[PATCH 2/2] read_info_alternates: warn on non-trivial errors

[Jeff King <peff@peff.net>]

When we fail to open $GIT_DIR/info/alternates, we silently
assume there are no alternates. This is the right thing to
do for ENOENT, but not for other errors.

A hard error is probably overkill here. If we fail to read
an alternates file then either we'll complete our operation
anyway, or we'll fail to find some needed object. Either
way, a warning is good idea. And we already have a helper
function to handle this pattern; let's just call
warn_on_fopen_error().

Note that technically the errno from strbuf_read_file()
might be from a read() error, not open(). But since read()
would never return ENOENT or ENOTDIR, and since it produces
a generic "unable to access" error, it's suitable for
handling errors from either.

Signed-off-by: Jeff King <peff@peff.net>
---
I'm pretty comfortable with the rationale in the final paragraph. But if
we're concerned that warn_on_fopen_errors() might change, we can swap
out strbuf_read_file() for fopen()+strbuf_read().

 sha1_file.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/sha1_file.c b/sha1_file.c
index b1e4193679..9cec326298 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -432,6 +432,7 @@ static void read_info_alternates(const char * relative_base, int depth)
 
 	path = xstrfmt("%s/info/alternates", relative_base);
 	if (strbuf_read_file(&buf, path, 1024) < 0) {
+		warn_on_fopen_errors(path);
 		free(path);
 		return;
 	}
-- 
2.14.1.1014.g252e627ae0