pattern: support type aliases

Author: dominikh

debug/debug.go

@@ -9,6 +9,7 @@ import (
 	"go/parser"
 	"go/token"
 	"go/types"
+	"sync"
 )
 
 // TypeCheck parses and type-checks a single-file Go package from a string.
@@ -45,3 +46,17 @@ func FormatNode(node ast.Node) string {
 	format.Node(&buf, fset, node)
 	return buf.String()
 }
+
+var aliasesDefaultOnce sync.Once
+var gotypesaliasDefault bool
+
+func AliasesEnabled() bool {
+	// Dynamically check if Aliases will be produced from go/types.
+	aliasesDefaultOnce.Do(func() {
+		fset := token.NewFileSet()
+		f, _ := parser.ParseFile(fset, "a.go", "package p; type A = int", 0)
+		pkg, _ := new(types.Config).Check("p", fset, []*ast.File{f}, nil)
+		_, gotypesaliasDefault = pkg.Scope().Lookup("A").Type().(*types.Alias)
+	})
+	return gotypesaliasDefault
+}

pattern/match.go

@@ -586,13 +586,28 @@ func (fn Symbol) Match(m *Matcher, node interface{}) (interface{}, bool) {
 	case *types.Builtin:
 		name = obj.Name()
 	case *types.TypeName:
-		if obj.Pkg() == nil {
-			return nil, false
-		}
-		if obj.Parent() != obj.Pkg().Scope() {
-			return nil, false
+		origObj := obj
+		for {
+			if obj.Parent() != obj.Pkg().Scope() {
+				return nil, false
+			}
+			name = types.TypeString(obj.Type(), nil)
+			_, ok = match(m, fn.Name, name)
+			if ok || !obj.IsAlias() {
+				return origObj, ok
+			} else {
+				// FIXME(dh): we should peel away one layer of alias at a time; this is blocked on
+				// github.com/golang/go/issues/66559
+				switch typ := types.Unalias(obj.Type()).(type) {
+				case interface{ Obj() *types.TypeName }:
+					obj = typ.Obj()
+				case *types.Basic:
+					return match(m, fn.Name, typ.Name())
+				default:
+					return nil, false
+				}
+			}
 		}
-		name = types.TypeString(obj.Type(), nil)
 	case *types.Const, *types.Var:
 		if obj.Pkg() == nil {
 			return nil, false

pattern/parser_test.go

@@ -11,6 +11,8 @@ import (
 	"runtime"
 	"strings"
 	"testing"
+
+	"honnef.co/go/tools/debug"
 )
 
 func TestParse(t *testing.T) {
@@ -112,3 +114,34 @@ func FuzzParse(f *testing.F) {
 		}
 	})
 }
+
+func TestMatchAlias(t *testing.T) {
+	p1 := MustParse(`(CallExpr (Symbol "foo.Alias") _)`)
+	p2 := MustParse(`(CallExpr (Symbol "int") _)`)
+
+	f, _, info, err := debug.TypeCheck(`
+package pkg
+type Alias = int
+func _() { _ = Alias(0) }
+`)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	m := &Matcher{
+		TypesInfo: info,
+	}
+	node := f.Decls[1].(*ast.FuncDecl).Body.List[0].(*ast.AssignStmt).Rhs[0]
+
+	if debug.AliasesEnabled() {
+		// Check that we can match on the name of the alias
+		if ok := m.Match(p1, node); !ok {
+			t.Errorf("%s did not match", p1.Root)
+		}
+	}
+
+	// Check that we can match on the name of the alias's target
+	if ok := m.Match(p2, node); !ok {
+		t.Errorf("%s did not match", p2.Root)
+	}
+}