From b17dedc4e2f3828d043ebce3032d820d454ab5d8 Mon Sep 17 00:00:00 2001
From: Sunil Srivastava <sunil_srivastava@playstation.sony.com>
Date: Mon, 25 Jul 2016 17:17:06 +0000
Subject: [PATCH] Support '#pragma once' in headers when using PCH

The '#pragma once' directive was erroneously ignored when encountered
in the header-file specified in generate-PCH-mode. This resulted in
compile-time errors in some cases with legal code, and also a misleading
warning being produced.

Patch by Warren Ristow!

Differential Revision: http://reviews.llvm.org/D19815


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@276653 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Lex/Pragma.cpp            |  4 +++-
 test/PCH/Inputs/pragma-once.h |  5 +++++
 test/PCH/pragma-once.c        | 13 +++++++++++++
 3 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 test/PCH/Inputs/pragma-once.h
 create mode 100644 test/PCH/pragma-once.c

diff --git a/lib/Lex/Pragma.cpp b/lib/Lex/Pragma.cpp
index d6e651727c..1ce4b4391f 100644
--- a/lib/Lex/Pragma.cpp
+++ b/lib/Lex/Pragma.cpp
@@ -352,7 +352,9 @@ void Preprocessor::HandleMicrosoft__pragma(Token &Tok) {
 /// HandlePragmaOnce - Handle \#pragma once.  OnceTok is the 'once'.
 ///
 void Preprocessor::HandlePragmaOnce(Token &OnceTok) {
-  if (isInPrimaryFile()) {
+  // Don't honor the 'once' when handling the primary source file, unless
+  // this is a prefix to a TU, which indicates we're generating a PCH file.
+  if (isInPrimaryFile() && TUKind != TU_Prefix) {
     Diag(OnceTok, diag::pp_pragma_once_in_main_file);
     return;
   }
diff --git a/test/PCH/Inputs/pragma-once.h b/test/PCH/Inputs/pragma-once.h
new file mode 100644
index 0000000000..831cf553c7
--- /dev/null
+++ b/test/PCH/Inputs/pragma-once.h
@@ -0,0 +1,5 @@
+#pragma once
+
+/* For use with the pragma-once.c test */
+
+int x = 3;
diff --git a/test/PCH/pragma-once.c b/test/PCH/pragma-once.c
new file mode 100644
index 0000000000..15e8503c11
--- /dev/null
+++ b/test/PCH/pragma-once.c
@@ -0,0 +1,13 @@
+// Test this without pch.
+// RUN: %clang_cc1 -include %S/Inputs/pragma-once.h -fsyntax-only -verify %s
+
+// Test with pch.
+// RUN: %clang_cc1 -emit-pch -o %t %S/Inputs/pragma-once.h
+// RUN: %clang_cc1 -include-pch %t -fsyntax-only -verify %s
+
+// expected-no-diagnostics
+
+// Including "pragma-once.h" twice, to verify the 'once' aspect is honored.
+#include "Inputs/pragma-once.h"
+#include "Inputs/pragma-once.h"
+int foo(void) { return 0; }
-- 
2.40.0