merge-ll: rename from ll-merge

A long term (but rather minor) pet-peeve of mine was the name
ll-merge.[ch].  I thought it made it harder to realize what stuff was
related to merging when I was working on the merge machinery and trying
to improve it.

Further, back in d1cbe1e6d8a ("hash-ll.h: split out of hash.h to remove
dependency on repository.h", 2023-04-22), we have split the portions of
hash.h that do not depend upon repository.h into a "hash-ll.h" (due to
the recommendation to use "ll" for "low-level" in its name[1], but which
I used as a suffix precisely because of my distaste for "ll-merge").
When we discussed adding additional "*-ll.h" files, a request was made
that we use "ll" consistently as either a prefix or a suffix.  Since it
is already in use as both a prefix and a suffix, the only way to do so
is to rename some files.

Besides my distaste for the ll-merge.[ch] name, let me also note that
the files
  ll-fsmonitor.h, ll-hash.h, ll-merge.h, ll-object-store.h, ll-read-cache.h
would have essentially nothing to do with each other and make no sense
to group.  But giving them the common "ll-" prefix would group them.  Using
"-ll" as a suffix thus seems just much more logical to me.  Rename
ll-merge.[ch] to merge-ll.[ch] to achieve this consistency, and to
ensure we get a more logical grouping of files.

[1] https://lore.kernel.org/git/kl6lsfcu1g8w.fsf@chooglen-macbookpro.roam.corp.google.com/

