go/types: adjust type-checking of shifts to match compilers

For #14822.

Change-Id: Ia3f5558f3e0dcb8ee2dab54a6e9588eecc22511f
Reviewed-on: https://go-review.googlesource.com/45074Reviewed-by: Alan Donovan <adonovan@google.com>

src/go/types/expr.go

@@ -633,13 +633,13 @@ func (check *Checker) shift(x, y *operand, e *ast.BinaryExpr, op token.Token) {
 	}
 
 	// spec: "The right operand in a shift expression must have unsigned
-	// integer type or be an untyped constant that can be converted to
-	// unsigned integer type."
+	// integer type or be an untyped constant representable by a value of
+	// type uint."
 	switch {
 	case isUnsigned(y.typ):
 		// nothing to do
 	case isUntyped(y.typ):
-		check.convertUntyped(y, Typ[UntypedInt])
+		check.convertUntyped(y, Typ[Uint])
 		if y.mode == invalid {
 			x.mode = invalid
 			return

src/go/types/testdata/shifts.src

@@ -10,7 +10,7 @@ func shifts0() {
 		s = 10
 		_ = 0<<0
 		_ = 1<<s
-		_ = 1<<- /* ERROR "invalid shift" */ 1
+		_ = 1<<- /* ERROR "overflows uint" */ 1
 		_ = 1<<1075 /* ERROR "invalid shift" */
 		_ = 2.0<<1
 
@@ -39,12 +39,18 @@ func shifts1() {
 		_ = 1<<u
 		_ = 1<<"foo" /* ERROR "cannot convert" */
 		_ = i<<0
-		_ = i<<- /* ERROR "must not be negative" */ 1
+		_ = i<<- /* ERROR "overflows uint" */ 1
 		_ = 1 /* ERROR "overflows" */ <<100
 
 		_ uint = 1 << 0
 		_ uint = 1 << u
 		_ float32 = 1 /* ERROR "must be integer" */ << u
+
+		// for issue 14822
+		_ = 1<<( /* ERROR "invalid shift count" */ 1<<63)
+		_ = 1<<( /* ERROR "overflows uint" */ 1<<64)
+		_ = u<<(1<<63) // valid
+		_ = u<<( /* ERROR "overflows uint" */ 1<<64)
 	)
 }
 
@@ -321,11 +327,11 @@ func issue5895() {
 }
 
 func issue11325() {
-	var _ = 0 >> 1.1 /* ERROR "must be unsigned integer" */ // example from issue 11325
-	_ = 0 >> 1.1 /* ERROR "must be unsigned integer" */
-	_ = 0 << 1.1 /* ERROR "must be unsigned integer" */
+	var _ = 0 >> 1.1 /* ERROR "truncated to uint" */ // example from issue 11325
+	_ = 0 >> 1.1 /* ERROR "truncated to uint" */
+	_ = 0 << 1.1 /* ERROR "truncated to uint" */
 	_ = 0 >> 1.
-	_ = 1 >> 1.1 /* ERROR "must be unsigned integer" */
+	_ = 1 >> 1.1 /* ERROR "truncated to uint" */
 	_ = 1 >> 1.
 	_ = 1. >> 1
 	_ = 1. >> 1.