fix: provider cache path handling in Windows

internal/tf/cache/services/provider_cache.go

@@ -13,6 +13,7 @@ import (
 	"path"
 	"path/filepath"
 	"slices"
+	"strings"
 	"sync"
 	"time"
 
@@ -318,12 +319,20 @@ func (cache *ProviderCache) warmUp(ctx context.Context) error {
 		return errors.Errorf("not found provider download url")
 	}
 
-	downloadURLExists, err := vfs.FileExists(fs, cache.DownloadURL)
-	if err != nil {
-		return errors.New(err)
+	// DownloadURL can be a local file path or a remote URL.
+	// On Windows, passing a URL to FileExists fails because the colon in "https:" is invalid path syntax.
+	var downloadURLIsLocalFile bool
+
+	if !strings.Contains(cache.DownloadURL, "://") {
+		var err error
+
+		downloadURLIsLocalFile, err = vfs.FileExists(fs, cache.DownloadURL)
+		if err != nil {
+			return errors.New(err)
+		}
 	}
 
-	if downloadURLExists {
+	if downloadURLIsLocalFile {
 		cache.archivePath = cache.DownloadURL
 	} else {
 		if err := util.DoWithRetry(ctx, fmt.Sprintf("Fetching provider %s", cache.Provider), maxRetriesFetchFile, retryDelayFetchFile, cache.logger, log.DebugLevel, func(ctx context.Context) error {

test/fixtures/provider-cache/windows-remote-url/main.tf

@@ -0,0 +1,10 @@
+terraform {
+  required_providers {
+    null = {
+      source  = "hashicorp/null"
+      version = "3.2.4"
+    }
+  }
+}
+
+resource "null_resource" "example" {}

test/fixtures/provider-cache/windows-remote-url/terragrunt.hcl

@@ -0,0 +1 @@
+# Intentionally empty

test/integration_windows_test.go

@@ -23,6 +23,7 @@ const (
 	testFixtureLocalRelativeArgsWindowsDownloadPath = "fixtures/download/local-windows"
 	testFixtureManifestRemoval                      = "fixtures/manifest-removal"
 	testFixtureTflintNoIssuesFound                  = "fixtures/tflint/no-issues-found"
+	testFixtureProviderCacheWindowsRemoteURL        = "fixtures/provider-cache/windows-remote-url"
 
 	tempDir = `C:\tmp`
 )
@@ -228,6 +229,27 @@ func TestWindowsScaffoldRef(t *testing.T) {
 	assert.NoError(t, err)
 }
 
+// TestWindowsProviderCacheWithRemoteURL verifies that provider caching works on Windows
+// when providers are fetched from remote URLs. Previously, passing a URL like
+// "https://github.com/..." to os.Stat caused a "syntax is incorrect" error on Windows
+// because the colon in "https:" is invalid Windows path syntax.
+func TestWindowsProviderCacheWithRemoteURL(t *testing.T) {
+	t.Parallel()
+
+	helpers.CleanupTerraformFolder(t, testFixtureProviderCacheWindowsRemoteURL)
+	tmpEnvPath := helpers.CopyEnvironment(t, testFixtureProviderCacheWindowsRemoteURL)
+	rootPath := filepath.Join(tmpEnvPath, testFixtureProviderCacheWindowsRemoteURL)
+
+	providerCacheDir := filepath.Join(t.TempDir(), "provider-cache-windows-test")
+
+	helpers.RunTerragrunt(t, fmt.Sprintf("terragrunt run init --provider-cache --provider-cache-dir %s --non-interactive --working-dir %s", providerCacheDir, rootPath))
+
+	// Verify the provider was cached
+	entries, err := os.ReadDir(providerCacheDir)
+	require.NoError(t, err)
+	assert.NotEmpty(t, entries, "provider cache dir should not be empty after init")
+}
+
 func CopyEnvironmentToPath(t *testing.T, environmentPath, targetPath string) {
 	if err := os.MkdirAll(targetPath, 0777); err != nil {
 		t.Fatalf("Failed to create temp dir %s due to error %v", targetPath, err)