[PATCH] Diffcore updates.

This moves the path selection logic from individual programs to a new
diffcore transformer (diff-tree still needs to have its own for
performance reasons).  Also the header printing code in diff-tree was
tweaked not to produce anything when pickaxe is in effect and there is
nothing interesting to report.  An interesting example is the following
in the GIT archive itself:

    $ git-whatchanged -p -C -S'or something in a real script'

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 63 insertions, 0 deletions

diff --git a/diffcore-pathspec.c b/diffcore-pathspec.c
new file mode 100644
index 0000000..25ab9ed
--- /dev/null
+++ b/diffcore-pathspec.c
@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2005 Junio C Hamano
+ */
+#include "cache.h"
+#include "diff.h"
+#include "diffcore.h"
+#include "delta.h"
+
+struct path_spec {
+	const char *spec;
+	int len;
+};
+
+static int matches_pathspec(const char *name, struct path_spec *s, int cnt)
+{
+	int i;
+	int namelen;
+
+	if (cnt == 0)
+		return 1;
+
+	namelen = strlen(name);
+	for (i = 0; i < cnt; i++) {
+		int len = s->len;
+		if (! strncmp(s->spec, name, len) &&
+		    len <= namelen &&
+		    (name[len] == 0 || name[len] == '/'))
+			return 1;
+	}
+	return 0;
+}
+
+void diffcore_pathspec(const char **pathspec)
+{
+	struct diff_queue_struct *q = &diff_queued_diff;
+	int i, speccnt;
+	struct diff_queue_struct outq;
+	struct path_spec *spec;
+
+	outq.queue = NULL;
+	outq.nr = outq.alloc = 0;
+
+	for (i = 0; pathspec[i]; i++)
+		;
+	speccnt = i;
+	spec = xmalloc(sizeof(*spec) * speccnt);
+	for (i = 0; pathspec[i]; i++) {
+		spec[i].spec = pathspec[i];
+		spec[i].len = strlen(pathspec[i]);
+	}
+
+	for (i = 0; i < q->nr; i++) {
+		struct diff_filepair *p = q->queue[i];
+		if (matches_pathspec(p->one->path, spec, speccnt) ||
+		    matches_pathspec(p->two->path, spec, speccnt))
+			diff_q(&outq, p);
+		else
+			diff_free_filepair(p);
+	}
+	free(q->queue);
+	*q = outq;
+	return;
+}