Teach "git apply" to prepend a prefix with "--root=<root>"

With "git apply --root=<root>", all file names in the patch are prepended
with <root>.  If a "-p" value was given, the paths are stripped _before_
prepending <root>.

Wished for by HPA.

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

Documentation/git-apply.txt

@@ -14,7 +14,7 @@ SYNOPSIS
 	  [--allow-binary-replacement | --binary] [--reject] [-z]
 	  [-pNUM] [-CNUM] [--inaccurate-eof] [--cached]
 	  [--whitespace=<nowarn|warn|fix|error|error-all>]
-	  [--exclude=PATH] [--verbose] [<patch>...]
+	  [--exclude=PATH] [--root=<root>] [--verbose] [<patch>...]
 
 DESCRIPTION
 -----------
@@ -177,6 +177,10 @@ behavior:
 	current patch being applied will be printed. This option will cause
 	additional information to be reported.
 
+--root=<root>::
+	Prepend <root> to all filenames.  If a "-p" argument was passed, too,
+	it is applied before prepending the new root.
+
 Configuration
 -------------
 

builtin-apply.c

@@ -57,6 +57,8 @@ static int whitespace_error;
 static int squelch_whitespace_errors = 5;
 static int applied_after_fixing_ws;
 static const char *patch_input_file;
+static const char *root;
+static int root_len;
 
 static void parse_whitespace_option(const char *option)
 {
@@ -331,6 +333,8 @@ static char *find_name(const char *line, char *def, int p_value, int terminate)
 				 */
 				strbuf_remove(&name, 0, cp - name.buf);
 				free(def);
+				if (root)
+					strbuf_insert(&name, 0, root, root_len);
 				return strbuf_detach(&name, NULL);
 			}
 		}
@@ -369,6 +373,14 @@ static char *find_name(const char *line, char *def, int p_value, int terminate)
 		free(def);
 	}
 
+	if (root) {
+		char *ret = xmalloc(root_len + len + 1);
+		strcpy(ret, root);
+		memcpy(ret + root_len, start, len);
+		ret[root_len + len] = '\0';
+		return ret;
+	}
+
 	return xmemdupz(start, len);
 }
 
@@ -3118,6 +3130,18 @@ int cmd_apply(int argc, const char **argv, const char *unused_prefix)
 			inaccurate_eof = 1;
 			continue;
 		}
+		if (!strncmp(arg, "--root=", strlen("--root="))) {
+			arg += strlen("--root=");
+			root_len = strlen(arg);
+			if (root_len && arg[root_len + 1] != '/') {
+				char *new_root;
+				root = new_root = xmalloc(root_len + 2);
+				strcpy(new_root, arg);
+				strcpy(new_root + root_len++, "/");
+			} else
+				root = arg;
+			continue;
+		}
 		if (0 < prefix_length)
 			arg = prefix_filename(prefix, prefix_length, arg);
 

t/t4128-apply-root.sh

@@ -0,0 +1,32 @@
+#!/bin/sh
+
+test_description='apply same filename'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+
+	mkdir -p some/sub/dir &&
+	echo Hello > some/sub/dir/file &&
+	git add some/sub/dir/file
+
+'
+
+cat > patch << EOF
+diff a/bla/blub/dir/file b/bla/blub/dir/file
+--- a/bla/blub/dir/file
++++ b/bla/blub/dir/file
+@@ -1,1 +1,1 @@
+-Hello
++Bello
+EOF
+
+test_expect_success 'apply --root -p --index' '
+
+	git apply --root=some/sub -p3 --index patch &&
+	test Bello = $(git show :some/sub/dir/file) &&
+	test Bello = $(cat some/sub/dir/file)
+
+'
+
+test_done