[RelatedIdents] Fix an assertion failure if two invalid declarations have the same base name

We need to check both the USR and the display name because multiple distinct decls might have the same USR. For example, the following declarations have the same USR with a single ERROR_TYPE parameter despite being distinct declarations.

```swift
func bar(body: Invalid) {}
func bar(ignoreCase: Bool, body: Invalid) {}
```

The display name contains the argument labels, which is sufficient to distinguish these declarations.

rdar://126803702

Author: ahoppen

include/swift/Index/Index.h

@@ -25,6 +25,7 @@ namespace index {
 void indexDeclContext(DeclContext *DC, IndexDataConsumer &consumer);
 void indexSourceFile(SourceFile *SF, IndexDataConsumer &consumer);
 void indexModule(ModuleDecl *module, IndexDataConsumer &consumer);
+bool printDisplayName(const swift::ValueDecl *D, llvm::raw_ostream &OS);
 
 } // end namespace index
 } // end namespace swift

lib/Index/Index.cpp

@@ -73,7 +73,7 @@ printArtificialName(const swift::AbstractStorageDecl *ASD, AccessorKind AK, llvm
   llvm_unreachable("Unhandled AccessorKind in switch.");
 }
 
-static bool printDisplayName(const swift::ValueDecl *D, llvm::raw_ostream &OS) {
+bool index::printDisplayName(const swift::ValueDecl *D, llvm::raw_ostream &OS) {
   if (!D->hasName() && !isa<ParamDecl>(D)) {
     auto *FD = dyn_cast<AccessorDecl>(D);
     if (!FD)

lib/Refactoring/LocalRename.cpp

@@ -194,7 +194,8 @@ swift::ide::getRenameInfo(ResolvedCursorInfoPtr cursorInfo) {
 }
 
 class RenameRangeCollector : public IndexDataConsumer {
-  StringRef usr;
+  SmallString<64> usr;
+  SmallString<64> displayName;
   std::unique_ptr<StringScratchSpace> stringStorage;
   std::vector<RenameLoc> locations;
 
@@ -204,10 +205,11 @@ class RenameRangeCollector : public IndexDataConsumer {
 
   RenameRangeCollector(const ValueDecl *D)
       : stringStorage(new StringScratchSpace()) {
-    SmallString<64> SS;
-    llvm::raw_svector_ostream OS(SS);
-    printValueDeclUSR(D, OS);
-    usr = stringStorage->copyString(SS.str());
+    llvm::raw_svector_ostream usrOS(usr);
+    printValueDeclUSR(D, usrOS);
+
+    llvm::raw_svector_ostream nameOS(displayName);
+    index::printDisplayName(D, nameOS);
   }
 
   RenameRangeCollector(RenameRangeCollector &&collector) = default;
@@ -228,7 +230,17 @@ class RenameRangeCollector : public IndexDataConsumer {
   bool finishDependency(bool isClangModule) override { return true; }
 
   Action startSourceEntity(const IndexSymbol &symbol) override {
-    if (symbol.USR != usr) {
+    // We need to check both the USR and the display name because multiple
+    // distinct decls might have the same USR. For example, the following
+    // declarations have the same USR with a single ERROR_TYPE parameter despite
+    // being distinct declarations.
+    //
+    // func bar(body: Invalid) {}
+    // func bar(ignoreCase: Bool, body: Invalid) {}
+    //
+    // The display name contains the argument labels, which is sufficient to
+    // distinguish these declarations.
+    if (symbol.USR != usr || symbol.name != displayName) {
       return IndexDataConsumer::Continue;
     }
     auto loc = indexSymbolToRenameLoc(symbol);

test/SourceKit/RelatedIdents/two_invalid_decls_with_same_base_name.swift

@@ -0,0 +1,6 @@
+struct Foo {
+  func bar(body: Invalid) {}
+
+// RUN: %sourcekitd-test -req=related-idents -pos=%(line + 1):8 %s -- %s
+  func bar(ignoreCase: Bool, body: Invalid) {}
+}