fix parsing of "?.." cascade operator

Fix dart-lang/sdk#37859

Change-Id: Ie29f4fd000199f0099137308603335e36af6ae26
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/116089
Commit-Queue: Dan Rubel <danrubel@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/analyzer/lib/dart/ast/ast.dart

@@ -825,7 +825,8 @@ abstract class BreakStatement implements Statement {
 ///        [Expression] cascadeSection*
 ///
 ///    cascadeSection ::=
-///        '..'  (cascadeSelector arguments*) (assignableSelector arguments*)*
+///        ('..' | '?..') (cascadeSelector arguments*)
+///        (assignableSelector arguments*)*
 ///        (assignmentOperator expressionWithoutCascade)?
 ///
 ///    cascadeSelector ::=

pkg/analyzer/lib/src/dart/ast/ast.dart

@@ -5913,8 +5913,8 @@ class IndexExpressionImpl extends ExpressionImpl implements IndexExpression {
   /// index expression is part of a cascade expression.
   ExpressionImpl _target;
 
-  /// The period ("..") before a cascaded index expression, or `null` if this
-  /// index expression is not part of a cascade expression.
+  /// The period (".." | "?..") before a cascaded index expression,
+  /// or `null` if this index expression is not part of a cascade expression.
   @override
   Token period;
 
@@ -7131,7 +7131,7 @@ class MethodInvocationImpl extends InvocationExpressionImpl
   /// The operator that separates the target from the method name, or `null`
   /// if there is no target. In an ordinary method invocation this will be a
   /// period ('.'). In a cascade section this will be the cascade operator
-  /// ('..').
+  /// ('..' | '?..').
   @override
   Token operator;
 
@@ -7180,7 +7180,9 @@ class MethodInvocationImpl extends InvocationExpressionImpl
 
   @override
   bool get isCascaded =>
-      operator != null && operator.type == TokenType.PERIOD_PERIOD;
+      operator != null &&
+      (operator.type == TokenType.PERIOD_PERIOD ||
+          operator.type == TokenType.QUESTION_PERIOD_PERIOD);
 
   @override
   SimpleIdentifier get methodName => _methodName;
@@ -8437,7 +8439,9 @@ class PropertyAccessImpl extends ExpressionImpl implements PropertyAccess {
 
   @override
   bool get isCascaded =>
-      operator != null && operator.type == TokenType.PERIOD_PERIOD;
+      operator != null &&
+      (operator.type == TokenType.PERIOD_PERIOD ||
+          operator.type == TokenType.QUESTION_PERIOD_PERIOD);
 
   @override
   Precedence get precedence => Precedence.postfix;

pkg/analyzer/lib/src/dart/ast/utilities.dart

@@ -7526,7 +7526,7 @@ class ToSourceVisitor implements AstVisitor<void> {
   @override
   void visitIndexExpression(IndexExpression node) {
     if (node.isCascaded) {
-      _writer.print("..");
+      _writer.print(node.period.lexeme);
     } else {
       _visitNode(node.target);
     }
@@ -7635,7 +7635,7 @@ class ToSourceVisitor implements AstVisitor<void> {
   @override
   void visitMethodInvocation(MethodInvocation node) {
     if (node.isCascaded) {
-      _writer.print("..");
+      _writer.print(node.operator.lexeme);
     } else {
       if (node.target != null) {
         node.target.accept(this);
@@ -7735,7 +7735,7 @@ class ToSourceVisitor implements AstVisitor<void> {
   @override
   void visitPropertyAccess(PropertyAccess node) {
     if (node.isCascaded) {
-      _writer.print("..");
+      _writer.print(node.operator.lexeme);
     } else {
       _visitNode(node.target);
       _writer.print(node.operator.lexeme);
@@ -8833,7 +8833,7 @@ class ToSourceVisitor2 implements AstVisitor<void> {
   @override
   void visitIndexExpression(IndexExpression node) {
     if (node.isCascaded) {
-      sink.write("..");
+      sink.write(node.period.lexeme);
     } else {
       safelyVisitNode(node.target);
     }
@@ -8942,7 +8942,7 @@ class ToSourceVisitor2 implements AstVisitor<void> {
   @override
   void visitMethodInvocation(MethodInvocation node) {
     if (node.isCascaded) {
-      sink.write("..");
+      sink.write(node.operator.lexeme);
     } else {
       if (node.target != null) {
         node.target.accept(this);
@@ -9042,7 +9042,7 @@ class ToSourceVisitor2 implements AstVisitor<void> {
   @override
   void visitPropertyAccess(PropertyAccess node) {
     if (node.isCascaded) {
-      sink.write("..");
+      sink.write(node.operator.lexeme);
     } else {
       safelyVisitNode(node.target);
       sink.write(node.operator.lexeme);

