add git-check-ignore sub-command

This works in a similar manner to git-check-attr.

Thanks to Jeff King and Junio C Hamano for the idea:
http://thread.gmane.org/gmane.comp.version-control.git/108671/focus=108815

Signed-off-by: Adam Spiers <git@adamspiers.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitignore

@@ -19,6 +19,7 @@
 /git-bundle
 /git-cat-file
 /git-check-attr
+/git-check-ignore
 /git-check-ref-format
 /git-checkout
 /git-checkout-index

Documentation/git-check-ignore.txt

@@ -0,0 +1,89 @@
+git-check-ignore(1)
+===================
+
+NAME
+----
+git-check-ignore - Debug gitignore / exclude files
+
+
+SYNOPSIS
+--------
+[verse]
+'git check-ignore' [options] pathname...
+'git check-ignore' [options] --stdin < <list-of-paths>
+
+DESCRIPTION
+-----------
+
+For each pathname given via the command-line or from a file via
+`--stdin`, show the pattern from .gitignore (or other input files to
+the exclude mechanism) that decides if the pathname is excluded or
+included.  Later patterns within a file take precedence over earlier
+ones.
+
+OPTIONS
+-------
+-q, --quiet::
+	Don't output anything, just set exit status.  This is only
+	valid with a single pathname.
+
+-v, --verbose::
+	Also output details about the matching pattern (if any)
+	for each given pathname.
+
+--stdin::
+	Read file names from stdin instead of from the command-line.
+
+-z::
+	The output format is modified to be machine-parseable (see
+	below).  If `--stdin` is also given, input paths are separated
+	with a NUL character instead of a linefeed character.
+
+OUTPUT
+------
+
+By default, any of the given pathnames which match an ignore pattern
+will be output, one per line.  If no pattern matches a given path,
+nothing will be output for that path; this means that path will not be
+ignored.
+
+If `--verbose` is specified, the output is a series of lines of the form:
+
+<source> <COLON> <linenum> <COLON> <pattern> <HT> <pathname>
+
+<pathname> is the path of a file being queried, <pattern> is the
+matching pattern, <source> is the pattern's source file, and <linenum>
+is the line number of the pattern within that source.  If the pattern
+contained a `!` prefix or `/` suffix, it will be preserved in the
+output.  <source> will be an absolute path when referring to the file
+configured by `core.excludesfile`, or relative to the repository root
+when referring to `.git/info/exclude` or a per-directory exclude file.
+
+If `-z` is specified, the pathnames in the output are delimited by the
+null character; if `--verbose` is also specified then null characters
+are also used instead of colons and hard tabs:
+
+<source> <NULL> <linenum> <NULL> <pattern> <NULL> <pathname> <NULL>
+
+
+EXIT STATUS
+-----------
+
+0::
+	One or more of the provided paths is ignored.
+
+1::
+	None of the provided paths are ignored.
+
+128::
+	A fatal error was encountered.
+
+SEE ALSO
+--------
+linkgit:gitignore[5]
+linkgit:gitconfig[5]
+linkgit:git-ls-files[5]
+
+GIT
+---
+Part of the linkgit:git[1] suite

Documentation/gitignore.txt

@@ -153,8 +153,10 @@ 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
 ---

Documentation/technical/api-directory-listing.txt

@@ -81,6 +81,6 @@ marked. If you to exclude files, make sure you have loaded index first.
 
 * Use `dir.entries[]`.
 
-* Call `free_directory()` when none of the contained elements are no longer in use.
+* Call `clear_directory()` when none of the contained elements are no longer in use.
 
 (JC)

Makefile

@@ -822,6 +822,7 @@ 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

builtin.h

@@ -58,6 +58,7 @@ 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);

