[parser] Improve error recovery for constant patterns

This allows the parser to parse constant patterns at lower precedence
level in order to recognize more expressions in this context. To
support this, _parsePrecedenceExpressionLoop special cases a few cases
that should _not_ be parsed as expression in a constant pattern context.

Closes #50996

Change-Id: I43bb0ce52d366bd2dfcf47e12eec5883402f668a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/282100
Commit-Queue: Johnni Winther <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Reviewed-by: Jens Johansen <[email protected]>

Author: johnniwinther

pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart

@@ -6925,6 +6925,34 @@ const MessageCode messageInvalidCodePoint = const MessageCode(
     problemMessage:
         r"""The escape sequence starting with '\u' isn't a valid code point.""");
 
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Template<
+    Message Function(
+        String
+            name)> templateInvalidConstantPatternBinary = const Template<
+        Message Function(String name)>(
+    problemMessageTemplate:
+        r"""The binary operator #name is not supported as a constant pattern.""",
+    correctionMessageTemplate:
+        r"""Try wrapping the expression in 'const ( ... )'.""",
+    withArguments: _withArgumentsInvalidConstantPatternBinary);
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Message Function(String name)> codeInvalidConstantPatternBinary =
+    const Code<Message Function(String name)>("InvalidConstantPatternBinary",
+        index: 141);
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+Message _withArgumentsInvalidConstantPatternBinary(String name) {
+  if (name.isEmpty) throw 'No name provided';
+  name = demangleMixinApplicationName(name);
+  return new Message(codeInvalidConstantPatternBinary,
+      problemMessage:
+          """The binary operator ${name} is not supported as a constant pattern.""",
+      correctionMessage: """Try wrapping the expression in 'const ( ... )'.""",
+      arguments: {'name': name});
+}
+
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Code<Null> codeInvalidConstantPatternConstPrefix =
     messageInvalidConstantPatternConstPrefix;

