6 files changed, 128 insertions, 3 deletions

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 f0dfe7780..2b0726869 100644
--- a/crates/ra_assists/src/assists/add_missing_impl_members.rs
+++ b/crates/ra_assists/src/assists/add_missing_impl_members.rs
@@ -139,6 +139,12 @@ fn add_missing_impl_members_inner(
 
     ctx.add_assist(AssistId(assist_id), label, |edit| {
         let n_existing_items = impl_item_list.impl_items().count();
+        let module = hir::SourceAnalyzer::new(
+            db,
+            hir::InFile::new(file_id.into(), impl_node.syntax()),
+            None,
+        )
+        .module();
         let substs = get_syntactic_substs(impl_node).unwrap_or_default();
         let generic_def: hir::GenericDef = trait_.into();
         let substs_by_param: HashMap<_, _> = generic_def
@@ -150,6 +156,10 @@ fn add_missing_impl_members_inner(
             .collect();
         let items = missing_items
             .into_iter()
+            .map(|it| match module {
+                Some(module) => qualify_paths(db, hir::InFile::new(file_id.into(), it), module),
+                None => it,
+            })
             .map(|it| {
                 substitute_type_params(db, hir::InFile::new(file_id.into(), it), &substs_by_param)
             })
@@ -227,6 +237,41 @@ fn substitute_type_params<N: AstNode>(
     }
 }
 
+use hir::PathResolution;
+
+// TODO handle partial paths, with generic args
+// TODO handle value ns?
+
+fn qualify_paths<N: AstNode>(db: &impl HirDatabase, node: hir::InFile<N>, from: hir::Module) -> N {
+    let path_replacements = node
+        .value
+        .syntax()
+        .descendants()
+        .filter_map(ast::Path::cast)
+        .filter_map(|p| {
+            let analyzer = hir::SourceAnalyzer::new(db, node.with_value(p.syntax()), None);
+            let resolution = analyzer.resolve_path(db, &p)?;
+            match resolution {
+                PathResolution::Def(def) => {
+                    let found_path = from.find_path(db, def)?;
+                    Some((p, found_path.to_ast()))
+                }
+                PathResolution::Local(_)
+                | PathResolution::TypeParam(_)
+                | PathResolution::SelfType(_) => None,
+                PathResolution::Macro(_) => None,
+                PathResolution::AssocItem(_) => None,
+            }
+        })
+        .collect::<Vec<_>>();
+
+    if path_replacements.is_empty() {
+        node.value
+    } else {
+        edit::replace_descendants(&node.value, path_replacements.into_iter())
+    }
+}
+
 /// Given an `ast::ImplBlock`, resolves the target trait (the one being
 /// implemented) to a `ast::TraitDef`.
 fn resolve_target_trait_def(
@@ -406,14 +451,14 @@ impl Foo for S {
             add_missing_impl_members,
             "
 mod foo {
-    struct Bar;
+    pub struct Bar;
     trait Foo { fn foo(&self, bar: Bar); }
 }
 struct S;
 impl foo::Foo for S { <|> }",
             "
 mod foo {
-    struct Bar;
+    pub struct Bar;
     trait Foo { fn foo(&self, bar: Bar); }
 }
 struct S;
diff --git a/crates/ra_hir/src/code_model.rs b/crates/ra_hir/src/code_model.rs
index cc42068a1..4da3db0d6 100644
--- a/crates/ra_hir/src/code_model.rs
+++ b/crates/ra_hir/src/code_model.rs
@@ -227,6 +227,19 @@ impl Module {
     pub(crate) fn with_module_id(self, module_id: LocalModuleId) -> Module {
         Module::new(self.krate(), module_id)
     }
+
+    pub fn find_path(
+        self,
+        db: &impl DefDatabase,
+        item: ModuleDef,
+    ) -> Option<hir_def::path::ModPath> {
+        // FIXME expose namespace choice
+        hir_def::find_path::find_path(
+            db,
+            hir_def::item_scope::ItemInNs::Types(item.into()),
+            self.into(),
+        )
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
diff --git a/crates/ra_hir/src/from_id.rs b/crates/ra_hir/src/from_id.rs
index 75a1a7772..c16c17072 100644
--- a/crates/ra_hir/src/from_id.rs
+++ b/crates/ra_hir/src/from_id.rs
@@ -91,6 +91,22 @@ impl From<ModuleDefId> for ModuleDef {
     }
 }
 
