internal/initwd: identify possible relative module sources

Identify module sources that look like relative paths ("child" instead
of "./child", for example) and surface a helpful error.

Previously, such module sources would be passed to go-getter, which
would fail because it was expecting an absolute, or properly relative,
path. This commit moves the check for improper relative paths sooner so
a user-friendly error can be displayed.

internal/initwd/from_module_test.go

@@ -52,17 +52,17 @@ func TestDirFromModule_registry(t *testing.T) {
 			Name:       "Install",
 			ModuleAddr: "root",
 			Version:    v,
-			LocalPath:  ".terraform/modules/root/hashicorp-terraform-aws-module-installer-acctest-5e87aff",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/root/hashicorp-terraform-aws-module-installer-acctest-5e87aff"),
 		},
 		{
 			Name:       "Install",
 			ModuleAddr: "root.child_a",
-			LocalPath:  ".terraform/modules/root/hashicorp-terraform-aws-module-installer-acctest-5e87aff/modules/child_a",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/root/hashicorp-terraform-aws-module-installer-acctest-5e87aff/modules/child_a"),
 		},
 		{
 			Name:       "Install",
 			ModuleAddr: "root.child_a.child_b",
-			LocalPath:  ".terraform/modules/root/hashicorp-terraform-aws-module-installer-acctest-5e87aff/modules/child_b",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/root/hashicorp-terraform-aws-module-installer-acctest-5e87aff/modules/child_b"),
 		},
 	}
 

internal/initwd/getter.go

@@ -78,7 +78,7 @@ type reusingGetter map[string]string
 // go-getter library, which have very inconsistent quality as
 // end-user-actionable error messages. At this time we do not have any
 // reasonable way to improve these error messages at this layer because
-// the underlying errors are not separatelyr recognizable.
+// the underlying errors are not separately recognizable.
 func (g reusingGetter) getWithGoGetter(instPath, addr string) (string, error) {
 	packageAddr, subDir := splitAddrSubdir(addr)
 
@@ -186,3 +186,19 @@ func isRegistrySourceAddr(addr string) bool {
 	_, err := regsrc.ParseModuleSource(addr)
 	return err == nil
 }
+
+func isMaybeRelativeLocalPath(addr, path string) bool {
+	realAddr, err := getter.Detect(addr, path, getter.Detectors)
+	// this error will be handled by the next function
+	if err != nil {
+		return false
+	} else {
+		if strings.HasPrefix(realAddr, "file://") {
+			_, err := os.Stat(realAddr[7:])
+			if err != nil {
+				return true
+			}
+		}
+	}
+	return false
+}

internal/initwd/module_install.go

@@ -199,6 +199,22 @@ func (i *ModuleInstaller) installDescendentModules(rootMod *tfconfig.Module, roo
 				diags = append(diags, mDiags...)
 				return mod, v, diags
 
+			case isMaybeRelativeLocalPath(req.SourceAddr, instPath):
+				log.Printf(
+					"[TRACE] ModuleInstaller: %s looks like a local path but is missing ./ or ../",
+					req.SourceAddr,
+				)
+				diags = diags.Append(tfdiags.Sourceless(
+					tfdiags.Error,
+					"Failed to locate local module source",
+					fmt.Sprintf(
+						"%s looks like a relative path, but Terraform cannot determine the module source. "+
+							"Add ./ at the start of the source string if this is a relative path.",
+						req.SourceAddr,
+					),
+				))
+				return nil, nil, diags
+
 			default:
 				log.Printf("[TRACE] ModuleInstaller: %s address %q will be handled by go-getter", key, req.SourceAddr)
 

internal/initwd/module_install_test.go

@@ -93,12 +93,30 @@ func TestModuleInstaller(t *testing.T) {
 	assertResultDeepEqual(t, gotTraces, wantTraces)
 }
 
+func TestModuleInstaller_error(t *testing.T) {
+	fixtureDir := filepath.Clean("test-fixtures/local-module-error")
+	dir, done := tempChdir(t, fixtureDir)
+	defer done()
+
+	hooks := &testInstallHooks{}
+
+	modulesDir := filepath.Join(dir, ".terraform/modules")
+	inst := NewModuleInstaller(modulesDir, nil)
+	_, diags := inst.InstallModules(".", false, hooks)
+
+	if !diags.HasErrors() {
+		t.Fatal("expected error")
+	} else {
+		assertDiagnosticSummary(t, diags, "Failed to locate local module source")
+	}
+}
+
 func TestLoaderInstallModules_registry(t *testing.T) {
 	if os.Getenv("TF_ACC") == "" {
 		t.Skip("this test accesses registry.terraform.io and github.com; set TF_ACC=1 to run it")
 	}
 
-	fixtureDir := filepath.Clean("test-fixtures/local-modules")
+	fixtureDir := filepath.Clean("test-fixtures/registry-modules")
 	dir, done := tempChdir(t, fixtureDir)
 	defer done()
 
@@ -125,7 +143,7 @@ func TestLoaderInstallModules_registry(t *testing.T) {
 			Name:       "Install",
 			ModuleAddr: "acctest_child_a",
 			Version:    v,
-			LocalPath:  ".terraform/modules/acctest_child_a/hashicorp-terraform-aws-module-installer-acctest-853d038/modules/child_a",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/acctest_child_a/hashicorp-terraform-aws-module-installer-acctest-853d038/modules/child_a"),
 		},
 