builtin/check-ignore.c

@@ -0,0 +1,173 @@
+#include "builtin.h"
+#include "cache.h"
+#include "dir.h"
+#include "quote.h"
+#include "pathspec.h"
+#include "parse-options.h"
+
+static int quiet, verbose, stdin_paths;
+static const char * const check_ignore_usage[] = {
+"git check-ignore [options] pathname...",
+"git check-ignore [options] --stdin < <list-of-paths>",
+NULL
+};
+
+static int null_term_line;
+
+static const struct option check_ignore_options[] = {
+	OPT__QUIET(&quiet, N_("suppress progress reporting")),
+	OPT__VERBOSE(&verbose, N_("be verbose")),
+	OPT_GROUP(""),
+	OPT_BOOLEAN(0, "stdin", &stdin_paths,
+		    N_("read file names from stdin")),
+	OPT_BOOLEAN('z', NULL, &null_term_line,
+		    N_("input paths are terminated by a null character")),
+	OPT_END()
+};
+
+static void output_exclude(const char *path, struct exclude *exclude)
+{
+	char *bang  = exclude->flags & EXC_FLAG_NEGATIVE  ? "!" : "";
+	char *slash = exclude->flags & EXC_FLAG_MUSTBEDIR ? "/" : "";
+	if (!null_term_line) {
+		if (!verbose) {
+			write_name_quoted(path, stdout, '\n');
+		} else {
+			quote_c_style(exclude->el->src, NULL, stdout, 0);
+			printf(":%d:%s%s%s\t",
+			       exclude->srcpos,
+			       bang, exclude->pattern, slash);
+			quote_c_style(path, NULL, stdout, 0);
+			fputc('\n', stdout);
+		}
+	} else {
+		if (!verbose) {
+			printf("%s%c", path, '\0');
+		} else {
+			printf("%s%c%d%c%s%s%s%c%s%c",
+			       exclude->el->src, '\0',
+			       exclude->srcpos, '\0',
+			       bang, exclude->pattern, slash, '\0',
+			       path, '\0');
+		}
+	}
+}
+
+static int check_ignore(const char *prefix, const char **pathspec)
+{
+	struct dir_struct dir;
+	const char *path, *full_path;
+	char *seen;
+	int num_ignored = 0, dtype = DT_UNKNOWN, i;
+	struct path_exclude_check check;
+	struct exclude *exclude;
+
+	/* 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 || !*pathspec) {
+		if (!quiet)
+			fprintf(stderr, "no pathspec given.\n");
+		return 0;
+	}
+
+	path_exclude_check_init(&check, &dir);
+	/*
+	 * look for pathspecs matching entries in the index, since these
+	 * should not be ignored, in order to be consistent with
+	 * 'git status', 'git add' etc.
+	 */
+	seen = find_pathspecs_matching_against_index(pathspec);
+	for (i = 0; pathspec[i]; i++) {
+		path = pathspec[i];
+		full_path = prefix_path(prefix, prefix
+					? strlen(prefix) : 0, path);
+		full_path = check_path_for_gitlink(full_path);
+		die_if_path_beyond_symlink(full_path, prefix);
+		if (!seen[i] && path[0]) {
+			exclude = last_exclude_matching_path(&check, full_path,
+							     -1, &dtype);
+			if (exclude) {
+				if (!quiet)
+					output_exclude(path, exclude);
+				num_ignored++;
+			}
+		}
+	}
+	free(seen);
+	clear_directory(&dir);
+	path_exclude_check_clear(&check);
+
+	return num_ignored;
+}
+
+static int 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';
+	int num_ignored;
+
+	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;
+	num_ignored = check_ignore(prefix, (const char **)pathspec);
+	maybe_flush_or_die(stdout, "attribute to stdout");
+	strbuf_release(&buf);
+	strbuf_release(&nbuf);
+	free(pathspec);
+	return num_ignored;
+}
+
+int cmd_check_ignore(int argc, const char **argv, const char *prefix)
+{
+	int num_ignored;
+
+	git_config(git_default_config, NULL);
+
+	argc = parse_options(argc, argv, prefix, check_ignore_options,
+			     check_ignore_usage, 0);
+
+	if (stdin_paths) {
+		if (argc > 0)
+			die(_("cannot specify pathnames with --stdin"));
+	} else {
+		if (null_term_line)
+			die(_("-z only makes sense with --stdin"));
+		if (argc == 0)
+			die(_("no path specified"));
+	}
+	if (quiet) {
+		if (argc > 1)
+			die(_("--quiet is only valid with a single pathname"));
+		if (verbose)
+			die(_("cannot have both --quiet and --verbose"));
+	}
+
+	if (stdin_paths) {
+		num_ignored = check_ignore_stdin_paths(prefix);
+	} else {
+		num_ignored = check_ignore(prefix, argv);
+		maybe_flush_or_die(stdout, "ignore to stdout");
+	}
+
+	return !num_ignored;
+}

command-list.txt

@@ -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

contrib/completion/git-completion.bash

@@ -842,6 +842,7 @@ __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;;

git.c

@@ -340,6 +340,7 @@ 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,