made the add_missing_impl_members and add_missing_default_members assists transform lifetimes

crates/hir/src/lib.rs

@@ -2637,14 +2637,19 @@ pub fn params(self, db: &dyn HirDatabase) -> Vec<GenericParam> {
                 Either::Right(x) => GenericParam::TypeParam(x),
             }
         });
-        let lt_params = generics
+        self.lifetime_params(db).into_iter().chain(ty_params).collect()
+    }
+
+    pub fn lifetime_params(self, db: &dyn HirDatabase) -> Vec<GenericParam> {
+        let generics = db.generic_params(self.into());
+        generics
             .lifetimes
             .iter()
             .map(|(local_id, _)| LifetimeParam {
                 id: LifetimeParamId { parent: self.into(), local_id },
             })
-            .map(GenericParam::LifetimeParam);
+            .map(GenericParam::LifetimeParam)
-        lt_params.chain(ty_params).collect()
+            .collect()
     }
 
     pub fn type_params(self, db: &dyn HirDatabase) -> Vec<TypeOrConstParam> {

crates/ide-assists/src/handlers/add_missing_impl_members.rs

@@ -365,6 +365,59 @@ fn foo(&self, t: U) -> &U {
         );
     }
 
+    #[test]
+    fn test_lifetime_substitution() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+pub trait Trait<'a, 'b, A, B, C> {
+    fn foo(&self, one: &'a A, anoter: &'b B) -> &'a C;
+}
+
+impl<'x, 'y, T, V, U> Trait<'x, 'y, T, V, U> for () {$0}"#,
+            r#"
+pub trait Trait<'a, 'b, A, B, C> {
+    fn foo(&self, one: &'a A, anoter: &'b B) -> &'a C;
+}
+
+impl<'x, 'y, T, V, U> Trait<'x, 'y, T, V, U> for () {
+    fn foo(&self, one: &'x T, anoter: &'y V) -> &'x U {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_lifetime_substitution_with_body() {
+        check_assist(
+            add_missing_default_members,
+            r#"
+pub trait Trait<'a, 'b, A, B, C: Default> {
+    fn foo(&self, _one: &'a A, _anoter: &'b B) -> (C, &'a i32) {
+        let value: &'a i32 = &0;
+        (C::default(), value)
+    }
+}
+
+impl<'x, 'y, T, V, U: Default> Trait<'x, 'y, T, V, U> for () {$0}"#,
+            r#"
+pub trait Trait<'a, 'b, A, B, C: Default> {
+    fn foo(&self, _one: &'a A, _anoter: &'b B) -> (C, &'a i32) {
+        let value: &'a i32 = &0;
+        (C::default(), value)
+    }
+}
+
+impl<'x, 'y, T, V, U: Default> Trait<'x, 'y, T, V, U> for () {
+    $0fn foo(&self, _one: &'x T, _anoter: &'y V) -> (U, &'x i32) {
+        let value: &'x i32 = &0;
+        (<U>::default(), value)
+    }
+}"#,
+        );
+    }
+
     #[test]
     fn test_cursor_after_empty_impl_def() {
         check_assist(

crates/ide-db/src/path_transform.rs

@@ -9,6 +9,14 @@
     ted, SyntaxNode,
 };
 
+#[derive(Default)]
+struct Substs {
+    types: Vec<ast::TypeArg>,
+    lifetimes: Vec<ast::LifetimeArg>,
+}
+
+type LifetimeName = String;
+
 /// `PathTransform` substitutes path in SyntaxNodes in bulk.
 ///
 /// This is mostly useful for IDE code generation. If you paste some existing
@@ -34,7 +42,7 @@
 /// ```
 pub struct PathTransform<'a> {
     generic_def: Option<hir::GenericDef>,
-    substs: Vec<ast::Type>,
+    substs: Substs,
     target_scope: &'a SemanticsScope<'a>,
     source_scope: &'a SemanticsScope<'a>,
 }
@@ -72,7 +80,7 @@ pub fn generic_transformation(
         target_scope: &'a SemanticsScope<'a>,
         source_scope: &'a SemanticsScope<'a>,
     ) -> PathTransform<'a> {
-        PathTransform { source_scope, target_scope, generic_def: None, substs: Vec::new() }
+        PathTransform { source_scope, target_scope, generic_def: None, substs: Substs::default() }
     }
 
