Support embedded interfaces in cmg

Before, Clue Mock Generator would not include the methods from embedded
interfaces, for example:

```golang
package something

import (
    "goa.design/clue/health"
)

type Client interface {
    Get() (string, error)

    health.Pinger
}
```

Would not include the methods from `health.Pinger` in the generated
mock. Now it will!

mock/cmd/cmg/pkg/generate/_tests/extensive/aliased/imported.go

@@ -2,4 +2,8 @@ package imported
 
 type (
 	Type byte
+
+	Interface interface {
+		Imported(Type) Type
+	}
 )

mock/cmd/cmg/pkg/generate/_tests/extensive/extensive.go

@@ -38,6 +38,13 @@ type (
 		NamedTypes(Struct, Array, io.Reader, imported.Type, goa.Endpoint, Generic[uint, string, Struct, Array]) (Struct, Array, io.Reader, imported.Type, goa.Endpoint, Generic[uint, string, Struct, Array])
 		FuncNamedTypes(func(Struct, Array, io.Reader, imported.Type, goa.Endpoint, Generic[uint, string, Struct, Array])) func(Struct, Array, io.Reader, imported.Type, goa.Endpoint, Generic[uint, string, Struct, Array])
 		VariableConflicts(f, m uint)
+
+		Embedded
+		imported.Interface
+	}
+
+	Embedded interface {
+		Embedded(int8) int8
 	}
 
 	Generic[K comparable, V ~int | bool | string, X, Y any] interface {

mock/cmd/cmg/pkg/parse/_tests/doer/doer.go

@@ -1,10 +1,22 @@
 package doer
 
+import (
+	"example.com/a/b/external"
+)
+
 type (
 	Doer interface {
 		Do(a, b int, c float64) (d, e int, err error)
 	}
 
+	EmbeddedDoer interface {
+		Doer
+	}
+
+	ExternalEmbeddedDoer interface {
+		external.Doer
+	}
+
 	doer interface { //nolint:unused
 		do(a, b int, c float64) (d, e int, err error)
 	}

mock/cmd/cmg/pkg/parse/_tests/external/doer.go

@@ -0,0 +1,7 @@
+package external
+
+type (
+	Doer interface {
+		Do(a, b int, c float64) (d, e int, err error)
+	}
+)

mock/cmd/cmg/pkg/parse/interface.go

@@ -51,13 +51,33 @@ func (i *interface_) TypeParameters() (typeParameters []Type) {
 	return
 }
 
-func (i *interface_) Methods() (methods []Method) {
-	for _, m := range i.interfaceType.Methods.List {
+func (i *interface_) Methods() []Method {
+	return i.methods(i.interfaceType)
+}
+
+func (i *interface_) methods(it *ast.InterfaceType) (methods []Method) {
+	for _, m := range it.Methods.List {
 		switch t := m.Type.(type) {
 		case *ast.FuncType:
 			for _, n := range m.Names {
 				o, _, _ := types.LookupFieldOrMethod(i.p.Types.Scope().Lookup(i.Name()).Type(), true, i.p.Types, n.Name)
-				methods = append(methods, newMethod(i.p, n, t, o.Type().Underlying().(*types.Signature).Variadic()))
+				methods = append(methods, newASTMethod(i.p, n, t, o.Type().Underlying().(*types.Signature).Variadic()))
+			}
+		case *ast.Ident:
+			switch dt := t.Obj.Decl.(type) {
+			case *ast.TypeSpec:
+				switch t := dt.Type.(type) {
+				case *ast.InterfaceType:
+					methods = append(methods, i.methods(t)...)
+				}
+			}
+		case *ast.SelectorExpr:
+			if tv, ok := i.p.TypesInfo.Types[t]; ok {
+				if ti, ok := tv.Type.Underlying().(*types.Interface); ok {
+					for j := 0; j < ti.NumMethods(); j++ {
+						methods = append(methods, newTypesMethod(ti.Method(j)))
+					}
+				}
 			}
 		}
 	}

mock/cmd/cmg/pkg/parse/interface_test.go

@@ -2,6 +2,7 @@ package parse
 
 import (
 	"go/ast"
+	"go/types"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -134,6 +135,28 @@ func TestInterface_Methods(t *testing.T) {
 	require.Len(t, ps, 1)
 	p := ps[0]
 