 		// acctest_child_a.child_b
@@ -133,7 +151,7 @@ func TestLoaderInstallModules_registry(t *testing.T) {
 		{
 			Name:       "Install",
 			ModuleAddr: "acctest_child_a.child_b",
-			LocalPath:  ".terraform/modules/acctest_child_a/hashicorp-terraform-aws-module-installer-acctest-853d038/modules/child_b",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/acctest_child_a/hashicorp-terraform-aws-module-installer-acctest-853d038/modules/child_b"),
 		},
 
 		// acctest_child_b accesses //modules/child_b directly
@@ -147,7 +165,7 @@ func TestLoaderInstallModules_registry(t *testing.T) {
 			Name:       "Install",
 			ModuleAddr: "acctest_child_b",
 			Version:    v,
-			LocalPath:  ".terraform/modules/acctest_child_b/hashicorp-terraform-aws-module-installer-acctest-853d038/modules/child_b",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/acctest_child_b/hashicorp-terraform-aws-module-installer-acctest-853d038/modules/child_b"),
 		},
 
 		// acctest_root
@@ -161,7 +179,7 @@ func TestLoaderInstallModules_registry(t *testing.T) {
 			Name:       "Install",
 			ModuleAddr: "acctest_root",
 			Version:    v,
-			LocalPath:  ".terraform/modules/acctest_root/hashicorp-terraform-aws-module-installer-acctest-853d038",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/acctest_root/hashicorp-terraform-aws-module-installer-acctest-853d038"),
 		},
 
 		// acctest_root.child_a
@@ -169,7 +187,7 @@ func TestLoaderInstallModules_registry(t *testing.T) {
 		{
 			Name:       "Install",
 			ModuleAddr: "acctest_root.child_a",
-			LocalPath:  ".terraform/modules/acctest_root/hashicorp-terraform-aws-module-installer-acctest-853d038/modules/child_a",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/acctest_root/hashicorp-terraform-aws-module-installer-acctest-853d038/modules/child_a"),
 		},
 
 		// acctest_root.child_a.child_b
@@ -177,7 +195,7 @@ func TestLoaderInstallModules_registry(t *testing.T) {
 		{
 			Name:       "Install",
 			ModuleAddr: "acctest_root.child_a.child_b",
-			LocalPath:  ".terraform/modules/acctest_root/hashicorp-terraform-aws-module-installer-acctest-853d038/modules/child_b",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/acctest_root/hashicorp-terraform-aws-module-installer-acctest-853d038/modules/child_b"),
 		},
 	}
 
@@ -248,7 +266,7 @@ func TestLoaderInstallModules_goGetter(t *testing.T) {
 		{
 			Name:       "Install",
 			ModuleAddr: "acctest_child_a",
-			LocalPath:  ".terraform/modules/acctest_child_a/modules/child_a",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/acctest_child_a/modules/child_a"),
 		},
 
 		// acctest_child_a.child_b
@@ -256,7 +274,7 @@ func TestLoaderInstallModules_goGetter(t *testing.T) {
 		{
 			Name:       "Install",
 			ModuleAddr: "acctest_child_a.child_b",
-			LocalPath:  ".terraform/modules/acctest_child_a/modules/child_b",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/acctest_child_a/modules/child_b"),
 		},
 
 		// acctest_child_b accesses //modules/child_b directly
@@ -268,7 +286,7 @@ func TestLoaderInstallModules_goGetter(t *testing.T) {
 		{
 			Name:       "Install",
 			ModuleAddr: "acctest_child_b",
-			LocalPath:  ".terraform/modules/acctest_child_b/modules/child_b",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/acctest_child_b/modules/child_b"),
 		},
 
 		// acctest_root
@@ -280,7 +298,7 @@ func TestLoaderInstallModules_goGetter(t *testing.T) {
 		{
 			Name:       "Install",
 			ModuleAddr: "acctest_root",
-			LocalPath:  ".terraform/modules/acctest_root",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/acctest_root"),
 		},
 
 		// acctest_root.child_a
@@ -288,7 +306,7 @@ func TestLoaderInstallModules_goGetter(t *testing.T) {
 		{
 			Name:       "Install",
 			ModuleAddr: "acctest_root.child_a",
-			LocalPath:  ".terraform/modules/acctest_root/modules/child_a",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/acctest_root/modules/child_a"),
 		},
 
 		// acctest_root.child_a.child_b
@@ -296,7 +314,7 @@ func TestLoaderInstallModules_goGetter(t *testing.T) {
 		{
 			Name:       "Install",
 			ModuleAddr: "acctest_root.child_a.child_b",
-			LocalPath:  ".terraform/modules/acctest_root/modules/child_b",
+			LocalPath:  filepath.Join(dir, ".terraform/modules/acctest_root/modules/child_b"),
 		},
 	}
 

internal/initwd/test-fixtures/local-module-error/child_a/main.tf

@@ -0,0 +1,8 @@
+variable "v" {
+  description = "in child_ba module"
+  default     = ""
+}
+
+output "hello" {
+  value = "Hello from child_a!"
+}

internal/initwd/test-fixtures/local-module-error/main.tf

@@ -0,0 +1,8 @@
+variable "v" {
+  description = "in root module"
+  default     = ""
+}
+
+module "child_a" {
+  source = "child_a"
+}