Fix regerror(..., nullptr, 0).

Found by passing a bad regular expression to the Google benchmark
code (https://github.com/google/benchmark).

(cherry picked from commit cac2908b08)

Change-Id: I317a7c2ea6535998c0853029023fcefc88cb3750

libc/Android.mk

@@ -856,7 +856,9 @@ include $(CLEAR_VARS)
 LOCAL_SRC_FILES := $(libc_upstream_netbsd_src_files)
 LOCAL_CFLAGS := \
     $(libc_common_cflags) \
-    -Wno-sign-compare -Wno-uninitialized \
+    -Wno-sign-compare \
+    -Wno-uninitialized \
+    -Wno-unused-parameter \
     -DPOSIX_MISTAKE \
     -include netbsd-compat.h \
 

libc/upstream-netbsd/android/include/netbsd-compat.h

@@ -20,17 +20,16 @@
 #define _BSD_SOURCE
 #define _GNU_SOURCE
 
-// NetBSD uses _DIAGASSERT to null-check arguments and the like.
+// NetBSD uses _DIAGASSERT to null-check arguments and the like,
-#include <assert.h>
+// but it's clear from the number of mistakes in their assertions
-#define _DIAGASSERT(e) ((e) ? (void) 0 : __assert2(__FILE__, __LINE__, __func__, #e))
+// that they don't actually test or ship with this.
-
+#define _DIAGASSERT(e) /* nothing */
-// TODO: update our <sys/cdefs.h> to support this properly.
-#define __type_fit(t, a) (0 == 0)
 
 // TODO: we don't yet have thread-safe environment variables.
 #define __readlockenv() 0
 #define __unlockenv() 0
 
+#include <sys/cdefs.h>
 #include <stddef.h>
 int reallocarr(void*, size_t, size_t);
 

tests/regex_test.cpp

@@ -46,3 +46,14 @@ TEST(regex, match_offsets) {
   ASSERT_EQ(2, matches[0].rm_eo);
   regfree(&re);
 }
+
+TEST(regex, regerror_NULL_0) {
+  regex_t re;
+  int error = regcomp(&re, "*", REG_EXTENDED);
+  ASSERT_NE(0, error);
+
+  // Passing a null pointer and a size of 0 is a legitimate way to ask
+  // how large a buffer we would need for the error message.
+  int error_length = regerror(error, &re, nullptr, 0);
+  ASSERT_GT(error_length, 0);
+}