interp: fix handling of redeclared variables in short declaration.

Fixes #1640.

_test/issue-1640.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"errors"
+)
+
+func ShortVariableDeclarations() (i int, err error) {
+	r, err := 1, errors.New("test")
+	i = r
+	return
+}
+
+func main() {
+	_, er := ShortVariableDeclarations()
+	if er != nil {
+		println("ShortVariableDeclarations ok")
+	} else {
+		println("ShortVariableDeclarations not ok")
+	}
+}
+
+// Output:
+// ShortVariableDeclarations ok

interp/cfg.go

@@ -681,7 +681,7 @@ func (interp *Interpreter) cfg(root *node, sc *scope, importPath, pkgName string
 					if dest.typ.incomplete {
 						return
 					}
-					if sc.global {
+					if sc.global || sc.isRedeclared(dest) {
 						// Do not overload existing symbols (defined in GTA) in global scope.
 						sym, _, _ = sc.lookup(dest.ident)
 					}

interp/run.go

@@ -1400,6 +1400,13 @@ func call(n *node) {
 		}
 		runCfg(def.child[3].start, nf, def, n)
 
+		// Set return values
+		for i, v := range rvalues {
+			if v != nil {
+				v(f).Set(nf.data[i])
+			}
+		}
+
 		// Handle branching according to boolean result
 		if fnext != nil && !nf.data[0].Bool() {
 			return fnext

interp/scope.go

@@ -145,6 +145,14 @@ func (s *scope) lookup(ident string) (*symbol, int, bool) {
 	return nil, 0, false
 }
 
+func (s *scope) isRedeclared(n *node) bool {
+	if !isNewDefine(n, s) {
+		return false
+	}
+	// Existing symbol in the scope indicates a redeclaration.
+	return s.sym[n.ident] != nil
+}
+
 func (s *scope) rangeChanType(n *node) *itype {
 	if sym, _, found := s.lookup(n.child[1].ident); found {
 		if t := sym.typ; len(n.child) == 3 && t != nil && (t.cat == chanT || t.cat == chanRecvT) {