interp: fix processing of aliased types

For a long time, there was a confusion between aliased types and named types (due to my misunderstanding of alias types in Go at that time). The type category `aliasT` has been renamed into `linkedT`, which is correct semantically. 

Aliased types are only declared using `typeSpecAssign`, and its processing is now distinct from `typeSpec` statement, used for named types.

A `linkedT` type is obtained by a statement like `type A uint32`, where `A` type category is therefore `linkedT`.

An aliased type is obtained by a statement like `type A = uint32` (notice the `=` sign, translating into `typeSpecAssign`).

The semantic difference is that in the first linkedT form, `A` and `uint32` are 2 distinct types, instead of being strictly equivalent in the `typeSpecAssign` form (the 2 names lead to one type definition).


Fixes #1416.

_test/issue-1416.go

@@ -0,0 +1,17 @@
+package main
+
+type Number int32
+
+type Number1 = Number
+
+type Number2 = Number1
+
+func (n Number2) IsValid() bool { return true }
+
+func main() {
+	a := Number(5)
+	println(a.IsValid())
+}
+
+// Output:
+// true

_test/alias3.go → _test/named3.go

@@ -1,17 +1,17 @@
 package main
 
-import "github.com/traefik/yaegi/_test/alias3"
+import "github.com/traefik/yaegi/_test/named3"
 
 var globalT *T
 
 func init() {
 	globalT = &T{A: "test"}
 }
 
-type T alias3.T
+type T named3.T
 
 func (t *T) PrintT() {
-	(*alias3.T)(t).Print()
+	(*named3.T)(t).Print()
 }
 
 func main() {

_test/alias3/alias3.go → _test/named3/named3.go

@@ -1,4 +1,4 @@
-package alias3
+package named3
 
 import (
 	"fmt"

interp/cfg.go

@@ -145,9 +145,9 @@ func (interp *Interpreter) cfg(root *node, sc *scope, importPath, pkgName string
 					}
 
 					switch o.typ.cat {
-					case valueT, aliasT:
+					case valueT, linkedT:
 						typ := o.typ.rtype
-						if o.typ.cat == aliasT {
+						if o.typ.cat == linkedT {
 							typ = o.typ.val.TypeOf()
 						}
 						switch typ.Kind() {
@@ -845,7 +845,7 @@ func (interp *Interpreter) cfg(root *node, sc *scope, importPath, pkgName string
 			}
 			wireChild(n)
 			t := n.child[0].typ
-			for t.cat == aliasT {
+			for t.cat == linkedT {
 				t = t.val
 			}
 			switch t.cat {
@@ -2894,7 +2894,7 @@ func typeSwichAssign(n *node) bool {
 
 func compositeGenerator(n *node, typ *itype, rtyp reflect.Type) (gen bltnGenerator) {
 	switch typ.cat {
-	case aliasT, ptrT:
+	case linkedT, ptrT:
 		gen = compositeGenerator(n, typ.val, rtyp)
 	case arrayT, sliceT:
 		gen = arrayLit

interp/gta.go

@@ -176,7 +176,7 @@ func (interp *Interpreter) gta(root *node, rpath, importPath, pkgName string) ([
 					revisit = append(revisit, n)
 					return false
 				}
-				if sym.kind != typeSym || (sym.node != nil && sym.node.kind == typeSpecAssign) {
+				if sym.typ.path != pkgName {
 					err = n.cfgErrorf("cannot define new methods on non-local type %s", baseType(sym.typ).id())
 					return false
 				}
@@ -298,7 +298,7 @@ func (interp *Interpreter) gta(root *node, rpath, importPath, pkgName string) ([
 			typeName := n.child[0].ident
 			if len(n.child) > 2 {
 				// Handle a generic type: skip definition as parameter is not instantiated yet.
-				n.typ = genericOf(nil, typeName, withNode(n.child[0]), withScope(sc))
+				n.typ = genericOf(nil, typeName, pkgName, withNode(n.child[0]), withScope(sc))
 				if _, exists := sc.sym[typeName]; !exists {
 					sc.sym[typeName] = &symbol{kind: typeSym, node: n}
 				}
@@ -312,6 +312,15 @@ func (interp *Interpreter) gta(root *node, rpath, importPath, pkgName string) ([
 				return false
 			}
 
