[clangd] Don't show inlay hints for PseudoObjectExprs in C++

This closes clangd/clangd#1813.

PseudoObjectExprs in C++ are currently not very interesting but probably
mess up inlay hints.

Author: zyn0217

clang-tools-extra/clangd/InlayHints.cpp

@@ -589,6 +589,19 @@ class InlayHintVisitor : public RecursiveASTVisitor<InlayHintVisitor> {
     return true;
   }
 
+  bool dataTraverseStmtPre(Stmt *S) {
+    // Do not show inlay hints for PseudoObjectExprs. They're never
+    // genuine user codes in C++.
+    //
+    // For example, __builtin_dump_struct would expand to a PseudoObjectExpr
+    // that includes a couple of calls to a printf function. Printing parameter
+    // names for that anyway would end up with duplicate parameter names (which,
+    // however, got de-duplicated after visiting) for the printf function.
+    if (AST.getLangOpts().CPlusPlus && isa<PseudoObjectExpr>(S))
+      return false;
+    return true;
+  }
+
   bool VisitCallExpr(CallExpr *E) {
     if (!Cfg.InlayHints.Parameters)
       return true;

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

@@ -1724,6 +1724,30 @@ TEST(InlayHints, RestrictRange) {
               ElementsAre(labelIs(": int"), labelIs(": char")));
 }
 
+TEST(ParameterHints, PseudoObjectExpr) {
+  Annotations Code(R"cpp(
+    struct S {
+      __declspec(property(get=GetX, put=PutX)) int x[];
+      int GetX(int y, int z) { return 42 + y; }
+      void PutX(int y) { x = y; } // Not `x = y: y`
+    };
+
+    int printf(const char *Format, ...);
+
+    int main() {
+      S s;
+      __builtin_dump_struct(&s, printf); // Not `Format: __builtin_dump_struct()`
+      printf($Param[["Hello, %d"]], 42); // Normal calls are not affected.
+      return s.x[1][2]; // Not `x[y: 1][z: 2]`
+    }
+  )cpp");
+  auto TU = TestTU::withCode(Code.code());
+  TU.ExtraArgs.push_back("-fms-extensions");
+  auto AST = TU.build();
+  EXPECT_THAT(inlayHints(AST, std::nullopt),
+              ElementsAre(HintMatcher(ExpectedHint{"Format: ", "Param"}, Code)));
+}
+
 TEST(ParameterHints, ArgPacksAndConstructors) {
   assertParameterHints(
       R"cpp(