Syntax check generated Android.bp snapshot

Checks the syntax of the Android.bp file generated for the sdk
snapshot. While this will not detect all possible problems with the
generated Android.bp file it will detect some and it is far better to
detect those issues during generation than when it is unpacked and
used.

Bug: 155628860
Test: m nothing
Change-Id: Ieec86a7a49fa2e3bd8b9f83aca540114232a3476
diff --git a/sdk/update.go b/sdk/update.go
index 476a4a5..1ba5806 100644
--- a/sdk/update.go
+++ b/sdk/update.go
@@ -350,6 +350,9 @@
 	bp = newGeneratedFile(ctx, "snapshot", "Android.bp")
 	generateBpContents(&bp.generatedContents, bpFile)
 
+	contents := bp.content.String()
+	syntaxCheckSnapshotBpFile(ctx, contents)
+
 	bp.build(pctx, ctx, nil)
 
 	filesToZip := builder.filesToZip
@@ -394,6 +397,36 @@
 	return outputZipFile
 }
 
+// Check the syntax of the generated Android.bp file contents and if they are
+// invalid then log an error with the contents (tagged with line numbers) and the
+// errors that were found so that it is easy to see where the problem lies.
+func syntaxCheckSnapshotBpFile(ctx android.ModuleContext, contents string) {
+	errs := android.CheckBlueprintSyntax(ctx, "Android.bp", contents)
+	if len(errs) != 0 {
+		message := &strings.Builder{}
+		_, _ = fmt.Fprint(message, `errors in generated Android.bp snapshot:
+
+Generated Android.bp contents
+========================================================================
+`)
+		for i, line := range strings.Split(contents, "\n") {
+			_, _ = fmt.Fprintf(message, "%6d:    %s\n", i+1, line)
+		}
+
+		_, _ = fmt.Fprint(message, `
+========================================================================
+
+Errors found:
+`)
+
+		for _, err := range errs {
+			_, _ = fmt.Fprintf(message, "%s\n", err.Error())
+		}
+
+		ctx.ModuleErrorf("%s", message.String())
+	}
+}
+
 func extractCommonProperties(ctx android.ModuleContext, extractor *commonValueExtractor, commonProperties interface{}, inputPropertiesSlice interface{}) {
 	err := extractor.extractCommonProperties(commonProperties, inputPropertiesSlice)
 	if err != nil {