pkg/_fe_analyzer_shared/lib/src/parser/parser_impl.dart

@@ -19,7 +19,9 @@ import '../scanner/token.dart'
         CASCADE_PRECEDENCE,
         EQUALITY_PRECEDENCE,
         Keyword,
+        MULTIPLICATIVE_PRECEDENCE,
         POSTFIX_PRECEDENCE,
+        PREFIX_PRECEDENCE,
         RELATIONAL_PRECEDENCE,
         SELECTOR_PRECEDENCE,
         SHIFT_PRECEDENCE,
@@ -5661,6 +5663,48 @@ class Parser {
     Token next = token.next!;
     TokenType type = next.type;
     int tokenLevel = _computePrecedence(next, forPattern: false);
+    if (constantPatternContext != ConstantPatternContext.none) {
+      // For error recovery we allow too much when parsing constant patterns,
+      // so for the cases that shouldn't be parsed as expressions in this
+      // context we return directly.
+      if (type == TokenType.BANG) {
+        if (tokenLevel == POSTFIX_PRECEDENCE) {
+          // This is a suffixed ! which is a null assert pattern.
+          return token;
+        } else if (optional('?', next.next!)) {
+          // This is a suffixed !? which is a null assert pattern in a null
+          // check pattern.
+          return token;
+        }
+      } else if (type == TokenType.AS) {
+        // This is a suffixed `as` which is a case pattern.
+        return token;
+      }
+    }
+    if (constantPatternContext != ConstantPatternContext.none &&
+        precedence <= tokenLevel &&
+        tokenLevel < SELECTOR_PRECEDENCE) {
+      // If we are parsing a constant pattern, only [SELECTOR_PRECEDENCE] is
+      // supported but we allow for parsing [EQUALITY_PRECEDENCE] and higher for
+      // better error recovery.
+      if (constantPatternContext == ConstantPatternContext.explicit) {
+        reportRecoverableError(
+            token, codes.messageInvalidConstantPatternConstPrefix);
+      } else if (tokenLevel <= MULTIPLICATIVE_PRECEDENCE) {
+        reportRecoverableError(
+            next,
+            codes.templateInvalidConstantPatternBinary
+                .withArguments(type.lexeme));
+      } else {
+        // These are prefix or postfix ++/-- and will not be constant
+        // expressions, anyway.
+        assert(
+            tokenLevel == POSTFIX_PRECEDENCE || tokenLevel == PREFIX_PRECEDENCE,
+            "Unexpected precedence level for $type: $tokenLevel");
+      }
+      // Avoid additional constant pattern errors.
+      constantPatternContext = ConstantPatternContext.none;
+    }
     bool enteredLoop = false;
     for (int level = tokenLevel; level >= precedence; --level) {
       int lastBinaryExpressionLevel = -1;
@@ -5801,6 +5845,24 @@ class Parser {
         next = token.next!;
         type = next.type;
         tokenLevel = _computePrecedence(next, forPattern: false);
+        if (constantPatternContext != ConstantPatternContext.none) {
+          // For error recovery we allow too much when parsing constant
+          // patterns, so for the cases that shouldn't be parsed as expressions
+          // in this context we break out of the parsing loop directly.
+          if (type == TokenType.BANG) {
+            if (tokenLevel == POSTFIX_PRECEDENCE) {
+              // This is a suffixed ! which is a null assert pattern.
+              return token;
+            } else if (optional('?', next.next!)) {
+              // This is a suffixed !? which is a null assert pattern in a null
+              // check pattern.
+              return token;
+            }
+          } else if (type == TokenType.AS) {
+            // This is a suffixed `as` which is a case pattern.
+            return token;
+          }
+        }
       }
       if (_recoverAtPrecedenceLevel && !_currentlyRecovering) {
         // Attempt recovery
@@ -9657,7 +9719,10 @@ class Parser {
         //                   | 'const' '(' expression ')'
         Token const_ = next;
         listener.beginConstantPattern(const_);
-        token = parsePrecedenceExpression(const_, SELECTOR_PRECEDENCE,
+        // The supported precedence is [SELECTOR_PRECEDENCE] but for better
+        // error recovery we allow for parsing [EQUALITY_PRECEDENCE] and higher,
+        // and report an error in [_parsePrecedenceExpressionLoop] instead.
+        token = parsePrecedenceExpression(const_, EQUALITY_PRECEDENCE,
             /* allowCascades = */ false, ConstantPatternContext.explicit);
         listener.endConstantPattern(const_);
         return token;
@@ -9728,7 +9793,10 @@ class Parser {
       token = beforeFirstIdentifier;
     }
     listener.beginConstantPattern(/* constKeyword = */ null);
-    token = parsePrecedenceExpression(token, SELECTOR_PRECEDENCE,
+    // The supported precedence is [SELECTOR_PRECEDENCE] but for better
+    // error recovery we allow for parsing [EQUALITY_PRECEDENCE] and higher,
+    // and report an error in [_parsePrecedenceExpressionLoop] instead.
+    token = parsePrecedenceExpression(token, EQUALITY_PRECEDENCE,
         /* allowCascades = */ false, ConstantPatternContext.implicit);
     listener.endConstantPattern(/* constKeyword = */ null);
     return token;

pkg/analysis_server/lib/src/services/correction/error_fix_status.yaml

@@ -2307,6 +2307,8 @@ ParserErrorCode.INVALID_COMMENT_REFERENCE:
   status: needsEvaluation
 ParserErrorCode.INVALID_CONSTANT_CONST_PREFIX:
   status: needsEvaluation
+ParserErrorCode.INVALID_CONSTANT_PATTERN_BINARY:
+  status: needsEvaluation
 ParserErrorCode.INVALID_CONSTANT_PATTERN_DUPLICATE_CONST:
   status: needsEvaluation
 ParserErrorCode.INVALID_CONSTANT_PATTERN_EMPTY_RECORD_LITERAL:

