Specify symlink type in .gitattributes

Documentation/gitattributes.txt

@@ -378,6 +378,36 @@ sign `$` upon checkout.  Any byte sequence that begins with
 with `$Id$` upon check-in.
 
 
+`symlink`
+^^^^^^^^^
+
+On Windows, symbolic links have a type: a "file symlink" must point at
+a file, and a "directory symlink" must point at a directory. If the
+type of symlink does not match its target, it doesn't work.
+
+Git does not record the type of symlink in the index or in a tree. On
+checkout it'll guess the type, which only works if the target exists
+at the time the symlink is created. This may often not be the case,
+for example when the link points at a directory inside a submodule.
+
+The `symlink` attribute allows you to explicitly set the type of symlink
+to `file` or `dir`, so Git doesn't have to guess. If you have a set of
+symlinks that point at other files, you can do:
+
+------------------------
+*.gif 	symlink=file
+------------------------
+
+To tell Git that a symlink points at a directory, use:
+
+------------------------
+tools_folder 	symlink=dir
+------------------------
+
+The `symlink` attribute is ignored on platforms other than Windows,
+since they don't distinguish between different types of symlinks.
+
+
 `filter`
 ^^^^^^^^
 

compat/mingw.c

@@ -10,6 +10,7 @@
 #include "win32/lazyload.h"
 #include "../config.h"
 #include "../string-list.h"
+#include "../attr.h"
 
 #define HCAST(type, handle) ((type)(intptr_t)handle)
 
@@ -401,6 +402,54 @@ static void process_phantom_symlinks(void)
 	LeaveCriticalSection(&phantom_symlinks_cs);
 }
 
+static int create_phantom_symlink(wchar_t *wtarget, wchar_t *wlink)
+{
+	int len;
+
+	/* create file symlink */
+	if (!CreateSymbolicLinkW(wlink, wtarget, symlink_file_flags)) {
+		errno = err_win_to_posix(GetLastError());
+		return -1;
+	}
+
+	/* convert to directory symlink if target exists */
+	switch (process_phantom_symlink(wtarget, wlink)) {
+	case PHANTOM_SYMLINK_RETRY: {
+		/* if target doesn't exist, add to phantom symlinks list */
+		wchar_t wfullpath[MAX_LONG_PATH];
+		struct phantom_symlink_info *psi;
+
+		/* convert to absolute path to be independent of cwd */
+		len = GetFullPathNameW(wlink, MAX_LONG_PATH, wfullpath, NULL);
+		if (!len || len >= MAX_LONG_PATH) {
+			errno = err_win_to_posix(GetLastError());
+			return -1;
+		}
+
+		/* over-allocate and fill phantom_symlink_info structure */
+		psi = xmalloc(sizeof(struct phantom_symlink_info) +
+			      sizeof(wchar_t) * (len + wcslen(wtarget) + 2));
+		psi->wlink = (wchar_t *)(psi + 1);
+		wcscpy(psi->wlink, wfullpath);
+		psi->wtarget = psi->wlink + len + 1;
+		wcscpy(psi->wtarget, wtarget);
+
+		EnterCriticalSection(&phantom_symlinks_cs);
+		psi->next = phantom_symlinks;
+		phantom_symlinks = psi;
+		LeaveCriticalSection(&phantom_symlinks_cs);
+		break;
+	}
+	case PHANTOM_SYMLINK_DIRECTORY:
+		/* if we created a dir symlink, process other phantom symlinks */
+		process_phantom_symlinks();
+		break;
+	default:
+		break;
+	}
+	return 0;
+}
+
 /* Normalizes NT paths as returned by some low-level APIs. */
 static wchar_t *normalize_ntpath(wchar_t *wbuf)
 {
@@ -2819,6 +2868,35 @@ int link(const char *oldpath, const char *newpath)
 	return 0;
 }
 
+enum symlink_type {
+	SYMLINK_TYPE_UNSPECIFIED = 0,
+	SYMLINK_TYPE_FILE,
+	SYMLINK_TYPE_DIRECTORY,
+};
+
+static enum symlink_type check_symlink_attr(const char *link)
+{
+	static struct attr_check *check;
+	const char *value;
+	int r;
+
+	if (!check)
+		check = attr_check_initl("symlink", NULL);
+
+	r = git_check_attr(&the_index, link, check);
+	assert(!r);
+
+	value = check->items[0].value;
+	if (value == NULL)
+		;
+	else if (!strcmp(value, "file"))
+		return SYMLINK_TYPE_FILE;
+	else if (!strcmp(value, "dir"))
+		return SYMLINK_TYPE_DIRECTORY;
+
+	return SYMLINK_TYPE_UNSPECIFIED;
+}
+
 int symlink(const char *target, const char *link)
 {
 	wchar_t wtarget[MAX_LONG_PATH], wlink[MAX_LONG_PATH];
@@ -2839,48 +2917,31 @@ int symlink(const char *target, const char *link)
 		if (wtarget[len] == '/')
 			wtarget[len] = '\\';
 
