rust: Refactor cfg and feature flag calculation

Move the cfg and feature flag calculation out of compilerFlags so that
it's a separate step.

The previous arrangement resulted in overridden compilerFlags which
must to set any additional cfgs/features before calling the base.
This is a bit confusing and undocumented behavior, so instead break
it out into a separate call that can itself be overriden.

Bug: N/A
Test: Soong tests pass
Change-Id: I28e4f707b3b3ca6eb621b7613c3737817f877bb8

rust/compiler.go

@@ -231,6 +231,7 @@ func (compiler *baseCompiler) cfgsToFlags() []string {
 	for _, cfg := range compiler.Properties.Cfgs {
 		flags = append(flags, "--cfg '"+cfg+"'")
 	}
+
 	return flags
 }
 
@@ -239,6 +240,24 @@ func (compiler *baseCompiler) featuresToFlags() []string {
 	for _, feature := range compiler.Properties.Features {
 		flags = append(flags, "--cfg 'feature=\""+feature+"\"'")
 	}
+
+	return flags
+}
+
+func (compiler *baseCompiler) featureFlags(ctx ModuleContext, flags Flags) Flags {
+	flags.RustFlags = append(flags.RustFlags, compiler.featuresToFlags()...)
+	flags.RustdocFlags = append(flags.RustdocFlags, compiler.featuresToFlags()...)
+
+	return flags
+}
+
+func (compiler *baseCompiler) cfgFlags(ctx ModuleContext, flags Flags) Flags {
+	if ctx.RustModule().UseVndk() {
+		compiler.Properties.Cfgs = append(compiler.Properties.Cfgs, "android_vndk")
+	}
+
+	flags.RustFlags = append(flags.RustFlags, compiler.cfgsToFlags()...)
+	flags.RustdocFlags = append(flags.RustdocFlags, compiler.cfgsToFlags()...)
 	return flags
 }
 
@@ -269,10 +288,6 @@ func (compiler *baseCompiler) compilerFlags(ctx ModuleContext, flags Flags) Flag
 
 	flags.RustFlags = append(flags.RustFlags, lintFlags)
 	flags.RustFlags = append(flags.RustFlags, compiler.Properties.Flags...)
-	flags.RustFlags = append(flags.RustFlags, compiler.cfgsToFlags()...)
-	flags.RustFlags = append(flags.RustFlags, compiler.featuresToFlags()...)
-	flags.RustdocFlags = append(flags.RustdocFlags, compiler.cfgsToFlags()...)
-	flags.RustdocFlags = append(flags.RustdocFlags, compiler.featuresToFlags()...)
 	flags.RustFlags = append(flags.RustFlags, "--edition="+compiler.edition())
 	flags.RustdocFlags = append(flags.RustdocFlags, "--edition="+compiler.edition())
 	flags.LinkFlags = append(flags.LinkFlags, compiler.Properties.Ld_flags...)
@@ -296,10 +311,6 @@ func (compiler *baseCompiler) compilerFlags(ctx ModuleContext, flags Flags) Flag
 		flags.LinkFlags = append(flags.LinkFlags, "-Wl,-rpath,"+rpathPrefix+"../"+rpath)
 	}
 
-	if ctx.RustModule().UseVndk() {
-		flags.RustFlags = append(flags.RustFlags, "--cfg 'android_vndk'")
-	}
-
 	return flags
 }
 

rust/library.go

@@ -430,15 +430,25 @@ func (library *libraryDecorator) sharedLibFilename(ctx ModuleContext) string {
 	return library.getStem(ctx) + ctx.toolchain().SharedLibSuffix()
 }
 
-func (library *libraryDecorator) compilerFlags(ctx ModuleContext, flags Flags) Flags {
+func (library *libraryDecorator) cfgFlags(ctx ModuleContext, flags Flags) Flags {
-	flags.RustFlags = append(flags.RustFlags, "-C metadata="+ctx.ModuleName())
+	flags = library.baseCompiler.cfgFlags(ctx, flags)
 	if library.dylib() {
 		// We need to add a dependency on std in order to link crates as dylibs.
 		// The hack to add this dependency is guarded by the following cfg so
 		// that we don't force a dependency when it isn't needed.
 		library.baseCompiler.Properties.Cfgs = append(library.baseCompiler.Properties.Cfgs, "android_dylib")
 	}
+
+	flags.RustFlags = append(flags.RustFlags, library.baseCompiler.cfgsToFlags()...)
+	flags.RustdocFlags = append(flags.RustdocFlags, library.baseCompiler.cfgsToFlags()...)
+
+	return flags
+}
+
+func (library *libraryDecorator) compilerFlags(ctx ModuleContext, flags Flags) Flags {
 	flags = library.baseCompiler.compilerFlags(ctx, flags)
+
+	flags.RustFlags = append(flags.RustFlags, "-C metadata="+ctx.ModuleName())
 	if library.shared() || library.static() {
 		library.includeDirs = append(library.includeDirs, android.PathsForModuleSrc(ctx, library.Properties.Include_dirs)...)
 	}

rust/rust.go

@@ -436,6 +436,8 @@ type RustLibrary struct {
 type compiler interface {
 	initialize(ctx ModuleContext)
 	compilerFlags(ctx ModuleContext, flags Flags) Flags
+	cfgFlags(ctx ModuleContext, flags Flags) Flags
+	featureFlags(ctx ModuleContext, flags Flags) Flags
 	compilerProps() []interface{}
 	compile(ctx ModuleContext, flags Flags, deps PathDeps) android.Path
 	compilerDeps(ctx DepsContext, deps Deps) Deps
@@ -847,8 +849,11 @@ func (mod *Module) GenerateAndroidBuildActions(actx android.ModuleContext) {
 		Toolchain: toolchain,
 	}
 
+	// Calculate rustc flags
 	if mod.compiler != nil {
 		flags = mod.compiler.compilerFlags(ctx, flags)
+		flags = mod.compiler.cfgFlags(ctx, flags)
+		flags = mod.compiler.featureFlags(ctx, flags)
 	}
 	if mod.coverage != nil {
 		flags, deps = mod.coverage.flags(ctx, flags, deps)