ICU-20784 Do not override clang compiler internal builtins

In the case several internal builtins defined by clang were not available,
ICU was replacing them by a stub implementation. But that was breaking
detection of availability of same methods in other parts of Chromium
(specifically in base/location.h).

Instead of that, this change creates ICU specific macros that will
map to those builtins when available, or to stub implementation if
not.

I.e. for the case of __has_builtin, previous implementation was
defining __has_builtin(x) as 0 in case it was not declared. With
new implementation, there is a macro UPRV_HAS_BUILTIN that maps
to __has_builtin if available, or 0 if not.

diff --git a/icu4c/source/common/unicode/platform.h b/icu4c/source/common/unicode/platform.h
index d6418a38e2da974714432adac9cca525aab212dc..9180a8de79cd96ef3259998042d8d9fd5034a16d 100644 (file)
--- a/icu4c/source/common/unicode/platform.h
+++ b/icu4c/source/common/unicode/platform.h
@@ -424,26 +424,40 @@
 #endif
 
 /* Compatibility with compilers other than clang: http://clang.llvm.org/docs/LanguageExtensions.html */
-#ifndef __has_attribute
-#    define __has_attribute(x) 0
+#ifdef __has_attribute
+#   define UPRV_HAS_ATTRIBUTE(x) __has_attribute(x)
+#else
+#   define UPRV_HAS_ATTRIBUTE(x) 0
 #endif
-#ifndef __has_cpp_attribute
-#    define __has_cpp_attribute(x) 0
+#ifdef __has_cpp_attribute
+#   define UPRV_HAS_CPP_ATTRIBUTE(x) __has_cpp_attribute(x)
+#else
+#   define UPRV_HAS_CPP_ATTRIBUTE(x) 0
 #endif
-#ifndef __has_declspec_attribute
-#    define __has_declspec_attribute(x) 0
+#ifdef __has_declspec_attribute
+#   define UPRV_HAS_DECLSPEC_ATTRIBUTE(x) __has_declspec_attribute(x)
+#else
+#   define UPRV_HAS_DECLSPEC_ATTRIBUTE(x) 0
 #endif
-#ifndef __has_builtin
-#    define __has_builtin(x) 0
+#ifdef __has_builtin
+#   define UPRV_HAS_BUILTIN(x) __has_builtin(x)
+#else
+#   define UPRV_HAS_BUILTIN(x) 0
 #endif
-#ifndef __has_feature
-#    define __has_feature(x) 0
+#ifdef __has_feature
+#   define UPRV_HAS_FEATURE(x) __has_feature(x)
+#else
+#   define UPRV_HAS_FEATURE(x) 0
 #endif
-#ifndef __has_extension
-#    define __has_extension(x) 0
+#ifdef __has_extension
+#   define UPRV_HAS_EXTENSION(x) __has_extension(x)
+#else
+#   define UPRV_HAS_EXTENSION(x) 0
 #endif
-#ifndef __has_warning
-#    define __has_warning(x) 0
+#ifdef __has_warning
+#   define UPRV_HAS_WARNING(x) __has_warning(x)
+#else
+#   define UPRV_HAS_WARNING(x) 0
 #endif
 
 /**
@@ -462,7 +476,9 @@
  * Attribute to specify the size of the allocated buffer for malloc-like functions
  * @internal
  */
-#if (defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3))) || __has_attribute(alloc_size)
+#if (defined(__GNUC__) &&                                            \
+        (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3))) || \
+        UPRV_HAS_ATTRIBUTE(alloc_size)
 #   define U_ALLOC_SIZE_ATTR(X) __attribute__ ((alloc_size(X)))
 #   define U_ALLOC_SIZE_ATTR2(X,Y) __attribute__ ((alloc_size(X,Y)))
 #else
@@ -526,8 +542,9 @@ namespace std {
 #elif defined(__clang__)
     // Test for compiler vs. feature separately.
     // Other compilers might choke on the feature test.
-#   if __has_cpp_attribute(clang::fallthrough) || \
-            (__has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough"))
+#    if UPRV_HAS_CPP_ATTRIBUTE(clang::fallthrough) || \
+             (UPRV_HAS_FEATURE(cxx_attributes) &&     \
+             UPRV_HAS_WARNING("-Wimplicit-fallthrough"))
 #       define U_FALLTHROUGH [[clang::fallthrough]]
 #   endif
 #elif defined(__GNUC__) && (__GNUC__ >= 7)
@@ -797,7 +814,8 @@ namespace std {
     /* Use the predefined value. */
 #elif defined(U_STATIC_IMPLEMENTATION)
 #   define U_EXPORT
-#elif defined(_MSC_VER) || (__has_declspec_attribute(dllexport) && __has_declspec_attribute(dllimport))
+#elif defined(_MSC_VER) || (UPRV_HAS_DECLSPEC_ATTRIBUTE(dllexport) && \
+                            UPRV_HAS_DECLSPEC_ATTRIBUTE(dllimport))
 #   define U_EXPORT __declspec(dllexport)
 #elif defined(__GNUC__)
 #   define U_EXPORT __attribute__((visibility("default")))
@@ -821,7 +839,8 @@ namespace std {
 
 #ifdef U_IMPORT
     /* Use the predefined value. */
-#elif defined(_MSC_VER) || (__has_declspec_attribute(dllexport) && __has_declspec_attribute(dllimport))
+#elif defined(_MSC_VER) || (UPRV_HAS_DECLSPEC_ATTRIBUTE(dllexport) && \
+                            UPRV_HAS_DECLSPEC_ATTRIBUTE(dllimport))
     /* Windows needs to export/import data. */
 #   define U_IMPORT __declspec(dllimport)
 #else