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

1 files changed, 432 insertions, 0 deletions

diff --git a/merge-ll.c b/merge-ll.c
new file mode 100644
index 0000000000..740b8c6bfd
--- /dev/null
+++ b/merge-ll.c
@@ -0,0 +1,432 @@
+/*
+ * Low level 3-way in-core file merge.
+ *
+ * Copyright (c) 2007 Junio C Hamano
+ */
+
+#include "git-compat-util.h"
+#include "config.h"
+#include "convert.h"
+#include "attr.h"
+#include "xdiff-interface.h"
+#include "run-command.h"
+#include "merge-ll.h"
+#include "quote.h"
+#include "strbuf.h"
+#include "wrapper.h"
+
+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,
+			   mmfile_t *src1, const char *name1,
+			   mmfile_t *src2, const char *name2,
+			   const struct ll_merge_options *opts,
+			   int marker_size);
+
+struct ll_merge_driver {
+	const char *name;
+	const char *description;
+	ll_merge_fn fn;
+	const char *recursive;
+	struct ll_merge_driver *next;
+	char *cmdline;
+};
+
+static struct attr_check *merge_attributes;
+static struct attr_check *load_merge_attributes(void)
+{
+	if (!merge_attributes)
+		merge_attributes = attr_check_initl("merge", "conflict-marker-size", NULL);
+	return merge_attributes;
+}
+
+void reset_merge_attributes(void)
+{
+	attr_check_free(merge_attributes);
+	merge_attributes = NULL;
+}
+
+/*
+ * Built-in low-levels
+ */
+static enum ll_merge_result ll_binary_merge(const struct ll_merge_driver *drv UNUSED,
+			   mmbuffer_t *result,
+			   const char *path UNUSED,
+			   mmfile_t *orig, const char *orig_name UNUSED,
+			   mmfile_t *src1, const char *name1 UNUSED,
+			   mmfile_t *src2, const char *name2 UNUSED,
+			   const struct ll_merge_options *opts,
+			   int marker_size UNUSED)
+{
+	enum ll_merge_result ret;
+	mmfile_t *stolen;
+	assert(opts);
+
+	/*
+	 * The tentative merge result is the common ancestor for an
+	 * internal merge.  For the final merge, it is "ours" by
+	 * default but -Xours/-Xtheirs can tweak the choice.
+	 */
+	if (opts->virtual_ancestor) {
+		stolen = orig;
+		ret = LL_MERGE_OK;
+	} else {
+		switch (opts->variant) {
+		default:
+			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;
+		}
+	}
+
+	result->ptr = stolen->ptr;
+	result->size = stolen->size;
+	stolen->ptr = NULL;
+
+	return ret;
+}
+
+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,
+			mmfile_t *src1, const char *name1,
+			mmfile_t *src2, const char *name2,
+			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 ||
+	    src1->size > MAX_XDIFF_SIZE ||
+	    src2->size > MAX_XDIFF_SIZE ||
+	    buffer_is_binary(orig->ptr, orig->size) ||
+	    buffer_is_binary(src1->ptr, src1->size) ||
+	    buffer_is_binary(src2->ptr, src2->size)) {
+		return ll_binary_merge(drv_unused, result,
+				       path,
+				       orig, orig_name,
+				       src1, name1,
+				       src2, name2,
+				       opts, marker_size);
+	}
+
+	memset(&xmp, 0, sizeof(xmp));
+	xmp.level = XDL_MERGE_ZEALOUS;
+	xmp.favor = opts->variant;
+	xmp.xpp.flags = opts->xdl_opts;
+	if (git_xmerge_style >= 0)
+		xmp.style = git_xmerge_style;
+	if (marker_size > 0)
+		xmp.marker_size = marker_size;
+	xmp.ancestor = orig_name;
+	xmp.file1 = name1;
+	xmp.file2 = name2;
+	status = xdl_merge(orig, src1, src2, &xmp, result);
+	ret = (status > 0) ? LL_MERGE_CONFLICT : status;
+	return ret;
+}
+
+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,
+			  mmfile_t *src1, const char *name1,
+			  mmfile_t *src2, const char *name2,
+			  const struct ll_merge_options *opts,
+			  int marker_size)
+{
+	/* Use union favor */
+	struct ll_merge_options o;
+	assert(opts);
+	o = *opts;
+	o.variant = XDL_MERGE_FAVOR_UNION;
+	return ll_xdl_merge(drv_unused, result, path,
+			    orig, orig_name, src1, name1, src2, name2,
+			    &o, marker_size);
+}
+
+#define LL_BINARY_MERGE 0
+#define LL_TEXT_MERGE 1
+#define LL_UNION_MERGE 2
+static struct ll_merge_driver ll_merge_drv[] = {
+	{ "binary", "built-in binary merge", ll_binary_merge },
+	{ "text", "built-in 3-way text merge", ll_xdl_merge },
+	{ "union", "built-in union merge", ll_union_merge },
+};
+
+static void create_temp(mmfile_t *src, char *path, size_t len)
+{
+	int fd;
+
+	xsnprintf(path, len, ".merge_file_XXXXXX");
+	fd = xmkstemp(path);
+	if (write_in_full(fd, src->ptr, src->size) < 0)
+		die_errno("unable to write temp-file");
+	close(fd);
+}
+
+/*
+ * User defined low-level merge driver support.
+ */
+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 UNUSED,
+			mmfile_t *src1, const char *name1 UNUSED,
+			mmfile_t *src2, const char *name2 UNUSED,
+			const struct ll_merge_options *opts,
+			int marker_size)
+{
+	char temp[4][50];
+	struct strbuf cmd = STRBUF_INIT;
+	struct strbuf_expand_dict_entry dict[6];
+	struct strbuf path_sq = STRBUF_INIT;
+	struct child_process child = CHILD_PROCESS_INIT;
+	int status, fd, i;
+	struct stat st;
+	enum ll_merge_result ret;
+	assert(opts);
+
+	sq_quote_buf(&path_sq, path);
+	dict[0].placeholder = "O"; dict[0].value = temp[0];
+	dict[1].placeholder = "A"; dict[1].value = temp[1];
+	dict[2].placeholder = "B"; dict[2].value = temp[2];
+	dict[3].placeholder = "L"; dict[3].value = temp[3];
+	dict[4].placeholder = "P"; dict[4].value = path_sq.buf;
+	dict[5].placeholder = NULL; dict[5].value = NULL;
+
+	if (!fn->cmdline)
+		die("custom merge driver %s lacks command line.", fn->name);
+
+	result->ptr = NULL;
+	result->size = 0;
+	create_temp(orig, temp[0], sizeof(temp[0]));
+	create_temp(src1, temp[1], sizeof(temp[1]));
+	create_temp(src2, temp[2], sizeof(temp[2]));
+	xsnprintf(temp[3], sizeof(temp[3]), "%d", marker_size);
+
+	strbuf_expand(&cmd, fn->cmdline, strbuf_expand_dict_cb, &dict);
+
+	child.use_shell = 1;
+	strvec_push(&child.args, cmd.buf);
