[clang] [clang] Don't fail `clang::ExecuteCompilerInvocation()` for unrelated errors (PR #158695)

[Jan Svoboda via cfe-commits]

https://github.com/jansvoboda11 updated https://github.com/llvm/llvm-project/pull/158695

>From 827307ddefb5e25c41406e736574a230a396b9cc Mon Sep 17 00:00:00 2001
From: Jan Svoboda <jan_svoboda at apple.com>
Date: Mon, 15 Sep 2025 09:55:11 -0700
Subject: [PATCH 1/2] [clang] Don't fail `clang::ExecuteCompilerInvocation()`
 for unrelated errors

---
 clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp b/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp
index 9a6844d5f7d40..f1965a4e27e07 100644
--- a/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp
+++ b/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp
@@ -210,6 +210,8 @@ CreateFrontendAction(CompilerInstance &CI) {
 }
 
 bool ExecuteCompilerInvocation(CompilerInstance *Clang) {
+  unsigned NumErrorsBefore = Clang->getDiagnostics().getNumErrors();
+
   // Honor -help.
   if (Clang->getFrontendOpts().ShowHelp) {
     driver::getDriverOptTable().printHelp(
@@ -293,7 +295,7 @@ bool ExecuteCompilerInvocation(CompilerInstance *Clang) {
 #endif
 
   // If there were errors in processing arguments, don't do anything else.
-  if (Clang->getDiagnostics().hasErrorOccurred())
+  if (Clang->getDiagnostics().getNumErrors() != NumErrorsBefore)
     return false;
   // Create and execute the frontend action.
   std::unique_ptr<FrontendAction> Act(CreateFrontendAction(*Clang));

>From 5200d1af7a3faec47e3012ba503383c0a037a932 Mon Sep 17 00:00:00 2001
From: Jan Svoboda <jan_svoboda at apple.com>
Date: Mon, 15 Sep 2025 14:07:50 -0700
Subject: [PATCH 2/2] Add comment

---
 clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp b/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp
index f1965a4e27e07..8b0ab2eb37189 100644
--- a/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp
+++ b/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp
@@ -294,9 +294,12 @@ bool ExecuteCompilerInvocation(CompilerInstance *Clang) {
   }
 #endif
 
-  // If there were errors in processing arguments, don't do anything else.
+  // If there were errors in the above, don't do anything else.
+  // This intentionally ignores errors emitted before this function to
+  // accommodate lenient callers that decided to make progress despite errors.
   if (Clang->getDiagnostics().getNumErrors() != NumErrorsBefore)
     return false;
+
   // Create and execute the frontend action.
   std::unique_ptr<FrontendAction> Act(CreateFrontendAction(*Clang));
   if (!Act)