read-cache: optionally disallow HFS+ .git variants

The point of disallowing ".git" in the index is that we
would never want to accidentally overwrite files in the
repository directory. But this means we need to respect the
filesystem's idea of when two paths are equal. The prior
commit added a helper to make such a comparison for HFS+;
let's use it in verify_path.

We make this check optional for two reasons:

  1. It restricts the set of allowable filenames, which is
     unnecessary for people who are not on HFS+. In practice
     this probably doesn't matter, though, as the restricted
     names are rather obscure and almost certainly would
     never come up in practice.

  2. It has a minor performance penalty for every path we
     insert into the index.

This patch ties the check to the core.protectHFS config
option. Though this is expected to be most useful on OS X,
we allow it to be set everywhere, as HFS+ may be mounted on
other platforms. The variable does default to on for OS X,
though.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

8 files changed, 45 insertions, 5 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index ab26963d61..0677bd8df5 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -234,6 +234,11 @@ core.precomposeunicode::
 	When false, file names are handled fully transparent by Git,
 	which is backward compatible with older versions of Git.
 
+core.protectHFS::
+	If set to true, do not allow checkout of paths that would
+	be considered equivalent to `.git` on an HFS+ filesystem.
+	Defaults to `true` on Mac OS, and `false` elsewhere.
+
 core.trustctime::
 	If false, the ctime differences between the index and the
 	working tree are ignored; useful when the inode change time
diff --git a/cache.h b/cache.h
index ce377e1354..b600a0c3e4 100644
--- a/cache.h
+++ b/cache.h
@@ -584,6 +584,7 @@ extern int fsync_object_files;
 extern int core_preload_index;
 extern int core_apply_sparse_checkout;
 extern int precomposed_unicode;
+extern int protect_hfs;
 
 /*
  * The character that begins a commented line in user-editable file
diff --git a/config.c b/config.c
index e1d66a145b..b519cedc01 100644
--- a/config.c
+++ b/config.c
@@ -881,6 +881,11 @@ static int git_default_core_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.protecthfs")) {
+		protect_hfs = git_config_bool(var, value);
+		return 0;
+	}
+
 	/* Add other config variables here and to Documentation/config.txt. */
 	return 0;
 }
diff --git a/config.mak.uname b/config.mak.uname
index 82d549e48b..23af148837 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -97,6 +97,7 @@ ifeq ($(uname_S),Darwin)
 	HAVE_DEV_TTY = YesPlease
 	COMPAT_OBJS += compat/precompose_utf8.o
 	BASIC_CFLAGS += -DPRECOMPOSE_UNICODE
+	BASIC_CFLAGS += -DPROTECT_HFS_DEFAULT=1
 endif
 ifeq ($(uname_S),SunOS)
 	NEEDS_SOCKET = YesPlease
diff --git a/environment.c b/environment.c
index 0a15349cfe..828b574a29 100644
--- a/environment.c
+++ b/environment.c
@@ -63,6 +63,11 @@ int precomposed_unicode = -1; /* see probe_utf8_pathname_composition() */
 struct startup_info *startup_info;
 unsigned long pack_size_limit_cfg;
 
+#ifndef PROTECT_HFS_DEFAULT
+#define PROTECT_HFS_DEFAULT 0
+#endif
+int protect_hfs = PROTECT_HFS_DEFAULT;
+
 /*
  * The character that begins a commented line in user-editable file
  * that is subject to stripspace.
diff --git a/read-cache.c b/read-cache.c
index 122be494f3..7f48a08c15 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -14,6 +14,7 @@
 #include "resolve-undo.h"
 #include "strbuf.h"
 #include "varint.h"
+#include "utf8.h"
 
 static struct cache_entry *refresh_cache_entry(struct cache_entry *ce, int really);
 
@@ -786,6 +787,8 @@ int verify_path(const char *path)
 			return 1;
 		if (is_dir_sep(c)) {
 inside:
+			if (protect_hfs && is_hfs_dotgit(path))
+				return 0;
 			c = *path++;
 			if ((c == '.' && !verify_dotfile(path)) ||
 			    is_dir_sep(c) || c == '\0')
diff --git a/t/t1014-read-tree-confusing.sh b/t/t1014-read-tree-confusing.sh
index eff8aedf7a..ec310d5938 100755
--- a/t/t1014-read-tree-confusing.sh
+++ b/t/t1014-read-tree-confusing.sh
@@ -11,23 +11,39 @@ test_expect_success 'create base tree' '
 	tree=$(git rev-parse HEAD^{tree})
 '
 
-while read path; do
-	test_expect_success "reject $path at end of path" '
+test_expect_success 'enable core.protectHFS for rejection tests' '
+	git config core.protectHFS true
+'
+
+while read path pretty; do
+	: ${pretty:=$path}
+	test_expect_success "reject $pretty at end of path" '
 		printf "100644 blob %s\t%s" "$blob" "$path" >tree &&
 		bogus=$(git mktree <tree) &&
 		test_must_fail git read-tree $bogus
 	'
 
-	test_expect_success "reject $path as subtree" '
+	test_expect_success "reject $pretty as subtree" '
 		printf "040000 tree %s\t%s" "$tree" "$path" >tree &&
 		bogus=$(git mktree <tree) &&
 		test_must_fail git read-tree $bogus
 	'
-done <<-\EOF
+done <<-EOF
 .
 ..
 .git
 .GIT
+${u200c}.Git {u200c}.Git
+.gI${u200c}T .gI{u200c}T
+.GiT${u200c} .GiT{u200c}
 EOF
 
+test_expect_success 'utf-8 paths allowed with core.protectHFS off' '
+	test_when_finished "git read-tree HEAD" &&
+	test_config core.protectHFS false &&
+	printf "100644 blob %s\t%s" "$blob" ".gi${u200c}t" >tree &&
+	ok=$(git mktree <tree) &&
+	git read-tree $ok
+'
+
 test_done
diff --git a/t/test-lib.sh b/t/test-lib.sh
index b25249ec4c..d4569f8df0 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -154,7 +154,11 @@ _z40=0000000000000000000000000000000000000000
 LF='
 '
 
-export _x05 _x40 _z40 LF
+# UTF-8 ZERO WIDTH NON-JOINER, which HFS+ ignores
+# when case-folding filenames
+u200c=$(printf '\342\200\214')
+
+export _x05 _x40 _z40 LF u200c
 
 # Each test should start with something like this, after copyright notices:
 #