interp: types should not recover data for aliases

When `nodeType` recovers names and methods, it can overwrite the data if the type is an aliasT. When aliasing a type, do not recover the methods, this will be done in the GTA typeSpec pass.

Related to traefik#1158

_test/alias3.go

@@ -0,0 +1,19 @@
+package main
+
+import "github.com/traefik/yaegi/_test/alias3"
+
+var globalT *T
+
+func init() {
+	globalT = &T{A: "test"}
+}
+
+type T alias3.T
+
+func (t *T) PrintT() {
+	(*alias3.T)(t).Print()
+}
+
+func main() {
+	globalT.PrintT()
+}

_test/alias3/alias3.go

@@ -0,0 +1,12 @@
+package alias3
+
+type T struct {
+	A string
+}
+
+func (t *T) Print() {
+	println(t.A)
+}
+
+// Output:
+// test

interp/gta.go

@@ -285,10 +285,15 @@ func (interp *Interpreter) gta(root *node, rpath, importPath, pkgName string) ([
 			sym, exists := sc.sym[typeName]
 			if !exists {
 				sc.sym[typeName] = &symbol{kind: typeSym}
-			} else if sym.typ == nil || len(sym.typ.method) == 0 {
-				// TODO(mpl): figure out how to detect redeclarations without breaking type aliases.
-				// Allow redeclarations for now.
-				sc.sym[typeName] = &symbol{kind: typeSym}
+			} else {
+				if sym.typ != nil && (len(sym.typ.method) > 0) {
+					// Type has already been seen as a receiver in a method function
+					n.typ.method = append(n.typ.method, sym.typ.method...)
+				} else {
+					// TODO(mpl): figure out how to detect redeclarations without breaking type aliases.
+					// Allow redeclarations for now.
+					sc.sym[typeName] = &symbol{kind: typeSym}
+				}
 			}
 			sc.sym[typeName].typ = n.typ
 			if !n.typ.isComplete() {

interp/type.go

@@ -888,11 +888,11 @@ func nodeType(interp *Interpreter, sc *scope, n *node) (*itype, error) {
 		err = n.cfgErrorf("use of untyped nil %s", t.name)
 	}
 
-	if n.anc.kind == typeSpec {
+	// The existing symbol data needs to be recovered, but not in the
+	// case where we are aliasing another type.
+	if n.anc.kind == typeSpec && n.kind != selectorExpr && n.kind != identExpr {
 		name := n.anc.child[0].ident
 		if sym := sc.sym[name]; sym != nil {
-			// Recover previously declared methods and set the type name.
-			t.method = sym.typ.method
 			t.path = sc.pkgName
 			t.name = name
 		}