[PATCH 0/9] new git check-ignore sub-command

@@ -311,7 +311,7 @@ static int no_wildcard(const char *string)
 }
 
 void add_exclude(const char *string, const char *base,
-		 int baselen, struct exclude_list *which)
+		 int baselen, struct exclude_list *el)
 {
 	struct exclude *x;
 	size_t len;

@@ -346,8 +346,8 @@ void add_exclude(const char *string, const char *base,
 	x->nowildcardlen = simple_length(string);
 	if (*string == '*' && no_wildcard(string+1))
 		x->flags |= EXC_FLAG_ENDSWITH;
-	ALLOC_GROW(which->excludes, which->nr + 1, which->alloc);
-	which->excludes[which->nr++] = x;
+	ALLOC_GROW(el->excludes, el->nr + 1, el->alloc);
+	el->excludes[el->nr++] = x;
 }
 
 static void *read_skip_worktree_file_from_index(const char *path, size_t *size)

@@ -389,7 +389,7 @@ int add_excludes_from_file_to_list(const char *fname,
 				   const char *base,
 				   int baselen,
 				   char **buf_p,
-				   struct exclude_list *which,
+				   struct exclude_list *el,
 				   int check_index)
 {
 	struct stat st;

@@ -436,7 +436,7 @@ int add_excludes_from_file_to_list(const char *fname,
 		if (buf[i] == '\n') {
 			if (entry != buf + i && entry[0] != '#') {
 				buf[i - (i && buf[i-1] == '\r')] = 0;
-				add_exclude(entry, base, baselen, which);
+				add_exclude(entry, base, baselen, el);
 			}
 			entry = buf + i + 1;
 		}

@@ -117,10 +117,10 @@ extern int path_excluded(struct path_exclude_check *, const char *, int namelen,
 
 
 extern int add_excludes_from_file_to_list(const char *fname, const char *base, int baselen,
-					  char **buf_p, struct exclude_list *which, int check_index);
+					  char **buf_p, struct exclude_list *el, int check_index);
 extern void add_excludes_from_file(struct dir_struct *, const char *fname);
 extern void add_exclude(const char *string, const char *base,
-			int baselen, struct exclude_list *which);
+			int baselen, struct exclude_list *el);
 extern void free_excludes(struct exclude_list *el);
 extern int file_exists(const char *);
 

@@ -640,6 +640,7 @@ LIB_H += pack-revindex.h
 LIB_H += pack.h
 LIB_H += parse-options.h
 LIB_H += patch-ids.h
+LIB_H += pathspec.h
 LIB_H += pkt-line.h
 LIB_H += progress.h
 LIB_H += prompt.h

@@ -760,6 +761,7 @@ LIB_OBJS += parse-options-cb.o
 LIB_OBJS += patch-delta.o
 LIB_OBJS += patch-ids.o
 LIB_OBJS += path.o
+LIB_OBJS += pathspec.o
 LIB_OBJS += pkt-line.o
 LIB_OBJS += preload-index.o
 LIB_OBJS += pretty.o

@@ -6,6 +6,7 @@
 #include "cache.h"
 #include "builtin.h"
 #include "dir.h"
+#include "pathspec.h"
 #include "exec_cmd.h"
 #include "cache-tree.h"
 #include "run-command.h"

@@ -97,39 +98,6 @@ int add_files_to_cache(const char *prefix, const char **pathspec, int flags)
 	return !!data.add_errors;
 }
 