pkg/analyzer/lib/src/dart/error/syntactic_errors.g.dart

@@ -155,6 +155,7 @@ final fastaAnalyzerErrorCodes = <ErrorCode?>[
   ParserErrorCode.INVALID_CONSTANT_PATTERN_EMPTY_RECORD_LITERAL,
   ParserErrorCode.INVALID_CONSTANT_PATTERN_GENERIC,
   ParserErrorCode.INVALID_CONSTANT_CONST_PREFIX,
+  ParserErrorCode.INVALID_CONSTANT_PATTERN_BINARY,
 ];
 
 class ParserErrorCode extends ErrorCode {
@@ -922,6 +923,13 @@ class ParserErrorCode extends ErrorCode {
         "Try wrapping the expression in 'const ( ... )' instead.",
   );
 
+  static const ParserErrorCode INVALID_CONSTANT_PATTERN_BINARY =
+      ParserErrorCode(
+    'INVALID_CONSTANT_PATTERN_BINARY',
+    "The binary operator {0} is not supported as a constant pattern.",
+    correctionMessage: "Try wrapping the expression in 'const ( ... )'.",
+  );
+
   static const ParserErrorCode INVALID_CONSTANT_PATTERN_DUPLICATE_CONST =
       ParserErrorCode(
     'INVALID_CONSTANT_PATTERN_DUPLICATE_CONST',

pkg/analyzer/lib/src/error/error_code_values.g.dart

@@ -763,6 +763,7 @@ const List<ErrorCode> errorCodeValues = [
   ParserErrorCode.INVALID_CODE_POINT,
   ParserErrorCode.INVALID_COMMENT_REFERENCE,
   ParserErrorCode.INVALID_CONSTANT_CONST_PREFIX,
+  ParserErrorCode.INVALID_CONSTANT_PATTERN_BINARY,
   ParserErrorCode.INVALID_CONSTANT_PATTERN_DUPLICATE_CONST,
   ParserErrorCode.INVALID_CONSTANT_PATTERN_EMPTY_RECORD_LITERAL,
   ParserErrorCode.INVALID_CONSTANT_PATTERN_GENERIC,

pkg/front_end/messages.yaml

@@ -6428,6 +6428,17 @@ InvalidConstantPatternConstPrefix:
       if (x case const 1) {}
     }
 
+InvalidConstantPatternBinary:
+  problemMessage: "The binary operator #name is not supported as a constant pattern."
+  correctionMessage: "Try wrapping the expression in 'const ( ... )'."
+  analyzerCode: ParserErrorCode.INVALID_CONSTANT_PATTERN_BINARY
+  index: 141
+  experiments: patterns
+  script: |
+    method(x) {
+      if (x case 1 + 2) {}
+    }
+
 PatternAssignmentDeclaresVariable:
   problemMessage: "Variable '#name' can't be declared in a pattern assignment."
   correctionMessage: "Try using a preexisting variable or changing the assignment to a pattern variable declaration."

pkg/front_end/parser_testcases/patterns/boolean_literal_inside_case.dart.intertwined.expect

@@ -72,7 +72,7 @@ parseUnit(test)
                   parsePattern(case, PatternContext.matching, precedence: 1)
                     parsePrimaryPattern(case, PatternContext.matching)
                       listener: beginConstantPattern(null)
-                      parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                      parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                         parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                           parsePrimary(case, expression, ConstantPatternContext.implicit)
                             parseLiteralBool(case)

pkg/front_end/parser_testcases/patterns/boolean_literal_inside_cast.dart.intertwined.expect

@@ -72,7 +72,7 @@ parseUnit(test)
                   parsePattern(case, PatternContext.matching, precedence: 1)
                     parsePrimaryPattern(case, PatternContext.matching)
                       listener: beginConstantPattern(null)
-                      parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                      parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                         parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                           parsePrimary(case, expression, ConstantPatternContext.implicit)
                             parseLiteralBool(case)

pkg/front_end/parser_testcases/patterns/boolean_literal_inside_if_case.dart.intertwined.expect

