(|| self.previous.get_substitution(node))
+    }
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
+        Box::new(QualifyPaths { previous: other, ..self })
+    }
+}
+
+fn path_to_ast(path: hir::ModPath) -> ast::Path {
+    let parse = ast::SourceFile::parse(&path.to_string());
+    parse.tree().syntax().descendants().find_map(ast::Path::cast).unwrap()
+}
diff --git a/crates/ra_assists/src/lib.rs b/crates/ra_assists/src/lib.rs
index 98fb20b22..712ff6f6a 100644
--- a/crates/ra_assists/src/lib.rs
+++ b/crates/ra_assists/src/lib.rs
@@ -11,6 +11,7 @@ mod marks;
 mod doc_tests;
 #[cfg(test)]
 mod test_db;
+pub mod ast_transform;
 
 use hir::db::HirDatabase;
 use ra_db::FileRange;