+impl From<ModuleDef> for ModuleDefId {
+    fn from(id: ModuleDef) -> Self {
+        match id {
+            ModuleDef::Module(it) => ModuleDefId::ModuleId(it.into()),
+            ModuleDef::Function(it) => ModuleDefId::FunctionId(it.into()),
+            ModuleDef::Adt(it) => ModuleDefId::AdtId(it.into()),
+            ModuleDef::EnumVariant(it) => ModuleDefId::EnumVariantId(it.into()),
+            ModuleDef::Const(it) => ModuleDefId::ConstId(it.into()),
+            ModuleDef::Static(it) => ModuleDefId::StaticId(it.into()),
+            ModuleDef::Trait(it) => ModuleDefId::TraitId(it.into()),
+            ModuleDef::TypeAlias(it) => ModuleDefId::TypeAliasId(it.into()),
+            ModuleDef::BuiltinType(it) => ModuleDefId::BuiltinType(it),
+        }
+    }
+}
+
 impl From<DefWithBody> for DefWithBodyId {
     fn from(def: DefWithBody) -> Self {
         match def {
diff --git a/crates/ra_hir/src/source_binder.rs b/crates/ra_hir/src/source_binder.rs
index 2c422af8b..71339565f 100644
--- a/crates/ra_hir/src/source_binder.rs
+++ b/crates/ra_hir/src/source_binder.rs
@@ -205,6 +205,10 @@ impl SourceAnalyzer {
         }
     }
 
+    pub fn module(&self) -> Option<crate::code_model::Module> {
+        Some(crate::code_model::Module { id: self.resolver.module_id()? })
+    }
+
     fn expr_id(&self, expr: &ast::Expr) -> Option<ExprId> {
         let src = InFile { file_id: self.file_id, value: expr };
         self.body_source_map.as_ref()?.node_expr(src)
diff --git a/crates/ra_hir_def/src/path.rs b/crates/ra_hir_def/src/path.rs
index 82cfa67a9..7dd1939b9 100644
--- a/crates/ra_hir_def/src/path.rs
+++ b/crates/ra_hir_def/src/path.rs
@@ -1,7 +1,7 @@
 //! A desugared representation of paths like `crate::foo` or `<Type as Trait>::bar`.
 mod lower;
 
-use std::{iter, sync::Arc};
+use std::{fmt::Display, iter, sync::Arc};
 
 use hir_expand::{
     hygiene::Hygiene,
@@ -78,6 +78,12 @@ impl ModPath {
         }
         self.segments.first()
     }
+
+    pub fn to_ast(&self) -> ast::Path {
+        use ast::AstNode;
+        let parse = ast::SourceFile::parse(&self.to_string());
+        parse.tree().syntax().descendants().find_map(ast::Path::cast).unwrap()
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -248,6 +254,42 @@ impl From<Name> for ModPath {
     }
 }
 
+impl Display for ModPath {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let mut first_segment = true;
+        let mut add_segment = |s| {
+            if !first_segment {
+                f.write_str("::")?;
+            }
+            first_segment = false;
+            f.write_str(s)?;
+            Ok(())
+        };
+        match self.kind {
+            PathKind::Plain => {}
+            PathKind::Super(n) => {
+                if n == 0 {
+                    add_segment("self")?;
+                }
+                for _ in 0..n {
+                    add_segment("super")?;
+                }
+            }
+            PathKind::Crate => add_segment("crate")?,
+            PathKind::Abs => add_segment("")?,
+            PathKind::DollarCrate(_) => add_segment("$crate")?,
+        }
+        for segment in &self.segments {
+            if !first_segment {
+                f.write_str("::")?;
+            }
+            first_segment = false;
+            write!(f, "{}", segment)?;
+        }
+        Ok(())
+    }
+}
+
 pub use hir_expand::name as __name;
 
 #[macro_export]
diff --git a/crates/ra_hir_def/src/resolver.rs b/crates/ra_hir_def/src/resolver.rs
index 5d16dd087..40d0cb588 100644
--- a/crates/ra_hir_def/src/resolver.rs
+++ b/crates/ra_hir_def/src/resolver.rs
@@ -411,6 +411,11 @@ impl Resolver {
         })
     }
 
+    pub fn module_id(&self) -> Option<ModuleId> {
+        let (def_map, local_id) = self.module()?;
+        Some(ModuleId { krate: def_map.krate, local_id })
+    }
+
     pub fn krate(&self) -> Option<CrateId> {
         self.module().map(|t| t.0.krate)
     }