@@ -64,7 +64,7 @@ parseUnit(test)
                     parsePattern(case, PatternContext.matching, precedence: 1)
                       parsePrimaryPattern(case, PatternContext.matching)
                         listener: beginConstantPattern(null)
-                        parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                        parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                           parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                             parsePrimary(case, expression, ConstantPatternContext.implicit)
                               parseLiteralBool(case)

pkg/front_end/parser_testcases/patterns/boolean_literal_inside_null_assert.dart.intertwined.expect

@@ -72,7 +72,7 @@ parseUnit(test)
                   parsePattern(case, PatternContext.matching, precedence: 1)
                     parsePrimaryPattern(case, PatternContext.matching)
                       listener: beginConstantPattern(null)
-                      parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                      parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                         parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                           parsePrimary(case, expression, ConstantPatternContext.implicit)
                             parseLiteralBool(case)

pkg/front_end/parser_testcases/patterns/boolean_literal_inside_null_check.dart.intertwined.expect

@@ -72,7 +72,7 @@ parseUnit(test)
                   parsePattern(case, PatternContext.matching, precedence: 1)
                     parsePrimaryPattern(case, PatternContext.matching)
                       listener: beginConstantPattern(null)
-                      parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                      parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                         parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                           parsePrimary(case, expression, ConstantPatternContext.implicit)
                             parseLiteralBool(case)

pkg/front_end/parser_testcases/patterns/caseHead_withClassicPattern_guarded_insideIfStatement.dart.intertwined.expect

@@ -61,7 +61,7 @@ parseUnit(void)
                     parsePattern(case, PatternContext.matching, precedence: 1)
                       parsePrimaryPattern(case, PatternContext.matching)
                         listener: beginConstantPattern(null)
-                        parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                        parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                           parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                             parsePrimary(case, expression, ConstantPatternContext.implicit)
                               parseLiteralInt(case)

pkg/front_end/parser_testcases/patterns/caseHead_withClassicPattern_guarded_insideSwitchStatement.dart.intertwined.expect

@@ -69,7 +69,7 @@ parseUnit(void)
                   parsePattern(case, PatternContext.matching, precedence: 1)
                     parsePrimaryPattern(case, PatternContext.matching)
                       listener: beginConstantPattern(null)
-                      parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                      parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                         parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                           parsePrimary(case, expression, ConstantPatternContext.implicit)
                             parseLiteralInt(case)

pkg/front_end/parser_testcases/patterns/caseHead_withClassicPattern_unguarded_insideIfStatement.dart.intertwined.expect

@@ -61,7 +61,7 @@ parseUnit(void)
                     parsePattern(case, PatternContext.matching, precedence: 1)
                       parsePrimaryPattern(case, PatternContext.matching)
                         listener: beginConstantPattern(null)
-                        parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                        parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                           parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                             parsePrimary(case, expression, ConstantPatternContext.implicit)
                               parseLiteralInt(case)

pkg/front_end/parser_testcases/patterns/caseHead_withClassicPattern_unguarded_insideSwitchStatement.dart.intertwined.expect

@@ -69,7 +69,7 @@ parseUnit(void)
                   parsePattern(case, PatternContext.matching, precedence: 1)
                     parsePrimaryPattern(case, PatternContext.matching)
                       listener: beginConstantPattern(null)
-                      parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                      parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                         parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                           parsePrimary(case, expression, ConstantPatternContext.implicit)
                             parseLiteralInt(case)

pkg/front_end/parser_testcases/patterns/caseHead_withNewPattern_guarded_insideIfStatement.dart.intertwined.expect

