Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

4 files changed, 1444 insertions, 0 deletions

diff --git a/third_party/rust/jsparagus/tests/__init__.py b/third_party/rust/jsparagus/tests/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/third_party/rust/jsparagus/tests/__init__.py
diff --git a/third_party/rust/jsparagus/tests/test.py b/third_party/rust/jsparagus/tests/test.py
new file mode 100755
index 0000000000..2d064098b5
--- /dev/null
+++ b/third_party/rust/jsparagus/tests/test.py
@@ -0,0 +1,1204 @@
+#!/usr/bin/env python3
+
+import io
+import re
+import unittest
+import typing
+
+import jsparagus
+from jsparagus import gen, lexer, rewrites
+from jsparagus.grammar import (Grammar, Production, CallMethod, Nt,
+                               Optional, LookaheadRule, NtDef, Var)
+from js_parser.parse_esgrammar import parse_esgrammar
+
+
+LispTokenizer = lexer.LexicalGrammar("( )", SYMBOL=r'[!%&*+:<=>?@A-Z^_a-z~]+')
+
+
+def prod(body, method_name):
+    return Production(body, CallMethod(method_name, list(range(len(body)))))
+
+
+class GenTestCase(unittest.TestCase):
+    def compile(self, tokenize, grammar, **kwargs):
+        """Compile a grammar. Use this when you expect compilation to
+        succeed."""
+        self.tokenize = tokenize
+        self.parser_class = gen.compile(grammar, **kwargs)
+
+    def parse(self, text, goal=None):
+        if goal is None:
+            parser = self.parser_class()
+        else:
+            parser = self.parser_class(goal=goal)
+        lexer = self.tokenize(parser)
+        lexer.write(text)
+        return lexer.close()
+
+    def compile_multi(self, tokenize, grammar):
+        self.tokenize = tokenize
+        obj = gen.compile_multi(grammar)
+        for attr in dir(obj):
+            if attr.startswith("parse_"):
+                setattr(self, attr, getattr(obj, attr))
+
+    def assertParse(self, s, expected=None, *, goal=None):
+        result = self.parse(s, goal=goal)
+        if expected is not None:
+            self.assertEqual(expected, result)
+
+    def assertNoParse(self, s, *, goal=None, message="banana"):
+        if goal is None:
+            kwargs = {}
+        else:
+            kwargs = {"goal": goal}
+        self.assertRaisesRegex(
+            SyntaxError,
+            re.escape(message),
+            lambda: self.parse(s, **kwargs))
+
+    def testSimple(self):
+        grammar = parse_esgrammar(
+            """
+            expr :
+                SYMBOL  => $0
+                `(` tail
+
+            tail :
+                `)`  => $0
+                expr tail
+            """,
+            terminal_names=["SYMBOL"]
+        )
+        self.compile(LispTokenizer, grammar)
+
+        self.assertParse(
+            "(lambda (x) (* x x))",
+            ('expr_1',
+                '(',
+                ('tail_1',
+                    'lambda',
+                    ('tail_1',
+                        ('expr_1', '(', ('tail_1', 'x', ')')),
+                        ('tail_1',
+                            ('expr_1',
+                                '(',
+                                ('tail_1',
+                                    '*',
+                                    ('tail_1',
+                                        'x',
+                                        ('tail_1', 'x', ')')))),
+                            ')')))))
+
+    def testEnd(self):
+        self.compile(
+            lexer.LexicalGrammar("ONE TWO"),
+            Grammar({
+                'goal': [
+                    ['ONE', 'TWO']
+                ]
+            })
+        )
+        self.assertNoParse("ONE TWO TWO",
+                           message="expected 'end of input', got 'TWO'")
+
+    def testList(self):
+        list_grammar = Grammar({
+            'prelist': [
+                ['word', 'list']
+            ],
+            'list': [
+                ['word'],
+                ['list', 'word'],
+            ],
+            'word': [
+                ['SYMBOL']
+            ],
+        })
+        self.compile(LispTokenizer, list_grammar)
+        self.assertParse(
+            "the quick brown fox jumped over the lazy dog",
+            ('prelist',
+                'the',
+                ('list_1',
+                    ('list_1',
+                        ('list_1',
+                            ('list_1',
+                                ('list_1',
+                                    ('list_1',
+                                        ('list_1',