-static void fill_pathspec_matches(const char **pathspec, char *seen, int specs)
-{
-	int num_unmatched = 0, i;
-
-	/*
-	 * Since we are walking the index as if we were walking the directory,
-	 * we have to mark the matched pathspec as seen; otherwise we will
-	 * mistakenly think that the user gave a pathspec that did not match
-	 * anything.
-	 */
-	for (i = 0; i < specs; i++)
-		if (!seen[i])
-			num_unmatched++;
-	if (!num_unmatched)
-		return;
-	for (i = 0; i < active_nr; i++) {
-		struct cache_entry *ce = active_cache[i];
-		match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, seen);
-	}
-}
-
-static char *find_used_pathspec(const char **pathspec)
-{
-	char *seen;
-	int i;
-
-	for (i = 0; pathspec[i];  i++)
-		; /* just counting */
-	seen = xcalloc(i, 1);
-	fill_pathspec_matches(pathspec, seen, i);
-	return seen;
-}
-
 static char *prune_directory(struct dir_struct *dir, const char **pathspec, int prefix)
 {
 	char *seen;

@@ -153,33 +121,6 @@ static char *prune_directory(struct dir_struct *dir, const char **pathspec, int
 	return seen;
 }
 
-static void treat_gitlinks(const char **pathspec)
-{
-	int i;
-
-	if (!pathspec || !*pathspec)
-		return;
-
-	for (i = 0; i < active_nr; i++) {
-		struct cache_entry *ce = active_cache[i];
-		if (S_ISGITLINK(ce->ce_mode)) {
-			int len = ce_namelen(ce), j;
-			for (j = 0; pathspec[j]; j++) {
-				int len2 = strlen(pathspec[j]);
-				if (len2 <= len || pathspec[j][len] != '/' ||
-				    memcmp(ce->name, pathspec[j], len))
-					continue;
-				if (len2 == len + 1)
-					/* strip trailing slash */
-					pathspec[j] = xstrndup(ce->name, len);
-				else
-					die (_("Path '%s' is in submodule '%.*s'"),
-						pathspec[j], len, ce->name);
-			}
-		}
-	}
-}
-
 static void refresh(int verbose, const char **pathspec)
 {
 	char *seen;

@@ -197,23 +138,6 @@ static void refresh(int verbose, const char **pathspec)
         free(seen);
 }
 
-static const char **validate_pathspec(int argc, const char **argv, const char *prefix)
-{
-	const char **pathspec = get_pathspec(prefix, argv);
-
-	if (pathspec) {
-		const char **p;
-		for (p = pathspec; *p; p++) {
-			if (has_symlink_leading_path(*p, strlen(*p))) {
-				int len = prefix ? strlen(prefix) : 0;
-				die(_("'%s' is beyond a symbolic link"), *p + len);
-			}
-		}
-	}
-
-	return pathspec;
-}
-
 int run_add_interactive(const char *revision, const char *patch_mode,
 			const char **pathspec)
 {

@@ -248,7 +172,7 @@ int interactive_add(int argc, const char **argv, const char *prefix, int patch)
 	const char **pathspec = NULL;
 
 	if (argc) {
-		pathspec = validate_pathspec(argc, argv, prefix);
+		pathspec = validate_pathspec(prefix, argv);
 		if (!pathspec)
 			return -1;
 	}

@@ -414,7 +338,7 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 		fprintf(stderr, _("Maybe you wanted to say 'git add .'?\n"));
 		return 0;
 	}
-	pathspec = validate_pathspec(argc, argv, prefix);
+	pathspec = validate_pathspec(prefix, argv);
 
 	if (read_cache() < 0)
 		die(_("index file corrupt"));

