Allow git-apply to recount the lines in a hunk (AKA recountdiff)

Sometimes, the easiest way to fix up a patch is to edit it directly, even
adding or deleting lines.  Now, many people are not as divine as certain
benevolent dictators as to update the hunk headers correctly at the first
try.

So teach the tool to do it for us.

[jc: with tests]

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 101 insertions, 43 deletions

diff --git a/Documentation/git-apply.txt b/Documentation/git-apply.txt
index c8347637d..c5ee636fa 100644
--- a/Documentation/git-apply.txt
+++ b/Documentation/git-apply.txt
@@ -12,7 +12,7 @@ SYNOPSIS
 'git-apply' [--stat] [--numstat] [--summary] [--check] [--index]
 	  [--apply] [--no-add] [--build-fake-ancestor <file>] [-R | --reverse]
 	  [--allow-binary-replacement | --binary] [--reject] [-z]
-	  [-pNUM] [-CNUM] [--inaccurate-eof] [--cached]
+	  [-pNUM] [-CNUM] [--inaccurate-eof] [--recount] [--cached]
 	  [--whitespace=<nowarn|warn|fix|error|error-all>]
 	  [--exclude=PATH] [--verbose] [<patch>...]
 
@@ -177,6 +177,11 @@ behavior:
 	current patch being applied will be printed. This option will cause
 	additional information to be reported.
 
+--recount::
+	Do not trust the line counts in the hunk headers, but infer them
+	by inspecting the patch (e.g. after editing the patch without
+	adjusting the hunk headers appropriately).
+
 Configuration
 -------------
 
diff --git a/builtin-apply.c b/builtin-apply.c
index c49788931..64cf8af8f 100644
--- a/builtin-apply.c
+++ b/builtin-apply.c
@@ -153,6 +153,7 @@ struct patch {
 	unsigned int is_binary:1;
 	unsigned int is_copy:1;
 	unsigned int is_rename:1;
+	unsigned int recount:1;
 	struct fragment *fragments;
 	char *result;
 	size_t resultsize;
@@ -882,6 +883,56 @@ static int parse_range(const char *line, int len, int offset, const char *expect
 	return offset + ex;
 }
 
+static void recount_diff(char *line, int size, struct fragment *fragment)
+{
+	int oldlines = 0, newlines = 0, ret = 0;
+
+	if (size < 1) {
+		warning("recount: ignore empty hunk");
+		return;
+	}
+
+	for (;;) {
+		int len = linelen(line, size);
+		size -= len;
+		line += len;
+
+		if (size < 1)
+			break;
+
+		switch (*line) {
+		case ' ': case '\n':
+			newlines++;
+			/* fall through */
+		case '-':
+			oldlines++;
+			continue;
+		case '+':
+			newlines++;
+			continue;
+		case '\\':
+			break;
+		case '@':
+			ret = size < 3 || prefixcmp(line, "@@ ");
+			break;
+		case 'd':
+			ret = size < 5 || prefixcmp(line, "diff ");
+			break;
+		default:
+			ret = -1;
+			break;
+		}
+		if (ret) {
+			warning("recount: unexpected line: %.*s",
+				(int)linelen(line, size), line);
+			return;
+		}
+		break;
+	}
+	fragment->oldlines = oldlines;
+	fragment->newlines = newlines;
+}
+
 /*
  * Parse a unified diff fragment header of the
  * form "@@ -a,b +c,d @@"
@@ -1013,6 +1064,8 @@ static int parse_fragment(char *line, unsigned long size,
 	offset = parse_fragment_header(line, len, fragment);
 	if (offset < 0)
 		return -1;
+	if (offset > 0 && patch->recount)
+		recount_diff(line + offset, size - offset, fragment);
 	oldlines = fragment->oldlines;
 	newlines = fragment->newlines;
 	leading = 0;
@@ -2912,7 +2965,10 @@ static void prefix_patches(struct patch *p)
 	}
 }
 
-static int apply_patch(int fd, const char *filename, int inaccurate_eof)
+#define INACCURATE_EOF	(1<<0)
+#define RECOUNT		(1<<1)
+
+static int apply_patch(int fd, const char *filename, int options)
 {
 	size_t offset;
 	struct strbuf buf;
@@ -2928,7 +2984,8 @@ static int apply_patch(int fd, const char *filename, int inaccurate_eof)
 		int nr;
 
 		patch = xcalloc(1, sizeof(*patch));
-		patch->inaccurate_eof = inaccurate_eof;
+		patch->inaccurate_eof = !!(options & INACCURATE_EOF);
+		patch->recount =  !!(options & RECOUNT);
 		nr = parse_chunk(buf.buf + offset, buf.len - offset, patch);
 		if (nr < 0)
 			break;
@@ -2997,7 +3054,7 @@ int cmd_apply(int argc, const char **argv, const char *unused_prefix)
 {
 	int i;
 	int read_stdin = 1;
-	int inaccurate_eof = 0;
+	int options = 0;
 	int errs = 0;
 	int is_not_gitdir;
 
