1 files changed, 34 insertions, 40 deletions

diff --git a/crates/assists/src/ast_transform.rs b/crates/assists/src/ast_transform.rs
index 835da3bb2..4307e0191 100644
--- a/crates/assists/src/ast_transform.rs
+++ b/crates/assists/src/ast_transform.rs
@@ -5,12 +5,13 @@ use hir::{HirDisplay, PathResolution, SemanticsScope};
 use syntax::{
     algo::SyntaxRewriter,
     ast::{self, AstNode},
+    SyntaxNode,
 };
 
 pub fn apply<'a, N: AstNode>(transformer: &dyn AstTransform<'a>, node: N) -> N {
     SyntaxRewriter::from_fn(|element| match element {
         syntax::SyntaxElement::Node(n) => {
-            let replacement = transformer.get_substitution(&n)?;
+            let replacement = transformer.get_substitution(&n, transformer)?;
             Some(replacement.into())
         }
         _ => None,
@@ -47,32 +48,35 @@ pub fn apply<'a, N: AstNode>(transformer: &dyn AstTransform<'a>, node: N) -> N {
 /// We'd want to somehow express this concept simpler, but so far nobody got to
 /// simplifying this!
 pub trait AstTransform<'a> {
-    fn get_substitution(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode>;
+    fn get_substitution(
+        &self,
+        node: &SyntaxNode,
+        recur: &dyn AstTransform<'a>,
+    ) -> Option<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))
+        Box::new(Or(Box::new(self), Box::new(other)))
     }
 }
 
-struct NullTransformer;
+struct Or<'a>(Box<dyn AstTransform<'a> + 'a>, Box<dyn AstTransform<'a> + 'a>);
 
-impl<'a> AstTransform<'a> for NullTransformer {
-    fn get_substitution(&self, _node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
-        None
-    }
-    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
-        other
+impl<'a> AstTransform<'a> for Or<'a> {
+    fn get_substitution(
+        &self,
+        node: &SyntaxNode,
+        recur: &dyn AstTransform<'a>,
+    ) -> Option<SyntaxNode> {
+        self.0.get_substitution(node, recur).or_else(|| self.1.get_substitution(node, recur))
     }
 }
 
 pub struct SubstituteTypeParams<'a> {
     source_scope: &'a SemanticsScope<'a>,
     substs: FxHashMap<hir::TypeParam, ast::Type>,
-    previous: Box<dyn AstTransform<'a> + 'a>,
 }
 
 impl<'a> SubstituteTypeParams<'a> {
@@ -111,11 +115,7 @@ impl<'a> SubstituteTypeParams<'a> {
                 }
             })
             .collect();
-        return SubstituteTypeParams {
-            source_scope,
-            substs: substs_by_param,
-            previous: Box::new(NullTransformer),
-        };
+        return SubstituteTypeParams { source_scope, substs: substs_by_param };
 
         // 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).
@@ -140,7 +140,14 @@ impl<'a> SubstituteTypeParams<'a> {
             Some(result)
         }
     }
-    fn get_substitution_inner(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
+}
+
+impl<'a> AstTransform<'a> for SubstituteTypeParams<'a> {
+    fn get_substitution(
+        &self,
+        node: &SyntaxNode,
+        _recur: &dyn AstTransform<'a>,
+    ) -> Option<SyntaxNode> {
         let type_ref = ast::Type::cast(node.clone())?;
         let path = match &type_ref {
             ast::Type::PathType(path_type) => path_type.path()?,
@@ -154,27 +161,23 @@ impl<'a> SubstituteTypeParams<'a> {
     }
 }
 
-impl<'a> AstTransform<'a> for SubstituteTypeParams<'a> {
-    fn get_substitution(&self, node: &syntax::SyntaxNode) -> Option<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> {
     target_scope: &'a SemanticsScope<'a>,
     source_scope: &'a SemanticsScope<'a>,
-    previous: Box<dyn AstTransform<'a> + 'a>,
 }
 
 impl<'a> QualifyPaths<'a> {
     pub fn new(target_scope: &'a SemanticsScope<'a>, source_scope: &'a SemanticsScope<'a>) -> Self {
-        Self { target_scope, source_scope, previous: Box::new(NullTransformer) }
+        Self { target_scope, source_scope }
     }
+}
 
-    fn get_substitution_inner(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode> {
+impl<'a> AstTransform<'a> for QualifyPaths<'a> {
+    fn get_substitution(
+        &self,
+        node: &SyntaxNode,
+        recur: &dyn AstTransform<'a>,
+    ) -> Option<SyntaxNode> {
         // FIXME handle value ns?
         let from = self.target_scope.module()?;
         let p = ast::Path::cast(node.clone())?;
@@ -191,7 +194,7 @@ impl<'a> QualifyPaths<'a> {
                 let type_args = p
                     .segment()
                     .and_then(|s| s.generic_arg_list())
-                    .map(|arg_list| apply(self, arg_list));
+                    .map(|arg_list| apply(recur, arg_list));
                 if let Some(type_args) = type_args {
                     let last_segment = path.segment().unwrap();
                     path = path.with_segment(last_segment.with_generic_args(type_args))
@@ -208,15 +211,6 @@ impl<'a> QualifyPaths<'a> {
     }
 }
 
-impl<'a> AstTransform<'a> for QualifyPaths<'a> {
-    fn get_substitution(&self, node: &syntax::SyntaxNode) -> Option<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 })
-    }
-}
-
 pub(crate) fn path_to_ast(path: hir::ModPath) -> ast::Path {
     let parse = ast::SourceFile::parse(&path.to_string());
     parse