@@ -0,0 +1,87 @@
+#include "cache.h"
+#include "dir.h"
+
+void validate_path(const char *prefix, const char *path)
+{
+	if (has_symlink_leading_path(path, strlen(path))) {
+		int len = prefix ? strlen(prefix) : 0;
+		die(_("'%s' is beyond a symbolic link"), path + len);
+	}
+}
+
+const char **validate_pathspec(const char *prefix, const char **files)
+{
+	const char **pathspec = get_pathspec(prefix, files);
+
+	if (pathspec) {
+		const char **p;
+		for (p = pathspec; *p; p++) {
+			validate_path(prefix, *p);
+		}
+	}
+
+	return pathspec;
+}
+
+void fill_pathspec_matches(const char **pathspec, char *seen, int specs)
+{
+	int num_unmatched = 0, i;
+
+	/*
+	 * Since we are walking the index as if we were walking the directory,
+	 * we have to mark the matched pathspec as seen; otherwise we will
+	 * mistakenly think that the user gave a pathspec that did not match
+	 * anything.
+	 */
+	for (i = 0; i < specs; i++)
+		if (!seen[i])
+			num_unmatched++;
+	if (!num_unmatched)
+		return;
+	for (i = 0; i < active_nr; i++) {
+		struct cache_entry *ce = active_cache[i];
+		match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, seen);
+	}
+}
+
+char *find_used_pathspec(const char **pathspec)
+{
+	char *seen;
+	int i;
+
+	for (i = 0; pathspec[i];  i++)
+		; /* just counting */
+	seen = xcalloc(i, 1);
+	fill_pathspec_matches(pathspec, seen, i);
+	return seen;
+}
+
+void treat_gitlink(const char *path)
+{
+	int i, len = strlen(path);
+	for (i = 0; i < active_nr; i++) {
+		struct cache_entry *ce = active_cache[i];
+		if (S_ISGITLINK(ce->ce_mode)) {
+			int len2 = ce_namelen(ce);
+			if (len <= len2 || path[len2] != '/' ||
+			    memcmp(ce->name, path, len2))
+				continue;
+			if (len == len2 + 1)
+				/* strip trailing slash */
+				path = xstrndup(ce->name, len2);
+			else
+				die (_("Path '%s' is in submodule '%.*s'"),
+				     path, len2, ce->name);
+		}
+	}
+}
+
+void treat_gitlinks(const char **pathspec)
+{
+	if (!pathspec || !*pathspec)
+		return;
+
+	int i;
+	for (i = 0; pathspec[i]; i++)
+		treat_gitlink(pathspec[i]);
+}

@@ -0,0 +1,6 @@
+extern void validate_path(const char *prefix, const char *path);
+extern const char **validate_pathspec(const char *prefix, const char **files);
+extern char *find_used_pathspec(const char **pathspec);
+extern void fill_pathspec_matches(const char **pathspec, char *seen, int specs);
+extern void treat_gitlink(const char *path);
+extern void treat_gitlinks(const char **pathspec);

@@ -99,7 +99,7 @@ int cmd_clean(int argc, const char **argv, const char *prefix)
 
 	for (i = 0; i < exclude_list.nr; i++)
 		add_exclude(exclude_list.items[i].string, "", 0,
-			    &dir.exclude_list[EXC_CMDL]);
+			    &dir.exclude_list[EXC_CMDL], "--exclude option", -(i+1));
 
 	pathspec = get_pathspec(prefix, argv);
 

@@ -35,6 +35,7 @@ static int error_unmatch;
 static char *ps_matched;
 static const char *with_tree;
 static int exc_given;
+static int exclude_args = 0;
 
 static const char *tag_cached = "";
 static const char *tag_unmerged = "";

@@ -423,7 +424,7 @@ static int option_parse_exclude(const struct option *opt,
 	struct exclude_list *list = opt->value;
 
 	exc_given = 1;
-	add_exclude(arg, "", 0, list);
+	add_exclude(arg, "", 0, list, "--exclude option", --exclude_args);
 
 	return 0;
 }

@@ -311,7 +311,7 @@ static int no_wildcard(const char *string)
 }
 
 void add_exclude(const char *string, const char *base,
-		 int baselen, struct exclude_list *el)
+		 int baselen, struct exclude_list *el, const char *src, int srcpos)
 {
 	struct exclude *x;
 	size_t len;

@@ -341,6 +341,8 @@ void add_exclude(const char *string, const char *base,
 	x->base = base;
 	x->baselen = baselen;
 	x->flags = flags;
+	x->src = src;
+	x->srcpos = srcpos;
 	if (!strchr(string, '/'))
 		x->flags |= EXC_FLAG_NODIR;
 	x->nowildcardlen = simple_length(string);

