check: fix cachedir creation when using default location

changelog/unreleased/issue-4437

@@ -7,3 +7,4 @@ The  `check` command now attempts to create the cache directory before initializ
 
 https://github.com/restic/restic/issues/4437
 https://github.com/restic/restic/pull/4805
+https://github.com/restic/restic/pull/4883

cmd/restic/cmd_check.go

@@ -176,12 +176,14 @@ func prepareCheckCache(opts CheckOptions, gopts *GlobalOptions, printer progress
 		cachedir = cache.EnvDir()
 	}
 
-	// use a cache in a temporary directory
-	err := os.MkdirAll(cachedir, 0755)
-	if err != nil {
-		Warnf("unable to create cache directory %s, disabling cache: %v\n", cachedir, err)
-		gopts.NoCache = true
-		return cleanup
+	if cachedir != "" {
+		// use a cache in a temporary directory
+		err := os.MkdirAll(cachedir, 0755)
+		if err != nil {
+			Warnf("unable to create cache directory %s, disabling cache: %v\n", cachedir, err)
+			gopts.NoCache = true
+			return cleanup
+		}
 	}
 	tempdir, err := os.MkdirTemp(cachedir, "restic-check-cache-")
 	if err != nil {

cmd/restic/cmd_check_test.go

@@ -8,6 +8,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/restic"
 	rtest "github.com/restic/restic/internal/test"
 	"github.com/restic/restic/internal/ui/progress"
@@ -229,3 +230,17 @@ func TestPrepareCheckCache(t *testing.T) {
 		})
 	}
 }
+
+func TestPrepareDefaultCheckCache(t *testing.T) {
+	gopts := GlobalOptions{CacheDir: ""}
+	cleanup := prepareCheckCache(CheckOptions{}, &gopts, &progress.NoopPrinter{})
+	_, err := os.ReadDir(gopts.CacheDir)
+	rtest.OK(t, err)
+
+	// Call the cleanup function to remove the temporary cache directory
+	cleanup()
+
+	// Verify that the cache directory has been removed
+	_, err = os.ReadDir(gopts.CacheDir)
+	rtest.Assert(t, errors.Is(err, os.ErrNotExist), "Expected cache directory to be removed, but it still exists")
+}