make fish buildable on OS X Snow Leopard

I noticed that the `test_convert()` function was randomly failing when
run on OS X Snow Leopard. I tracked it down to the `mbrtowc()` function on
that OS being broken. Explicitly testing for UTF-8 prefixes that identify
a sequence longer than four bytes (which the Unicode standard made illegal
long ago) keeps us from having encoding errors on those OS's.

This also makes the errors reported by the `test_convert()` function actually
useful and readable.

Lastly, it makes it possible to build fish on OS X Snow Leopard.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/wutil.cpp b/src/wutil.cpp
index 4299956a..9f975fab 100644
--- a/src/wutil.cpp
+++ b/src/wutil.cpp
@@ -343,7 +343,13 @@ wchar_t *wrealpath(const wcstring &pathname, wchar_t *resolved_path) {
         res = wcsdup(wide_res.c_str());
     }
 
+#if __APPLE__ && __DARWIN_C_LEVEL < 200809L
+    // OS X Snow Leopard is broken with respect to the dynamically allocated buffer returned by
+    // realpath(). It's not dynamically allocated so attempting to free that buffer triggers a
+    // malloc/free error. Thus we don't attempt the free in this case.
+#else
     free(narrow_res);
+#endif
 
     return res;
 }