ll-merge: make callers responsible for showing warnings

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.  Message printing
probably does not belong in a "low-level merge" anyway.

This commit continues printing the message as-is, just from the callers
instead of within ll_merge().  Future changes will start handling the
message differently in the merge-ort codepath.

There was one special case here: the callers in rerere.c do NOT check
for and print such a message; since those code paths explicitly skip
over binary files, there is no reason to check for a return status of
LL_MERGE_BINARY_CONFLICT or print the related message.

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

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)",
+			path, "ours", "theirs");
 	free(base_file.ptr);
 	free(our_file.ptr);
 	free(their_file.ptr);

builtin/checkout.c

@@ -245,6 +245,7 @@ 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;
@@ -275,13 +276,16 @@ 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",
+	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");
+	if (merge_status < 0 || !result_buf.ptr) {
 		free(result_buf.ptr);
 		return error(_("path '%s': cannot merge"), path);
 	}

ll-merge.c

@@ -14,7 +14,7 @@
 
 struct ll_merge_driver;
 
-typedef int (*ll_merge_fn)(const struct ll_merge_driver *,
+typedef enum ll_merge_result (*ll_merge_fn)(const struct ll_merge_driver *,
 			   mmbuffer_t *result,
 			   const char *path,
 			   mmfile_t *orig, const char *orig_name,
@@ -49,7 +49,7 @@ void reset_merge_attributes(void)
 /*
  * Built-in low-levels
  */
-static int ll_binary_merge(const struct ll_merge_driver *drv_unused,
+static enum ll_merge_result ll_binary_merge(const struct ll_merge_driver *drv_unused,
 			   mmbuffer_t *result,
 			   const char *path,
 			   mmfile_t *orig, const char *orig_name,
@@ -58,6 +58,7 @@ static int ll_binary_merge(const struct ll_merge_driver *drv_unused,
 			   const struct ll_merge_options *opts,
 			   int marker_size)
 {
+	enum ll_merge_result ret;
 	mmfile_t *stolen;
 	assert(opts);
 
@@ -68,16 +69,19 @@ static int ll_binary_merge(const struct ll_merge_driver *drv_unused,
 	 */
 	if (opts->virtual_ancestor) {
 		stolen = orig;
+		ret = LL_MERGE_OK;
 	} else {
 		switch (opts->variant) {
 		default:
-			warning("Cannot merge binary files: %s (%s vs. %s)",
-				path, name1, name2);
-			/* fallthru */
+			ret = LL_MERGE_BINARY_CONFLICT;
+			stolen = src1;
+			break;
 		case XDL_MERGE_FAVOR_OURS:
+			ret = LL_MERGE_OK;
 			stolen = src1;
 			break;
 		case XDL_MERGE_FAVOR_THEIRS:
+			ret = LL_MERGE_OK;
 			stolen = src2;
 			break;
 		}
@@ -87,16 +91,10 @@ static int ll_binary_merge(const struct ll_merge_driver *drv_unused,
 	result->size = stolen->size;
 	stolen->ptr = NULL;
 
-	/*
-	 * With -Xtheirs or -Xours, we have cleanly merged;
-	 * otherwise we got a conflict.
-	 */
-	return opts->variant == XDL_MERGE_FAVOR_OURS ||
-	       opts->variant == XDL_MERGE_FAVOR_THEIRS ?
-	       0 : 1;
+	return ret;
 }
 
