[libc] Use #undef isascii in specific header
Standard C allows all standard headers to declare macros for all
their functions. So after possibly including any standard header
like <ctype.h>, it's perfectly normal for any and all of the
functions it declares to be defined as macros. Standard C requires
explicit `#undef` before using that identifier in a way that is not
compatible with function-like macro definitions.
The C standard's rules for this are extended to POSIX as well for
the interfaces it defines, and it's the expected norm for
nonstandard extensions declared by standard C library headers too.
So far the only place this has come up for llvm-libc's code is with
the isascii function in Fuchsia's libc. But other cases can arise
for any standard (or common extension) function names that source
code in llvm-libc is using in nonstandard ways, i.e. as C++
identifiers.
The only correct and robust way to handle the possible inclusion of
standard C library headers when building llvm-libc source code is to
use `#undef` explicitly for each identifier before using it. The
easy and obvious place to do that is in the per-function header.
This requires that all code, such as test code, that might include
any standard C library headers, e.g. via utils/UnitTest/Test.h, make
sure to include those *first* before the per-function header.
This change does that for isascii and its test. But it should be
done uniformly for all the code and documented as a consistent
convention so new implementation files are sure to get this right.
Reviewed By: sivachandra
Differential Revision: https://reviews.llvm.org/D94642
GitOrigin-RevId: e7228062b2bb87abf762abcb77668452a1ed35d4
diff --git a/src/ctype/isascii.h b/src/ctype/isascii.h
index 8ec3044..7e31b3c 100644
--- a/src/ctype/isascii.h
+++ b/src/ctype/isascii.h
@@ -9,6 +9,8 @@
#ifndef LLVM_LIBC_SRC_CTYPE_ISASCII_H
#define LLVM_LIBC_SRC_CTYPE_ISASCII_H
+#undef isascii
+
namespace __llvm_libc {
int isascii(int c);
diff --git a/test/src/ctype/isascii_test.cpp b/test/src/ctype/isascii_test.cpp
index b5f66d7..e0a15a0 100644
--- a/test/src/ctype/isascii_test.cpp
+++ b/test/src/ctype/isascii_test.cpp
@@ -6,10 +6,10 @@
//
//===----------------------------------------------------------------------===//
-#include "src/ctype/isascii.h"
-
#include "utils/UnitTest/Test.h"
+#include "src/ctype/isascii.h"
+
TEST(IsAscii, DefaultLocale) {
// Loops through all characters, verifying that ascii characters
// (which are all 7 bit unsigned integers)
diff --git a/utils/UnitTest/FuchsiaTest.h b/utils/UnitTest/FuchsiaTest.h
index 0a19a98..b7b5b48 100644
--- a/utils/UnitTest/FuchsiaTest.h
+++ b/utils/UnitTest/FuchsiaTest.h
@@ -10,11 +10,5 @@
#define LLVM_LIBC_UTILS_UNITTEST_FUCHSIATEST_H
#include <zxtest/zxtest.h>
-// isascii is being undef'd because Fuchsia's headers define a macro for
-// isascii. that macro causes errors when isascii_test.cpp references
-// __llvm_libc::isascii since the macro is applied first.
-#ifdef isascii
-#undef isascii
-#endif
#endif // LLVM_LIBC_UTILS_UNITTEST_FUCHSIATEST_H
