[clang-tools-extra] [clangd] Guard against trivial FunctionProtoTypeLoc when creating inlay hints (PR #143087)

[Nathan Ridge via cfe-commits]

https://github.com/HighCommander4 created https://github.com/llvm/llvm-project/pull/143087

Fixes https://github.com/llvm/llvm-project/issues/142608

>From f44f250259cd09b20f6ab9095fc3718537d51563 Mon Sep 17 00:00:00 2001
From: Nathan Ridge <zeratul976 at hotmail.com>
Date: Fri, 6 Jun 2025 03:56:59 -0400
Subject: [PATCH] [clangd] Guard against trivial FunctionProtoTypeLoc when
 creating inlay hints

Fixes https://github.com/llvm/llvm-project/issues/142608
---
 clang-tools-extra/clangd/InlayHints.cpp               | 8 ++++++++
 clang-tools-extra/clangd/unittests/InlayHintTests.cpp | 5 +++++
 2 files changed, 13 insertions(+)

diff --git a/clang-tools-extra/clangd/InlayHints.cpp b/clang-tools-extra/clangd/InlayHints.cpp
index 1b1bcf78c9855..9a401b31eeee9 100644
--- a/clang-tools-extra/clangd/InlayHints.cpp
+++ b/clang-tools-extra/clangd/InlayHints.cpp
@@ -368,6 +368,14 @@ static FunctionProtoTypeLoc getPrototypeLoc(Expr *Fn) {
   }
 
   if (auto F = Target.getAs<FunctionProtoTypeLoc>()) {
+    // In some edge cases the AST can contain a "trivial" FunctionProtoTypeLoc
+    // which has null parameters. Avoid these as they don't contain useful
+    // information.
+    for (const auto *Param : F.getParams()) {
+      if (!Param)
+        return {};
+    }
+
     return F;
   }
 
diff --git a/clang-tools-extra/clangd/unittests/InlayHintTests.cpp b/clang-tools-extra/clangd/unittests/InlayHintTests.cpp
index 77d78b8777fe3..8ed8401f9fce9 100644
--- a/clang-tools-extra/clangd/unittests/InlayHintTests.cpp
+++ b/clang-tools-extra/clangd/unittests/InlayHintTests.cpp
@@ -997,11 +997,16 @@ 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"},