go/types: better error message when using multi-valued expressions in single-value context

Also: Added initial set of (missing and/or spread out) tests for binary operations.

Fixes #11896.

Change-Id: I037436d8318c18f9758b435eca2d45b3bdd17ef8
Reviewed-on: https://go-review.googlesource.com/14660
Reviewed-by: Alan Donovan <adonovan@google.com>

src/go/types/assignments.go

@@ -30,6 +30,8 @@ func (check *Checker) assignment(x *operand, T Type, reason *string) bool {
 
 	// x must be a single value
 	// (tuple types are never named - no need for underlying type)
+	// TODO(gri) We may be able to get rid of this check now that
+	// we check for single-valued expressions more rigorously.
 	if t, _ := x.typ.(*Tuple); t != nil {
 		assert(t.Len() > 1)
 		check.errorf(x.pos(), "%d-valued expression %s used as single value", t.Len(), x)
@@ -205,7 +207,7 @@ func (check *Checker) assignVar(lhs ast.Expr, x *operand) Type {
 // return expressions, and returnPos is the position of the return statement.
 func (check *Checker) initVars(lhs []*Var, rhs []ast.Expr, returnPos token.Pos) {
 	l := len(lhs)
-	get, r, commaOk := unpack(func(x *operand, i int) { check.expr(x, rhs[i]) }, len(rhs), l == 2 && !returnPos.IsValid())
+	get, r, commaOk := unpack(func(x *operand, i int) { check.multiExpr(x, rhs[i]) }, len(rhs), l == 2 && !returnPos.IsValid())
 	if get == nil || l != r {
 		// invalidate lhs and use rhs
 		for _, obj := range lhs {
@@ -244,7 +246,7 @@ func (check *Checker) initVars(lhs []*Var, rhs []ast.Expr, returnPos token.Pos)
 
 func (check *Checker) assignVars(lhs, rhs []ast.Expr) {
 	l := len(lhs)
-	get, r, commaOk := unpack(func(x *operand, i int) { check.expr(x, rhs[i]) }, len(rhs), l == 2)
+	get, r, commaOk := unpack(func(x *operand, i int) { check.multiExpr(x, rhs[i]) }, len(rhs), l == 2)
 	if get == nil {
 		return // error reported by unpack
 	}

src/go/types/builtins.go

@@ -44,7 +44,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 	switch id {
 	default:
 		// make argument getter
-		arg, nargs, _ = unpack(func(x *operand, i int) { check.expr(x, call.Args[i]) }, nargs, false)
+		arg, nargs, _ = unpack(func(x *operand, i int) { check.multiExpr(x, call.Args[i]) }, nargs, false)
 		if arg == nil {
 			return
 		}

src/go/types/call.go

@@ -61,7 +61,7 @@ func (check *Checker) call(x *operand, e *ast.CallExpr) exprKind {
 			return statement
 		}
 
-		arg, n, _ := unpack(func(x *operand, i int) { check.expr(x, e.Args[i]) }, len(e.Args), false)
+		arg, n, _ := unpack(func(x *operand, i int) { check.multiExpr(x, e.Args[i]) }, len(e.Args), false)
 		if arg == nil {
 			x.mode = invalid
 			x.expr = e

src/go/types/expr.go

@@ -1453,23 +1453,40 @@ func (check *Checker) typeAssertion(pos token.Pos, x *operand, xtyp *Interface,
 	check.errorf(pos, "%s cannot have dynamic type %s (%s %s)", x, T, msg, method.name)
 }
 
