Subject: Re: [PATCH 2/9] ll-merge: make callers responsible for showing warnings

From: Junio C Hamano <[email-masked]>
Date: Tue, 21 Dec 2021 15:44:28 -0800

"Elijah Newren via GitGitGadget" <[email-masked]> writes:

> From: Elijah Newren <[email-masked]>
>
> Since some callers may want to send warning messages to somewhere other
> than stdout/stderr, stop printing "warning: Cannot merge binary files"
> from ll-merge and instead modify the return status of ll_merge() to
> indicate when a merge of binary files has occurred.
>
> Note that my methodology included first modifying ll_merge() to return
> a struct, so that the compiler would catch all the callers for me and
> ensure I had modified all of them.  After modifying all of them, I then
> changed the struct to an enum.
>
> Signed-off-by: Elijah Newren <[email-masked]>
> ---
>  apply.c            |  5 ++++-
>  builtin/checkout.c | 12 ++++++++----
>  ll-merge.c         | 40 ++++++++++++++++++++++------------------
>  ll-merge.h         |  9 ++++++++-
>  merge-blobs.c      |  5 ++++-
>  merge-ort.c        |  5 ++++-
>  merge-recursive.c  |  5 ++++-
>  notes-merge.c      |  5 ++++-
>  rerere.c           | 10 +++++++---
>  9 files changed, 65 insertions(+), 31 deletions(-)
>
> diff --git a/apply.c b/apply.c
> index 43a0aebf4ee..12ea9c72a6b 100644
> --- a/apply.c
> +++ b/apply.c
> @@ -3492,7 +3492,7 @@ static int three_way_merge(struct apply_state *state,
>  {
>  	mmfile_t base_file, our_file, their_file;
>  	mmbuffer_t result = { NULL };
> -	int status;
> +	enum ll_merge_result status;
>  
>  	/* resolve trivial cases first */
>  	if (oideq(base, ours))
> @@ -3509,6 +3509,9 @@ static int three_way_merge(struct apply_state *state,
>  			  &their_file, "theirs",
>  			  state->repo->index,
>  			  NULL);
> +	if (status == LL_MERGE_BINARY_CONFLICT)
> +		warning("Cannot merge binary files: %s (%s vs. %s)",
> +			"base", "ours", "theirs");

This used to come from ll_merge()

> -			warning("Cannot merge binary files: %s (%s vs. %s)",
> -				path, name1, name2);
> -			/* fallthru */

And our call to ll_merge() above (half of it invisible in the
pre-context of the hunk) gave "ours" and "theirs" to our_label and
their_label, which in turn are called name1 and name2, respectively,
in ll_merge_binary() driver.

I am not sure about the "base" string, though.  I suspect that your
"base" should be a reference to the parameter 'path' of three_way_merge()
function.

> diff --git a/builtin/checkout.c b/builtin/checkout.c
> index cbf73b8c9f6..3a559d69303 100644
> --- a/builtin/checkout.c
> +++ b/builtin/checkout.c
> @@ -237,6 +237,7 @@ static int checkout_merged(int pos, const struct checkout *state,
>  	struct cache_entry *ce = active_cache[pos];
>  	const char *path = ce->name;
>  	mmfile_t ancestor, ours, theirs;
> +	enum ll_merge_result merge_status;
>  	int status;
>  	struct object_id oid;
>  	mmbuffer_t result_buf;
> @@ -267,13 +268,16 @@ static int checkout_merged(int pos, const struct checkout *state,
>  	memset(&ll_opts, 0, sizeof(ll_opts));
>  	git_config_get_bool("merge.renormalize", &renormalize);
>  	ll_opts.renormalize = renormalize;
> -	status = ll_merge(&result_buf, path, &ancestor, "base",
> -			  &ours, "ours", &theirs, "theirs",
> -			  state->istate, &ll_opts);
> +	merge_status = ll_merge(&result_buf, path, &ancestor, "base",
> +				&ours, "ours", &theirs, "theirs",
> +				state->istate, &ll_opts);
>  	free(ancestor.ptr);
>  	free(ours.ptr);
>  	free(theirs.ptr);
> -	if (status < 0 || !result_buf.ptr) {
> +	if (merge_status == LL_MERGE_BINARY_CONFLICT)
> +		warning("Cannot merge binary files: %s (%s vs. %s)",
> +			path, "ours", "theirs");

This one looks correct.

> +	if (merge_status < 0 || !result_buf.ptr) {
>  		free(result_buf.ptr);
>  		return error(_("path '%s': cannot merge"), path);
>  	}

> diff --git a/merge-blobs.c b/merge-blobs.c
> index ee0a0e90c94..8138090f81c 100644
> --- a/merge-blobs.c
> +++ b/merge-blobs.c
> @@ -36,7 +36,7 @@ static void *three_way_filemerge(struct index_state *istate,
>  				 mmfile_t *their,
>  				 unsigned long *size)
>  {
> -	int merge_status;
> +	enum ll_merge_result merge_status;
>  	mmbuffer_t res;
>  
>  	/*
> @@ -50,6 +50,9 @@ static void *three_way_filemerge(struct index_state *istate,
>  				istate, NULL);
>  	if (merge_status < 0)
>  		return NULL;
> +	if (merge_status == LL_MERGE_BINARY_CONFLICT)
> +		warning("Cannot merge binary files: %s (%s vs. %s)",
> +			path, ".our", ".their");

OK.

