3 files changed, 48 insertions, 0 deletions

diff --git a/android/apex.go b/android/apex.go
index 79d8cdda3..0d5cac812 100644
--- a/android/apex.go
+++ b/android/apex.go
@@ -257,6 +257,9 @@ type ApexProperties struct {
 }
 
 // Marker interface that identifies dependencies that are excluded from APEX contents.
+//
+// Unless the tag also implements the AlwaysRequireApexVariantTag this will prevent an apex variant
+// from being created for the module.
 type ExcludeFromApexContentsTag interface {
 	blueprint.DependencyTag
 
@@ -264,6 +267,17 @@ type ExcludeFromApexContentsTag interface {
 	ExcludeFromApexContents()
 }
 
+// Marker interface that identifies dependencies that always requires an APEX variant to be created.
+//
+// It is possible for a dependency to require an apex variant but exclude the module from the APEX
+// contents. See sdk.sdkMemberDependencyTag.
+type AlwaysRequireApexVariantTag interface {
+	blueprint.DependencyTag
+
+	// Return true if this tag requires that the target dependency has an apex variant.
+	AlwaysRequireApexVariant() bool
+}
+
 // Marker interface that identifies dependencies that should inherit the DirectlyInAnyApex state
 // from the parent to the child. For example, stubs libraries are marked as DirectlyInAnyApex if
 // their implementation is in an apex.
diff --git a/apex/apex.go b/apex/apex.go
index c0561ef8f..429465d80 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -846,6 +846,19 @@ func (a *apexBundle) ApexInfoMutator(mctx android.TopDownMutatorContext) {
 		if !ok || !am.CanHaveApexVariants() {
 			return false
 		}
+		depTag := mctx.OtherModuleDependencyTag(child)
+
+		// Check to see if the tag always requires that the child module has an apex variant for every
+		// apex variant of the parent module. If it does not then it is still possible for something
+		// else, e.g. the DepIsInSameApex(...) method to decide that a variant is required.
+		if required, ok := depTag.(android.AlwaysRequireApexVariantTag); ok && required.AlwaysRequireApexVariant() {
+			return true
+		}
+		if _, ok := depTag.(android.ExcludeFromApexContentsTag); ok {
+			// The tag defines a dependency that never requires the child module to be part of the same
+			// apex as the parent so it does not need an apex variant created.
+			return false
+		}
 		if !parent.(android.DepIsInSameApex).DepIsInSameApex(mctx, child) {
 			return false
 		}
diff --git a/sdk/sdk.go b/sdk/sdk.go
index 2c84a2e88..6ca851217 100644
--- a/sdk/sdk.go
+++ b/sdk/sdk.go
@@ -358,15 +358,36 @@ var _ android.ExcludeFromApexContentsTag = dependencyTag{}
 
 // For dependencies from an in-development version of an SDK member to frozen versions of the same member
 // e.g. libfoo -> libfoo.mysdk.11 and libfoo.mysdk.12
+//
+// The dependency represented by this tag requires that for every APEX variant created for the
+// `from` module that an equivalent APEX variant is created for the 'to' module. This is because an
+// APEX that requires a specific version of an sdk (via the `uses_sdks` property will replace
+// dependencies on the unversioned sdk member with a dependency on the appropriate versioned sdk
+// member. In order for that to work the versioned sdk member needs to have a variant for that APEX.
+// As it is not known at the time that the APEX variants are created which specific APEX variants of
+// a versioned sdk members will be required it is necessary for the versioned sdk members to have
+// variants for any APEX that it could be used within.
+//
+// If the APEX selects a versioned sdk member then it will not have a dependency on the `from`
+// module at all so any dependencies of that module will not affect the APEX. However, if the APEX
+// selects the unversioned sdk member then it must exclude all the versioned sdk members. In no
+// situation would this dependency cause the `to` module to be added to the APEX hence why this tag
+// also excludes the `to` module from being added to the APEX contents.
 type sdkMemberVersionedDepTag struct {
 	dependencyTag
 	member  string
 	version string
 }
 
+func (t sdkMemberVersionedDepTag) AlwaysRequireApexVariant() bool {
+	return true
+}
+
 // Mark this tag so dependencies that use it are excluded from visibility enforcement.
 func (t sdkMemberVersionedDepTag) ExcludeFromVisibilityEnforcement() {}
 
+var _ android.AlwaysRequireApexVariantTag = sdkMemberVersionedDepTag{}
+
 // Step 1: create dependencies from an SDK module to its members.
 func memberMutator(mctx android.BottomUpMutatorContext) {
 	if s, ok := mctx.Module().(*sdk); ok {