patchdiff: add configuration option for disabling diff prefixes.

Documentation/config.txt, diff.c

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 92f851e..e883952 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -796,6 +796,8 @@ diff.mnemonicprefix::
 	standard "a/" and "b/" depending on what is being compared.  When
 	this configuration is in effect, reverse diff output also swaps
 	the order of the prefixes:
+diff.noprefix::
+	If set, 'git diff' does not show any source or destination prefix.
 `git diff`;;
 	compares the (i)ndex and the (w)ork tree;
 `git diff HEAD`;;
diff --git a/diff.c b/diff.c
index d0ecbc3..07269c2 100644
--- a/diff.c
+++ b/diff.c
@@ -30,6 +30,7 @@ static const char *diff_word_regex_cfg;
 static const char *external_diff_cmd_cfg;
 int diff_auto_refresh_index = 1;
 static int diff_mnemonic_prefix;
+static int diff_no_prefix;
 
 static char diff_colors[][COLOR_MAXLEN] = {
 	GIT_COLOR_RESET,
@@ -100,6 +101,10 @@ int git_diff_ui_config(const char *var, const char *value, void *cb)
 		diff_mnemonic_prefix = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "diff.noprefix")) {
+		diff_no_prefix = git_config_bool(var, value);
+		return 0;
+	}
 	if (!strcmp(var, "diff.external"))
 		return git_config_string(&external_diff_cmd_cfg, var, value);
 	if (!strcmp(var, "diff.wordregex"))
@@ -2559,7 +2564,9 @@ void diff_setup(struct diff_options *options)
 		DIFF_OPT_SET(options, COLOR_DIFF);
 	options->detect_rename = diff_detect_rename_default;
 
-	if (!diff_mnemonic_prefix) {
+	if (diff_no_prefix) {
+		options->a_prefix = options->b_prefix = "";
+	} else if (!diff_mnemonic_prefix) {
 		options->a_prefix = "a/";
 		options->b_prefix = "b/";
 	}

Documentation/config.txt, Documentation/diff-generate-patch.txt, diff.c

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 92f851e..652365e 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -807,6 +807,10 @@ diff.mnemonicprefix::
 `git diff --no-index a b`;;
 	compares two non-git things (1) and (2).
 
+diff.path::
+	Always add a 'path <path>' extended header into the diff output,
+	for non-copies and non-renames.
+
 diff.renameLimit::
 	The number of files to consider when performing the copy/rename
 	detection; equivalent to the 'git diff' option '-l'.
diff --git a/Documentation/diff-generate-patch.txt b/Documentation/diff-generate-patch.txt
index 8f9a241..67ba78f 100644
--- a/Documentation/diff-generate-patch.txt
+++ b/Documentation/diff-generate-patch.txt
@@ -30,6 +30,7 @@ the file that rename/copy produces, respectively.
        new mode <mode>
        deleted file mode <mode>
        new file mode <mode>
+       path <path>
        copy from <path>
        copy to <path>
        rename from <path>
@@ -38,6 +39,9 @@ the file that rename/copy produces, respectively.
        dissimilarity index <number>
        index <hash>..<hash> <mode>
 
+    The 'path' header will only show up, if the diff.path configure option
+    is set.
+
 3.  TAB, LF, double quote and backslash characters in pathnames
     are represented as `\t`, `\n`, `\"` and `\\`, respectively.
     If there is need for such substitution then the whole
diff --git a/diff.c b/diff.c
index d0ecbc3..fa33b9c 100644
--- a/diff.c
+++ b/diff.c
@@ -30,6 +30,7 @@ static const char *diff_word_regex_cfg;
 static const char *external_diff_cmd_cfg;
 int diff_auto_refresh_index = 1;
 static int diff_mnemonic_prefix;
+static int diff_path;
 
 static char diff_colors[][COLOR_MAXLEN] = {
 	GIT_COLOR_RESET,
@@ -104,6 +105,10 @@ int git_diff_ui_config(const char *var, const char *value, void *cb)
 		return git_config_string(&external_diff_cmd_cfg, var, value);
 	if (!strcmp(var, "diff.wordregex"))
 		return git_config_string(&diff_word_regex_cfg, var, value);
+	if (!strcmp(var, "diff.path")) {
+		diff_path = git_config_bool(var, value);
+		return 0;
+	}
 
 	return git_diff_basic_config(var, value, cb);
 }
@@ -2351,8 +2356,11 @@ static void fill_metainfo(struct strbuf *msg,
 		}
 		/* fallthru */
 	default:
-		/* nothing */
-		;
+		if (diff_path) {
+			strbuf_addstr(msg, "path ");
+			quote_c_style(name, msg, NULL, 0);
+			strbuf_addch(msg, '\n');
+		}
 	}
 	if (one && two && hashcmp(one->sha1, two->sha1)) {
 		int abbrev = DIFF_OPT_TST(o, FULL_INDEX) ? 40 : DEFAULT_ABBREV;