+func (check *Checker) singleValue(x *operand) {
+	if x.mode == value {
+		// tuple types are never named - no need for Underlying() below
+		if t, ok := x.typ.(*Tuple); ok && t.Len() != 1 {
+			check.errorf(x.pos(), "%d-valued %s in single-value context", t.Len(), x)
+			x.mode = invalid
+		}
+	}
+}
+
 // expr typechecks expression e and initializes x with the expression value.
+// The result must be a single value.
 // If an error occurred, x.mode is set to invalid.
 //
 func (check *Checker) expr(x *operand, e ast.Expr) {
+	check.multiExpr(x, e)
+	check.singleValue(x)
+}
+
+// multiExpr is like expr but the result may be a multi-value.
+func (check *Checker) multiExpr(x *operand, e ast.Expr) {
 	check.rawExpr(x, e, nil)
 	var msg string
 	switch x.mode {
 	default:
 		return
 	case novalue:
-		msg = "used as value"
+		msg = "%s used as value"
 	case builtin:
-		msg = "must be called"
+		msg = "%s must be called"
 	case typexpr:
-		msg = "is not an expression"
+		msg = "%s is not an expression"
 	}
-	check.errorf(x.pos(), "%s %s", x, msg)
+	check.errorf(x.pos(), msg, x)
 	x.mode = invalid
 }
 
@@ -1480,18 +1497,19 @@ func (check *Checker) expr(x *operand, e ast.Expr) {
 func (check *Checker) exprWithHint(x *operand, e ast.Expr, hint Type) {
 	assert(hint != nil)
 	check.rawExpr(x, e, hint)
+	check.singleValue(x)
 	var msg string
 	switch x.mode {
 	default:
 		return
 	case novalue:
-		msg = "used as value"
+		msg = "%s used as value"
 	case builtin:
-		msg = "must be called"
+		msg = "%s must be called"
 	case typexpr:
-		msg = "is not an expression"
+		msg = "%s is not an expression"
 	}
-	check.errorf(x.pos(), "%s %s", x, msg)
+	check.errorf(x.pos(), msg, x)
 	x.mode = invalid
 }
 
@@ -1500,6 +1518,7 @@ func (check *Checker) exprWithHint(x *operand, e ast.Expr, hint Type) {
 //
 func (check *Checker) exprOrType(x *operand, e ast.Expr) {
 	check.rawExpr(x, e, nil)
+	check.singleValue(x)
 	if x.mode == novalue {
 		check.errorf(x.pos(), "%s used as value or type", x)
 		x.mode = invalid

src/go/types/testdata/expr0.src

@@ -172,3 +172,9 @@ var (
 	p3 P = &p2
 )
 
+func g() (a, b int) { return }
+
+func _() {
+	_ = -g /* ERROR 2-valued g */ ()
+	_ = <-g /* ERROR 2-valued g */ ()
+}