@@ -393,7 +395,7 @@ int add_excludes_from_file_to_list(const char *fname,
 				   int check_index)
 {
 	struct stat st;
-	int fd, i;
+	int fd, i, lineno = 1;
 	size_t size = 0;
 	char *buf, *entry;
 

@@ -436,8 +438,9 @@ int add_excludes_from_file_to_list(const char *fname,
 		if (buf[i] == '\n') {
 			if (entry != buf + i && entry[0] != '#') {
 				buf[i - (i && buf[i-1] == '\r')] = 0;
-				add_exclude(entry, base, baselen, el);
+				add_exclude(entry, base, baselen, el, fname, lineno);
 			}
+			lineno++;
 			entry = buf + i + 1;
 		}
 	}

@@ -472,8 +475,10 @@ static void prep_exclude(struct dir_struct *dir, const char *base, int baselen)
 		    !strncmp(dir->basebuf, base, stk->baselen))
 			break;
 		dir->exclude_stack = stk->prev;
-		while (stk->exclude_ix < el->nr)
-			free(el->excludes[--el->nr]);
+		while (stk->exclude_ix < el->nr) {
+			struct exclude *exclude = el->excludes[--el->nr];
+			free(exclude);
+		}
 		free(stk->filebuf);
 		free(stk);
 	}

@@ -500,7 +505,15 @@ static void prep_exclude(struct dir_struct *dir, const char *base, int baselen)
 		memcpy(dir->basebuf + current, base + current,
 		       stk->baselen - current);
 		strcpy(dir->basebuf + stk->baselen, dir->exclude_per_dir);
-		add_excludes_from_file_to_list(dir->basebuf,
+
+		/* dir->basebuf gets reused by the traversal, but we
+		 * need fname to remain unchanged to ensure the src
+		 * member of each struct exclude correctly back-references
+		 * its source file.
+		 */
+		char *fname = strdup(dir->basebuf);
+
+		add_excludes_from_file_to_list(fname,
 					       dir->basebuf, stk->baselen,
 					       &stk->filebuf, el, 1);
 		dir->exclude_stack = stk;

@@ -31,6 +31,9 @@ struct exclude_list {
 		int baselen;
 		int to_exclude;
 		int flags;
+		const char *src;
+		int srcpos; /* counting starts from 1 for line numbers in ignore files,
+			       and from -1 decrementing for patterns from CLI (--exclude) */
 	} **excludes;
 };
 

@@ -123,7 +126,7 @@ extern int add_excludes_from_file_to_list(const char *fname, const char *base, i
 					  char **buf_p, struct exclude_list *el, int check_index);
 extern void add_excludes_from_file(struct dir_struct *, const char *fname);
 extern void add_exclude(const char *string, const char *base,
-			int baselen, struct exclude_list *el);
+			int baselen, struct exclude_list *el, const char *src, int srcpos);
 extern void free_excludes(struct exclude_list *el);
 extern int file_exists(const char *);
 

@@ -603,23 +603,42 @@ int excluded_from_list(const char *pathname,
 	return -1; /* undecided */
 }
 
-static int excluded(struct dir_struct *dir, const char *pathname, int *dtype_p)
+/*
+ * Loads the exclude lists for the directory containing pathname, then
+ * scans all exclude lists to determine whether pathname is excluded.
+ * Returns the exclude_list element which matched, or NULL for
+ * undecided.
+ */
+static struct exclude *excluded_1(struct dir_struct *dir, const char *pathname, int *dtype_p)
 {
 	int pathlen = strlen(pathname);
 	int st;
+	struct exclude *exclude;
 	const char *basename = strrchr(pathname, '/');
 	basename = (basename) ? basename+1 : pathname;
 
