Simplify case-insensitivity checks on Mac OS X

* src/fileio.c (file_name_case_insensitive_p): Try skipping the
Darwin code and instead using pathconf with _PC_CASE_SENSITIVE.
Leave in two alternatives conditionally compiled based on
DARWIN_OS_CASE_SENSITIVE_FIXME in case pathconf doesn't work.

* etc/PROBLEMS: Mention the possible problem with pathconf on
Mac OS X.

2 files changed, 69 insertions, 24 deletions

diff --git a/etc/PROBLEMS b/etc/PROBLEMS
index 62d2bd1d26d..bbf865cf3f8 100644
--- a/etc/PROBLEMS
+++ b/etc/PROBLEMS
@@ -2415,6 +2415,18 @@ If this does not work, please inform bug-gnu-emacs@gnu.org.  Then
 please call support for your X-server and see if you can get a fix.
 If you do, please send it to bug-gnu-emacs@gnu.org so we can list it here.
 
+
+* Runtime problems specific to Mac OS X
+
+** On Mac OS X, file-name-case-insensitive-p may be unreliable
+
+The implementation of that function on Mac OS X uses pathconf with the
+_PC_CASE_SENSITIVE flag.  There have been reports that this use of
+pathconf does not work reliably.  If you have a problem, please
+recompile Emacs with -DDARWIN_OS_CASE_SENSITIVE_FIXME=1 or
+-DDARWIN_OS_CASE_SENSITIVE_FIXME=2, and file a bug report saying
+whether this fixed your problem.
+
 * Build-time problems
 
 ** Configuration
diff --git a/src/fileio.c b/src/fileio.c
index f3f8f421618..70799eb2cd1 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -2251,33 +2251,66 @@ internal_delete_file (Lisp_Object filename)
 static bool
 file_name_case_insensitive_p (const char *filename)
 {
-#ifdef DOS_NT
-  return 1;
-#elif defined CYGWIN
-/* As of Cygwin-2.6.1, pathconf supports _PC_CASE_INSENSITIVE.  */
-# ifdef _PC_CASE_INSENSITIVE
+  /* Use pathconf with _PC_CASE_INSENSITIVE or _PC_CASE_SENSITIVE if
+     those flags are available.  As of this writing (2016-11-14),
+     Cygwin is the only platform known to support the former (starting
+     with Cygwin-2.6.1), and Mac OS X is the only platform known to
+     support the latter.
+
+     There have been reports that pathconf with _PC_CASE_SENSITIVE
+     does not work reliably on Mac OS X.  If you have a problem,
+     please recompile Emacs with -DDARWIN_OS_CASE_SENSITIVE_FIXME=1 or
+     -DDARWIN_OS_CASE_SENSITIVE_FIXME=2, and file a bug report saying
+     whether this fixed your problem.  */
+
+#ifdef _PC_CASE_INSENSITIVE
   int res = pathconf (filename, _PC_CASE_INSENSITIVE);
-  if (res < 0)
-    return 1;
-  return res > 0;
-# else
-  return 1;
+  if (res >= 0)
+    return res > 0;
+#elif defined _PC_CASE_SENSITIVE && !defined DARWIN_OS_CASE_SENSITIVE_FIXME
+  int res = pathconf (filename, _PC_CASE_SENSITIVE);
+  if (res >= 0)
+    return res == 0;
+#endif
+
+#ifdef DARWIN_OS
+# ifndef DARWIN_OS_CASE_SENSITIVE_FIXME
+  int DARWIN_OS_CASE_SENSITIVE_FIXME = 0;
 # endif
-#elif defined DARWIN_OS
-  /* The following is based on
-     http://lists.apple.com/archives/darwin-dev/2007/Apr/msg00010.html.  */
-  struct attrlist alist;
-  unsigned char buffer[sizeof (vol_capabilities_attr_t) + sizeof (size_t)];
-
-  memset (&alist, 0, sizeof (alist));
-  alist.volattr = ATTR_VOL_CAPABILITIES;
-  if (getattrlist (filename, &alist, buffer, sizeof (buffer), 0)
-      || !(alist.volattr & ATTR_VOL_CAPABILITIES))
-    return 0;
-  vol_capabilities_attr_t *vcaps = buffer;
-  return !(vcaps->capabilities[0] & VOL_CAP_FMT_CASE_SENSITIVE);
+
+  if (DARWIN_OS_CASE_SENSITIVE_FIXME == 1)
+    {
+      /* This is based on developer.apple.com's getattrlist man page.  */
+      struct attrlist alist = {.volattr = ATTR_VOL_CAPABILITIES};
+      struct vol_capabilities_attr_t vcaps;
+      if (getattrlist (filename, &alist, &vcaps, sizeof vcaps, 0) == 0)
+        {
+          if (vcaps.valid[VOL_CAPABILITIES_FORMAT] & VOL_CAP_FMT_CASE_SENSITIVE)
+            return ! (vcaps.capabilities[VOL_CAPABILITIES_FORMAT]
+                      & VOL_CAP_FMT_CASE_SENSITIVE);
+        }
+    }
+  else if (DARWIN_OS_CASE_SENSITIVE_FIXME == 2)
+    {
+      /* The following is based on
+         http://lists.apple.com/archives/darwin-dev/2007/Apr/msg00010.html.  */
+      struct attrlist alist;
+      unsigned char buffer[sizeof (vol_capabilities_attr_t)  sizeof (size_t)];
+
+      memset (&alist, 0, sizeof (alist));
+      alist.volattr = ATTR_VOL_CAPABILITIES;
+      if (getattrlist (filename, &alist, buffer, sizeof (buffer), 0)
+          || !(alist.volattr & ATTR_VOL_CAPABILITIES))
+        return 0;
+      vol_capabilities_attr_t *vcaps = buffer;
+      return !(vcaps->capabilities[0] & VOL_CAP_FMT_CASE_SENSITIVE);
+    }
+#endif  /* DARWIN_OS */
+
+#if defined CYGWIN || defined DOS_NT
+  return true;
 #else
-  return 0;
+  return false;
 #endif
 }