checkout tests: test symlinks based on support, not platform

When testing whether symlinks are correctly checked out, examine the
`core.symlinks` configuration option to determine if symlinks are
supported in a repository, don't simply assume that Windows means that
symbolic links are not supported.

Further, when testing the expected default behavior of `core.symlinks`,
test the filesystem's support to determine if symlinks are supported.

Finally, ensure that `core.symlinks=true` fails on a system where
symlinks are actually not supported.  This aligns with the behavior of
Git for Windows.

tests/checkout/conflict.c

@@ -2,6 +2,7 @@
 #include "git2/repository.h"
 #include "git2/sys/index.h"
 #include "fileops.h"
+#include "repository.h"
 
 static git_repository *g_repo;
 static git_index *g_index;
@@ -184,11 +185,18 @@ static void ensure_workdir(const char *path, int mode, const char *oid_str)
 	ensure_workdir_oid(path, oid_str);
 }
 
-static void ensure_workdir_link(const char *path, const char *target)
+static void ensure_workdir_link(
+	git_repository *repo,
+	const char *path,
+	const char *target)
 {
-#ifdef GIT_WIN32
+	int symlinks;
+
+	cl_git_pass(git_repository__cvar(&symlinks, repo, GIT_CVAR_SYMLINKS));
+
+	if (!symlinks) {
 		ensure_workdir_contents(path, target);
-#else
+	} else {
 		git_buf fullpath = GIT_BUF_INIT;
 		char actual[1024];
 		struct stat st;
@@ -205,7 +213,7 @@ static void ensure_workdir_link(const char *path, const char *target)
 		cl_assert(strcmp(actual, target) == 0);
 
 		git_buf_dispose(&fullpath);
-#endif
+	}
 }
 
 void test_checkout_conflict__ignored(void)
@@ -415,8 +423,8 @@ void test_checkout_conflict__links(void)
 	cl_git_pass(git_checkout_index(g_repo, g_index, &opts));
 
 	/* Conflicts with links always keep the ours side (even with -Xtheirs) */
-	ensure_workdir_link("link-1", LINK_OURS_TARGET);
-	ensure_workdir_link("link-2", LINK_OURS_TARGET);
+	ensure_workdir_link(g_repo, "link-1", LINK_OURS_TARGET);
+	ensure_workdir_link(g_repo, "link-2", LINK_OURS_TARGET);
 }
 
 void test_checkout_conflict__add_add(void)

tests/checkout/icase.c

@@ -3,6 +3,7 @@
 #include "git2/checkout.h"
 #include "refs.h"
 #include "path.h"
+#include "repository.h"
 
 #ifdef GIT_WIN32
 # include <windows.h>
@@ -91,6 +92,18 @@ static void assert_name_is(const char *expected)
 	free(actual);
 }
 
+static int symlink_or_fake(git_repository *repo, const char *a, const char *b)
+{
+	int symlinks;
+
+	cl_git_pass(git_repository__cvar(&symlinks, repo, GIT_CVAR_SYMLINKS));
+
+	if (symlinks)
+		return p_symlink(a, b);
+	else
+		return git_futils_fake_symlink(a, b);
+}
+
 void test_checkout_icase__refuses_to_overwrite_files_for_files(void)
 {
 	checkout_opts.checkout_strategy = GIT_CHECKOUT_SAFE|GIT_CHECKOUT_RECREATE_MISSING;
@@ -117,7 +130,7 @@ void test_checkout_icase__refuses_to_overwrite_links_for_files(void)
 {
 	checkout_opts.checkout_strategy = GIT_CHECKOUT_SAFE|GIT_CHECKOUT_RECREATE_MISSING;
 
-	cl_must_pass(p_symlink("../tmp", "testrepo/BRANCH_FILE.txt"));
+	cl_must_pass(symlink_or_fake(repo, "../tmp", "testrepo/BRANCH_FILE.txt"));
 
 	cl_git_fail(git_checkout_tree(repo, obj, &checkout_opts));
 
@@ -129,7 +142,7 @@ void test_checkout_icase__overwrites_links_for_files_when_forced(void)
 {
 	checkout_opts.checkout_strategy = GIT_CHECKOUT_FORCE;
 
-	cl_must_pass(p_symlink("../tmp", "testrepo/NEW.txt"));
+	cl_must_pass(symlink_or_fake(repo, "../tmp", "testrepo/NEW.txt"));
 
 	cl_git_pass(git_checkout_tree(repo, obj, &checkout_opts));
 