 	prep_exclude(dir, pathname, basename-pathname);
 	for (st = EXC_CMDL; st <= EXC_FILE; st++) {
-		switch (excluded_from_list(pathname, pathlen, basename,
-					   dtype_p, &dir->exclude_list[st])) {
-		case 0:
-			return 0;
-		case 1:
-			return 1;
+		exclude = excluded_from_list_1(pathname, pathlen, basename,
+					       dtype_p, &dir->exclude_list[st]);
+		if (exclude) {
+			return exclude;
 		}
 	}
+	return NULL;
+}
+
+/*
+ * Loads the exclude lists for the directory containing pathname, then
+ * scans all exclude lists to determine whether pathname is excluded.
+ * Returns 1 if true, otherwise 0.
+ */
+static int excluded(struct dir_struct *dir, const char *pathname, int *dtype_p)
+{
+	struct exclude *exclude = excluded_1(dir, pathname, dtype_p);
+	if (exclude) {
+		return exclude->to_exclude;
+	}
 	return 0;
 }
 

@@ -627,6 +646,7 @@ void path_exclude_check_init(struct path_exclude_check *check,
 			     struct dir_struct *dir)
 {
 	check->dir = dir;
+	check->exclude = NULL;
 	strbuf_init(&check->path, 256);
 }
 

@@ -636,18 +656,20 @@ void path_exclude_check_clear(struct path_exclude_check *check)
 }
 
 /*
- * Is this name excluded?  This is for a caller like show_files() that
- * do not honor directory hierarchy and iterate through paths that are
- * possibly in an ignored directory.
+ * For each subdirectory in name, starting with the top-most, checks
+ * to see if that subdirectory is excluded, and if so, returns the
+ * corresponding exclude structure.  Otherwise, checks whether name
+ * itself (which is presumably a file) is excluded.
  *
  * A path to a directory known to be excluded is left in check->path to
  * optimize for repeated checks for files in the same excluded directory.
  */
-int path_excluded(struct path_exclude_check *check,
-		  const char *name, int namelen, int *dtype)
+struct exclude *path_excluded_1(struct path_exclude_check *check,
+				const char *name, int namelen, int *dtype)
 {
 	int i;
 	struct strbuf *path = &check->path;
+	struct exclude *exclude;
 
 	/*
 	 * we allow the caller to pass namelen as an optimization; it

@@ -657,11 +679,18 @@ int path_excluded(struct path_exclude_check *check,
 	if (namelen < 0)
 		namelen = strlen(name);
 
+	/*
+	 * If path is non-empty, and name is equal to path or a
+	 * subdirectory of path, name should be excluded, because
+	 * it's inside a directory which is already known to be
+	 * excluded and was previously left in check->path.
+	 */
 	if (path->len &&
 	    path->len <= namelen &&
 	    !memcmp(name, path->buf, path->len) &&
-	    (!name[path->len] || name[path->len] == '/'))
-		return 1;
+	    (!name[path->len] || name[path->len] == '/')) {
+		return check->exclude;
+	}
 
 	strbuf_setlen(path, 0);
 	for (i = 0; name[i]; i++) {

@@ -669,8 +698,11 @@ int path_excluded(struct path_exclude_check *check,
 
 		if (ch == '/') {
 			int dt = DT_DIR;
-			if (excluded(check->dir, path->buf, &dt))
-				return 1;
+			exclude = excluded_1(check->dir, path->buf, &dt);
+			if (exclude) {
+				check->exclude = exclude;
+				return exclude;
+			}
 		}
 		strbuf_addch(path, ch);
 	}

@@ -678,7 +710,22 @@ int path_excluded(struct path_exclude_check *check,
 	/* An entry in the index; cannot be a directory with subentries */
 	strbuf_setlen(path, 0);
 