+	var (
+		externalDoerSelectorExpr *ast.SelectorExpr
+		externalDoerInterface    *types.Interface
+	)
+	for at, tv := range p.TypesInfo.Types {
+		if se, ok := at.(*ast.SelectorExpr); ok {
+			if i, ok := se.X.(*ast.Ident); ok {
+				if i.Name != "external" {
+					continue
+				}
+				if se.Sel.Name == "Doer" {
+					externalDoerSelectorExpr = se
+					externalDoerInterface, _ = tv.Type.Underlying().(*types.Interface)
+					break
+				}
+			}
+		}
+	}
+	require.NotNil(t, externalDoerSelectorExpr)
+	require.NotNil(t, externalDoerInterface)
+	require.Greater(t, externalDoerInterface.NumMethods(), 0)
+
 	cases := []struct {
 		Name          string
 		TypeSpec      *ast.TypeSpec
@@ -159,7 +182,7 @@ func TestInterface_Methods(t *testing.T) {
 				},
 			}}},
 			Expected: []Method{
-				newMethod(p, ast.NewIdent("Do"), &ast.FuncType{
+				newASTMethod(p, ast.NewIdent("Do"), &ast.FuncType{
 					Params: &ast.FieldList{List: []*ast.Field{
 						{Names: []*ast.Ident{ast.NewIdent("a"), ast.NewIdent("b")}, Type: ast.NewIdent("int")},
 						{Names: []*ast.Ident{ast.NewIdent("c")}, Type: ast.NewIdent("float64")},
@@ -171,6 +194,49 @@ func TestInterface_Methods(t *testing.T) {
 				}, false),
 			},
 		},
+		{
+			Name:     "embedded interface",
+			TypeSpec: &ast.TypeSpec{Name: ast.NewIdent("EmbeddedDoer")},
+			InterfaceType: &ast.InterfaceType{Methods: &ast.FieldList{List: []*ast.Field{{
+				Type: &ast.Ident{Name: "Doer", Obj: &ast.Object{Kind: ast.Typ, Decl: &ast.TypeSpec{
+					Type: &ast.InterfaceType{Methods: &ast.FieldList{List: []*ast.Field{
+						{
+							Names: []*ast.Ident{ast.NewIdent("Do")},
+							Type: &ast.FuncType{
+								Params: &ast.FieldList{List: []*ast.Field{
+									{Names: []*ast.Ident{ast.NewIdent("a"), ast.NewIdent("b")}, Type: ast.NewIdent("int")},
+									{Names: []*ast.Ident{ast.NewIdent("c")}, Type: ast.NewIdent("float64")},
+								}},
+								Results: &ast.FieldList{List: []*ast.Field{
+									{Names: []*ast.Ident{ast.NewIdent("d"), ast.NewIdent("e")}, Type: ast.NewIdent("int")},
+									{Names: []*ast.Ident{ast.NewIdent("err")}, Type: ast.NewIdent("error")},
+								}},
+							},
+						},
+					}}},
+				}}}}},
+			}},
+			Expected: []Method{
+				newASTMethod(p, ast.NewIdent("Do"), &ast.FuncType{
+					Params: &ast.FieldList{List: []*ast.Field{
+						{Names: []*ast.Ident{ast.NewIdent("a"), ast.NewIdent("b")}, Type: ast.NewIdent("int")},
+						{Names: []*ast.Ident{ast.NewIdent("c")}, Type: ast.NewIdent("float64")},
+					}},
+					Results: &ast.FieldList{List: []*ast.Field{
+						{Names: []*ast.Ident{ast.NewIdent("d"), ast.NewIdent("e")}, Type: ast.NewIdent("int")},
+						{Names: []*ast.Ident{ast.NewIdent("err")}, Type: ast.NewIdent("error")},
+					}},
+				}, false),
+			},
+		},
+		{
+			Name:          "external embedded interface",
+			TypeSpec:      &ast.TypeSpec{Name: ast.NewIdent("ExternalEmbeddedDoer")},
+			InterfaceType: &ast.InterfaceType{Methods: &ast.FieldList{List: []*ast.Field{{Type: externalDoerSelectorExpr}}}},
+			Expected: []Method{
+				newTypesMethod(externalDoerInterface.Method(0)),
+			},
+		},
 	}
 
