Subject: Re: [PATCH] diff: do not reuse_worktree_file for submodules

From: Thomas Rast <[email-masked]>
Date: Sat, 22 Feb 2014 12:27:29 +0100

Junio C Hamano <[email-masked]> writes:

> Thomas Rast <[email-masked]> writes:
>
>> @@ -2845,8 +2845,9 @@ static struct diff_tempfile *prepare_temp_file(const char *name,
>>  		remove_tempfile_installed = 1;
>>  	}
>>  
>> -	if (!one->sha1_valid ||
>> -	    reuse_worktree_file(name, one->sha1, 1)) {
>> +	if (!S_ISGITLINK(one->mode) &&
>> +	    (!one->sha1_valid ||
>> +	     reuse_worktree_file(name, one->sha1, 1))) {
>
> I agree with the goal/end result, but I have to wonder if the
> reuse_worktree_file() be the helper function that ought to
> encapsulate such a logic?
>
> Instead of feeding it an object name and a path, if we passed a
> diff_filespec to the helper, it would have access to the mode as
> well.  It would result in a more intrusive change, so I'd prefer to
> see your patch applied first and then build such a refactor on top,
> perhaps like the attached.

I see that you already queued 721e727, which has the change you
described plus moving the S_ISGITLINK test into reuse_worktree_file.
The change looks good to me.  However, two nits about the comments:
diff.c now says

  /*
   * Given a name and sha1 pair, if the index tells us the file in
   * the work tree has that object contents, return true, so that
   * prepare_temp_file() does not have to inflate and extract.
   */
  static int reuse_worktree_file(const struct diff_filespec *spec, int want_file)
  {
          const struct cache_entry *ce;
          struct stat st;
          int pos, len;
          const char *name = spec->path;
          const unsigned char *sha1 = spec->sha1;

          /* reading the directory will not give us "Submodule commit XYZ" */
          if (S_ISGITLINK(spec->mode))
                  return 0;

But the function comment is no longer accurate, and the comment about
the S_ISGITLINK exit is rather obscure if one doesn't know what the
callers want.  So how about this on top?

 diff.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git i/diff.c w/diff.c
index a342ea6..dabf913 100644
--- i/diff.c
+++ w/diff.c
@@ -2578,9 +2578,14 @@ void fill_filespec(struct diff_filespec *spec, const unsigned char *sha1,
 }
 
 /*
- * Given a name and sha1 pair, if the index tells us the file in
- * the work tree has that object contents, return true, so that
- * prepare_temp_file() does not have to inflate and extract.
+ * Given a diff_filespec, determine if the corresponding worktree file
+ * can be used for diffing instead of reading the object from the
+ * repository.
+ *
+ * We normally try packfiles, worktree, loose objects in this order.
+ *
+ * If want_file=1 or git was compiled with NO_FAST_WORKING_DIRECTORY,
+ * the order is: worktree, packfiles, loose objects.
  */
 static int reuse_worktree_file(const struct diff_filespec *spec, int want_file)
 {
@@ -2590,7 +2595,11 @@ static int reuse_worktree_file(const struct diff_filespec *spec, int want_file)
 	const char *name = spec->path;
 	const unsigned char *sha1 = spec->sha1;
 
-	/* reading the directory will not give us "Submodule commit XYZ" */
+	/*
+	 * The diff representation of a submodule is "Submodule commit
+	 * XYZ", but in the worktree we have a directory.  So they
+	 * never match.
+	 */
 	if (S_ISGITLINK(spec->mode))
 		return 0;

-- 
Thomas Rast
[email-masked]