[PATCH 2/2] give exclude mechanism a debug option

Users can set GIT_DEBUG_IGNORE in the environment to get the
exclusion mechanism to dump to stderr files mentioned in
.gitignore along with the pattern that matched. The output
looks something like:

  foo.c: exclude: *.c

This implementation has several shortcomings that make it
unsuitable for inclusion:

  1. Doing it as a debug environment variable is hack-ish.
     A nicer interface would be a .gitignore equivalent of
     "git check-attr".

  2. If you ask for "foo/bar", and "foo/" is ignored, the
     output will show only "foo: exclude: foo". This is an
     artifact of the calling interface: you don't ask "is
     foo/bar excluded", but rather while recursing through
     "foo/" you ask "should I bother even recursing into
     foo?". So the exclusion code never even knows that you
     might have cared about foo/bar in the first place.

  3. There is no indication of where patterns came from. We
     could specify whether it came from the command-line,
     from per-directory files, or from another file. But what
     is most interesting is the actual _filename_ that it
     came from. I.e., something like:

       sub/foo.c: exclude: sub/.gitignore: *.c

     But that information seems to have been forgotten by
     the time we are actually doing excludes.

Signed-off-by: Jeff King <redacted>
---
In addition to the problems above, this is hardly tested. ;)

 dir.c |   21 +++++++++++++++++++++
 1 files changed, 21 insertions(+), 0 deletions(-)

diff --git a/dir.c b/dir.c
index 0ea81b7..1052496 100644
--- a/dir.c
+++ b/dir.c

@@ -8,6 +8,7 @@
 #include "cache.h"
 #include "dir.h"
 #include "refs.h"
+#include "quote.h"
 
 struct path_simplify {
 	int len;

@@ -354,6 +355,24 @@ static struct exclude *excluded_1(const char *pathname,
 	return NULL;
 }
 
+static int debug_ignore(void)
+{
+	static int ignore = -1;
+	if (ignore == -1) {
+		const char *env = getenv("GIT_DEBUG_IGNORE");
+		ignore = env ? git_config_bool("GIT_DEBUG_IGNORE", env) : 0;
+	}
+	return ignore;
+}
+
+static void show_ignore(const char *path, struct exclude *x)
+{
+	quote_c_style(path, NULL, stderr, 0);
+	fprintf(stderr, ": %s: %.*s\n",
+		(x->to_exclude ? "exclude" : "include"),
+		x->patternlen, x->pattern);
+}
+
 int excluded(struct dir_struct *dir, const char *pathname, int *dtype_p)
 {
 	int pathlen = strlen(pathname);

@@ -367,6 +386,8 @@ int excluded(struct dir_struct *dir, const char *pathname, int *dtype_p)
 					dtype_p, &dir->exclude_list[st]);
 		if (!x)
 			continue;
+		if (debug_ignore())
+			show_ignore(pathname, x);
 		switch (x->to_exclude) {
 		case 0:
 			return 0;

-- 
1.6.1.2.552.g1682c.dirty