Wrap C APIs with pragmas enforcing -Werror=strict-prototypes

Force `-Werror=strict-prototypes` so that C API tests fail to compile if
we add a non-prototype declaration.  This should help avoid regressions
like bddecba4b333f7772029b4937d2c34f9f2fda6ca was fixing.

https://reviews.llvm.org/D70285
rdar://problem/57203137

9 files changed, 75 insertions, 53 deletions

diff --git a/clang/include/clang-c/BuildSystem.h b/clang/include/clang-c/BuildSystem.h
index 8f26a861171..4e9f6dee027 100644
--- a/clang/include/clang-c/BuildSystem.h
+++ b/clang/include/clang-c/BuildSystem.h
@@ -14,13 +14,12 @@
 #ifndef LLVM_CLANG_C_BUILDSYSTEM_H
 #define LLVM_CLANG_C_BUILDSYSTEM_H
 
-#include "clang-c/Platform.h"
 #include "clang-c/CXErrorCode.h"
 #include "clang-c/CXString.h"
+#include "clang-c/ExternC.h"
+#include "clang-c/Platform.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_CLANG_C_EXTERN_C_BEGIN
 
 /**
  * \defgroup BUILD_SYSTEM Build system utilities
@@ -148,9 +147,7 @@ CINDEX_LINKAGE void clang_ModuleMapDescriptor_dispose(CXModuleMapDescriptor);
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_CLANG_C_EXTERN_C_END
 
 #endif /* CLANG_C_BUILD_SYSTEM_H */
 
diff --git a/clang/include/clang-c/CXCompilationDatabase.h b/clang/include/clang-c/CXCompilationDatabase.h
index 2669c1a792c..2b336e5464a 100644
--- a/clang/include/clang-c/CXCompilationDatabase.h
+++ b/clang/include/clang-c/CXCompilationDatabase.h
@@ -15,12 +15,11 @@
 #ifndef LLVM_CLANG_C_CXCOMPILATIONDATABASE_H
 #define LLVM_CLANG_C_CXCOMPILATIONDATABASE_H
 
-#include "clang-c/Platform.h"
 #include "clang-c/CXString.h"
+#include "clang-c/ExternC.h"
+#include "clang-c/Platform.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_CLANG_C_EXTERN_C_BEGIN
 
 /** \defgroup COMPILATIONDB CompilationDatabase functions
  * \ingroup CINDEX
@@ -169,8 +168,7 @@ clang_CompileCommand_getMappedSourceContent(CXCompileCommand, unsigned I);
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_CLANG_C_EXTERN_C_END
+
 #endif
 
diff --git a/clang/include/clang-c/CXErrorCode.h b/clang/include/clang-c/CXErrorCode.h
index fed195ec1f3..b3a0b9d66d5 100644
--- a/clang/include/clang-c/CXErrorCode.h
+++ b/clang/include/clang-c/CXErrorCode.h
@@ -14,11 +14,10 @@
 #ifndef LLVM_CLANG_C_CXERRORCODE_H
 #define LLVM_CLANG_C_CXERRORCODE_H
 
+#include "clang-c/ExternC.h"
 #include "clang-c/Platform.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_CLANG_C_EXTERN_C_BEGIN
 
 /**
  * Error codes returned by libclang routines.
@@ -57,8 +56,7 @@ enum CXErrorCode {
   CXError_ASTReadError = 4
 };
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_CLANG_C_EXTERN_C_END
+
 #endif
 
diff --git a/clang/include/clang-c/CXString.h b/clang/include/clang-c/CXString.h
index 1eb3442ccb2..f117010c71a 100644
--- a/clang/include/clang-c/CXString.h
+++ b/clang/include/clang-c/CXString.h
@@ -14,11 +14,10 @@
 #ifndef LLVM_CLANG_C_CXSTRING_H
 #define LLVM_CLANG_C_CXSTRING_H
 
+#include "clang-c/ExternC.h"
 #include "clang-c/Platform.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_CLANG_C_EXTERN_C_BEGIN
 
 /**
  * \defgroup CINDEX_STRING String manipulation routines
@@ -64,8 +63,7 @@ CINDEX_LINKAGE void clang_disposeStringSet(CXStringSet *set);
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_CLANG_C_EXTERN_C_END
+
 #endif
 
diff --git a/clang/include/clang-c/Documentation.h b/clang/include/clang-c/Documentation.h
index 4af8c93a367..ad3dd3bc78b 100644
--- a/clang/include/clang-c/Documentation.h
+++ b/clang/include/clang-c/Documentation.h
@@ -15,11 +15,10 @@
 #ifndef LLVM_CLANG_C_DOCUMENTATION_H
 #define LLVM_CLANG_C_DOCUMENTATION_H
 
+#include "clang-c/ExternC.h"
 #include "clang-c/Index.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_CLANG_C_EXTERN_C_BEGIN
 
 /**
  * \defgroup CINDEX_COMMENT Comment introspection
@@ -545,10 +544,7 @@ CINDEX_LINKAGE CXString clang_FullComment_getAsXML(CXComment Comment);
  * @}
  */
 