+	status = run_command(&child);
+	fd = open(temp[1], O_RDONLY);
+	if (fd < 0)
+		goto bad;
+	if (fstat(fd, &st))
+		goto close_bad;
+	result->size = st.st_size;
+	result->ptr = xmallocz(result->size);
+	if (read_in_full(fd, result->ptr, result->size) != result->size) {
+		FREE_AND_NULL(result->ptr);
+		result->size = 0;
+	}
+ close_bad:
+	close(fd);
+ bad:
+	for (i = 0; i < 3; i++)
+		unlink_or_warn(temp[i]);
+	strbuf_release(&cmd);
+	strbuf_release(&path_sq);
+	ret = (status > 0) ? LL_MERGE_CONFLICT : status;
+	return ret;
+}
+
+/*
+ * merge.default and merge.driver configuration items
+ */
+static struct ll_merge_driver *ll_user_merge, **ll_user_merge_tail;
+static const char *default_ll_merge;
+
+static int read_merge_config(const char *var, const char *value,
+			     void *cb UNUSED)
+{
+	struct ll_merge_driver *fn;
+	const char *key, *name;
+	size_t namelen;
+
+	if (!strcmp(var, "merge.default"))
+		return git_config_string(&default_ll_merge, var, value);
+
+	/*
+	 * We are not interested in anything but "merge.<name>.variable";
+	 * especially, we do not want to look at variables such as
+	 * "merge.summary", "merge.tool", and "merge.verbosity".
+	 */
+	if (parse_config_key(var, "merge", &name, &namelen, &key) < 0 || !name)
+		return 0;
+
+	/*
+	 * Find existing one as we might be processing merge.<name>.var2
+	 * after seeing merge.<name>.var1.
+	 */
+	for (fn = ll_user_merge; fn; fn = fn->next)
+		if (!strncmp(fn->name, name, namelen) && !fn->name[namelen])
+			break;
+	if (!fn) {
+		CALLOC_ARRAY(fn, 1);
+		fn->name = xmemdupz(name, namelen);
+		fn->fn = ll_ext_merge;
+		*ll_user_merge_tail = fn;
+		ll_user_merge_tail = &(fn->next);
+	}
+
+	if (!strcmp("name", key))
+		return git_config_string(&fn->description, var, value);
+
+	if (!strcmp("driver", key)) {
+		if (!value)
+			return error("%s: lacks value", var);
+		/*
+		 * merge.<name>.driver specifies the command line:
+		 *
+		 *	command-line
+		 *
+		 * The command-line will be interpolated with the following
+		 * tokens and is given to the shell:
+		 *
+		 *    %O - temporary file name for the merge base.
+		 *    %A - temporary file name for our version.
+		 *    %B - temporary file name for the other branches' version.
+		 *    %L - conflict marker length
+		 *    %P - the original path (safely quoted for the shell)
+		 *
+		 * The external merge driver should write the results in the
+		 * file named by %A, and signal that it has done with zero exit
+		 * status.
+		 */
+		fn->cmdline = xstrdup(value);
+		return 0;
+	}
+
+	if (!strcmp("recursive", key))
+		return git_config_string(&fn->recursive, var, value);
+
+	return 0;
+}
+
+static void initialize_ll_merge(void)
+{
+	if (ll_user_merge_tail)
+		return;
+	ll_user_merge_tail = &ll_user_merge;
+	git_config(read_merge_config, NULL);
+}
+
+static const struct ll_merge_driver *find_ll_merge_driver(const char *merge_attr)
+{
+	struct ll_merge_driver *fn;
+	const char *name;
+	int i;
+
+	initialize_ll_merge();
+
+	if (ATTR_TRUE(merge_attr))
+		return &ll_merge_drv[LL_TEXT_MERGE];
+	else if (ATTR_FALSE(merge_attr))
+		return &ll_merge_drv[LL_BINARY_MERGE];
+	else if (ATTR_UNSET(merge_attr)) {
+		if (!default_ll_merge)
+			return &ll_merge_drv[LL_TEXT_MERGE];
+		else
+			name = default_ll_merge;
+	}
+	else
+		name = merge_attr;
+
+	for (fn = ll_user_merge; fn; fn = fn->next)
+		if (!strcmp(fn->name, name))
+			return fn;
+
+	for (i = 0; i < ARRAY_SIZE(ll_merge_drv); i++)
+		if (!strcmp(ll_merge_drv[i].name, name))
+			return &ll_merge_drv[i];
+
+	/* default to the 3-way */
+	return &ll_merge_drv[LL_TEXT_MERGE];
+}
+
+static void normalize_file(mmfile_t *mm, const char *path, struct index_state *istate)
+{
+	struct strbuf strbuf = STRBUF_INIT;
+	if (renormalize_buffer(istate, path, mm->ptr, mm->size, &strbuf)) {
+		free(mm->ptr);
+		mm->size = strbuf.len;
+		mm->ptr = strbuf_detach(&strbuf, NULL);
+	}
+}
+
+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,
+	     mmfile_t *theirs, const char *their_label,
+	     struct index_state *istate,
+	     const struct ll_merge_options *opts)
+{
+	struct attr_check *check = load_merge_attributes();
+	static const struct ll_merge_options default_opts;
+	const char *ll_driver_name = NULL;
+	int marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
+	const struct ll_merge_driver *driver;
+
+	if (!opts)
+		opts = &default_opts;
+
+	if (opts->renormalize) {
+		normalize_file(ancestor, path, istate);
+		normalize_file(ours, path, istate);
+		normalize_file(theirs, path, istate);
+	}
+
+	git_check_attr(istate, path, check);
+	ll_driver_name = check->items[0].value;
+	if (check->items[1].value) {
+		marker_size = atoi(check->items[1].value);
+		if (marker_size <= 0)
+			marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
+	}
+	driver = find_ll_merge_driver(ll_driver_name);
+
+	if (opts->virtual_ancestor) {
+		if (driver->recursive)
+			driver = find_ll_merge_driver(driver->recursive);
+	}
+	if (opts->extra_marker_size) {
+		marker_size += opts->extra_marker_size;
+	}
+	return driver->fn(driver, result_buf, path, ancestor, ancestor_label,
+			  ours, our_label, theirs, their_label,
+			  opts, marker_size);
+}
+
+int ll_merge_marker_size(struct index_state *istate, const char *path)
+{
+	static struct attr_check *check;
+	int marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
+
+	if (!check)
+		check = attr_check_initl("conflict-marker-size", NULL);
+	git_check_attr(istate, path, check);
+	if (check->items[0].value) {
+		marker_size = atoi(check->items[0].value);
+		if (marker_size <= 0)
+			marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
+	}
+	return marker_size;
+}