 	for _, tc := range cases {

mock/cmd/cmg/pkg/parse/method.go

@@ -2,6 +2,7 @@ package parse
 
 import (
 	"go/ast"
+	"go/types"
 
 	"golang.org/x/tools/go/packages"
 )
@@ -15,54 +16,89 @@ type (
 		Variadic() bool
 	}
 
-	method struct {
+	astMethod struct {
 		p        *packages.Package
 		ident    *ast.Ident
 		funcType *ast.FuncType
 		variadic bool
 	}
+
+	typesMethod struct {
+		f *types.Func
+		s *types.Signature
+	}
 )
 
-func newMethod(p *packages.Package, ident *ast.Ident, funcType *ast.FuncType, variadic bool) Method {
-	return &method{p: p, ident: ident, funcType: funcType, variadic: variadic}
+func newASTMethod(p *packages.Package, ident *ast.Ident, funcType *ast.FuncType, variadic bool) Method {
+	return &astMethod{p: p, ident: ident, funcType: funcType, variadic: variadic}
 }
 
-func (m *method) Name() string {
-	return m.ident.Name
+func (am *astMethod) Name() string {
+	return am.ident.Name
 }
 
-func (m *method) IsExported() bool {
-	return m.ident.IsExported()
+func (am *astMethod) IsExported() bool {
+	return am.ident.IsExported()
 }
 
-func (m *method) Parameters() (parameters []Value) {
-	for _, p := range m.funcType.Params.List {
+func (am *astMethod) Parameters() (parameters []Value) {
+	for _, p := range am.funcType.Params.List {
 		idents := []*ast.Ident{nil}
 		if p.Names != nil {
 			idents = p.Names
 		}
 		for _, ident := range idents {
-			parameters = append(parameters, newValue(m.p, ident, p.Type))
+			parameters = append(parameters, newASTValue(am.p, ident, p.Type))
 		}
 	}
 	return
 }
 
-func (m *method) Results() (results []Value) {
-	if m.funcType.Results != nil {
-		for _, r := range m.funcType.Results.List {
+func (am *astMethod) Results() (results []Value) {
+	if am.funcType.Results != nil {
+		for _, r := range am.funcType.Results.List {
 			idents := []*ast.Ident{nil}
 			if r.Names != nil {
 				idents = r.Names
 			}
 			for _, ident := range idents {
-				results = append(results, newValue(m.p, ident, r.Type))
+				results = append(results, newASTValue(am.p, ident, r.Type))
 			}
 		}
 	}
 	return
 }
 
-func (m *method) Variadic() bool {
-	return m.variadic
+func (am *astMethod) Variadic() bool {
+	return am.variadic
+}
+
+func newTypesMethod(f *types.Func) Method {
+	return &typesMethod{f: f, s: f.Type().(*types.Signature)}
+}
+
+func (tm *typesMethod) Name() string {
+	return tm.f.Name()
+}
+
+func (tm *typesMethod) IsExported() bool {
+	return tm.f.Exported()
+}
+
+func (tm *typesMethod) Parameters() (parameters []Value) {
+	for i := 0; i < tm.s.Params().Len(); i++ {
+		parameters = append(parameters, newTypesValue(tm.s.Params().At(i)))
+	}
+	return
+}
+
+func (tm *typesMethod) Results() (results []Value) {
+	for i := 0; i < tm.s.Results().Len(); i++ {
+		results = append(results, newTypesValue(tm.s.Results().At(i)))
+	}
+	return
+}
+
+func (tm *typesMethod) Variadic() bool {
+	return tm.s.Variadic()
 }