patch, 4 parts.gitignore, reinclude rules, take 2

diff --git a/dir.c b/dir.c
index f0b6d0a..bcaafac 100644
--- a/dir.c
+++ b/dir.c
@@ -878,7 +878,7 @@ int match_pathname(const char *pathname, int pathlen,
 		 * then our prefix match is all we need; we
 		 * do not need to call fnmatch at all.
 		 */
-		if (!patternlen && !namelen)
+		if (!patternlen && (!namelen || *name == '/'))
 			return 1;
 	}
 

Documentation/git-check-ignore.txt, Documentation/git.txt, dir.c

diff --git a/Documentation/git-check-ignore.txt b/Documentation/git-check-ignore.txt
index e94367a..f60ee05 100644
--- a/Documentation/git-check-ignore.txt
+++ b/Documentation/git-check-ignore.txt
@@ -114,6 +114,7 @@ SEE ALSO
 linkgit:gitignore[5]
 linkgit:gitconfig[5]
 linkgit:git-ls-files[1]
+GIT_TRACE_EXCLUDE in linkgit:git[1]
 
 GIT
 ---
diff --git a/Documentation/git.txt b/Documentation/git.txt
index d987ad2..2c4f0f2 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -1064,6 +1064,11 @@ of clones and fetches.
 	cloning of shallow repositories.
 	See 'GIT_TRACE' for available trace output options.
 
+'GIT_TRACE_EXCLUDE'::
+	Enables trace messages that can help debugging .gitignore
+	processing. See 'GIT_TRACE' for available trace output
+	options.
+
 'GIT_LITERAL_PATHSPECS'::
 	Setting this variable to `1` will cause Git to treat all
 	pathspecs literally, rather than as glob patterns. For example,
diff --git a/dir.c b/dir.c
index bcaafac..0be7cf1 100644
--- a/dir.c
+++ b/dir.c
@@ -53,6 +53,8 @@ static enum path_treatment read_directory_recursive(struct dir_struct *dir,
 	int check_only, const struct path_simplify *simplify);
 static int get_dtype(struct dirent *de, const char *path, int len);
 
+static struct trace_key trace_exclude = TRACE_KEY_INIT(EXCLUDE);
+
 /* helper string functions with support for the ignore_case flag */
 int strcmp_icase(const char *a, const char *b)
 {
@@ -905,6 +907,8 @@ static struct exclude *last_exclude_matching_from_list(const char *pathname,
 	if (!el->nr)
 		return NULL;	/* undefined */
 
+	trace_printf_key(&trace_exclude, "exclude: from %s\n", el->src);
+
 	for (i = el->nr - 1; 0 <= i; i--) {
 		struct exclude *x = el->excludes[i];
 		const char *exclude = x->pattern;
@@ -936,6 +940,16 @@ static struct exclude *last_exclude_matching_from_list(const char *pathname,
 			break;
 		}
 	}
+
+	if (!exc) {
+		trace_printf_key(&trace_exclude, "exclude: %.*s => n/a\n",
+				 pathlen, pathname);
+		return NULL;
+	}
+
+	trace_printf_key(&trace_exclude, "exclude: %.*s vs %s at line %d => %s\n",
+			 pathlen, pathname, exc->pattern, exc->srcpos,
+			 exc->flags & EXC_FLAG_NEGATIVE ? "no" : "yes");
 	return exc;
 }
 
@@ -1683,9 +1697,13 @@ static enum path_treatment read_directory_recursive(struct dir_struct *dir,
 	struct cached_dir cdir;
 	enum path_treatment state, subdir_state, dir_state = path_none;
 	struct strbuf path = STRBUF_INIT;
+	static int level = 0;
 
 	strbuf_add(&path, base, baselen);
 
+	trace_printf_key(&trace_exclude, "exclude: [%d] enter '%.*s'\n",
+			 level++, baselen, base);
+
 	if (open_cached_dir(&cdir, dir, untracked, &path, check_only))
 		goto out;
 
@@ -1749,6 +1767,8 @@ static enum path_treatment read_directory_recursive(struct dir_struct *dir,
 	}
 	close_cached_dir(&cdir);
  out:
+	trace_printf_key(&trace_exclude, "exclude: [%d] leave '%.*s'\n",
+			 --level, baselen, base);
 	strbuf_release(&path);
 
 	return dir_state;

dir.c, dir.h

diff --git a/dir.c b/dir.c
index 0be7cf1..8a9d8c0 100644
--- a/dir.c
+++ b/dir.c
@@ -521,6 +521,7 @@ void add_exclude(const char *string, const char *base,
 	x->baselen = baselen;
 	x->flags = flags;
 	x->srcpos = srcpos;
+	string_list_init(&x->sticky_paths, 1);
 	ALLOC_GROW(el->excludes, el->nr + 1, el->alloc);
 	el->excludes[el->nr++] = x;
 	x->el = el;
@@ -561,8 +562,10 @@ void clear_exclude_list(struct exclude_list *el)
 {
 	int i;
 