pkg/analyzer/lib/src/fasta/ast_builder.dart

@@ -169,7 +169,7 @@ class AstBuilder extends StackListener {
   }
 
   void beginCascade(Token token) {
-    assert(optional('..', token));
+    assert(optional('..', token) || optional('?..', token));
     debugEvent("beginCascade");
 
     Expression expression = pop();
@@ -577,12 +577,14 @@ class AstBuilder extends StackListener {
     assert(operatorToken.isOperator ||
         optional('.', operatorToken) ||
         optional('?.', operatorToken) ||
-        optional('..', operatorToken));
+        optional('..', operatorToken) ||
+        optional('?..', operatorToken));
     debugEvent("BinaryExpression");
 
     if (identical(".", operatorToken.stringValue) ||
         identical("?.", operatorToken.stringValue) ||
-        identical("..", operatorToken.stringValue)) {
+        identical("..", operatorToken.stringValue) ||
+        identical("?..", operatorToken.stringValue)) {
       doDotExpression(operatorToken);
     } else {
       Expression right = pop();

pkg/analyzer/test/generated/parser_fasta_test.dart

@@ -2544,6 +2544,16 @@ class NNBDParserTest_Fasta extends FastaParserTestCase {
     parseCompilationUnit('D? foo(X? x) { X? x1; X? x2 = x + bar(7); }');
   }
 
+  void test_assignment_complex2() {
+    parseCompilationUnit(r'''
+main() {
+  A? a;
+  String? s = '';
+  a?..foo().length..x27 = s!..toString().length;
+}
+''');
+  }
+
   void test_assignment_simple() {
     parseCompilationUnit('D? foo(X? x) { X? x1; X? x2 = x; }');
   }
@@ -2561,6 +2571,39 @@ class NNBDParserTest_Fasta extends FastaParserTestCase {
     expect(rhs.name, 'x2');
   }
 
+  void test_cascade_withNullCheck_indexExpression() {
+    var unit = parseCompilationUnit('main() { a?..[27]; }');
+    FunctionDeclaration funct = unit.declarations[0];
+    BlockFunctionBody body = funct.functionExpression.body;
+    ExpressionStatement statement = body.block.statements[0];
+    CascadeExpression cascade = statement.expression;
+    IndexExpression indexExpression = cascade.cascadeSections[0];
+    expect(indexExpression.period.lexeme, '?..');
+    expect(indexExpression.toSource(), '?..[27]');
+  }
+
+  void test_cascade_withNullCheck_methodInvocation() {
+    var unit = parseCompilationUnit('main() { a?..foo(); }');
+    FunctionDeclaration funct = unit.declarations[0];
+    BlockFunctionBody body = funct.functionExpression.body;
+    ExpressionStatement statement = body.block.statements[0];
+    CascadeExpression cascade = statement.expression;
+    MethodInvocation invocation = cascade.cascadeSections[0];
+    expect(invocation.operator.lexeme, '?..');
+    expect(invocation.toSource(), '?..foo()');
+  }
+
+  void test_cascade_withNullCheck_propertyAccess() {
+    var unit = parseCompilationUnit('main() { a?..x27; }');
+    FunctionDeclaration funct = unit.declarations[0];
+    BlockFunctionBody body = funct.functionExpression.body;
+    ExpressionStatement statement = body.block.statements[0];
+    CascadeExpression cascade = statement.expression;
+    PropertyAccess propertyAccess = cascade.cascadeSections[0];
+    expect(propertyAccess.operator.lexeme, '?..');
+    expect(propertyAccess.toSource(), '?..x27');
+  }
+
   void test_conditional() {
     parseCompilationUnit('D? foo(X? x) { X ? 7 : y; }');
   }

