[clangd] Guard against trivial FunctionProtoTypeLoc when creating inlay hints (llvm#143087)

Fixes llvm#142608

Author: HighCommander4

clang-tools-extra/clangd/InlayHints.cpp

@@ -33,6 +33,7 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/ADT/identity.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FormatVariadic.h"
@@ -375,7 +376,11 @@ static FunctionProtoTypeLoc getPrototypeLoc(Expr *Fn) {
   }
 
   if (auto F = Target.getAs<FunctionProtoTypeLoc>()) {
-    return F;
+    // In some edge cases the AST can contain a "trivial" FunctionProtoTypeLoc
+    // which has null parameters. Avoid these as they don't contain useful
+    // information.
+    if (llvm::all_of(F.getParams(), llvm::identity<ParmVarDecl *>()))
+      return F;
   }
 
   return {};

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

@@ -1011,11 +1011,16 @@ TEST(ParameterHints, FunctionPointer) {
     f3_t f3;
     using f4_t = void(__stdcall *)(int param);
     f4_t f4;
+    __attribute__((noreturn)) f4_t f5;
     void bar() {
       f1($f1[[42]]);
       f2($f2[[42]]);
       f3($f3[[42]]);
       f4($f4[[42]]);
+      // This one runs into an edge case in clang's type model
+      // and we can't extract the parameter name. But at least
+      // we shouldn't crash.
+      f5(42);
     }
   )cpp",
       ExpectedHint{"param: ", "f1"}, ExpectedHint{"param: ", "f2"},