Add cc_prebuilt_library_headers

In preparation for adding cc_library_headers support to
sdk/module_exports.

Two changes were needed to make the prebuilt version work.
1) Had to stop the prebuilt version of the library from creating static
   and shared variants for header only.
2) Had to allow the code to export/reexport include dirs to run even
   when no src is provided.

Bug: 148933848
Test: m nothing
Change-Id: Idd50ed38bc90d1d93551f78e6310f167941487d9

4 files changed, 58 insertions, 22 deletions

diff --git a/cc/library.go b/cc/library.go
index f9bc49eb8..6ffb7fc1e 100644
--- a/cc/library.go
+++ b/cc/library.go
@@ -1303,22 +1303,28 @@ func LinkageMutator(mctx android.BottomUpMutatorContext) {
 	if cc_prebuilt {
 		library := mctx.Module().(*Module).linker.(prebuiltLibraryInterface)
 
-		// Always create both the static and shared variants for prebuilt libraries, and then disable the one
-		// that is not being used.  This allows them to share the name of a cc_library module, which requires that
-		// all the variants of the cc_library also exist on the prebuilt.
-		modules := mctx.CreateLocalVariations("static", "shared")
-		static := modules[0].(*Module)
-		shared := modules[1].(*Module)
-
-		static.linker.(prebuiltLibraryInterface).setStatic()
-		shared.linker.(prebuiltLibraryInterface).setShared()
-
-		if !library.buildStatic() {
-			static.linker.(prebuiltLibraryInterface).disablePrebuilt()
-		}
-		if !library.buildShared() {
-			shared.linker.(prebuiltLibraryInterface).disablePrebuilt()
+		// Differentiate between header only and building an actual static/shared library
+		if library.buildStatic() || library.buildShared() {
+			// Always create both the static and shared variants for prebuilt libraries, and then disable the one
+			// that is not being used.  This allows them to share the name of a cc_library module, which requires that
+			// all the variants of the cc_library also exist on the prebuilt.
+			modules := mctx.CreateLocalVariations("static", "shared")
+			static := modules[0].(*Module)
+			shared := modules[1].(*Module)
+
+			static.linker.(prebuiltLibraryInterface).setStatic()
+			shared.linker.(prebuiltLibraryInterface).setShared()
+
+			if !library.buildStatic() {
+				static.linker.(prebuiltLibraryInterface).disablePrebuilt()
+			}
+			if !library.buildShared() {
+				shared.linker.(prebuiltLibraryInterface).disablePrebuilt()
+			}
+		} else {
+			// Header only
 		}
+
 	} else if library, ok := mctx.Module().(LinkableInterface); ok && library.CcLibraryInterface() {
 
 		// Non-cc.Modules may need an empty variant for their mutators.
diff --git a/cc/library_headers.go b/cc/library_headers.go
index 0a15112d5..c7edb9a6d 100644
--- a/cc/library_headers.go
+++ b/cc/library_headers.go
@@ -22,6 +22,7 @@ func init() {
 
 func RegisterLibraryHeadersBuildComponents(ctx android.RegistrationContext) {
 	ctx.RegisterModuleType("cc_library_headers", LibraryHeaderFactory)
+	ctx.RegisterModuleType("cc_prebuilt_library_headers", prebuiltLibraryHeaderFactory)
 }
 
 // cc_library_headers contains a set of c/c++ headers which are imported by
@@ -33,3 +34,10 @@ func LibraryHeaderFactory() android.Module {
 	library.HeaderOnly()
 	return module.Init()
 }
+
+// cc_prebuilt_library_headers is a prebuilt version of cc_library_headers
+func prebuiltLibraryHeaderFactory() android.Module {
+	module, library := NewPrebuiltLibrary(android.HostAndDeviceSupported)
+	library.HeaderOnly()
+	return module.Init()
+}
diff --git a/cc/library_headers_test.go b/cc/library_headers_test.go
index 42d37350a..564ef61fb 100644
--- a/cc/library_headers_test.go
+++ b/cc/library_headers_test.go
@@ -39,3 +39,24 @@ func TestLibraryHeaders(t *testing.T) {
 		t.Errorf("cflags for libsystem must contain -Imy_include, but was %#v.", cflags)
 	}
 }
+
+func TestPrebuiltLibraryHeaders(t *testing.T) {
+	ctx := testCc(t, `
+	cc_prebuilt_library_headers {
+		name: "headers",
+		export_include_dirs: ["my_include"],
+	}
+	cc_library_static {
+		name: "lib",
+		srcs: ["foo.c"],
+		header_libs: ["headers"],
+	}
+	`)
+
+	// test if header search paths are correctly added
+	cc := ctx.ModuleForTests("lib", "android_arm64_armv8-a_static").Rule("cc")
+	cflags := cc.Args["cFlags"]
+	if !strings.Contains(cflags, " -Imy_include ") {
+		t.Errorf("cflags for libsystem must contain -Imy_include, but was %#v.", cflags)
+	}
+}
diff --git a/cc/prebuilt.go b/cc/prebuilt.go
index b0cf4890e..2c18ac3a2 100644
--- a/cc/prebuilt.go
+++ b/cc/prebuilt.go
@@ -87,15 +87,16 @@ func (p *prebuiltLibraryLinker) linkerProps() []interface{} {
 
 func (p *prebuiltLibraryLinker) link(ctx ModuleContext,
 	flags Flags, deps PathDeps, objs Objects) android.Path {
+
+	p.libraryDecorator.exportIncludes(ctx)
+	p.libraryDecorator.reexportDirs(deps.ReexportedDirs...)
+	p.libraryDecorator.reexportSystemDirs(deps.ReexportedSystemDirs...)
+	p.libraryDecorator.reexportFlags(deps.ReexportedFlags...)
+	p.libraryDecorator.reexportDeps(deps.ReexportedDeps...)
+	p.libraryDecorator.addExportedGeneratedHeaders(deps.ReexportedGeneratedHeaders...)
+
 	// TODO(ccross): verify shared library dependencies
 	if len(p.properties.Srcs) > 0 {
-		p.libraryDecorator.exportIncludes(ctx)
-		p.libraryDecorator.reexportDirs(deps.ReexportedDirs...)
-		p.libraryDecorator.reexportSystemDirs(deps.ReexportedSystemDirs...)
-		p.libraryDecorator.reexportFlags(deps.ReexportedFlags...)
-		p.libraryDecorator.reexportDeps(deps.ReexportedDeps...)
-		p.libraryDecorator.addExportedGeneratedHeaders(deps.ReexportedGeneratedHeaders...)
-
 		builderFlags := flagsToBuilderFlags(flags)
 
 		in := p.Prebuilt.SingleSourcePath(ctx)