From ff3a5b31c00354e1146dced9880863a8219395c9 Mon Sep 17 00:00:00 2001
From: Ivan Lozano <ivanlozano@google.com>
Date: Wed, 5 Aug 2020 13:28:32 -0400
Subject: [PATCH] Make source_stem required for Rust SourceProviders

This removes ambiguity for developers with the 'stem' property.

Bug: 159064919
Test: New Soong test; error is produced if this property is undefined.
Change-Id: I790fbcfa6cd7dbf6df63b5cf5c22983426ec072e
---
 rust/Android.bp              |  1 +
 rust/source_provider.go      | 13 ++++++-------
 rust/source_provider_test.go | 31 +++++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 7 deletions(-)
 create mode 100644 rust/source_provider_test.go

diff --git a/rust/Android.bp b/rust/Android.bp
index e03bf4f6c..bbeb28d0b 100644
--- a/rust/Android.bp
+++ b/rust/Android.bp
@@ -34,6 +34,7 @@ bootstrap_go_package {
         "library_test.go",
         "project_json_test.go",
         "rust_test.go",
+        "source_provider_test.go",
         "test_test.go",
     ],
     pluginFor: ["soong_build"],
diff --git a/rust/source_provider.go b/rust/source_provider.go
index 8bb784951..503880f84 100644
--- a/rust/source_provider.go
+++ b/rust/source_provider.go
@@ -19,9 +19,8 @@ import (
 )
 
 type SourceProviderProperties struct {
-	// name for the generated source file. Defaults to module name (e.g. moduleNameFoo.rs is produced by default).
-	// Importantly, the inherited "stem" property for this module sets the output filename for the generated library
-	// variants only
+	// filename for the generated source file (<source_stem>.rs). This field is required.
+	// The inherited "stem" property sets the output filename for the generated library variants only.
 	Source_stem *string `android:"arch_variant"`
 
 	// crate name, used for the library variant of this source provider. See additional details in rust_library.
@@ -65,11 +64,11 @@ func NewSourceProvider() *baseSourceProvider {
 }
 
 func (sp *baseSourceProvider) getStem(ctx android.ModuleContext) string {
-	stem := ctx.ModuleName()
-	if String(sp.Properties.Source_stem) != "" {
-		stem = String(sp.Properties.Source_stem)
+	if String(sp.Properties.Source_stem) == "" {
+		ctx.PropertyErrorf("source_stem",
+			"source_stem property is undefined but required for rust_bindgen modules")
 	}
-	return stem
+	return String(sp.Properties.Source_stem)
 }
 
 func (sp *baseSourceProvider) sourceProviderDeps(ctx DepsContext, deps Deps) Deps {
diff --git a/rust/source_provider_test.go b/rust/source_provider_test.go
new file mode 100644
index 000000000..6e68ae62c
--- /dev/null
+++ b/rust/source_provider_test.go
@@ -0,0 +1,31 @@
+// Copyright 2020 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package rust
+
+import (
+	"testing"
+)
+
+var stemRequiredError = "source_stem property is undefined but required for rust_bindgen modules"
+
+func TestSourceProviderRequiredFields(t *testing.T) {
+	testRustError(t, stemRequiredError, `
+		rust_bindgen {
+			name: "libbindgen",
+			wrapper_src: "src/any.h",
+			crate_name: "bindgen",
+		}
+	`)
+}