-	for (i = 0; i < el->nr; i++)
+	for (i = 0; i < el->nr; i++) {
+		string_list_clear(&el->excludes[i]->sticky_paths, 0);
 		free(el->excludes[i]);
+	}
 	free(el->excludes);
 	free(el->filebuf);
 
@@ -889,6 +892,44 @@ int match_pathname(const char *pathname, int pathlen,
 				 WM_PATHNAME) == 0;
 }
 
+static void add_sticky(struct exclude *exc, const char *pathname, int pathlen)
+{
+	struct strbuf sb = STRBUF_INIT;
+	int i;
+
+	for (i = exc->sticky_paths.nr - 1; i >= 0; i--) {
+		const char *sticky = exc->sticky_paths.items[i].string;
+		int len = strlen(sticky);
+
+		if (pathlen < len && sticky[pathlen] == '/' &&
+		    !strncmp(pathname, sticky, pathlen))
+			return;
+	}
+
+	strbuf_add(&sb, pathname, pathlen);
+	string_list_append_nodup(&exc->sticky_paths, strbuf_detach(&sb, NULL));
+}
+
+static int match_sticky(struct exclude *exc, const char *pathname, int pathlen, int dtype)
+{
+	int i;
+
+	for (i = exc->sticky_paths.nr - 1; i >= 0; i--) {
+		const char *sticky = exc->sticky_paths.items[i].string;
+		int len = strlen(sticky);
+
+		if (pathlen == len && dtype == DT_DIR &&
+		    !strncmp(pathname, sticky, len))
+			return 1;
+
+		if (pathlen > len && pathname[len] == '/' &&
+		    !strncmp(pathname, sticky, len))
+			return 1;
+	}
+
+	return 0;
+}
+
 /*
  * Scan the given exclude list in reverse to see whether pathname
  * should be ignored.  The first match (i.e. the last on the list), if
@@ -914,6 +955,16 @@ static struct exclude *last_exclude_matching_from_list(const char *pathname,
 		const char *exclude = x->pattern;
 		int prefix = x->nowildcardlen;
 
+		if (x->sticky_paths.nr) {
+			if (*dtype == DT_UNKNOWN)
+				*dtype = get_dtype(NULL, pathname, pathlen);
+			if (match_sticky(x, pathname, pathlen, *dtype)) {
+				exc = x;
+				break;
+			}
+			continue;
+		}
+
 		if (x->flags & EXC_FLAG_MUSTBEDIR) {
 			if (*dtype == DT_UNKNOWN)
 				*dtype = get_dtype(NULL, pathname, pathlen);
@@ -947,9 +998,10 @@ static struct exclude *last_exclude_matching_from_list(const char *pathname,
 		return NULL;
 	}
 
-	trace_printf_key(&trace_exclude, "exclude: %.*s vs %s at line %d => %s\n",
+	trace_printf_key(&trace_exclude, "exclude: %.*s vs %s at line %d => %s%s\n",
 			 pathlen, pathname, exc->pattern, exc->srcpos,
-			 exc->flags & EXC_FLAG_NEGATIVE ? "no" : "yes");
+			 exc->flags & EXC_FLAG_NEGATIVE ? "no" : "yes",
+			 exc->sticky_paths.nr ? " (stuck)" : "");
 	return exc;
 }
 
@@ -2005,6 +2057,25 @@ static struct untracked_cache_dir *validate_untracked_cache(struct dir_struct *d
 	return root;
 }
 
+static void clear_sticky(struct dir_struct *dir)
+{
+	struct exclude_list_group *g;
+	struct exclude_list *el;
+	struct exclude *x;
+	int i, j, k;
+
+	for (i = EXC_CMDL; i <= EXC_FILE; i++) {
+		g = &dir->exclude_list_group[i];
+		for (j = g->nr - 1; j >= 0; j--) {
+			el = &g->el[j];
+			for (k = el->nr - 1; 0 <= k; k--) {
+				x = el->excludes[k];
+				string_list_clear(&x->sticky_paths, 0);
+			}
+		}
+	}
+}
+
 int read_directory(struct dir_struct *dir, const char *path, int len, const struct pathspec *pathspec)
 {
 	struct path_simplify *simplify;
diff --git a/dir.h b/dir.h
index cd46f30..3ec3fb0 100644
--- a/dir.h
+++ b/dir.h
@@ -4,6 +4,7 @@
 /* See Documentation/technical/api-directory-listing.txt */
 