-	return excluded(check->dir, name, dtype);
+	return excluded_1(check->dir, name, dtype);
+}
+
+/*
+ * Is this name excluded?  This is for a caller like show_files() that
+ * do not honor directory hierarchy and iterate through paths that are
+ * possibly in an ignored directory.
+ */
+int path_excluded(struct path_exclude_check *check,
+		  const char *name, int namelen, int *dtype)
+{
+	struct exclude *exclude = path_excluded_1(check, name, namelen, dtype);
+	if (exclude) {
+		return exclude->to_exclude;
+	}
+	return 0;
 }
 
 static struct dir_entry *dir_entry_new(const char *pathname, int len)

@@ -109,10 +109,13 @@ struct dir_entry *dir_add_ignored(struct dir_struct *dir, const char *pathname,
  */
 struct path_exclude_check {
 	struct dir_struct *dir;
+	struct exclude *exclude;
 	struct strbuf path;
 };
 extern void path_exclude_check_init(struct path_exclude_check *, struct dir_struct *);
 extern void path_exclude_check_clear(struct path_exclude_check *);
+extern struct exclude *path_excluded_1(struct path_exclude_check *, const char *,
+				       int namelen, int *dtype);
 extern int path_excluded(struct path_exclude_check *, const char *, int namelen, int *dtype);
 
 

@@ -22,6 +22,7 @@
 /git-bundle
 /git-cat-file
 /git-check-attr
+/git-check-ignore
 /git-check-ref-format
 /git-checkout
 /git-checkout-index

@@ -0,0 +1,58 @@
+git-check-ignore(1)
+=================
+
+NAME
+----
+git-check-ignore - Debug gitignore / exclude files
+
+
+SYNOPSIS
+--------
+[verse]
+'git check-ignore' pathname...
+'git check-ignore' --stdin [-z] < <list-of-paths>
+
+DESCRIPTION
+-----------
+
+For each pathname given via the command-line or from a file via
+`--stdin`, this command will list the first exclude pattern found (if
+any) which explicitly excludes or includes that pathname.  Note that
+within any given exclude file, later patterns take precedence over
+earlier ones, so any matching pattern which this command outputs may
+not be the one you would immediately expect.
+
+OPTIONS
+-------
+--stdin::
+	Read file names from stdin instead of from the command-line.
+
+-z::
+	Only meaningful with `--stdin`; paths are separated with a
+	NUL character instead of a linefeed character.
+
+OUTPUT
+------
+
+The output is a series of lines of the form:
+
+<path> COLON SP <type> SP <pattern> SP <source> SP <position> LF
+
+<path> is the path of a file being queried, <type> is either
+'excluded' or 'included' (for patterns prefixed with '!'), <pattern>
+is the matching pattern, <source> is the pattern's source file (either
+as an absolute path or relative to the repository root), and
+<position> is the position of the pattern within that source.
+
+If no pattern matches a given path, nothing will be output for that
+path.
+
+SEE ALSO
+--------
+linkgit:gitignore[5]
+linkgit:gitconfig[5]
+linkgit:git-ls-files[5]
+
+GIT
+---
+Part of the linkgit:git[1] suite

@@ -155,8 +155,10 @@ The second .gitignore prevents git from ignoring
 
 SEE ALSO
 --------
-linkgit:git-rm[1], linkgit:git-update-index[1],
-linkgit:gitrepository-layout[5]
+linkgit:git-rm[1],
+linkgit:git-update-index[1],
+linkgit:gitrepository-layout[5],
+linkgit:git-check-ignore[1]
 
 GIT
 ---

@@ -825,6 +825,7 @@ BUILTIN_OBJS += builtin/branch.o
 BUILTIN_OBJS += builtin/bundle.o
 BUILTIN_OBJS += builtin/cat-file.o
 BUILTIN_OBJS += builtin/check-attr.o
+BUILTIN_OBJS += builtin/check-ignore.o
 BUILTIN_OBJS += builtin/check-ref-format.o
 BUILTIN_OBJS += builtin/checkout-index.o
 BUILTIN_OBJS += builtin/checkout.o