-
-#ifdef __cplusplus
-}
-#endif
+LLVM_CLANG_C_EXTERN_C_END
 
 #endif /* CLANG_C_DOCUMENTATION_H */
 
diff --git a/clang/include/clang-c/ExternC.h b/clang/include/clang-c/ExternC.h
new file mode 100644
index 00000000000..384f24d47b0
--- /dev/null
+++ b/clang/include/clang-c/ExternC.h
@@ -0,0 +1,39 @@
+/*===- clang-c/ExternC.h - Wrapper for 'extern "C"' ---------------*- C -*-===*\
+|*                                                                            *|
+|* Part of the LLVM Project, under the Apache License v2.0 with LLVM          *|
+|* Exceptions.                                                                *|
+|* See https://llvm.org/LICENSE.txt for license information.                  *|
+|* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception                    *|
+|*                                                                            *|
+|*===----------------------------------------------------------------------===*|
+|*                                                                            *|
+|* This file defines an 'extern "C"' wrapper.                                 *|
+|*                                                                            *|
+\*===----------------------------------------------------------------------===*/
+
+#ifndef LLVM_CLANG_C_EXTERN_C_H
+#define LLVM_CLANG_C_EXTERN_C_H
+
+#ifdef __clang__
+#define LLVM_CLANG_C_STRICT_PROTOTYPES_BEGIN                                   \
+  _Pragma("clang diagnostic push")                                             \
+      _Pragma("clang diagnostic error \"-Wstrict-prototypes\"")
+#define LLVM_CLANG_C_STRICT_PROTOTYPES_END _Pragma("clang diagnostic pop")
+#else
+#define LLVM_CLANG_C_STRICT_PROTOTYPES_BEGIN
+#define LLVM_CLANG_C_STRICT_PROTOTYPES_END
+#endif
+
+#ifdef __cplusplus
+#define LLVM_CLANG_C_EXTERN_C_BEGIN                                            \
+  extern "C" {                                                                 \
+  LLVM_CLANG_C_STRICT_PROTOTYPES_BEGIN
+#define LLVM_CLANG_C_EXTERN_C_END                                              \
+  LLVM_CLANG_C_STRICT_PROTOTYPES_END                                           \
+  }
+#else
+#define LLVM_CLANG_C_EXTERN_C_BEGIN LLVM_CLANG_C_STRICT_PROTOTYPES_BEGIN
+#define LLVM_CLANG_C_EXTERN_C_END LLVM_CLANG_C_STRICT_PROTOTYPES_END
+#endif
+
+#endif
diff --git a/clang/include/clang-c/FatalErrorHandler.h b/clang/include/clang-c/FatalErrorHandler.h
index ce8ff2cae73..22f34fa815c 100644
--- a/clang/include/clang-c/FatalErrorHandler.h
+++ b/clang/include/clang-c/FatalErrorHandler.h
@@ -10,9 +10,9 @@
 #ifndef LLVM_CLANG_C_FATAL_ERROR_HANDLER_H
 #define LLVM_CLANG_C_FATAL_ERROR_HANDLER_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+#include "clang-c/ExternC.h"
+
+LLVM_CLANG_C_EXTERN_C_BEGIN
 
 /**
  * Installs error handler that prints error message to stderr and calls abort().
@@ -27,7 +27,6 @@ void clang_install_aborting_llvm_fatal_error_handler(void);
  */
 void clang_uninstall_llvm_fatal_error_handler(void);
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_CLANG_C_EXTERN_C_END
+
 #endif
diff --git a/clang/include/clang-c/Index.h b/clang/include/clang-c/Index.h
index 438ee3698a1..5ff887ea5bc 100644
--- a/clang/include/clang-c/Index.h
+++ b/clang/include/clang-c/Index.h
@@ -18,10 +18,11 @@
 
 #include <time.h>
 
-#include "clang-c/Platform.h"
+#include "clang-c/BuildSystem.h"
 #include "clang-c/CXErrorCode.h"
 #include "clang-c/CXString.h"
-#include "clang-c/BuildSystem.h"
+#include "clang-c/ExternC.h"
+#include "clang-c/Platform.h"
 
 /**
  * The version constants for the libclang API.
@@ -51,9 +52,7 @@
     CINDEX_VERSION_MAJOR,                               \
     CINDEX_VERSION_MINOR)
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_CLANG_C_EXTERN_C_BEGIN
 
 /** \defgroup CINDEX libclang: C Interface to Clang
  *
@@ -6774,7 +6773,6 @@ CINDEX_LINKAGE unsigned clang_Type_visitFields(CXType T,
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_CLANG_C_EXTERN_C_END
+
 #endif
diff --git a/clang/include/clang-c/Platform.h b/clang/include/clang-c/Platform.h
index 5284b533253..3bb66bb0df4 100644
--- a/clang/include/clang-c/Platform.h
+++ b/clang/include/clang-c/Platform.h
@@ -14,9 +14,9 @@
 #ifndef LLVM_CLANG_C_PLATFORM_H
 #define LLVM_CLANG_C_PLATFORM_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+#include "clang-c/ExternC.h"
+
+LLVM_CLANG_C_EXTERN_C_BEGIN
 
 /* MSVC DLL import/export. */
 #ifdef _MSC_VER
@@ -39,7 +39,6 @@ extern "C" {
   #endif
 #endif
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_CLANG_C_EXTERN_C_END
+
 #endif