 #include "strbuf.h"
+#include "string-list.h"
 
 struct dir_entry {
 	unsigned int len;
@@ -34,6 +35,8 @@ struct exclude {
 	 * and from -1 decrementing for patterns from CLI args.
 	 */
 	int srcpos;
+
+	struct string_list sticky_paths;
 };
 
 /*

Documentation/gitignore.txt, dir.c, t/t3001-ls-files-others-exclude.sh, t/t3007-ls-files-other-negative.sh

diff --git a/Documentation/gitignore.txt b/Documentation/gitignore.txt
index 473623d..3ded6fd 100644
--- a/Documentation/gitignore.txt
+++ b/Documentation/gitignore.txt
@@ -82,12 +82,12 @@ PATTERN FORMAT
 
  - An optional prefix "`!`" which negates the pattern; any
    matching file excluded by a previous pattern will become
-   included again. It is not possible to re-include a file if a parent
-   directory of that file is excluded. Git doesn't list excluded
-   directories for performance reasons, so any patterns on contained
-   files have no effect, no matter where they are defined.
+   included again.
    Put a backslash ("`\`") in front of the first "`!`" for patterns
    that begin with a literal "`!`", for example, "`\!important!.txt`".
+   It is possible to re-include a file if a parent directory of that
+   file is excluded if certain conditions are met. See section NOTES
+   for detail.
 
  - If the pattern ends with a slash, it is removed for the
    purpose of the following description, but it would only find
@@ -141,6 +141,15 @@ not tracked by Git remain untracked.
 To stop tracking a file that is currently tracked, use
 'git rm --cached'.
 
+To re-include files or directories when their parent directory is
+excluded, the following conditions must be met:
+
+ - The rules to exclude a directory and re-include a subset back must
+   be in the same .gitignore file.
+
+ - The directory part in the re-include rules must be literal (i.e. no
+   wildcards)
+
 EXAMPLES
 --------
 
diff --git a/dir.c b/dir.c
index 8a9d8c0..552af23 100644
--- a/dir.c
+++ b/dir.c
@@ -930,6 +930,75 @@ static int match_sticky(struct exclude *exc, const char *pathname, int pathlen,
 	return 0;
 }
 
+static inline int different_decisions(const struct exclude *a,
+				      const struct exclude *b)
+{
+	return (a->flags & EXC_FLAG_NEGATIVE) != (b->flags & EXC_FLAG_NEGATIVE);
+}
+
+/*
+ * Return non-zero if pathname is a directory and an ancestor of the
+ * literal path in a pattern.
+ */
+static int match_directory_part(const char *pathname, int pathlen,
+				int *dtype, struct exclude *x)
+{
+	const char	*base	    = x->base;
+	int		 baselen    = x->baselen ? x->baselen - 1 : 0;
+	const char	*pattern    = x->pattern;
+	int		 prefix	    = x->nowildcardlen;
+	int		 patternlen = x->patternlen;
+
+	if (*dtype == DT_UNKNOWN)
+		*dtype = get_dtype(NULL, pathname, pathlen);
+	if (*dtype != DT_DIR)
+		return 0;
+
+	if (*pattern == '/') {
+		pattern++;
+		patternlen--;
+		prefix--;
+	}
+
+	if (baselen) {
+		if (((pathlen < baselen && base[pathlen] == '/') ||
+		     pathlen == baselen) &&
+		    !strncmp_icase(pathname, base, pathlen))
+			return 1;
+		pathname += baselen + 1;
+		pathlen  -= baselen + 1;
+	}
+
+
+	if (prefix &&
+	    (((pathlen < prefix && pattern[pathlen] == '/') ||
+	      pathlen == prefix) &&
+	     !strncmp_icase(pathname, pattern, pathlen)))
+		return 1;
+
+	return 0;
+}
+
+static struct exclude *should_descend(const char *pathname, int pathlen,
+				      int *dtype, struct exclude_list *el,
+				      struct exclude *exc)
+{
+	int i;
+
+	for (i = el->nr - 1; 0 <= i; i--) {
+		struct exclude *x = el->excludes[i];
+
+		if (x == exc)
+			break;
+
+		if (!(x->flags & EXC_FLAG_NODIR) &&
+		    different_decisions(x, exc) &&
+		    match_directory_part(pathname, pathlen, dtype, x))
+			return x;
+	}
+	return NULL;
+}
+
 /*
  * Scan the given exclude list in reverse to see whether pathname
  * should be ignored.  The first match (i.e. the last on the list), if
@@ -943,7 +1012,7 @@ static struct exclude *last_exclude_matching_from_list(const char *pathname,
 						       struct exclude_list *el)
 {
 	struct exclude *exc = NULL; /* undecided */
-	int i;
+	int i, maybe_descend = 0;
 
