internal/shader: bug fix: crash on assignment mismatches

internal/shader/stmt.go

@@ -492,8 +492,8 @@ func (cs *compileState) assign(block *block, fname string, pos token.Pos, lhs, r
 	var rhsTypes []shaderir.Type
 	allblank := true
 
-	for i, e := range lhs {
 	if len(lhs) == len(rhs) {
+		for i, e := range lhs {
 			// Prase RHS first for the order of the statements.
 			r, rts, ss, ok := cs.parseExpr(block, fname, rhs[i], true)
 			if !ok {
@@ -627,20 +627,21 @@ func (cs *compileState) assign(block *block, fname string, pos token.Pos, lhs, r
 						},
 					})
 			}
+		}
 	} else {
-			if i == 0 {
 		var ss []shaderir.Stmt
 		var ok bool
 		rhsExprs, rhsTypes, ss, ok = cs.parseExpr(block, fname, rhs[0], true)
 		if !ok {
 			return nil, false
 		}
-				if len(rhsExprs) != len(lhs) {
+		if len(lhs) != len(rhsExprs) {
-					cs.addError(pos, "single-value context and multiple-value context cannot be mixed")
+			cs.addError(pos, fmt.Sprintf("assignment mismatch: %d variables but %d", len(lhs), len(rhsExprs)))
+			return nil, false
 		}
 		stmts = append(stmts, ss...)
-			}
 
+		for i, e := range lhs {
 			if define {
 				if _, ok := e.(*ast.Ident); !ok {
 					cs.addError(pos, "non-name on the left side of :=")

internal/shader/syntax_test.go

@@ -4103,6 +4103,48 @@ func Bar() {
 `)); err != nil {
 		t.Error(err)
 	}
+
+	if _, err := compileToIR([]byte(`package main
+
+func Foo() {
+	a, b := 0
+	_, _ = a, b
+}
+`)); err == nil {
+		t.Error("compileToIR must return an error but did not")
+	}
+
+	if _, err := compileToIR([]byte(`package main
+
+func Foo() {
+	a, b, c := 0, 0
+	_, _ = a, b, c
+}
+`)); err == nil {
+		t.Error("compileToIR must return an error but did not")
+	}
+
+	if _, err := compileToIR([]byte(`package main
+
+func Foo() {
+	var a, b int
+	a, b = 0
+	_, _ = a, b
+}
+`)); err == nil {
+		t.Error("compileToIR must return an error but did not")
+	}
+
+	if _, err := compileToIR([]byte(`package main
+
+func Foo() {
+	var a, b, c int
+	a, b, c = 0, 0
+	_, _ = a, b, c
+}
+`)); err == nil {
+		t.Error("compileToIR must return an error but did not")
+	}
 }
 
 func TestSyntaxBitwiseOperator(t *testing.T) {