3 files changed, 22 insertions, 8 deletions

diff --git a/crates/ra_syntax/src/algo.rs b/crates/ra_syntax/src/algo.rs
index 2b2b295f9..30a479f01 100644
--- a/crates/ra_syntax/src/algo.rs
+++ b/crates/ra_syntax/src/algo.rs
@@ -184,17 +184,17 @@ pub fn replace_children(
 /// to create a type-safe abstraction on top of it instead.
 pub fn replace_descendants(
     parent: &SyntaxNode,
-    map: &FxHashMap<SyntaxElement, SyntaxElement>,
+    map: &impl Fn(&SyntaxElement) -> Option<SyntaxElement>,
 ) -> SyntaxNode {
     //  FIXME: this could be made much faster.
     let new_children = parent.children_with_tokens().map(|it| go(map, it)).collect::<Vec<_>>();
     return with_children(parent, new_children);
 
     fn go(
-        map: &FxHashMap<SyntaxElement, SyntaxElement>,
+        map: &impl Fn(&SyntaxElement) -> Option<SyntaxElement>,
         element: SyntaxElement,
     ) -> NodeOrToken<rowan::GreenNode, rowan::GreenToken> {
-        if let Some(replacement) = map.get(&element) {
+        if let Some(replacement) = map(&element) {
             return match replacement {
                 NodeOrToken::Node(it) => NodeOrToken::Node(it.green().clone()),
                 NodeOrToken::Token(it) => NodeOrToken::Token(it.green().clone()),
diff --git a/crates/ra_syntax/src/ast/edit.rs b/crates/ra_syntax/src/ast/edit.rs
index ae5d63927..b736098ac 100644
--- a/crates/ra_syntax/src/ast/edit.rs
+++ b/crates/ra_syntax/src/ast/edit.rs
@@ -236,8 +236,8 @@ pub fn replace_descendants<N: AstNode, D: AstNode>(
 ) -> N {
     let map = replacement_map
         .map(|(from, to)| (from.syntax().clone().into(), to.syntax().clone().into()))
-        .collect::<FxHashMap<_, _>>();
-    let new_syntax = algo::replace_descendants(parent.syntax(), &map);
+        .collect::<FxHashMap<SyntaxElement, _>>();
+    let new_syntax = algo::replace_descendants(parent.syntax(), &|n| map.get(n).cloned());
     N::cast(new_syntax).unwrap()
 }
 
@@ -292,7 +292,7 @@ impl IndentLevel {
                 )
             })
             .collect();
-        algo::replace_descendants(&node, &replacements)
+        algo::replace_descendants(&node, &|n| replacements.get(n).cloned())
     }
 
     pub fn decrease_indent<N: AstNode>(self, node: N) -> N {
@@ -320,7 +320,7 @@ impl IndentLevel {
                 )
             })
             .collect();
-        algo::replace_descendants(&node, &replacements)
+        algo::replace_descendants(&node, &|n| replacements.get(n).cloned())
     }
 }
 
diff --git a/crates/ra_syntax/src/ast/make.rs b/crates/ra_syntax/src/ast/make.rs
index 04a5408fe..9781b748f 100644
--- a/crates/ra_syntax/src/ast/make.rs
+++ b/crates/ra_syntax/src/ast/make.rs
@@ -2,7 +2,7 @@
 //! of smaller pieces.
 use itertools::Itertools;
 
-use crate::{ast, AstNode, SourceFile};
+use crate::{algo, ast, AstNode, SourceFile};
 
 pub fn name(text: &str) -> ast::Name {
     ast_from_text(&format!("mod {};", text))
@@ -21,6 +21,20 @@ pub fn path_qualified(qual: ast::Path, name_ref: ast::NameRef) -> ast::Path {
 fn path_from_text(text: &str) -> ast::Path {
     ast_from_text(text)
 }
+pub fn path_with_type_arg_list(path: ast::Path, args: Option<ast::TypeArgList>) -> ast::Path {
+    if let Some(args) = args {
+        let syntax = path.syntax();
+        // FIXME: remove existing type args
+        let new_syntax = algo::insert_children(
+            syntax,
+            crate::algo::InsertPosition::Last,
+            &mut Some(args).into_iter().map(|n| n.syntax().clone().into()),
+        );
+        ast::Path::cast(new_syntax).unwrap()
+    } else {
+        path
+    }
+}
 
 pub fn record_field(name: ast::NameRef, expr: Option<ast::Expr>) -> ast::RecordField {
     return match expr {