@@ -57,6 +57,7 @@ extern int cmd_cat_file(int argc, const char **argv, const char *prefix);
 extern int cmd_checkout(int argc, const char **argv, const char *prefix);
 extern int cmd_checkout_index(int argc, const char **argv, const char *prefix);
 extern int cmd_check_attr(int argc, const char **argv, const char *prefix);
+extern int cmd_check_ignore(int argc, const char **argv, const char *prefix);
 extern int cmd_check_ref_format(int argc, const char **argv, const char *prefix);
 extern int cmd_cherry(int argc, const char **argv, const char *prefix);
 extern int cmd_cherry_pick(int argc, const char **argv, const char *prefix);

@@ -273,7 +273,7 @@ static int add_files(struct dir_struct *dir, int flags)
 		fprintf(stderr, _(ignore_error));
 		for (i = 0; i < dir->ignored_nr; i++)
 			fprintf(stderr, "%s\n", dir->ignored[i]->name);
-		fprintf(stderr, _("Use -f if you really want to add them.\n"));
+		fprintf(stderr, _("Use -f if you really want to add them, or git check-ignore to see\nwhy they're ignored.\n"));
 		die(_("no files added"));
 	}
 

@@ -0,0 +1,150 @@
+#include "builtin.h"
+#include "cache.h"
+#include "dir.h"
+#include "quote.h"
+#include "pathspec.h"
+#include "parse-options.h"
+
+static int stdin_paths;
+static const char * const check_ignore_usage[] = {
+"git check-ignore pathname...",
+"git check-ignore --stdin [-z] < <list-of-paths>",
+NULL
+};
+
+static int null_term_line;
+
+static const struct option check_ignore_options[] = {
+	OPT_BOOLEAN(0 , "stdin", &stdin_paths, "read file names from stdin"),
+	OPT_BOOLEAN('z', NULL, &null_term_line,
+		"input paths are terminated by a null character"),
+	OPT_END()
+};
+
+static void output_exclude(const char *path, struct exclude *exclude)
+{
+	char *type = exclude->to_exclude ? "excluded" : "included";
+	char *bang = exclude->to_exclude ? "" : "!";
+	char *dir  = (exclude->flags & EXC_FLAG_MUSTBEDIR) ? "/" : "";
+	printf(_("%s: %s %s%s%s "), path, type, bang, exclude->pattern, dir);
+	if (exclude->srcpos > 0) {
+		printf("%s %d", exclude->src, exclude->srcpos);
+	}
+	else {
+		/* Exclude was from CLI parameter.  This code path is
+		 * currently impossible to hit, but later on we might
+		 * want to add ignore tracing to other commands such
+		 * as git clean, which does accept --exclude.
+		 */
+		/* printf("%s %d", exclude->src, -exclude->srcpos); */
+	}
+	printf("\n");
+}
+
+static void check_ignore(const char *prefix, const char **pathspec)
+{
+	struct dir_struct dir;
+	const char *path;
+	char *seen = NULL;
+
+	/* read_cache() is only necessary so we can watch out for submodules. */
+	if (read_cache() < 0)
+		die(_("index file corrupt"));
+
+	memset(&dir, 0, sizeof(dir));
+	dir.flags |= DIR_COLLECT_IGNORED;
+	setup_standard_excludes(&dir);
+
+	if (pathspec) {
+		int i;
+		struct path_exclude_check check;
+		struct exclude *exclude;
+
+		path_exclude_check_init(&check, &dir);
+		if (!seen)
+			seen = find_used_pathspec(pathspec);
+		for (i = 0; pathspec[i]; i++) {
+			path = pathspec[i];
+			char *full_path =
+				prefix_path(prefix, prefix ? strlen(prefix) : 0, path);
+			treat_gitlink(full_path);
+			validate_path(prefix, full_path);
+			if (!seen[i] && path[0]) {
+				int dtype = DT_UNKNOWN;
+				exclude = path_excluded_1(&check, full_path, -1, &dtype);
+				if (exclude) {
+					output_exclude(path, exclude);
+				}
+			}
+		}
+		free(seen);
+		free_directory(&dir);
+		path_exclude_check_clear(&check);
+	}
+	else {
+		printf("no pathspec\n");
+	}
+}
+
+static void check_ignore_stdin_paths(const char *prefix)
+{
+	struct strbuf buf, nbuf;
+	char **pathspec = NULL;
+	size_t nr = 0, alloc = 0;
+	int line_termination = null_term_line ? 0 : '\n';
+
+	strbuf_init(&buf, 0);
+	strbuf_init(&nbuf, 0);
+	while (strbuf_getline(&buf, stdin, line_termination) != EOF) {
+		if (line_termination && buf.buf[0] == '"') {
+			strbuf_reset(&nbuf);
+			if (unquote_c_style(&nbuf, buf.buf, NULL))
+				die("line is badly quoted");
+			strbuf_swap(&buf, &nbuf);
+		}
+		ALLOC_GROW(pathspec, nr + 1, alloc);
+		pathspec[nr] = xcalloc(strlen(buf.buf) + 1, sizeof(*buf.buf));
+		strcpy(pathspec[nr++], buf.buf);
+	}
+	ALLOC_GROW(pathspec, nr + 1, alloc);
+	pathspec[nr] = NULL;
+	check_ignore(prefix, (const char **)pathspec);
+	maybe_flush_or_die(stdout, "attribute to stdout");
+	strbuf_release(&buf);
+	strbuf_release(&nbuf);
+	free(pathspec);
+}
+
+static NORETURN void error_with_usage(const char *msg)
+{
+	error("%s", msg);
+	usage_with_options(check_ignore_usage, check_ignore_options);
+}
+
+int cmd_check_ignore(int argc, const char **argv, const char *prefix)
+{
+	git_config(git_default_config, NULL);
+
+	argc = parse_options(argc, argv, prefix, check_ignore_options,
+			     check_ignore_usage, 0);
+
+	if (stdin_paths) {
+		if (0 < argc)
+			error_with_usage("Can't specify files with --stdin");
+	} else {
+		if (null_term_line)
+			error_with_usage("-z only makes sense with --stdin");
+
+		if (argc == 0)
+			error_with_usage("No path specified");
+	}
+
+	if (stdin_paths)
+		check_ignore_stdin_paths(prefix);
+	else {
+		check_ignore(prefix, argv);
+		maybe_flush_or_die(stdout, "ignore to stdout");
+	}
+
+	return 0;
+}

