[PATCH 1/2] compat-util: is_missing_file_error()

[Junio C Hamano <gitster@pobox.com>]

Our code often opens a path to an optional file, to work on its
contents when we can successfully open it.  We can ignore a failure
to open if such an optional file does not exist, but we do want to
report a failure in opening for other reasons (e.g. we got an I/O
error, or the file is there, but we lack the permission to open).

The exact errors we need to ignore are ENOENT (obviously) and
ENOTDIR (less obvious).  Instead of repeating comparison of errno
with these two constants, introduce a helper function to do so.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * Now this is independent of nd/fopen-errors topic.  We could tweak
   nd/fopen-errors topic to use this later, after both of these two
   topics have graduated.

 git-compat-util.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/git-compat-util.h b/git-compat-util.h
index 8a4a3f85e7..8a3c680626 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -1115,6 +1115,21 @@ struct tm *git_gmtime_r(const time_t *, struct tm *);
 #define getc_unlocked(fh) getc(fh)
 #endif
 
+/*
+ * Our code often opens a path to an optional file, to work on its
+ * contents when we can successfully open it.  We can ignore a failure
+ * to open if such an optional file does not exist, but we do want to
+ * report a failure in opening for other reasons (e.g. we got an I/O
+ * error, or the file is there, but we lack the permission to open).
+ *
+ * Call this function after seeing an error from open() or fopen() to
+ * see if the errno indicates a missing file that we can safely ignore.
+ */
+static inline int is_missing_file_error(int errno_)
+{
+	return (errno_ == ENOENT || errno_ == ENOTDIR);
+}
+
 extern int cmd_main(int, const char **);
 
 #endif
-- 
2.13.0-496-ga689fffbe2