qml/parser: Implement nullish coalescing

Implements the '??' operator as specified in https://github.com/tc39/proposal-nullish-coalescing.

Also adds a few tests.

Task-number: QTBUG-77926
Change-Id: I3993450c192d11bf1ade0662d945c1553b4c6976
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

3 files changed, 49 insertions, 5 deletions

diff --git a/src/qml/parser/qqmljs.g b/src/qml/parser/qqmljs.g
index ea105e7e22..6fbb9df164 100644
--- a/src/qml/parser/qqmljs.g
+++ b/src/qml/parser/qqmljs.g
@@ -80,6 +80,7 @@
 %token T_COMMENT "comment"
 %token T_COMPATIBILITY_SEMICOLON
 %token T_ARROW "=>"
+%token T_QUESTION_QUESTION "??"
 %token T_ENUM "enum"
 %token T_ELLIPSIS "..."
 %token T_YIELD "yield"
@@ -2638,13 +2639,48 @@ LogicalORExpression_In: LogicalORExpression_In T_OR_OR LogicalANDExpression_In;
     } break;
 ./
 
+CoalesceExpression: LogicalORExpression;
+CoalesceExpression_In: LogicalORExpression_In;
 
-ConditionalExpression: LogicalORExpression;
-ConditionalExpression_In: LogicalORExpression_In;
+CoalesceExpression: CoalesceExpression T_QUESTION_QUESTION LogicalORExpression;
+/.  case $rule_number: Q_FALLTHROUGH(); ./
+CoalesceExpression_In: CoalesceExpression_In T_QUESTION_QUESTION LogicalORExpression_In;
+/.
+    case $rule_number: {
+
+        auto *lhs = sym(1).Expression;
+        auto *rhs = sym(3).Expression;
+
+        // Check if lhs or rhs contain || or &&
+
+        if (lhs->binaryExpressionCast() != nullptr) {
+            auto *binaryExpr = lhs->binaryExpressionCast();
+            if (binaryExpr->op == QSOperator::And || binaryExpr->op == QSOperator::Or) {
+                syntaxError(binaryExpr->operatorToken, "Left-hand side may not contain || or &&");
+                return false;
+            }
+        }
+
+        if (rhs->binaryExpressionCast() != nullptr) {
+            auto *binaryExpr = rhs->binaryExpressionCast();
+            if (binaryExpr->op == QSOperator::And || binaryExpr->op == QSOperator::Or) {
+                syntaxError(binaryExpr->operatorToken, "Right-hand side may not contain || or &&");
+                return false;
+            }
+        }
+
+        AST::BinaryExpression *node = new (pool) AST::BinaryExpression(lhs, QSOperator::Coalesce, rhs);
+        node->operatorToken = loc(2);
+        sym(1).Node = node;
+    } break;
+./
+
+ConditionalExpression: CoalesceExpression;
+ConditionalExpression_In: CoalesceExpression_In;
 
-ConditionalExpression: LogicalORExpression T_QUESTION AssignmentExpression_In T_COLON AssignmentExpression;
+ConditionalExpression: CoalesceExpression T_QUESTION AssignmentExpression_In T_COLON AssignmentExpression;
 /.  case $rule_number: Q_FALLTHROUGH(); ./
-ConditionalExpression_In: LogicalORExpression_In T_QUESTION AssignmentExpression_In T_COLON AssignmentExpression_In;
+ConditionalExpression_In: CoalesceExpression_In T_QUESTION AssignmentExpression_In T_COLON AssignmentExpression_In;
 /.
     case $rule_number: {
         AST::ConditionalExpression *node = new (pool) AST::ConditionalExpression(sym(1).Expression, sym(3).Expression, sym(5).Expression);
diff --git a/src/qml/parser/qqmljsast_p.h b/src/qml/parser/qqmljsast_p.h
index bc0a467f40..aa355fed85 100644
--- a/src/qml/parser/qqmljsast_p.h
+++ b/src/qml/parser/qqmljsast_p.h
@@ -105,6 +105,7 @@ enum Op {
     InplaceURightShift,
     InplaceXor,
     As,
+    Coalesce,
     Invalid
 };
 
diff --git a/src/qml/parser/qqmljslexer.cpp b/src/qml/parser/qqmljslexer.cpp
index 443e1a7476..80d883e52f 100644
--- a/src/qml/parser/qqmljslexer.cpp
+++ b/src/qml/parser/qqmljslexer.cpp
@@ -580,7 +580,14 @@ again:
 
     case ']': return T_RBRACKET;
     case '[': return T_LBRACKET;
-    case '?': return T_QUESTION;
+    case '?': {
+        if (_char == QLatin1Char('?')) {
+            scanChar();
+            return T_QUESTION_QUESTION;
+        }
+
+        return T_QUESTION;
+    }
 
     case '>':
         if (_char == QLatin1Char('>')) {