 	if (!el->nr)
 		return NULL;	/* undefined */
@@ -955,6 +1024,10 @@ static struct exclude *last_exclude_matching_from_list(const char *pathname,
 		const char *exclude = x->pattern;
 		int prefix = x->nowildcardlen;
 
+		if (!maybe_descend && i < el->nr - 1 &&
+		    different_decisions(x, el->excludes[i+1]))
+			maybe_descend = 1;
+
 		if (x->sticky_paths.nr) {
 			if (*dtype == DT_UNKNOWN)
 				*dtype = get_dtype(NULL, pathname, pathlen);
@@ -998,6 +1071,34 @@ static struct exclude *last_exclude_matching_from_list(const char *pathname,
 		return NULL;
 	}
 
+	/*
+	 * We have found a matching pattern "exc" that may exclude whole
+	 * directory. We also found that there may be a pattern that matches
+	 * something inside the directory and reincludes stuff.
+	 *
+	 * Go through the patterns again, find that pattern and double check.
+	 * If it's true, return "undecided" and keep descending in. "exc" is
+	 * marked sticky so that it continues to match inside the directory.
+	 */
+	if (!(exc->flags & EXC_FLAG_NEGATIVE) && maybe_descend) {
+		struct exclude *x;
+
+		if (*dtype == DT_UNKNOWN)
+			*dtype = get_dtype(NULL, pathname, pathlen);
+
+		if (*dtype == DT_DIR &&
+		    (x = should_descend(pathname, pathlen, dtype, el, exc))) {
+			add_sticky(exc, pathname, pathlen);
+			trace_printf_key(&trace_exclude,
+					 "exclude: %.*s vs %s at line %d => %s,"
+					 " forced open by %s at line %d => n/a\n",
+					 pathlen, pathname, exc->pattern, exc->srcpos,
+					 exc->flags & EXC_FLAG_NEGATIVE ? "no" : "yes",
+					 x->pattern, x->srcpos);
+			return NULL;
+		}
+	}
+
 	trace_printf_key(&trace_exclude, "exclude: %.*s vs %s at line %d => %s%s\n",
 			 pathlen, pathname, exc->pattern, exc->srcpos,
 			 exc->flags & EXC_FLAG_NEGATIVE ? "no" : "yes",
@@ -2097,6 +2198,12 @@ int read_directory(struct dir_struct *dir, const char *path, int len, const stru
 		return dir->nr;
 
 	/*
+	 * Stay on the safe side. if read_directory() has run once on
+	 * "dir", some sticky flag may have been left. Clear them all.
+	 */
+	clear_sticky(dir);
+
+	/*
 	 * exclude patterns are treated like positive ones in
 	 * create_simplify. Usually exclude patterns should be a
 	 * subset of positive ones, which has no impacts on
diff --git a/t/t3001-ls-files-others-exclude.sh b/t/t3001-ls-files-others-exclude.sh
index 3fc484e..d043078 100755
--- a/t/t3001-ls-files-others-exclude.sh
+++ b/t/t3001-ls-files-others-exclude.sh
@@ -175,13 +175,10 @@ test_expect_success 'negated exclude matches can override previous ones' '
 	grep "^a.1" output
 '
 
-test_expect_success 'excluded directory overrides content patterns' '
+test_expect_success 'excluded directory does not override content patterns' '
 
 	git ls-files --others --exclude="one" --exclude="!one/a.1" >output &&
-	if grep "^one/a.1" output
-	then
-		false
-	fi
+	grep "^one/a.1" output
 '
 
