Extend coverage mutator to allow variants with coverage on and off

Bug: http://b/116873221

This allows us to enable coverage for a module (typically static
libraries) even if a dependent module cannot build with coverage.  In
this case, the dependent module can just pick the variant with coverage
off.

- Create the following variants from the coverage mutator:
  - "" (empty): Don't build  with coverage and always pick the
                non-coverage variants for dependents.  This variant is
                created for modules with 'native_coverage: false'.
  - "cov":      If this module's path is covered by the COVERAGE_PATHS
                option, build this module with coverage.  If not, build
                this module without coverage.  In either case, pick
                coverage variants ("cov") for dependencies if available.

- Do not enable coverage:
  - for NDK stub libraries
  - if sdk_version < 23 since libc doesn't export 'stderr' which is
    needed by the coverage/profile runtime library.
  - for VNDK libraries

Test: In AOSP: m COVERAGE_PATHS=system/security NATIVE_COVERAGE=true nothing

Change-Id: I4d08790d35cdeaf12fb3c4f999d69a870e65836a

cc/cc.go

@@ -63,7 +63,7 @@ func init() {
 		ctx.TopDown("sanitize_runtime_deps", sanitizerRuntimeDepsMutator)
 		ctx.BottomUp("sanitize_runtime", sanitizerRuntimeMutator).Parallel()
 
-		ctx.BottomUp("coverage", coverageLinkingMutator).Parallel()
+		ctx.BottomUp("coverage", coverageMutator).Parallel()
 		ctx.TopDown("vndk_deps", sabiDepsMutator)
 
 		ctx.TopDown("lto_deps", ltoDepsMutator)
@@ -258,6 +258,7 @@ type ModuleContextIntf interface {
 	baseModuleName() string
 	getVndkExtendsModuleName() string
 	isPgoCompile() bool
+	isNDKStubLibrary() bool
 	useClangLld(actx ModuleContext) bool
 	apexName() string
 	hasStubsVariants() bool
@@ -497,6 +498,10 @@ func (c *Module) useVndk() bool {
 	return c.Properties.UseVndk
 }
 
+func (c *Module) isCoverageVariant() bool {
+	return c.coverage.Properties.IsCoverageVariant
+}
+
 func (c *Module) isNdk() bool {
 	return inList(c.Name(), ndkMigratedLibs)
 }
@@ -530,6 +535,13 @@ func (c *Module) isPgoCompile() bool {
 	return false
 }
 
+func (c *Module) isNDKStubLibrary() bool {
+	if _, ok := c.compiler.(*stubDecorator); ok {
+		return true
+	}
+	return false
+}
+
 func (c *Module) isVndkSp() bool {
 	if vndkdep := c.vndkdep; vndkdep != nil {
 		return vndkdep.isVndkSp()
@@ -675,6 +687,10 @@ func (ctx *moduleContextImpl) isPgoCompile() bool {
 	return ctx.mod.isPgoCompile()
 }
 
+func (ctx *moduleContextImpl) isNDKStubLibrary() bool {
+	return ctx.mod.isNDKStubLibrary()
+}
+
 func (ctx *moduleContextImpl) isVndkSp() bool {
 	return ctx.mod.isVndkSp()
 }
@@ -956,7 +972,8 @@ func (c *Module) GenerateAndroidBuildActions(actx android.ModuleContext) {
 		// module is marked with 'bootstrap: true').
 		if c.HasStubsVariants() &&
 			android.DirectlyInAnyApex(ctx, ctx.baseModuleName()) &&
-			!c.inRecovery() && !c.useVndk() && !c.static() && c.IsStubs() {
+			!c.inRecovery() && !c.useVndk() && !c.static() && !c.isCoverageVariant() &&
+			c.IsStubs() {
 			c.Properties.HideFromMake = false // unhide
 			// Note: this is still non-installable
 		}