diff --dirstat-by-file: count changed files, not lines

This new option --dirstat-by-file is the same as --dirstat, but it
counts "impacted files" instead of "impacted lines" (lines that are
added or removed).
Signed-off-by: NHeikki Orsila <heikki.orsila@iki.fi>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/diff-options.txt

@@ -65,6 +65,9 @@ endif::git-format-patch[]
 	can be set with "--dirstat=limit". Changes in a child directory is not
 	counted for the parent directory, unless "--cumulative" is used.
 
+--dirstat-by-file[=limit]::
+	Same as --dirstat, but counts changed files instead of lines.
+
 --summary::
 	Output a condensed summary of extended header information
 	such as creations, renames and mode changes.

diff.c

@@ -1110,9 +1110,13 @@ static void show_dirstat(struct diff_options *options)
 		/*
 		 * Original minus copied is the removed material,
 		 * added is the new material.  They are both damages
-		 * made to the preimage.
+		 * made to the preimage. In --dirstat-by-file mode, count
+		 * damaged files, not damaged lines. This is done by
+		 * counting only a single damaged line per file.
 		 */
 		damage = (p->one->size - copied) + added;
+		if (DIFF_OPT_TST(options, DIRSTAT_BY_FILE) && damage > 0)
+			damage = 1;
 
 		ALLOC_GROW(dir.files, dir.nr + 1, dir.alloc);
 		dir.files[dir.nr].name = name;
@@ -2476,6 +2480,10 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 	else if (!strcmp(arg, "--cumulative")) {
 		options->output_format |= DIFF_FORMAT_DIRSTAT;
 		DIFF_OPT_SET(options, DIRSTAT_CUMULATIVE);
+	} else if (opt_arg(arg, 0, "dirstat-by-file",
+			   &options->dirstat_percent)) {
+		options->output_format |= DIFF_FORMAT_DIRSTAT;
+		DIFF_OPT_SET(options, DIRSTAT_BY_FILE);
 	}
 	else if (!strcmp(arg, "--check"))
 		options->output_format |= DIFF_FORMAT_CHECKDIFF;

diff.h

@@ -64,6 +64,7 @@ typedef void (*diff_format_fn_t)(struct diff_queue_struct *q,
 #define DIFF_OPT_RELATIVE_NAME       (1 << 17)
 #define DIFF_OPT_IGNORE_SUBMODULES   (1 << 18)
 #define DIFF_OPT_DIRSTAT_CUMULATIVE  (1 << 19)
+#define DIFF_OPT_DIRSTAT_BY_FILE     (1 << 20)
 #define DIFF_OPT_TST(opts, flag)    ((opts)->flags & DIFF_OPT_##flag)
 #define DIFF_OPT_SET(opts, flag)    ((opts)->flags |= DIFF_OPT_##flag)
 #define DIFF_OPT_CLR(opts, flag)    ((opts)->flags &= ~DIFF_OPT_##flag)