Flag to control if generated SDK prebuilts are preferred.

This is needed because:
- the SDK prebuilt drop is being automated, including the Android.bp
- We want to control the prefer flag on a per-module level

It augments the existing SOONG_SDK_SNAPSHOT_PREFER which now overrides
this new flag when set to true.

Bug: 188427719
Test: m nothing
Change-Id: Ieb5ab9fab53a34c615345b7a9d19cadf713eec26

1 files changed, 6 insertions, 5 deletions

diff --git a/sdk/update.go b/sdk/update.go
index b146b62c8..2ab45d7c1 100644
--- a/sdk/update.go
+++ b/sdk/update.go
@@ -32,8 +32,9 @@ import (
 // ========================================================
 //
 // SOONG_SDK_SNAPSHOT_PREFER
-//     By default every unversioned module in the generated snapshot has prefer: false. Building it
-//     with SOONG_SDK_SNAPSHOT_PREFER=true will force them to use prefer: true.
+//     By default every unversioned module in the generated snapshot has prefer set by the
+//     sdk.prebuilts_prefer property. Building it with SOONG_SDK_SNAPSHOT_PREFER=true will force
+//     them to use prefer: true.
 //
 // SOONG_SDK_SNAPSHOT_VERSION
 //     This provides control over the version of the generated snapshot.
@@ -1623,11 +1624,11 @@ func (s *sdk) createMemberSnapshot(ctx *memberContext, member *sdkMember, bpModu
 
 	// Do not add the prefer property if the member snapshot module is a source module type.
 	if !memberType.UsesSourceModuleTypeInSnapshot() {
-		// Set the prefer based on the environment variable. This is a temporary work around to allow a
-		// snapshot to be created that sets prefer: true.
+		// Set the prefer based on the environment variable if present, else the sdk.prefer_prebuilts
+		// value.
 		// TODO(b/174997203): Remove once the ability to select the modules to prefer can be done
 		//  dynamically at build time not at snapshot generation time.
-		prefer := ctx.sdkMemberContext.Config().IsEnvTrue("SOONG_SDK_SNAPSHOT_PREFER")
+		prefer := ctx.sdkMemberContext.Config().IsEnvTrue("SOONG_SDK_SNAPSHOT_PREFER") || s.PreferPrebuilts()
 
 		// Set prefer. Setting this to false is not strictly required as that is the default but it does
 		// provide a convenient hook to post-process the generated Android.bp file, e.g. in tests to