@@ -205,7 +218,7 @@ void test_checkout_icase__refuses_to_overwrite_links_for_folders(void)
 {
 	checkout_opts.checkout_strategy = GIT_CHECKOUT_SAFE|GIT_CHECKOUT_RECREATE_MISSING;
 
-	cl_must_pass(p_symlink("..", "testrepo/A"));
+	cl_must_pass(symlink_or_fake(repo, "..", "testrepo/A"));
 
 	cl_git_fail(git_checkout_tree(repo, obj, &checkout_opts));
 
@@ -217,7 +230,7 @@ void test_checkout_icase__overwrites_links_for_folders_when_forced(void)
 {
 	checkout_opts.checkout_strategy = GIT_CHECKOUT_FORCE;
 
-	cl_must_pass(p_symlink("..", "testrepo/A"));
+	cl_must_pass(symlink_or_fake(repo, "..", "testrepo/A"));
 
 	cl_git_pass(git_checkout_tree(repo, obj, &checkout_opts));
 

tests/checkout/index.c

@@ -136,6 +136,25 @@ void test_checkout_index__honor_coreautocrlf_setting_set_to_true(void)
 #endif
 }
 
+static bool supports_symlinks(const char *dir)
+{
+	git_buf path = GIT_BUF_INIT;
+	struct stat st;
+	bool supports_symlinks = 1;
+
+	cl_git_pass(git_buf_joinpath(&path, dir, "test"));
+
+	/* see if symlinks are supported in the "symlink" directory */
+	if (p_symlink("target", path.ptr) < 0 ||
+	    p_lstat(path.ptr, &st) < 0 ||
+	    ! (S_ISLNK(st.st_mode)))
+		supports_symlinks = 0;
+
+	git_buf_dispose(&path);
+
+	return supports_symlinks;
+}
+
 void test_checkout_index__honor_coresymlinks_default(void)
 {
 	git_repository *repo;
@@ -162,10 +181,9 @@ void test_checkout_index__honor_coresymlinks_default(void)
 	git_object_free(target);
 	git_repository_free(repo);
 
-#ifdef GIT_WIN32
+	if (!supports_symlinks("symlink")) {
 		check_file_contents("./symlink/link_to_new.txt", "new.txt");
-#else
-	{
+	} else {
 		char link_data[1024];
 		size_t link_size = 1024;
 
@@ -175,14 +193,33 @@ void test_checkout_index__honor_coresymlinks_default(void)
 		cl_assert_equal_s(link_data, "new.txt");
 		check_file_contents("./symlink/link_to_new.txt", "my new file\n");
 	}
-#endif
 
 	cl_fixture_cleanup("symlink");
 }
 
+void test_checkout_index__coresymlinks_set_to_true_fails_when_unsupported(void)
+{
+	git_checkout_options opts = GIT_CHECKOUT_OPTIONS_INIT;
+
+	if (supports_symlinks("testrepo")) {
+		cl_skip();
+	}
+
+	cl_repo_set_bool(g_repo, "core.symlinks", true);
+
+	opts.checkout_strategy = GIT_CHECKOUT_SAFE | GIT_CHECKOUT_RECREATE_MISSING;
+	cl_git_fail(git_checkout_index(g_repo, NULL, &opts));
+}
+
 void test_checkout_index__honor_coresymlinks_setting_set_to_true(void)
 {
 	git_checkout_options opts = GIT_CHECKOUT_OPTIONS_INIT;
+	char link_data[GIT_PATH_MAX];
+	size_t link_size = GIT_PATH_MAX;
+
+	if (!supports_symlinks("testrepo")) {
+		cl_skip();
+	}
 
 	cl_repo_set_bool(g_repo, "core.symlinks", true);
 
@@ -190,20 +227,11 @@ void test_checkout_index__honor_coresymlinks_setting_set_to_true(void)
 
 	cl_git_pass(git_checkout_index(g_repo, NULL, &opts));
 
-#ifdef GIT_WIN32
-	check_file_contents("./testrepo/link_to_new.txt", "new.txt");
-#else
-	{
-		char link_data[1024];
-		size_t link_size = 1024;
-
 	link_size = p_readlink("./testrepo/link_to_new.txt", link_data, link_size);
 	link_data[link_size] = '\0';
 	cl_assert_equal_i(link_size, strlen("new.txt"));
 	cl_assert_equal_s(link_data, "new.txt");
 	check_file_contents("./testrepo/link_to_new.txt", "my new file\n");
-	}
-#endif
 }
 
 void test_checkout_index__honor_coresymlinks_setting_set_to_false(void)