+                                            'quick',
+                                            'brown'),
+                                        'fox'),
+                                    'jumped'),
+                                'over'),
+                            'the'),
+                        'lazy'),
+                    'dog')))
+
+    def testArithmetic(self):
+        tokenize = lexer.LexicalGrammar(
+            "+ - * / ( )",
+            NUM=r'[0-9]\w*',
+            VAR=r'[A-Za-z]\w*')
+        arith_grammar = Grammar({
+            'expr': [
+                ['term'],
+                ['expr', '+', 'term'],
+                ['expr', '-', 'term'],
+            ],
+            'term': [
+                ['prim'],
+                ['term', '*', 'prim'],
+                ['term', '/', 'prim'],
+            ],
+            'prim': [
+                ['NUM'],
+                ['VAR'],
+                ['(', 'expr', ')'],
+            ],
+        })
+        self.compile(tokenize, arith_grammar)
+
+        self.assertParse(
+            '2 * 3 + 4 * (5 + 7)',
+            ('expr_1',
+                ('term_1', '2', '*', '3'),
+                '+',
+                ('term_1',
+                    '4',
+                    '*',
+                    ('prim_2',
+                        '(',
+                        ('expr_1', '5', '+', '7'),
+                        ')'))))
+
+        self.assertNoParse(
+            "(",
+            message="unexpected end of input")
+        self.assertNoParse(
+            ")",
+            message="expected one of ['(', 'NUM', 'VAR'], got ')'")
+
+    def testAmbiguous(self):
+        # This grammar should fail verification.
+        # It's ambiguous: is ABC s(A)y(BC) or s(AB)y(C)?
+        grammar = Grammar({
+            'goal': [
+                ['s', 'y'],
+            ],
+            's': [
+                ['A'],
+                ['s', 'B'],
+            ],
+            'y': [
+                ['C'],
+                ['B', 'C'],
+            ],
+        })
+
+        out = io.StringIO()
+        self.assertRaisesRegex(ValueError, r"conflict",
+                               lambda: gen.generate_parser(out, grammar))
+
+    def testAmbiguousEmpty(self):
+        """Reject grammars that are ambiguous due to empty productions.
+
+        (Empty productions are ones that match the empty string.)"""
+
+        def check(rules):
+            grammar = Grammar(rules, goal_nts=['goal'])
+            out = io.StringIO()
+            self.assertRaisesRegex(
+                ValueError,
+                r"ambiguous grammar|conflict",
+                lambda: gen.generate_parser(out, grammar))
+
+        check({'goal': [[], []]})
+        check({'goal': [[Optional('X')], []]})
+        check({'goal': [[Optional('X')], [Optional('Y')]]})
+        check({'goal': [[Optional('X'), Optional('Y')], [Optional('Z')]]})
+
+        # Issue #3: This also has an abiguity; empty string matches either
+        # `goal ::= [empty]` or `goal ::= phrase, phrase ::= [empty]`.
+        check({
+            'goal': [[Optional('phrase')]],
+            'phrase': [[Optional('X')]],
+        })
+
+        # Input "X" is ambiguous, could be ('goal', ('a', None), ('a', 'X'))
+        # or the other 'a' could be the one that's missing.
+        check({
+            'goal': [['a', 'a']],
+            'a': [[Optional('X')]],
+        })
+
+    def testLeftFactor(self):
+        """Most basic left-factoring test."""
+        tokenize = lexer.LexicalGrammar("A B")
+        grammar = Grammar({
+            'goal': [
+                ['A'],
+                ['A', 'B'],
+            ],
+        })
+
+        self.compile(tokenize, grammar)
+        self.assertParse("A", 'A')
+        self.assertParse("A B", ('goal_1', 'A', 'B'))
+
+    def testLeftFactorMulti(self):
+        """Test left-factoring with common prefix of length >1."""
+        tokenize = lexer.LexicalGrammar("A B C D E")
+        grammar = Grammar({
+            'goal': [
+                ['A', 'B', 'C', 'D'],
+                ['A', 'B', 'C', 'E'],
+            ],
+        })
+        self.compile(tokenize, grammar)
+        self.assertParse(
+            "A B C D",
+            ('goal_0', 'A', 'B', 'C', 'D'))
+        self.assertParse(
+            "A B C E",
+            ('goal_1', 'A', 'B', 'C', 'E'))
+
+    def testLeftFactorMultiLevel(self):
+        """Test left-factoring again on a nonterminal introduced by
+        left-factoring."""