@@ -61,7 +61,7 @@ parseUnit(void)
                     parsePattern(case, PatternContext.matching, precedence: 1)
                       parsePrimaryPattern(case, PatternContext.matching)
                         listener: beginConstantPattern(null)
-                        parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                        parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                           parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                             parsePrimary(case, expression, ConstantPatternContext.implicit)
                               parseLiteralInt(case)

pkg/front_end/parser_testcases/patterns/caseHead_withNewPattern_guarded_insideSwitchStatement.dart.intertwined.expect

@@ -69,7 +69,7 @@ parseUnit(void)
                   parsePattern(case, PatternContext.matching, precedence: 1)
                     parsePrimaryPattern(case, PatternContext.matching)
                       listener: beginConstantPattern(null)
-                      parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                      parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                         parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                           parsePrimary(case, expression, ConstantPatternContext.implicit)
                             parseLiteralInt(case)

pkg/front_end/parser_testcases/patterns/caseHead_withNewPattern_unguarded_insideIfStatement.dart.intertwined.expect

@@ -61,7 +61,7 @@ parseUnit(void)
                     parsePattern(case, PatternContext.matching, precedence: 1)
                       parsePrimaryPattern(case, PatternContext.matching)
                         listener: beginConstantPattern(null)
-                        parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                        parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                           parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                             parsePrimary(case, expression, ConstantPatternContext.implicit)
                               parseLiteralInt(case)

pkg/front_end/parser_testcases/patterns/caseHead_withNewPattern_unguarded_insideSwitchStatement.dart.intertwined.expect

@@ -69,7 +69,7 @@ parseUnit(void)
                   parsePattern(case, PatternContext.matching, precedence: 1)
                     parsePrimaryPattern(case, PatternContext.matching)
                       listener: beginConstantPattern(null)
-                      parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                      parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                         parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                           parsePrimary(case, expression, ConstantPatternContext.implicit)
                             parseLiteralInt(case)

pkg/front_end/parser_testcases/patterns/cast_inside_case.dart.intertwined.expect

@@ -101,7 +101,7 @@ parseUnit(test)
                   parsePattern(case, PatternContext.matching, precedence: 1)
                     parsePrimaryPattern(case, PatternContext.matching)
                       listener: beginConstantPattern(null)
-                      parsePrecedenceExpression(case, 17, false, ConstantPatternContext.implicit)
+                      parsePrecedenceExpression(case, 7, false, ConstantPatternContext.implicit)
                         parseUnaryExpression(case, false, ConstantPatternContext.implicit)
                           parsePrimary(case, expression, ConstantPatternContext.implicit)
                             parseSendOrFunctionLiteral(case, expression, ConstantPatternContext.implicit)

pkg/front_end/parser_testcases/patterns/cast_inside_extractor_pattern.dart.intertwined.expect

@@ -122,7 +122,7 @@ parseUnit(class)
                         parsePattern(:, PatternContext.matching, precedence: 1)
                           parsePrimaryPattern(:, PatternContext.matching)
                             listener: beginConstantPattern(null)
-                            parsePrecedenceExpression(:, 17, false, ConstantPatternContext.implicit)
+                            parsePrecedenceExpression(:, 7, false, ConstantPatternContext.implicit)
                               parseUnaryExpression(:, false, ConstantPatternContext.implicit)
                                 parsePrimary(:, expression, ConstantPatternContext.implicit)
                                   parseLiteralInt(:)

pkg/front_end/parser_testcases/patterns/cast_inside_list_pattern.dart.intertwined.expect

@@ -76,7 +76,7 @@ parseUnit(test)
                         parsePattern([, PatternContext.matching, precedence: 1)
                           parsePrimaryPattern([, PatternContext.matching)
                             listener: beginConstantPattern(null)
-                            parsePrecedenceExpression([, 17, false, ConstantPatternContext.implicit)
+                            parsePrecedenceExpression([, 7, false, ConstantPatternContext.implicit)
                               parseUnaryExpression([, false, ConstantPatternContext.implicit)
                                 parsePrimary([, expression, ConstantPatternContext.implicit)
                                   parseLiteralInt([)