+			if n.kind == typeSpecAssign {
+				// Create an aliased type in the current scope
+				sc.sym[typeName] = &symbol{kind: typeSym, node: n, typ: typ}
+				n.typ = typ
+				break
+			}
+
+			// else we are not an alias (typeSpec)
+
 			switch n.child[1].kind {
 			case identExpr, selectorExpr:
 				n.typ = namedOf(typ, pkgName, typeName, withNode(n.child[0]), withScope(sc))
@@ -333,24 +342,15 @@ func (interp *Interpreter) gta(root *node, rpath, importPath, pkgName string) ([
 			}
 			sym, exists := sc.sym[typeName]
 			if !exists {
-				sc.sym[typeName] = &symbol{kind: typeSym, node: n}
-			} else {
-				if sym.typ != nil && (len(sym.typ.method) > 0) {
-					if n.kind == typeSpecAssign {
-						err = n.cfgErrorf("cannot define new methods on non-local type %s", baseType(typ).id())
-						return false
-					}
-					// Type has already been seen as a receiver in a method function
-					for _, m := range sym.typ.method {
-						n.typ.addMethod(m)
-					}
-				} else {
-					// TODO(mpl): figure out how to detect redeclarations without breaking type aliases.
-					// Allow redeclarations for now.
-					sc.sym[typeName] = &symbol{kind: typeSym, node: n}
+				sym = &symbol{kind: typeSym, node: n}
+				sc.sym[typeName] = sym
+			} else if sym.typ != nil && (len(sym.typ.method) > 0) {
+				// Type has already been seen as a receiver in a method function
+				for _, m := range sym.typ.method {
+					n.typ.addMethod(m)
 				}
 			}
-			sc.sym[typeName].typ = n.typ
+			sym.typ = n.typ
 			if !n.typ.isComplete() {
 				revisit = append(revisit, n)
 			}
@@ -368,7 +368,7 @@ func (interp *Interpreter) gta(root *node, rpath, importPath, pkgName string) ([
 func baseType(t *itype) *itype {
 	for {
 		switch t.cat {
-		case ptrT, aliasT:
+		case ptrT, linkedT:
 			t = t.val
 		default:
 			return t
@@ -440,7 +440,7 @@ func definedType(typ *itype) error {
 			return err
 		}
 		fallthrough
-	case aliasT, arrayT, chanT, chanSendT, chanRecvT, ptrT, variadicT:
+	case linkedT, arrayT, chanT, chanSendT, chanRecvT, ptrT, variadicT:
 		if err := definedType(typ.val); err != nil {
 			return err
 		}

interp/interp_eval_test.go

@@ -219,6 +219,8 @@ func TestEvalTypeSpec(t *testing.T) {
 	runTests(t, i, []testCase{
 		{src: `type _ struct{}`, err: "1:19: cannot use _ as value"},
 		{src: `a := struct{a, _ int}{32, 0}`, res: "{32 0}"},
+		{src: "type A int; type A = string", err: "1:31: A redeclared in this block"},
+		{src: "type B int; type B string", err: "1:31: B redeclared in this block"},
 	})
 }
 

interp/run.go

@@ -2616,7 +2616,7 @@ func doCompositeBinStruct(n *node, hasType bool) {
 	next := getExec(n.tnext)
 	value := valueGenerator(n, n.findex)
 	typ := n.typ.rtype
-	if n.typ.cat == ptrT || n.typ.cat == aliasT {
+	if n.typ.cat == ptrT || n.typ.cat == linkedT {
 		typ = n.typ.val.rtype
 	}
 	child := n.child
@@ -2683,7 +2683,7 @@ func doComposite(n *node, hasType bool, keyed bool) {
 	value := valueGenerator(n, n.findex)
 	next := getExec(n.tnext)
 	typ := n.typ
-	if typ.cat == ptrT || typ.cat == aliasT {
+	if typ.cat == ptrT || typ.cat == linkedT {
 		typ = typ.val
 	}
 	child := n.child