-static int ll_xdl_merge(const struct ll_merge_driver *drv_unused,
+static enum ll_merge_result ll_xdl_merge(const struct ll_merge_driver *drv_unused,
 			mmbuffer_t *result,
 			const char *path,
 			mmfile_t *orig, const char *orig_name,
@@ -105,7 +103,9 @@ static int ll_xdl_merge(const struct ll_merge_driver *drv_unused,
 			const struct ll_merge_options *opts,
 			int marker_size)
 {
+	enum ll_merge_result ret;
 	xmparam_t xmp;
+	int status;
 	assert(opts);
 
 	if (orig->size > MAX_XDIFF_SIZE ||
@@ -133,10 +133,12 @@ static int ll_xdl_merge(const struct ll_merge_driver *drv_unused,
 	xmp.ancestor = orig_name;
 	xmp.file1 = name1;
 	xmp.file2 = name2;
-	return xdl_merge(orig, src1, src2, &xmp, result);
+	status = xdl_merge(orig, src1, src2, &xmp, result);
+	ret = (status > 0) ? LL_MERGE_CONFLICT : status;
+	return ret;
 }
 
-static int ll_union_merge(const struct ll_merge_driver *drv_unused,
+static enum ll_merge_result ll_union_merge(const struct ll_merge_driver *drv_unused,
 			  mmbuffer_t *result,
 			  const char *path,
 			  mmfile_t *orig, const char *orig_name,
@@ -178,7 +180,7 @@ static void create_temp(mmfile_t *src, char *path, size_t len)
 /*
  * User defined low-level merge driver support.
  */
-static int ll_ext_merge(const struct ll_merge_driver *fn,
+static enum ll_merge_result ll_ext_merge(const struct ll_merge_driver *fn,
 			mmbuffer_t *result,
 			const char *path,
 			mmfile_t *orig, const char *orig_name,
@@ -194,6 +196,7 @@ static int ll_ext_merge(const struct ll_merge_driver *fn,
 	const char *args[] = { NULL, NULL };
 	int status, fd, i;
 	struct stat st;
+	enum ll_merge_result ret;
 	assert(opts);
 
 	sq_quote_buf(&path_sq, path);
@@ -236,7 +239,8 @@ static int ll_ext_merge(const struct ll_merge_driver *fn,
 		unlink_or_warn(temp[i]);
 	strbuf_release(&cmd);
 	strbuf_release(&path_sq);
-	return status;
+	ret = (status > 0) ? LL_MERGE_CONFLICT : status;
+	return ret;
 }
 
 /*
@@ -362,7 +366,7 @@ static void normalize_file(mmfile_t *mm, const char *path, struct index_state *i
 	}
 }
 
-int ll_merge(mmbuffer_t *result_buf,
+enum ll_merge_result ll_merge(mmbuffer_t *result_buf,
 	     const char *path,
 	     mmfile_t *ancestor, const char *ancestor_label,
 	     mmfile_t *ours, const char *our_label,

ll-merge.h

@@ -82,13 +82,20 @@ struct ll_merge_options {
 	long xdl_opts;
 };
 
+enum ll_merge_result {
+	LL_MERGE_ERROR = -1,
+	LL_MERGE_OK = 0,
+	LL_MERGE_CONFLICT,
+	LL_MERGE_BINARY_CONFLICT,
+};
+
 /**
  * Perform a three-way single-file merge in core.  This is a thin wrapper
  * around `xdl_merge` that takes the path and any merge backend specified in
  * `.gitattributes` or `.git/info/attributes` into account.
  * Returns 0 for a clean merge.
  */
-int ll_merge(mmbuffer_t *result_buf,
+enum ll_merge_result ll_merge(mmbuffer_t *result_buf,
 	     const char *path,
 	     mmfile_t *ancestor, const char *ancestor_label,
 	     mmfile_t *ours, const char *our_label,

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");
 
 	*size = res.size;
 	return res.ptr;

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);
 
 	free(base);
 	free(name1);

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);
 
 	free(base);
 	free(name1);

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);
 	if ((status < 0) || !result_buf.ptr)
 		die("Failed to execute internal merge");
 

rerere.c

@@ -609,19 +609,20 @@ 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
+	    read_mmfile(&other, rerere_path(id, "postimage"))) {
+		ret = LL_MERGE_CONFLICT;
+	} else {
 		/*
 		 * 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);
+	}
 
 	free(base.ptr);
 	free(other.ptr);