[clang] [Modules] [HeaderSearch] Don't reenter headers if it is pragma once o… (PR #76119)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-modules

Author: Chuanqi Xu (ChuanqiXu9)

<details>
<summary>Changes</summary>

…f #import

Close https://github.com/llvm/llvm-project/issues/73023

The direct issue of https://github.com/llvm/llvm-project/issues/73023 is that we entered a header which is marked as pragma once since the compiler think it is OK if there is controlling macro.

It doesn't make sense. I feel like it should be sufficient to skip it after we see the '#pragma once'.

>From the context, it looks like the workaround is primarily for ObjectiveC. So we might need reviewers from OC.

---
Full diff: https://github.com/llvm/llvm-project/pull/76119.diff


2 Files Affected:

- (modified) clang/lib/Lex/HeaderSearch.cpp (+1-1) 
- (added) clang/test/Modules/pr73023.cpp (+20) 


``````````diff
diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index 0f1090187734ff..9020a661321faf 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -1458,7 +1458,7 @@ bool HeaderSearch::ShouldEnterIncludeFile(Preprocessor &PP,
   } else {
     // Otherwise, if this is a #include of a file that was previously #import'd
     // or if this is the second #include of a #pragma once file, ignore it.
-    if ((FileInfo.isPragmaOnce || FileInfo.isImport) && !TryEnterImported())
+    if (FileInfo.isPragmaOnce || FileInfo.isImport)
       return false;
   }
 
diff --git a/clang/test/Modules/pr73023.cpp b/clang/test/Modules/pr73023.cpp
new file mode 100644
index 00000000000000..d80306d39ef48c
--- /dev/null
+++ b/clang/test/Modules/pr73023.cpp
@@ -0,0 +1,20 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/foo.cpp -I%t -fsyntax-only -verify
+
+//--- i.h
+#ifndef FOO_H
+#pragma once
+struct S{};
+#endif
+
+//--- foo.cpp
+// expected-no-diagnostics
+#include "i.h"
+#include "i.h"
+
+int foo() {
+    return sizeof(S);
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/76119