fix: correct automatic type conversion for untyped constants

_test/shift3.go

@@ -0,0 +1,10 @@
+package main
+
+const a = 1.0
+
+const b = a + 3
+
+func main() { println(b << (1)) }
+
+// Output:
+// 8

interp/cfg.go

@@ -3,6 +3,7 @@ package interp
 import (
 	"fmt"
 	"log"
+	"math"
 	"path"
 	"reflect"
 	"unicode"
@@ -403,7 +404,7 @@ func (interp *Interpreter) cfg(root *node) ([]*node, error) {
 						err = n.cfgErrorf("illegal operand types for '%v' operator", n.action)
 					}
 				case aShlAssign, aShrAssign:
-					if !(isInt(t0) && isUint(t1)) {
+					if !(dest.isInteger() && src.isNatural()) {
 						err = n.cfgErrorf("illegal operand types for '%v' operator", n.action)
 					}
 				default:
@@ -521,7 +522,7 @@ func (interp *Interpreter) cfg(root *node) ([]*node, error) {
 					err = n.cfgErrorf("illegal operand types for '%v' operator", n.action)
 				}
 			case aShl, aShr:
-				if !(isInt(t0) && isUint(t1)) {
+				if !(c0.isInteger() && c1.isNatural()) {
 					err = n.cfgErrorf("illegal operand types for '%v' operator", n.action)
 				}
 				n.typ = c0.typ
@@ -1506,7 +1507,57 @@ func wireChild(n *node) {
 	}
 }
 
-// last returns the last child of a node
+// isInteger returns true if node type is integer, false otherwise
+func (n *node) isInteger() bool {
+	if isInt(n.typ.TypeOf()) {
+		return true
+	}
+	if n.typ.untyped && n.rval.IsValid() {
+		t := n.rval.Type()
+		if isInt(t) {
+			return true
+		}
+		if isFloat(t) {
+			// untyped float constant with null decimal part is ok
+			f := n.rval.Float()
+			if f == math.Round(f) {
+				n.rval = reflect.ValueOf(int(f))
+				n.typ.rtype = n.rval.Type()
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// isNatural returns true if node type is natural, false otherwise
+func (n *node) isNatural() bool {
+	if isUint(n.typ.TypeOf()) {
+		return true
+	}
+	if n.typ.untyped && n.rval.IsValid() {
+		t := n.rval.Type()
+		if isUint(t) {
+			return true
+		}
+		if isInt(t) && n.rval.Int() >= 0 {
+			// positive untyped integer constant is ok
+			return true
+		}
+		if isFloat(t) {
+			// positive untyped float constant with null decimal part is ok
+			f := n.rval.Float()
+			if f == math.Round(f) && f >= 0 {
+				n.rval = reflect.ValueOf(uint(f))
+				n.typ.rtype = n.rval.Type()
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// lastChild returns the last child of a node
 func (n *node) lastChild() *node { return n.child[len(n.child)-1] }
 
 func isKey(n *node) bool {

interp/interp_eval_test.go

@@ -44,11 +44,13 @@ func TestEvalArithmetic(t *testing.T) {
 		{desc: "rem_FI", src: "8.0 % 4", err: "1:28: illegal operand types for '%' operator"},
 		{desc: "shl_II", src: "1 << 8", res: "256"},
 		{desc: "shl_IN", src: "1 << -1", err: "1:28: illegal operand types for '<<' operator"},
-		{desc: "shl_IF", src: "1 << 1.0", err: "1:28: illegal operand types for '<<' operator"},
-		{desc: "shl_IF", src: "1.0 << 1", err: "1:28: illegal operand types for '<<' operator"},
+		{desc: "shl_IF", src: "1 << 1.0", res: "2"},
+		{desc: "shl_IF1", src: "1 << 1.1", err: "1:28: illegal operand types for '<<' operator"},
+		{desc: "shl_IF", src: "1.0 << 1", res: "2"},
 		{desc: "shr_II", src: "1 >> 8", res: "0"},
 		{desc: "shr_IN", src: "1 >> -1", err: "1:28: illegal operand types for '>>' operator"},
-		{desc: "shr_IF", src: "1 >> 1.0", err: "1:28: illegal operand types for '>>' operator"},
+		{desc: "shr_IF", src: "1 >> 1.0", res: "0"},
+		{desc: "shr_IF1", src: "1 >> 1.1", err: "1:28: illegal operand types for '>>' operator"},
 	})
 }
 

interp/type.go

@@ -215,14 +215,8 @@ func nodeType(interp *Interpreter, sc *scope, n *node) (*itype, error) {
 			t.name = "float64"
 			t.untyped = true
 		case int:
-			if isShiftOperand(n) && v >= 0 {
-				t.cat = uintT
-				t.name = "uint"
-				n.rval = reflect.ValueOf(uint(v))
-			} else {
-				t.cat = intT
-				t.name = "int"
-			}
+			t.cat = intT
+			t.name = "int"
 			t.untyped = true
 		case uint:
 			t.cat = uintT
@@ -909,13 +903,6 @@ func isShiftNode(n *node) bool {
 	return false
 }
 
-func isShiftOperand(n *node) bool {
-	if isShiftNode(n.anc) {
-		return n.anc.lastChild() == n
-	}
-	return false
-}
-
 func isInterface(t *itype) bool { return t.cat == interfaceT || t.TypeOf().Kind() == reflect.Interface }
 
 func isStruct(t *itype) bool { return t.TypeOf().Kind() == reflect.Struct }