Per-path attribute based hunk header selection.

This makes"diff -p" hunk headers customizable via gitattributes mechanism.
It is based on Johannes's earlier patch that allowed to define a single
regexp to be used for everything.

The mechanism to arrive at the regexp that is used to define hunk header
is the same as other use of gitattributes.  You assign an attribute, funcname
(because "diff -p" typically uses the name of the function the patch is about
as the hunk header), a simple string value.  This can be one of the names of
built-in pattern (currently, "java" is defined) or a custom pattern name, to
be looked up from the configuration file.

  (in .gitattributes)
  *.java   funcname=java
  *.perl   funcname=perl

  (in .git/config)
  [funcname]
    java = ... # ugly and complicated regexp to override the built-in one.
    perl = ... # another ugly and complicated regexp to define a new one.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 95 insertions, 1 deletions

diff --git a/diff.c b/diff.c
index d10e848c7..04e7e91ad 100644
--- a/diff.c
+++ b/diff.c
@@ -1101,22 +1101,26 @@ static void emit_binary_diff(mmfile_t *one, mmfile_t *two)
 static void setup_diff_attr_check(struct git_attr_check *check)
 {
 	static struct git_attr *attr_diff;
+	static struct git_attr *attr_diff_func_name;
 
 	if (!attr_diff) {
 		attr_diff = git_attr("diff", 4);
+		attr_diff_func_name = git_attr("funcname", 8);
 	}
 	check[0].attr = attr_diff;
+	check[1].attr = attr_diff_func_name;
 }
 
 static void diff_filespec_check_attr(struct diff_filespec *one)
 {
-	struct git_attr_check attr_diff_check[1];
+	struct git_attr_check attr_diff_check[2];
 
 	if (one->checked_attr)
 		return;
 
 	setup_diff_attr_check(attr_diff_check);
 	one->is_binary = 0;
+	one->hunk_header_ident = NULL;
 
 	if (!git_checkattr(one->path, ARRAY_SIZE(attr_diff_check), attr_diff_check)) {
 		const char *value;
@@ -1127,6 +1131,13 @@ static void diff_filespec_check_attr(struct diff_filespec *one)
 			;
 		else if (ATTR_FALSE(value))
 			one->is_binary = 1;
+
+		/* hunk header ident */
+		value = attr_diff_check[1].value;
+		if (ATTR_TRUE(value) || ATTR_FALSE(value) || ATTR_UNSET(value))
+			;
+		else
+			one->hunk_header_ident = value;
 	}
 
 	if (!one->data && DIFF_FILE_VALID(one))
@@ -1143,6 +1154,82 @@ int diff_filespec_is_binary(struct diff_filespec *one)
 	return one->is_binary;
 }
 
+static struct hunk_header_regexp {
+	char *name;
+	char *regexp;
+	struct hunk_header_regexp *next;
+} *hunk_header_regexp_list, **hunk_header_regexp_tail;
+
+static int hunk_header_config(const char *var, const char *value)
+{
+	static const char funcname[] = "funcname.";
+	struct hunk_header_regexp *hh;
+
+	if (prefixcmp(var, funcname))
+		return 0;
+	var += strlen(funcname);
+	for (hh = hunk_header_regexp_list; hh; hh = hh->next)
+		if (!strcmp(var, hh->name)) {
+			free(hh->regexp);
+			hh->regexp = xstrdup(value);
+			return 0;
+		}
+	hh = xcalloc(1, sizeof(*hh));
+	hh->name = xstrdup(var);
+	hh->regexp = xstrdup(value);
+	hh->next = NULL;
+	*hunk_header_regexp_tail = hh;
+	return 0;
+}
+
+static const char *hunk_header_regexp(const char *ident)
+{
+	struct hunk_header_regexp *hh;
+
+	if (!hunk_header_regexp_tail) {
+		hunk_header_regexp_tail = &hunk_header_regexp_list;
+		git_config(hunk_header_config);
+	}
+	for (hh = hunk_header_regexp_list; hh; hh = hh->next)
+		if (!strcmp(ident, hh->name))
+			return hh->regexp;
+	return NULL;
+}
+
+static const char *diff_hunk_header_regexp(struct diff_filespec *one)
+{
+	const char *ident, *regexp;
+
+	diff_filespec_check_attr(one);
+	ident = one->hunk_header_ident;
+
+	if (!ident)
+		/*
+		 * If the config file has "funcname.default" defined, that
+		 * regexp is used; otherwise NULL is returned and xemit uses
+		 * the built-in default.
+		 */
+		return hunk_header_regexp("default");
+
+	/* Look up custom "funcname.$ident" regexp from config. */
+	regexp = hunk_header_regexp(ident);
+	if (regexp)
+		return regexp;
+
+	/*
+	 * And define built-in fallback patterns here.  Note that
+	 * these can be overriden by the user's config settings.
+	 */
+	if (!strcmp(ident, "java"))
+		return "!^[ 	]*\\(catch\\|do\\|for\\|if\\|instanceof\\|"
+			"new\\|return\\|switch\\|throw\\|while\\)\n"
+			"^[ 	]*\\(\\([ 	]*"
+			"[A-Za-z_][A-Za-z_0-9]*\\)\\{2,\\}"
+			"[ 	]*([^;]*$\\)";
+
+	return NULL;
+}
+
 static void builtin_diff(const char *name_a,
 			 const char *name_b,
 			 struct diff_filespec *one,
@@ -1217,6 +1304,11 @@ static void builtin_diff(const char *name_a,
 		xdemitconf_t xecfg;
 		xdemitcb_t ecb;
 		struct emit_callback ecbdata;
+		const char *hunk_header_regexp;
+
+		hunk_header_regexp = diff_hunk_header_regexp(one);
+		if (!hunk_header_regexp)
+			hunk_header_regexp = diff_hunk_header_regexp(two);
 
 		memset(&xecfg, 0, sizeof(xecfg));
 		memset(&ecbdata, 0, sizeof(ecbdata));
@@ -1226,6 +1318,8 @@ static void builtin_diff(const char *name_a,
 		xpp.flags = XDF_NEED_MINIMAL | o->xdl_opts;
 		xecfg.ctxlen = o->context;
 		xecfg.flags = XDL_EMIT_FUNCNAMES;
+		if (hunk_header_regexp)
+			xdiff_set_find_func(&xecfg, hunk_header_regexp);
 		if (!diffopts)
 			;
 		else if (!prefixcmp(diffopts, "--unified="))