> diff --git a/merge-ort.c b/merge-ort.c
> index 0342f104836..c24da2ba3cb 100644
> --- a/merge-ort.c
> +++ b/merge-ort.c
> @@ -1743,7 +1743,7 @@ static int merge_3way(struct merge_options *opt,
>  	mmfile_t orig, src1, src2;
>  	struct ll_merge_options ll_opts = {0};
>  	char *base, *name1, *name2;
> -	int merge_status;
> +	enum ll_merge_result merge_status;
>  
>  	if (!opt->priv->attr_index.initialized)
>  		initialize_attr_index(opt);
> @@ -1787,6 +1787,9 @@ static int merge_3way(struct merge_options *opt,
>  	merge_status = ll_merge(result_buf, path, &orig, base,
>  				&src1, name1, &src2, name2,
>  				&opt->priv->attr_index, &ll_opts);
> +	if (merge_status == LL_MERGE_BINARY_CONFLICT)
> +		warning("Cannot merge binary files: %s (%s vs. %s)",
> +			path, name1, name2);

OK; this is your code and I do not have to read it too carefully,
but all we need is conveniently in the pre-context of the hunk ;-).

> diff --git a/merge-recursive.c b/merge-recursive.c
> index d9457797dbb..bc73c52dd84 100644
> --- a/merge-recursive.c
> +++ b/merge-recursive.c
> @@ -1044,7 +1044,7 @@ static int merge_3way(struct merge_options *opt,
>  	mmfile_t orig, src1, src2;
>  	struct ll_merge_options ll_opts = {0};
>  	char *base, *name1, *name2;
> -	int merge_status;
> +	enum ll_merge_result merge_status;
>  
>  	ll_opts.renormalize = opt->renormalize;
>  	ll_opts.extra_marker_size = extra_marker_size;
> @@ -1090,6 +1090,9 @@ static int merge_3way(struct merge_options *opt,
>  	merge_status = ll_merge(result_buf, a->path, &orig, base,
>  				&src1, name1, &src2, name2,
>  				opt->repo->index, &ll_opts);
> +	if (merge_status == LL_MERGE_BINARY_CONFLICT)
> +		warning("Cannot merge binary files: %s (%s vs. %s)",
> +			a->path, name1, name2);

OK.

> diff --git a/notes-merge.c b/notes-merge.c
> index b4a3a903e86..01d596920ea 100644
> --- a/notes-merge.c
> +++ b/notes-merge.c
> @@ -344,7 +344,7 @@ static int ll_merge_in_worktree(struct notes_merge_options *o,
>  {
>  	mmbuffer_t result_buf;
>  	mmfile_t base, local, remote;
> -	int status;
> +	enum ll_merge_result status;
>  
>  	read_mmblob(&base, &p->base);
>  	read_mmblob(&local, &p->local);
> @@ -358,6 +358,9 @@ static int ll_merge_in_worktree(struct notes_merge_options *o,
>  	free(local.ptr);
>  	free(remote.ptr);
>  
> +	if (status == LL_MERGE_BINARY_CONFLICT)
> +		warning("Cannot merge binary files: %s (%s vs. %s)",
> +			oid_to_hex(&p->obj), o->local_ref, o->remote_ref);

This uses another slot in the rotating buffer used by oid_to_hex(),
but I do not think anybody grabbed a pointer to one of them and held
onto it before we got here, so it would be OK.

> diff --git a/rerere.c b/rerere.c
> index d83d58df4fb..46fd01819b8 100644
> --- a/rerere.c
> +++ b/rerere.c
> @@ -609,19 +609,23 @@ static int try_merge(struct index_state *istate,
>  		     const struct rerere_id *id, const char *path,
>  		     mmfile_t *cur, mmbuffer_t *result)
>  {
> -	int ret;
> +	enum ll_merge_result ret;
>  	mmfile_t base = {NULL, 0}, other = {NULL, 0};
>  
>  	if (read_mmfile(&base, rerere_path(id, "preimage")) ||
>  	    read_mmfile(&other, rerere_path(id, "postimage")))
> -		ret = 1;
> -	else
> +		ret = LL_MERGE_CONFLICT;
> +	else {

Let's have {} around the if clause now the corresponding else clause
needs it.

>  		/*
>  		 * A three-way merge. Note that this honors user-customizable
>  		 * low-level merge driver settings.
>  		 */
>  		ret = ll_merge(result, path, &base, NULL, cur, "", &other, "",
>  			       istate, NULL);
> +		if (ret == LL_MERGE_BINARY_CONFLICT)
> +			warning("Cannot merge binary files: %s (%s vs. %s)",
> +				path, "", "");
> +	}

This is a faithful conversion of what should not happen in practice,
as the rerere logic would not be able to reach here.  In a binary
file, we won't be able to identify <<< === >>> blocks, hash the text
in the conflicted block to come up with the conflict ID to find the
preimage and postimage files.  These files are the input to the low
level merge driver call we are making here.

Looking almost good except for a warning message bug I spotted
earlier.

Thanks.