@@ -12,6 +12,7 @@ git-branch                              mainporcelain common
 git-bundle                              mainporcelain
 git-cat-file                            plumbinginterrogators
 git-check-attr                          purehelpers
+git-check-ignore                        purehelpers
 git-checkout                            mainporcelain common
 git-checkout-index                      plumbingmanipulators
 git-check-ref-format                    purehelpers

@@ -594,6 +594,7 @@ __git_list_porcelain_commands ()
 		archimport)       : import;;
 		cat-file)         : plumbing;;
 		check-attr)       : plumbing;;
+		check-ignore)     : plumbing;;
 		check-ref-format) : plumbing;;
 		checkout-index)   : plumbing;;
 		commit-tree)      : plumbing;;

@@ -338,6 +338,7 @@ static void handle_internal_command(int argc, const char **argv)
 		{ "bundle", cmd_bundle, RUN_SETUP_GENTLY },
 		{ "cat-file", cmd_cat_file, RUN_SETUP },
 		{ "check-attr", cmd_check_attr, RUN_SETUP },
+		{ "check-ignore", cmd_check_ignore, RUN_SETUP | NEED_WORK_TREE },
 		{ "check-ref-format", cmd_check_ref_format },
 		{ "checkout", cmd_checkout, RUN_SETUP | NEED_WORK_TREE },
 		{ "checkout-index", cmd_checkout_index,