[clangd] Reduce superfluous rename conflicts (llvm#121515)

This commit adds a namespace check to the code for detecting name
collisions, allowing `bar` to be renamed to `foo` in the following
snippet:

```c
typedef struct foo {} Foo;
Foo bar;
```

Previously, such a rename would fail because a declaration for `foo`
already exists in the same scope.

Author: ujan-r

clang-tools-extra/clangd/refactor/Rename.cpp

@@ -338,7 +338,8 @@ const NamedDecl *lookupSiblingWithinEnclosingScope(ASTContext &Ctx,
     for (const auto &Child : DS->getDeclGroup())
       if (const auto *ND = dyn_cast<NamedDecl>(Child))
         if (ND != &RenamedDecl && ND->getDeclName().isIdentifier() &&
-            ND->getName() == Name)
+            ND->getName() == Name &&
+            ND->getIdentifierNamespace() & RenamedDecl.getIdentifierNamespace())
           return ND;
     return nullptr;
   };
@@ -380,7 +381,9 @@ const NamedDecl *lookupSiblingWithinEnclosingScope(ASTContext &Ctx,
     // Also check if there is a name collision with function arguments.
     if (const auto *Function = ScopeParent->get<FunctionDecl>())
       for (const auto *Parameter : Function->parameters())
-        if (Parameter->getName() == NewName)
+        if (Parameter->getName() == NewName &&
+            Parameter->getIdentifierNamespace() &
+                RenamedDecl.getIdentifierNamespace())
           return Parameter;
     return nullptr;
   }
@@ -405,7 +408,9 @@ const NamedDecl *lookupSiblingWithinEnclosingScope(ASTContext &Ctx,
   if (const auto *EnclosingFunction = Parent->get<FunctionDecl>()) {
     // Check for conflicts with other arguments.
     for (const auto *Parameter : EnclosingFunction->parameters())
-      if (Parameter != &RenamedDecl && Parameter->getName() == NewName)
+      if (Parameter != &RenamedDecl && Parameter->getName() == NewName &&
+          Parameter->getIdentifierNamespace() &
+              RenamedDecl.getIdentifierNamespace())
         return Parameter;
     // FIXME: We don't modify all references to function parameters when
     // renaming from forward declaration now, so using a name colliding with
@@ -450,7 +455,8 @@ const NamedDecl *lookupSiblingsWithinContext(ASTContext &Ctx,
   }
   // Lookup may contain the RenameDecl itself, exclude it.
   for (const auto *D : LookupResult)
-    if (D->getCanonicalDecl() != RenamedDecl.getCanonicalDecl())
+    if (D->getCanonicalDecl() != RenamedDecl.getCanonicalDecl() &&
+        D->getIdentifierNamespace() & RenamedDecl.getIdentifierNamespace())
       return D;
   return nullptr;
 }

clang-tools-extra/clangd/unittests/RenameTests.cpp

@@ -1269,6 +1269,39 @@ TEST(RenameTest, Renameable) {
       )cpp",
        "conflict", !HeaderFile, "Conflict"},
 
+      {R"cpp(
+        struct conflict {};
+        enum v^ar {};
+      )cpp",
+       "conflict", !HeaderFile, "conflict"},
+
+      {R"cpp(
+        struct conflict {};
+        int [[v^ar]];
+      )cpp",
+       nullptr, !HeaderFile, "conflict"},
+
+      {R"cpp(
+        enum conflict {};
+        int [[v^ar]];
+      )cpp",
+       nullptr, !HeaderFile, "conflict"},
+
+      {R"cpp(
+        void func(int conflict) {
+          struct [[t^ag]] {};
+        }
+      )cpp",
+       nullptr, !HeaderFile, "conflict"},
+
+      {R"cpp(
+        void func(void) {
+          struct conflict {};
+          int [[v^ar]];
+        }
+      )cpp",
+       nullptr, !HeaderFile, "conflict"},
+
       {R"cpp(
         void func(int);
         void [[o^therFunc]](double);