Add ModuleContext method to get dependency by name

Instead of forcing every mutator or module to use VisitDirectDeps
to iterate through its deps, allow it to request a dependency by
name to return the Module.

Change-Id: I18b23bffa324bb9d93a7743b6e2a19c07058c775

module_ctx.go

@@ -147,6 +147,9 @@ type ModuleContext interface {
 	OtherModuleErrorf(m Module, fmt string, args ...interface{})
 	OtherModuleDependencyTag(m Module) DependencyTag
 
+	GetDirectDepWithTag(name string, tag DependencyTag) Module
+	GetDirectDep(name string) (Module, DependencyTag)
+
 	VisitDirectDeps(visit func(Module))
 	VisitDirectDepsIf(pred func(Module) bool, visit func(Module))
 	VisitDepsDepthFirst(visit func(Module))
@@ -300,6 +303,34 @@ func (m *baseModuleContext) OtherModuleDependencyTag(logicModule Module) Depende
 	return nil
 }
 
+// GetDirectDep returns the Module and DependencyTag for the direct dependency with the specified
+// name, or nil if none exists.
+func (m *baseModuleContext) GetDirectDep(name string) (Module, DependencyTag) {
+	for _, dep := range m.module.directDeps {
+		if dep.module.Name() == name {
+			return dep.module.logicModule, dep.tag
+		}
+	}
+
+	return nil, nil
+}
+
+// GetDirectDepWithTag returns the Module the direct dependency with the specified name, or nil if
+// none exists.  It panics if the dependency does not have the specified tag.
+func (m *baseModuleContext) GetDirectDepWithTag(name string, tag DependencyTag) Module {
+	for _, dep := range m.module.directDeps {
+		if dep.module.Name() == name {
+			if dep.tag != tag {
+				panic(fmt.Errorf("found dependency %q with tag %#v, expected tag %#v",
+					dep.module, dep.tag, tag))
+			}
+			return dep.module.logicModule
+		}
+	}
+
+	return nil
+}
+
 func (m *baseModuleContext) VisitDirectDeps(visit func(Module)) {
 	defer func() {
 		if r := recover(); r != nil {
@@ -488,6 +519,9 @@ type TopDownMutatorContext interface {
 	OtherModuleErrorf(m Module, fmt string, args ...interface{})
 	OtherModuleDependencyTag(m Module) DependencyTag
 
+	GetDirectDepWithTag(name string, tag DependencyTag) Module
+	GetDirectDep(name string) (Module, DependencyTag)
+
 	VisitDirectDeps(visit func(Module))
 	VisitDirectDepsIf(pred func(Module) bool, visit func(Module))
 	VisitDepsDepthFirst(visit func(Module))