Add failing test for missing computed map entries

The map output from the module "mod" loses the computed value from the
template when we validate. If the "extra" field is removed from the map,
the validation fails earlier with map "does not have any elements so
cannot determine type".

Apply will work, because the computed value will exist in the map.

terraform/context_validate_test.go

@@ -821,3 +821,29 @@ func TestContext2Validate_interpolateComputedModuleVarDef(t *testing.T) {
 		t.Fatal("err:", e)
 	}
 }
+
+// Computed values are lost when a map is output from a module
+func TestContext2Validate_interpolateMap(t *testing.T) {
+	input := new(MockUIInput)
+
+	m := testModule(t, "issue-9549")
+	p := testProvider("null")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+
+	ctx := testContext2(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"template": testProviderFuncFixed(p),
+		},
+		UIInput: input,
+	})
+
+	w, e := ctx.Validate()
+	if w != nil {
+		t.Log("warnings:", w)
+	}
+	if e != nil {
+		t.Fatal("err:", e)
+	}
+}

terraform/test-fixtures/issue-9549/main.tf

@@ -0,0 +1,7 @@
+module "mod" {
+  source = "./mod"
+}
+
+resource "template_file" "root_template" {
+  template = "ext: ${module.mod.base_config["base_template"]}"
+}

terraform/test-fixtures/issue-9549/mod/main.tf

@@ -0,0 +1,12 @@
+resource "template_file" "example" {
+  template = "template text"
+}
+
+output "base_config" {
+  value = {
+    base_template = "${template_file.example.rendered}"
+
+    # without this we fail with no entries
+    extra = "value"
+  }
+}