branch -v: align even when branch names are in UTF-8

Branch names are usually in ASCII so they are not the problem. The
problem most likely comes from "(no branch)" translation, which is
in UTF-8 and makes display-width calculation just wrong.  Clarify
this by renaming the field "len" in struct ref_item to "width", as
it stores the display-width and is used to compute the width of the
screen needed to show the names of all the branches, and compute the
display width using utf8_strwidth(), not byte-length with strlen().

Update document to mention the fact that we may want ref names in
UTF-8. Encodings that produce invalid UTF-8 are safe as utf8_strwidth()
falls back to strlen(). The ones that incidentally produce valid UTF-8
sequences will cause misalignment.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/revisions.txt

@@ -55,6 +55,8 @@ when you run `git cherry-pick`.
 +
 Note that any of the 'refs/*' cases above may come either from
 the '$GIT_DIR/refs' directory or from the '$GIT_DIR/packed-refs' file.
+While the ref name encoding is unspecified, UTF-8 is prefered as
+some output processing may assume ref names in UTF-8.
 
 '<refname>@\{<date>\}', e.g. 'master@\{yesterday\}', 'HEAD@\{5 minutes ago\}'::
   A ref followed by the suffix '@' with a date specification

builtin/branch.c

@@ -17,6 +17,7 @@
 #include "revision.h"
 #include "string-list.h"
 #include "column.h"
+#include "utf8.h"
 
 static const char * const builtin_branch_usage[] = {
 	"git branch [options] [-r | -a] [--merged | --no-merged]",
@@ -249,7 +250,7 @@ static int delete_branches(int argc, const char **argv, int force, int kinds,
 struct ref_item {
 	char *name;
 	char *dest;
-	unsigned int kind, len;
+	unsigned int kind, width;
 	struct commit *commit;
 };
 
@@ -354,14 +355,14 @@ static int append_ref(const char *refname, const unsigned char *sha1, int flags,
 	newitem->name = xstrdup(refname);
 	newitem->kind = kind;
 	newitem->commit = commit;
-	newitem->len = strlen(refname);
+	newitem->width = utf8_strwidth(refname);
 	newitem->dest = resolve_symref(orig_refname, prefix);
 	/* adjust for "remotes/" */
 	if (newitem->kind == REF_REMOTE_BRANCH &&
 	    ref_list->kinds != REF_REMOTE_BRANCH)
-		newitem->len += 8;
-	if (newitem->len > ref_list->maxwidth)
-		ref_list->maxwidth = newitem->len;
+		newitem->width += 8;
+	if (newitem->width > ref_list->maxwidth)
+		ref_list->maxwidth = newitem->width;
 
 	return 0;
 }
@@ -490,11 +491,12 @@ static void print_ref_item(struct ref_item *item, int maxwidth, int verbose,
 	}
 
 	strbuf_addf(&name, "%s%s", prefix, item->name);
-	if (verbose)
+	if (verbose) {
+		int utf8_compensation = strlen(name.buf) - utf8_strwidth(name.buf);
 		strbuf_addf(&out, "%c %s%-*s%s", c, branch_get_color(color),
-			    maxwidth, name.buf,
+			    maxwidth + utf8_compensation, name.buf,
 			    branch_get_color(BRANCH_COLOR_RESET));
-	else
+	} else
 		strbuf_addf(&out, "%c %s%s%s", c, branch_get_color(color),
 			    name.buf, branch_get_color(BRANCH_COLOR_RESET));
 
@@ -519,8 +521,8 @@ static int calc_maxwidth(struct ref_list *refs)
 	for (i = 0; i < refs->index; i++) {
 		if (!matches_merge_filter(refs->list[i].commit))
 			continue;
-		if (refs->list[i].len > w)
-			w = refs->list[i].len;
+		if (refs->list[i].width > w)
+			w = refs->list[i].width;
 	}
 	return w;
 }
@@ -533,12 +535,12 @@ static void show_detached(struct ref_list *ref_list)
 	if (head_commit && is_descendant_of(head_commit, ref_list->with_commit)) {
 		struct ref_item item;
 		item.name = xstrdup(_("(no branch)"));
-		item.len = strlen(item.name);
+		item.width = utf8_strwidth(item.name);
 		item.kind = REF_LOCAL_BRANCH;
 		item.dest = NULL;
 		item.commit = head_commit;
-		if (item.len > ref_list->maxwidth)
-			ref_list->maxwidth = item.len;
+		if (item.width > ref_list->maxwidth)
+			ref_list->maxwidth = item.width;
 		print_ref_item(&item, ref_list->maxwidth, ref_list->verbose, ref_list->abbrev, 1, "");
 		free(item.name);
 	}