starlark/types: computed, new fn function to wrap computed values

Author: mcuadros

starlark/runtime/runtime.go

@@ -54,6 +54,7 @@ func NewRuntime(pm *terraform.PluginManager) *Runtime {
 			"provisioner": types.BuiltinProvisioner(pm),
 			"backend":     types.BuiltinBackend(),
 			"hcl":         types.BuiltinHCL(),
+			"fn":          types.BuiltinFunctionComputed(),
 			"struct":      starlark.NewBuiltin("struct", starlarkstruct.Make),
 		},
 	}

starlark/types/computed.go

@@ -118,3 +118,28 @@ func (c *Computed) Len() int {
 
 	return 1024
 }
+
+func BuiltinFunctionComputed() starlark.Value {
+	return starlark.NewBuiltin("fn", func(_ *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
+		var function starlark.String
+		var computed *Computed
+		switch len(args) {
+		case 2:
+			var ok bool
+			function, ok = args.Index(0).(starlark.String)
+			if !ok {
+				return nil, fmt.Errorf("expected string, got %s", args.Index(0).Type())
+			}
+
+			computed, ok = args.Index(1).(*Computed)
+			if !ok {
+				return nil, fmt.Errorf("expected Computed, got %s", args.Index(1).Type())
+			}
+		default:
+			return nil, fmt.Errorf("unexpected positional arguments count")
+		}
+
+		path := fmt.Sprintf("%s(%s)", function.GoString(), computed.path)
+		return NewComputedWithPath(computed.r, computed.t, computed.name, path), nil
+	})
+}

starlark/types/provider.go

@@ -20,14 +20,14 @@ func BuiltinProvider(pm *terraform.PluginManager) starlark.Value {
 			var ok bool
 			alias, ok = args.Index(2).(starlark.String)
 			if !ok {
-				return nil, fmt.Errorf("expected string, go %s", args.Index(2).Type())
+				return nil, fmt.Errorf("expected string, got %s", args.Index(2).Type())
 			}
 			fallthrough
 		case 2:
 			var ok bool
 			version, ok = args.Index(1).(starlark.String)
 			if !ok {
-				return nil, fmt.Errorf("expected string, go %s", args.Index(1).Type())
+				return nil, fmt.Errorf("expected string, got %s", args.Index(1).Type())
 			}
 			fallthrough
 		case 1:

starlark/types/provider_test.go

@@ -62,6 +62,7 @@ func doTest(t *testing.T, filename string) {
 		"provisioner": BuiltinProvisioner(pm),
 		"backend":     BuiltinBackend(),
 		"hcl":         BuiltinHCL(),
+		"fn":          BuiltinFunctionComputed(),
 	}
 
 	_, err := starlark.ExecFile(thread, filename, nil, predeclared)

starlark/types/testdata/computed.star

@@ -35,3 +35,6 @@ gcp = provider("google", "3.13.0")
 # computed on list with MaxItem:1
 cluster = gcp.resource.container_cluster("foo")
 assert.eq(str(cluster.master_auth.client_certificate), '"${google_container_cluster.foo.master_auth.0.client_certificate}"')
+
+# fn wrapping
+assert.eq(str(fn("base64encode", web.ami)), '"${base64encode(data.aws_ami.id_3.id)}"')