-	/* create file symlink */
-	if (!CreateSymbolicLinkW(wlink, wtarget, symlink_file_flags)) {
-		errno = err_win_to_posix(GetLastError());
-		return -1;
-	}
-
-	/* convert to directory symlink if target exists */
-	switch (process_phantom_symlink(wtarget, wlink)) {
-	case PHANTOM_SYMLINK_RETRY:	{
-		/* if target doesn't exist, add to phantom symlinks list */
-		wchar_t wfullpath[MAX_LONG_PATH];
-		struct phantom_symlink_info *psi;
-
-		/* convert to absolute path to be independent of cwd */
-		len = GetFullPathNameW(wlink, MAX_LONG_PATH, wfullpath, NULL);
-		if (!len || len >= MAX_LONG_PATH) {
-			errno = err_win_to_posix(GetLastError());
-			return -1;
-		}
-
-		/* over-allocate and fill phantom_symlink_info structure */
-		psi = xmalloc(sizeof(struct phantom_symlink_info)
-			+ sizeof(wchar_t) * (len + wcslen(wtarget) + 2));
-		psi->wlink = (wchar_t *)(psi + 1);
-		wcscpy(psi->wlink, wfullpath);
-		psi->wtarget = psi->wlink + len + 1;
-		wcscpy(psi->wtarget, wtarget);
-
-		EnterCriticalSection(&phantom_symlinks_cs);
-		psi->next = phantom_symlinks;
-		phantom_symlinks = psi;
-		LeaveCriticalSection(&phantom_symlinks_cs);
-		break;
-	}
-	case PHANTOM_SYMLINK_DIRECTORY:
-		/* if we created a dir symlink, process other phantom symlinks */
+	switch (check_symlink_attr(link)) {
+	case SYMLINK_TYPE_UNSPECIFIED:
+		/* Create a phantom symlink: it is initially created as a file
+		 * symlink, but may change to a directory symlink later if/when
+		 * the target exists. */
+		return create_phantom_symlink(wtarget, wlink);
+	case SYMLINK_TYPE_FILE:
+		if (!CreateSymbolicLinkW(wlink, wtarget, symlink_file_flags))
+			break;
+		return 0;
+	case SYMLINK_TYPE_DIRECTORY:
+		if (!CreateSymbolicLinkW(wlink, wtarget,
+					 symlink_directory_flags))
+			break;
+		/* There may be dangling phantom symlinks that point at this
+		 * one, which should now morph into directory symlinks. */
 		process_phantom_symlinks();
-		break;
+		return 0;
 	default:
-		break;
+		BUG("unhandled symlink type");
 	}
-	return 0;
+
+	/* CreateSymbolicLinkW failed. */
+	errno = err_win_to_posix(GetLastError());
+	return -1;
 }
 
 #ifndef _WINNT_H

t/t2040-checkout-symlink-attr.sh

@@ -0,0 +1,51 @@
+#!/bin/sh
+
+test_description='checkout symlinks with `symlink` attribute on Windows
+
+Ensures that Git for Windows creates symlinks of the right type,
+as specified by the `symlink` attribute in `.gitattributes`.'
+
+# Tell MSYS to create native symlinks. Without this flag test-lib's
+# prerequisite detection for SYMLINKS doesn't detect the right thing.
+MSYS=winsymlinks:nativestrict && export MSYS
+
+. ./test-lib.sh
+
+if ! test_have_prereq MINGW,SYMLINKS
+then
+	skip_all='skipping $0: MinGW-only test, which requires symlink support.'
+	test_done
+fi
+
+# Adds a symlink to the index without clobbering the work tree.
+cache_symlink () {
+	sha=$(printf '%s' "$1" | git hash-object --stdin -w) &&
+	git update-index --add --cacheinfo 120000,$sha,"$2"
+}
+
+# MSYS2 is very forgiving, it will resolve symlinks even if the
+# symlink type isn't correct. To make this test meaningful, try
+# them with a native, non-MSYS executable.
+cat_native () {
+	filename=$(cygpath -w "$1") &&
+	cmd.exe /c "type \"$filename\""
+}
+
+test_expect_success 'checkout symlinks with attr' '
+	cache_symlink file1 file-link &&
+	cache_symlink dir dir-link &&
+
+	printf "file-link symlink=file\ndir-link symlink=dir\n" >.gitattributes &&
+	git add .gitattributes &&
+
+	git checkout . &&
+
+	mkdir dir &&
+	echo "contents1" >file1 &&
+	echo "contents2" >dir/file2 &&
+
+	test "$(cat_native file-link)" = "contents1" &&
+	test "$(cat_native dir-link/file2)" = "contents2"
+'
+
+test_done