 test_expect_success 'negated directory doesn'\''t affect content patterns' '
diff --git a/t/t3007-ls-files-other-negative.sh b/t/t3007-ls-files-other-negative.sh
new file mode 100755
index 0000000..0797b86
--- /dev/null
+++ b/t/t3007-ls-files-other-negative.sh
@@ -0,0 +1,153 @@
+#!/bin/sh
+
+test_description='test re-include patterns'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	mkdir -p fooo foo/bar tmp &&
+	touch abc foo/def foo/bar/ghi foo/bar/bar
+'
+
+test_expect_success 'no match, do not enter subdir and waste cycles' '
+	cat >.gitignore <<-\EOF &&
+	/tmp
+	/foo
+	!fooo/bar/bar
+	EOF
+	GIT_TRACE_EXCLUDE="$(pwd)/tmp/trace" git ls-files -o --exclude-standard >tmp/actual &&
+	! grep "enter .foo/.\$" tmp/trace &&
+	cat >tmp/expected <<-\EOF &&
+	.gitignore
+	abc
+	EOF
+	test_cmp tmp/expected tmp/actual
+'
+
+test_expect_success 'match, excluded by literal pathname pattern' '
+	cat >.gitignore <<-\EOF &&
+	/tmp
+	/fooo
+	/foo
+	!foo/bar/bar
+	EOF
+	cat >fooo/.gitignore <<-\EOF &&
+	!/*
+	EOF	git ls-files -o --exclude-standard >tmp/actual &&
+	cat >tmp/expected <<-\EOF &&
+	.gitignore
+	abc
+	foo/bar/bar
+	EOF
+	test_cmp tmp/expected tmp/actual
+'
+
+test_expect_success 'match, excluded by wildcard pathname pattern' '
+	cat >.gitignore <<-\EOF &&
+	/tmp
+	/fooo
+	/fo?
+	!foo/bar/bar
+	EOF
+	git ls-files -o --exclude-standard >tmp/actual &&
+	cat >tmp/expected <<-\EOF &&
+	.gitignore
+	abc
+	foo/bar/bar
+	EOF
+	test_cmp tmp/expected tmp/actual
+'
+
+test_expect_success 'match, excluded by literal basename pattern' '
+	cat >.gitignore <<-\EOF &&
+	/tmp
+	/fooo
+	foo
+	!foo/bar/bar
+	EOF
+	git ls-files -o --exclude-standard >tmp/actual &&
+	cat >tmp/expected <<-\EOF &&
+	.gitignore
+	abc
+	foo/bar/bar
+	EOF
+	test_cmp tmp/expected tmp/actual
+'
+
+test_expect_success 'match, excluded by wildcard basename pattern' '
+	cat >.gitignore <<-\EOF &&
+	/tmp
+	/fooo
+	fo?
+	!foo/bar/bar
+	EOF
+	git ls-files -o --exclude-standard >tmp/actual &&
+	cat >tmp/expected <<-\EOF &&
+	.gitignore
+	abc
+	foo/bar/bar
+	EOF
+	test_cmp tmp/expected tmp/actual
+'
+
+test_expect_success 'match, excluded by literal mustbedir, basename pattern' '
+	cat >.gitignore <<-\EOF &&
+	/tmp
+	/fooo
+	foo/
+	!foo/bar/bar
+	EOF
+	git ls-files -o --exclude-standard >tmp/actual &&
+	cat >tmp/expected <<-\EOF &&
+	.gitignore
+	abc
+	foo/bar/bar
+	EOF
+	test_cmp tmp/expected tmp/actual
+'
+
+test_expect_success 'match, excluded by literal mustbedir, pathname pattern' '
+	cat >.gitignore <<-\EOF &&
+	/tmp
+	/fooo
+	/foo/
+	!foo/bar/bar
+	EOF
+	git ls-files -o --exclude-standard >tmp/actual &&
+	cat >tmp/expected <<-\EOF &&
+	.gitignore
+	abc
+	foo/bar/bar
+	EOF
+	test_cmp tmp/expected tmp/actual
+'
+
+test_expect_success 'prepare for nested negatives' '
+	cat >.git/info/exclude <<-\EOF &&
+	/.gitignore
+	/tmp
+	/foo
+	/abc
+	EOF
+	git ls-files -o --exclude-standard >tmp/actual &&
+	test_must_be_empty tmp/actual &&
+	mkdir -p 1/2/3/4 &&
+	touch 1/f 1/2/f 1/2/3/f 1/2/3/4/f
+'
+
+test_expect_success 'match, literal pathname, nested negatives' '
+	cat >.gitignore <<-\EOF &&
+	/1
+	!1/2
+	1/2/3
+	!1/2/3/4
+	EOF
+	git ls-files -o --exclude-standard >tmp/actual &&
+	cat >tmp/expected <<-\EOF &&
+	1/2/3/4/f
+	1/2/f
+	EOF
+	test_cmp tmp/expected tmp/actual
+'
+
+test_done