Allow cc.LinkabeInterfaces to request "" variants.

cc.LinkableInterfaces should be able to request if an empty variant is
required from the LinkageMutator. We were previously assuming that if only
static or shared libraries were being built, then we didn't need the
empty variant. However this should be explicit to handle cases where the
default set of variants being created may not include both static and
shared libraries.

Bug: 144861059
Test: m -j crosvm.experimental
Change-Id: I66724bdc16ff350b06dfa4d049c82f33019979a5

cc/cc.go

@@ -562,6 +562,10 @@ func (c *Module) CcLibraryInterface() bool {
 	return false
 }
 
+func (c *Module) NonCcVariants() bool {
+	return false
+}
+
 func (c *Module) SetBuildStubs() {
 	if c.linker != nil {
 		if library, ok := c.linker.(*libraryDecorator); ok {

cc/library.go

@@ -1262,14 +1262,16 @@ func LinkageMutator(mctx android.BottomUpMutatorContext) {
 			shared.linker.(prebuiltLibraryInterface).disablePrebuilt()
 		}
 	} else if library, ok := mctx.Module().(LinkableInterface); ok && library.CcLibraryInterface() {
-		if library.BuildStaticVariant() && library.BuildSharedVariant() {
-			variations := []string{"static", "shared"}
 
-			// Non-cc.Modules need an empty variant for their mutators.
-			if _, ok := mctx.Module().(*Module); !ok {
+		// Non-cc.Modules may need an empty variant for their mutators.
+		variations := []string{}
+		if library.NonCcVariants() {
 			variations = append(variations, "")
 		}
 
+		if library.BuildStaticVariant() && library.BuildSharedVariant() {
+			variations := append([]string{"static", "shared"}, variations...)
+
 			modules := mctx.CreateLocalVariations(variations...)
 			static := modules[0].(LinkableInterface)
 			shared := modules[1].(LinkableInterface)
@@ -1281,16 +1283,18 @@ func LinkageMutator(mctx android.BottomUpMutatorContext) {
 				reuseStaticLibrary(mctx, static.(*Module), shared.(*Module))
 			}
 		} else if library.BuildStaticVariant() {
-			modules := mctx.CreateLocalVariations("static")
+			variations := append([]string{"static"}, variations...)
+
+			modules := mctx.CreateLocalVariations(variations...)
 			modules[0].(LinkableInterface).SetStatic()
 		} else if library.BuildSharedVariant() {
-			modules := mctx.CreateLocalVariations("shared")
-			modules[0].(LinkableInterface).SetShared()
-		} else if _, ok := mctx.Module().(*Module); !ok {
-			// Non-cc.Modules need an empty variant for their mutators.
-			mctx.CreateLocalVariations("")
-		}
+			variations := append([]string{"shared"}, variations...)
 
+			modules := mctx.CreateLocalVariations(variations...)
+			modules[0].(LinkableInterface).SetShared()
+		} else if len(variations) > 0 {
+			mctx.CreateLocalVariations(variations...)
+		}
 	}
 }
 

cc/linkable.go

@@ -20,6 +20,8 @@ type LinkableInterface interface {
 	HasStaticVariant() bool
 	GetStaticVariant() LinkableInterface
 
+	NonCcVariants() bool
+
 	StubsVersions() []string
 	BuildStubs() bool
 	SetBuildStubs()

rust/rust.go

@@ -89,6 +89,19 @@ func (mod *Module) SelectedStl() string {
 	return ""
 }
 
+func (mod *Module) NonCcVariants() bool {
+	if mod.compiler != nil {
+		if library, ok := mod.compiler.(libraryInterface); ok {
+			if library.buildRlib() || library.buildDylib() {
+				return true
+			} else {
+				return false
+			}
+		}
+	}
+	panic(fmt.Errorf("NonCcVariants called on non-library module: %q", mod.BaseModuleName()))
+}
+
 func (mod *Module) ApiLevel() string {
 	panic(fmt.Errorf("Called ApiLevel on Rust module %q; stubs libraries are not yet supported.", mod.BaseModuleName()))
 }