+        tokenize = lexer.LexicalGrammar("FOR IN TO BY ( ) = ;",
+                                        VAR=r'[A-Za-z]+')
+
+        # The first left-factoring pass on `stmt` will left-factor `FOR ( VAR`.
+        # A second pass is needed to left-factor `= expr TO expr`.
+        grammar = Grammar({
+            'stmt': [
+                ['expr', ';'],
+                ['FOR', '(', 'VAR', 'IN', 'expr', ')', 'stmt'],
+                ['FOR', '(', 'VAR', '=', 'expr', 'TO', 'expr', ')', 'stmt'],
+                ['FOR', '(', 'VAR', '=', 'expr', 'TO', 'expr',
+                 'BY', 'expr', ')', 'stmt'],
+                ['IF', '(', 'expr', ')', 'stmt'],
+            ],
+            'expr': [
+                ['VAR'],
+            ],
+        })
+        self.compile(tokenize, grammar)
+        self.assertParse(
+            "FOR (x IN y) z;",
+            ('stmt_1', 'FOR', '(', 'x', 'IN', 'y', ')',
+             ('stmt_0', 'z', ';')))
+        self.assertParse(
+            "FOR (x = y TO z) x;",
+            ('stmt_2', 'FOR', '(', 'x', '=', 'y', 'TO', 'z', ')',
+             ('stmt_0', 'x', ';')))
+        self.assertParse(
+            "FOR (x = y TO z BY w) x;",
+            ('stmt_3', 'FOR', '(', 'x', '=', 'y', 'TO', 'z', 'BY', 'w', ')',
+             ('stmt_0', 'x', ';')))
+
+    def testFirstFirstConflict(self):
+        """This grammar is unambiguous, but is not LL(1) due to a first/first conflict.
+
+        Cribbed from: https://stackoverflow.com/a/17047370/94977
+        """
+
+        tokenize = lexer.LexicalGrammar("A B C")
+        grammar = Grammar({
+            's': [
+                ['x', 'B'],
+                ['y', 'C'],
+            ],
+            'x': [
+                prod(['A'], "x"),
+            ],
+            'y': [
+                prod(['A'], "y"),
+            ],
+        })
+        self.compile(tokenize, grammar)
+
+        self.assertParse("A B", ('s_0', ('x', 'A'), 'B'))
+        self.assertParse("A C", ('s_1', ('y', 'A'), 'C'))
+
+    def testLeftHandSideExpression(self):
+        """Example of a grammar that's in SLR(1) but hard to smoosh into an LL(1) form.
+
+        This is taken from the ECMAScript grammar.
+
+        ...Of course, it's not really possible to enforce the desired syntactic
+        restrictions in LR(k) either; the ES grammar matches `(x + y) = z` and
+        an additional attribute grammar (IsValidSimpleAssignmentTarget) is
+        necessary to rule it out.
+        """
+        self.compile(
+            lexer.LexicalGrammar("= +", VAR=r'[a-z]+\b'),
+            Grammar({
+                'AssignmentExpression': [
+                    ['AdditiveExpression'],
+                    ['LeftHandSideExpression', '=', 'AssignmentExpression'],
+                ],
+                'AdditiveExpression': [
+                    ['LeftHandSideExpression'],
+                    ['AdditiveExpression', '+', 'LeftHandSideExpression'],
+                ],
+                'LeftHandSideExpression': [
+                    ['VAR'],
+                ]
+            })
+        )
+        self.assertParse("z = x + y")
+        self.assertNoParse(
+            "x + y = z",
+            message="expected one of ['+', 'end of input'], got '='")
+
+    def testDeepRecursion(self):
+        grammar = Grammar({
+            'expr': [
+                ['SYMBOL'],
+                ['(', ')'],
+                ['(', 'exprs', ')'],
+            ],
+            'exprs': [
+                ['expr'],
+                ['exprs', 'expr'],
+            ],
+        })
+        self.compile(LispTokenizer, grammar)
+
+        N = 3000
+        s = "x"
+        t = ('expr_0', 'x')
+        for i in range(N):
+            s = "(" + s + ")"
+            t = ('expr_2', '(', t, ')')
+
+        result = self.parse(s)
+
+        # Python can't check that result == t; it causes a RecursionError.