@@ -3015,7 +3072,7 @@ int cmd_apply(int argc, const char **argv, const char *unused_prefix)
 		int fd;
 
 		if (!strcmp(arg, "-")) {
-			errs |= apply_patch(0, "<stdin>", inaccurate_eof);
+			errs |= apply_patch(0, "<stdin>", options);
 			read_stdin = 0;
 			continue;
 		}
@@ -3115,7 +3172,11 @@ int cmd_apply(int argc, const char **argv, const char *unused_prefix)
 			continue;
 		}
 		if (!strcmp(arg, "--inaccurate-eof")) {
-			inaccurate_eof = 1;
+			options |= INACCURATE_EOF;
+			continue;
+		}
+		if (!strcmp(arg, "--recount")) {
+			options |= RECOUNT;
 			continue;
 		}
 		if (0 < prefix_length)
@@ -3126,12 +3187,12 @@ int cmd_apply(int argc, const char **argv, const char *unused_prefix)
 			die("can't open patch '%s': %s", arg, strerror(errno));
 		read_stdin = 0;
 		set_default_whitespace_mode(whitespace_option);
-		errs |= apply_patch(fd, arg, inaccurate_eof);
+		errs |= apply_patch(fd, arg, options);
 		close(fd);
 	}
 	set_default_whitespace_mode(whitespace_option);
 	if (read_stdin)
-		errs |= apply_patch(0, "<stdin>", inaccurate_eof);
+		errs |= apply_patch(0, "<stdin>", options);
 	if (whitespace_error) {
 		if (squelch_whitespace_errors &&
 		    squelch_whitespace_errors < whitespace_error) {
diff --git a/t/t4100-apply-stat.sh b/t/t4100-apply-stat.sh
index 8073a5a1f..be837bb98 100755
--- a/t/t4100-apply-stat.sh
+++ b/t/t4100-apply-stat.sh
@@ -3,44 +3,36 @@
 # Copyright (c) 2005 Junio C Hamano
 #
 
-test_description='git apply --stat --summary test.
+test_description='git apply --stat --summary test, with --recount
 
 '
 . ./test-lib.sh
 
-test_expect_success \
-    'rename' \
-    'git apply --stat --summary <../t4100/t-apply-1.patch >current &&
-    test_cmp ../t4100/t-apply-1.expect current'
-
-test_expect_success \
-    'copy' \
-    'git apply --stat --summary <../t4100/t-apply-2.patch >current &&
-    test_cmp ../t4100/t-apply-2.expect current'
-
-test_expect_success \
-    'rewrite' \
-    'git apply --stat --summary <../t4100/t-apply-3.patch >current &&
-    test_cmp ../t4100/t-apply-3.expect current'
-
-test_expect_success \
-    'mode' \
-    'git apply --stat --summary <../t4100/t-apply-4.patch >current &&
-    test_cmp ../t4100/t-apply-4.expect current'
-
-test_expect_success \
-    'non git' \
-    'git apply --stat --summary <../t4100/t-apply-5.patch >current &&
-    test_cmp ../t4100/t-apply-5.expect current'
-
-test_expect_success \
-    'non git' \
-    'git apply --stat --summary <../t4100/t-apply-6.patch >current &&
-    test_cmp ../t4100/t-apply-6.expect current'
-
-test_expect_success \
-    'non git' \
-    'git apply --stat --summary <../t4100/t-apply-7.patch >current &&
-    test_cmp ../t4100/t-apply-7.expect current'
+UNC='s/^\(@@ -[1-9][0-9]*\),[0-9]* \(+[1-9][0-9]*\),[0-9]* @@/\1,999 \2,999 @@/'
+
+num=0
+while read title
+do
+	num=$(( $num + 1 ))
+	test_expect_success "$title" '
+		git apply --stat --summary \
+			<"$TEST_DIRECTORY/t4100/t-apply-$num.patch" >current &&
+		test_cmp ../t4100/t-apply-$num.expect current
+	'
+
+	test_expect_success "$title with recount" '
+		sed -e "$UNC" <"$TEST_DIRECTORY/t4100/t-apply-$num.patch" |
+		git apply --recount --stat --summary >current &&
+		test_cmp ../t4100/t-apply-$num.expect current
+	'
+done <<\EOF
+rename
+copy
+rewrite
+mode
+non git (1)
+non git (2)
+non git (3)
+EOF
 
 test_done