src/go/types/testdata/expr1.src

@@ -5,3 +5,123 @@
 // binary expressions
 
 package expr1
+
+type mybool bool
+
+func _(x, y bool, z mybool) {
+	x = x || y
+	x = x || true
+	x = x || false
+	x = x && y
+	x = x && true
+	x = x && false
+
+	z = z /* ERROR mismatched types */ || y
+	z = z || true
+	z = z || false
+	z = z /* ERROR mismatched types */ && y
+	z = z && true
+	z = z && false
+}
+
+type myint int
+
+func _(x, y int, z myint) {
+	x = x + 1
+	x = x + 1.0
+	x = x + 1.1 // ERROR truncated to int
+	x = x + y
+	x = x - y
+	x = x * y
+	x = x / y
+	x = x % y
+	x = x << y // ERROR must be unsigned integer
+	x = x >> y // ERROR must be unsigned integer
+
+	z = z + 1
+	z = z + 1.0
+	z = z + 1.1 // ERROR truncated to int
+	z = z /* ERROR mismatched types */ + y
+	z = z /* ERROR mismatched types */ - y
+	z = z /* ERROR mismatched types */ * y
+	z = z /* ERROR mismatched types */ / y
+	z = z /* ERROR mismatched types */ % y
+	z = z << y // ERROR must be unsigned integer
+	z = z >> y // ERROR must be unsigned integer
+}
+
+type myuint uint
+
+func _(x, y uint, z myuint) {
+	x = x + 1
+	x = x + - /* ERROR overflows uint */ 1
+	x = x + 1.0
+	x = x + 1.1 // ERROR truncated to uint
+	x = x + y
+	x = x - y
+	x = x * y
+	x = x / y
+	x = x % y
+	x = x << y
+	x = x >> y
+
+	z = z + 1
+	z = x + - /* ERROR overflows uint */ 1
+	z = z + 1.0
+	z = z + 1.1 // ERROR truncated to uint
+	z = z /* ERROR mismatched types */ + y
+	z = z /* ERROR mismatched types */ - y
+	z = z /* ERROR mismatched types */ * y
+	z = z /* ERROR mismatched types */ / y
+	z = z /* ERROR mismatched types */ % y
+	z = z << y
+	z = z >> y
+}
+
+type myfloat64 float64
+
+func _(x, y float64, z myfloat64) {
+	x = x + 1
+	x = x + -1
+	x = x + 1.0
+	x = x + 1.1
+	x = x + y
+	x = x - y
+	x = x * y
+	x = x / y
+	x = x /* ERROR not defined */ % y
+	x = x /* ERROR operand x .* must be integer */ << y
+	x = x /* ERROR operand x .* must be integer */ >> y
+
+	z = z + 1
+	z = z + -1
+	z = z + 1.0
+	z = z + 1.1
+	z = z /* ERROR mismatched types */ + y
+	z = z /* ERROR mismatched types */ - y
+	z = z /* ERROR mismatched types */ * y
+	z = z /* ERROR mismatched types */ / y
+	z = z /* ERROR mismatched types */ % y
+	z = z /* ERROR operand z .* must be integer */ << y
+	z = z /* ERROR operand z .* must be integer */ >> y
+}
+
+type mystring string
+
+func _(x, y string, z mystring) {
+	x = x + "foo"
+	x = x /* ERROR not defined */ - "foo"
+	x = x + 1 // ERROR cannot convert
+	x = x + y
+	x = x /* ERROR not defined */ - y
+	x = x * 10 // ERROR cannot convert
+}
+
+func f() (a, b int) { return }
+
+func _(x int) {
+	_ = f /* ERROR 2-valued f */ () + 1
+	_ = x + f /* ERROR 2-valued f */ ()
+	_ = f /* ERROR 2-valued f */ () + f
+	_ = f /* ERROR 2-valued f */ () + f /* ERROR 2-valued f */ ()
+}

src/go/types/testdata/stmt0.src

@@ -631,14 +631,14 @@ func issue11667() {
 
 func issue11687() {
 	f := func() (_, _ int) { return }
-	switch f /* ERROR "2-valued expression" */ () {
+	switch f /* ERROR "2-valued f" */ () {
 	}
 	var x int
-	switch f /* ERROR "2-valued expression" */ () {
+	switch f /* ERROR "2-valued f" */ () {
 	case x:
 	}
 	switch x {
-	case f /* ERROR "cannot compare" */ (): // TODO(gri) better error message (issue 11896)
+	case f /* ERROR "2-valued f" */ ():
 	}
 }
 

src/go/types/testdata/vardecl.src

@@ -31,7 +31,7 @@ var _ = 1, 2 /* ERROR "extra init expr 2" */
 var _, _ = 1 /* ERROR "assignment count mismatch" */
 var _, _, _ /* ERROR "missing init expr for _" */ = 1, 2
 
-var _ = g /* ERROR "2-valued expr" */ ()
+var _ = g /* ERROR "2-valued g" */ ()
 var _, _ = g()
 var _, _, _ = g /* ERROR "assignment count mismatch" */ ()
 
@@ -50,7 +50,7 @@ var (
 	_, _ = 1 /* ERROR "assignment count mismatch" */
 	_, _, _ /* ERROR "missing init expr for _" */ = 1, 2
 
-	_ = g /* ERROR "2-valued expr" */ ()
+	_ = g /* ERROR "2-valued g" */ ()
 	_, _ = g()
 	_, _, _ = g /* ERROR "assignment count mismatch" */ ()