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -1479,7 +1479,9 @@ class BodyBuilder extends ScopeListener<JumpTarget>
   @override
   void endBinaryExpression(Token token) {
     debugEvent("BinaryExpression");
-    if (optional(".", token) || optional("..", token)) {
+    if (optional(".", token) ||
+        optional("..", token) ||
+        optional("?..", token)) {
       return doDotOrCascadeExpression(token);
     }
     if (optional("&&", token) || optional("||", token)) {

pkg/front_end/lib/src/fasta/parser/parser.dart

@@ -4285,7 +4285,7 @@ class Parser {
 
   Token parseCascadeExpression(Token token) {
     Token cascadeOperator = token = token.next;
-    assert(optional('..', cascadeOperator));
+    assert(optional('..', cascadeOperator) || optional('?..', cascadeOperator));
     listener.beginCascade(cascadeOperator);
     if (optional('[', token.next)) {
       token = parseArgumentOrIndexStar(token, noTypeParamOrArg);

pkg/front_end/lib/src/fasta/scanner/abstract_scanner.dart

@@ -877,16 +877,22 @@ abstract class AbstractScanner implements Scanner {
   }
 
   int tokenizeQuestion(int next) {
-    // ? ?. ?? ??=
+    // ? ?. ?.. ?? ??=
     next = advance();
     if (identical(next, $QUESTION)) {
       return select(
           $EQ, TokenType.QUESTION_QUESTION_EQ, TokenType.QUESTION_QUESTION);
     } else if (identical(next, $PERIOD)) {
       next = advance();
-      if (_enableNonNullable && identical($OPEN_SQUARE_BRACKET, next)) {
-        appendBeginGroup(TokenType.QUESTION_PERIOD_OPEN_SQUARE_BRACKET);
-        return advance();
+      if (_enableNonNullable) {
+        if (identical($PERIOD, next)) {
+          appendPrecedenceToken(TokenType.QUESTION_PERIOD_PERIOD);
+          return advance();
+        }
+        if (identical($OPEN_SQUARE_BRACKET, next)) {
+          appendBeginGroup(TokenType.QUESTION_PERIOD_OPEN_SQUARE_BRACKET);
+          return advance();
+        }
       }
       appendPrecedenceToken(TokenType.QUESTION_PERIOD);
       return next;

pkg/front_end/lib/src/fasta/scanner/token_constants.dart

@@ -90,3 +90,5 @@ const int GT_GT_GT_TOKEN = GENERIC_METHOD_TYPE_LIST_TOKEN + 1;
 const int PERIOD_PERIOD_PERIOD_QUESTION_TOKEN = GT_GT_GT_TOKEN + 1;
 const int GT_GT_GT_EQ_TOKEN = PERIOD_PERIOD_PERIOD_QUESTION_TOKEN + 1;
 const int QUESTION_PERIOD_OPEN_SQUARE_BRACKET_TOKEN = GT_GT_GT_EQ_TOKEN + 1;
+const int QUESTION_PERIOD_PERIOD_TOKEN =
+    QUESTION_PERIOD_OPEN_SQUARE_BRACKET_TOKEN + 1;

pkg/front_end/lib/src/scanner/token.dart

@@ -1450,6 +1450,12 @@ class TokenType {
       SELECTOR_PRECEDENCE,
       QUESTION_PERIOD_OPEN_SQUARE_BRACKET_TOKEN);
 
+  static const TokenType QUESTION_PERIOD_PERIOD = const TokenType(
+      '?..',
+      'QUESTION_PERIOD_PERIOD',
+      CASCADE_PRECEDENCE,
+      QUESTION_PERIOD_PERIOD_TOKEN);
+
   static const TokenType AS = Keyword.AS;
 
   static const TokenType IS = Keyword.IS;