     pub fn apply(&self, syntax: &SyntaxNode) {
@@ -91,11 +99,11 @@ fn build_ctx(&self) -> Ctx<'a> {
         let target_module = self.target_scope.module();
         let source_module = self.source_scope.module();
         let skip = match self.generic_def {
-            // this is a trait impl, so we need to skip the first type parameter -- this is a bit hacky
+            // this is a trait impl, so we need to skip the first type parameter (i.e. Self) -- this is a bit hacky
             Some(hir::GenericDef::Trait(_)) => 1,
             _ => 0,
         };
-        let substs_by_param: FxHashMap<_, _> = self
+        let type_substs: FxHashMap<_, _> = self
             .generic_def
             .into_iter()
             .flat_map(|it| it.type_params(db))
@@ -106,31 +114,35 @@ fn build_ctx(&self) -> Ctx<'a> {
             // can still hit those trailing values and check if they actually have
             // a default type. If they do, go for that type from `hir` to `ast` so
             // the resulting change can be applied correctly.
-            .zip(self.substs.iter().map(Some).chain(std::iter::repeat(None)))
+            .zip(self.substs.types.iter().map(Some).chain(std::iter::repeat(None)))
             .filter_map(|(k, v)| match k.split(db) {
-                Either::Left(_) => None,
+                Either::Left(_) => None, // FIXME: map const types too
                 Either::Right(t) => match v {
-                    Some(v) => Some((k, v.clone())),
+                    Some(v) => Some((k, v.ty()?.clone())),
                     None => {
                         let default = t.default(db)?;
-                        Some((
+                        let v = ast::make::ty(
-                            k,
+                            &default.display_source_code(db, source_module.into(), false).ok()?,
-                            ast::make::ty(
+                        );
-                                &default
+                        Some((k, v))
-                                    .display_source_code(db, source_module.into(), false)
-                                    .ok()?,
-                            ),
-                        ))
                     }
                 },
             })
             .collect();
-        Ctx { substs: substs_by_param, target_module, source_scope: self.source_scope }
+        let lifetime_substs: FxHashMap<_, _> = self
+            .generic_def
+            .into_iter()
+            .flat_map(|it| it.lifetime_params(db))
+            .zip(self.substs.lifetimes.clone())
+            .filter_map(|(k, v)| Some((k.name(db).to_string(), v.lifetime()?)))
+            .collect();
+        Ctx { type_substs, lifetime_substs, target_module, source_scope: self.source_scope }
     }
 }
 
 struct Ctx<'a> {
-    substs: FxHashMap<hir::TypeOrConstParam, ast::Type>,
+    type_substs: FxHashMap<hir::TypeOrConstParam, ast::Type>,
+    lifetime_substs: FxHashMap<LifetimeName, ast::Lifetime>,
     target_module: hir::Module,
     source_scope: &'a SemanticsScope<'a>,
 }
@@ -152,7 +164,24 @@ fn apply(&self, item: &SyntaxNode) {
         for path in paths {
             self.transform_path(path);
         }
+
+        item.preorder()
+            .filter_map(|event| match event {
+                syntax::WalkEvent::Enter(_) => None,
+                syntax::WalkEvent::Leave(node) => Some(node),
+            })
+            .filter_map(ast::Lifetime::cast)
+            .for_each(|lifetime| {
+                if let Some(subst) = self.lifetime_substs.get(&lifetime.syntax().text().to_string())
+                {
+                    ted::replace(
+                        lifetime.syntax(),
+                        subst.clone_subtree().clone_for_update().syntax(),
+                    );
+                }
+            });
     }
+
     fn transform_path(&self, path: ast::Path) -> Option<()> {
         if path.qualifier().is_some() {
             return None;
@@ -169,7 +198,7 @@ fn transform_path(&self, path: ast::Path) -> Option<()> {
 
         match resolution {
             hir::PathResolution::TypeParam(tp) => {
-                if let Some(subst) = self.substs.get(&tp.merge()) {
+                if let Some(subst) = self.type_substs.get(&tp.merge()) {
                     let parent = path.syntax().parent()?;
                     if let Some(parent) = ast::Path::cast(parent.clone()) {
                         // Path inside path means that there is an associated
@@ -250,7 +279,7 @@ fn transform_path(&self, path: ast::Path) -> Option<()> {
 
 // 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_def: ast::Impl) -> Option<Vec<ast::Type>> {
+fn get_syntactic_substs(impl_def: ast::Impl) -> Option<Substs> {
     let target_trait = impl_def.trait_()?;
     let path_type = match target_trait {
         ast::Type::PathType(path) => path,
@@ -261,13 +290,13 @@ fn get_syntactic_substs(impl_def: ast::Impl) -> Option<Vec<ast::Type>> {
     get_type_args_from_arg_list(generic_arg_list)
 }
 
-fn get_type_args_from_arg_list(generic_arg_list: ast::GenericArgList) -> Option<Vec<ast::Type>> {
+fn get_type_args_from_arg_list(generic_arg_list: ast::GenericArgList) -> Option<Substs> {
-    let mut result = Vec::new();
+    let mut result = Substs::default();
-    for generic_arg in generic_arg_list.generic_args() {
+    generic_arg_list.generic_args().for_each(|generic_arg| match generic_arg {
-        if let ast::GenericArg::TypeArg(type_arg) = generic_arg {
+        ast::GenericArg::TypeArg(type_arg) => result.types.push(type_arg),
-            result.push(type_arg.ty()?)
+        ast::GenericArg::LifetimeArg(l_arg) => result.lifetimes.push(l_arg),
-        }
+        _ => (), // FIXME: don't filter out const params
-    }
+    });
 
     Some(result)
 }