+        # Testing that repr(result) == repr(t), same deal. So:
+        for i in range(N):
+            self.assertIsInstance(result, tuple)
+            self.assertEqual(len(result), 4)
+            self.assertEqual(result[0], 'expr_2')
+            self.assertEqual(result[1], '(')
+            self.assertEqual(result[3], ')')
+            result = result[2]
+
+    def testExpandOptional(self):
+        grammar = Grammar({'goal': [[]]})
+        empties = {}
+        # Unit test for rewrites.expand_optional_symbols_in_rhs
+        self.assertEqual(
+            list(rewrites.expand_optional_symbols_in_rhs(['ONE', 'TWO', '3'],
+                                                         grammar, empties)),
+            [(['ONE', 'TWO', '3'], {})])
+        self.assertEqual(
+            list(rewrites.expand_optional_symbols_in_rhs(
+                ['a', 'b', Optional('c')], grammar, empties)),
+            [(['a', 'b'], {2: None}),
+             (['a', 'b', 'c'], {})])
+        self.assertEqual(
+            list(rewrites.expand_optional_symbols_in_rhs(
+                [Optional('a'), Optional('b')], grammar, empties)),
+            [([], {0: None, 1: None}),
+             (['a'], {1: None}),
+             (['b'], {0: None}),
+             (['a', 'b'], {})])
+
+    def testEmptyGrammar(self):
+        tokenize = lexer.LexicalGrammar("X")
+        self.compile(tokenize, Grammar({'goal': [[]]}))
+        self.assertParse("", ('goal',))
+        self.assertNoParse(
+            "X",
+            message="expected 'end of input', got 'X' (line 1)")
+
+    def testOptionalEmpty(self):
+        tokenize = lexer.LexicalGrammar("X Y")
+        grammar = Grammar({
+            'a': [
+                [Optional('b'), Optional('c')],
+            ],
+            'b': [
+                prod(['X'], 'b'),
+            ],
+            'c': [
+                prod(['Y'], 'c'),
+            ]
+        })
+        self.compile(tokenize, grammar)
+        self.assertParse("", ('a', None, None))
+        self.assertParse("X", ('a', ('b', 'X'), None))
+        self.assertParse("Y", ('a', None, ('c', 'Y')))
+        self.assertParse("X Y", ('a', ('b', 'X'), ('c', 'Y')))
+
+    def testOptional(self):
+        tokenize = lexer.LexicalGrammar('[ ] , X')
+        grammar = Grammar({
+            'array': [
+                ['[', Optional('elision'), ']'],
+                ['[', 'elements', ']'],
+                ['[', 'elements', ',', Optional('elision'), ']']
+            ],
+            'elements': [
+                [Optional('elision'), 'X'],
+                ['elements', ',', Optional('elision'), 'X']
+            ],
+            'elision': [
+                [','],
+                ['elision', ',']
+            ]
+        })
+        self.compile(tokenize, grammar)
+        self.assertParse("[]",
+                         ('array_0', '[', None, ']'))
+        self.assertParse("[,]",
+                         ('array_0', '[', ',', ']'))
+        self.assertParse(
+            "[,,X,,X,]",
+            ('array_2',
+                '[',
+                ('elements_1',
+                    ('elements_0',
+                        ('elision_1',
+                            ',',
+                            ','),
+                        'X'),
+                    ',',
+                    ',',
+                    'X'),
+                ',',
+                None,
+                ']'))
+
+    def testPositiveLookahead(self):
+        self.compile(
+            lexer.LexicalGrammar('A B + ( )'),
+            Grammar({
+                'goal': [
+                    [LookaheadRule(frozenset({'A', 'B'}), True), 'expr'],
+                ],
+                'expr': [
+                    ['term'],
+                    ['expr', '+', 'term'],
+                ],
+                'term': [
+                    ['A'],
+                    ['B'],
+                    ['(', 'expr', ')'],
+                ]
+            })
+        )
+        self.assertNoParse(
+            "(A)",
+            message="expected one of ['A', 'B'], got '('")
+        self.assertParse("A + B")
+
+    def testNegativeLookahead(self):
+        tokenize = lexer.LexicalGrammar('a b')
+        rules = {
+            'goal': [
+                [LookaheadRule(frozenset({'a'}), False), 'abs'],
+            ],
+            'abs': [
+                ['a'],
+                ['b'],
+                ['abs', 'a'],
+                ['abs', 'b'],
+            ],
+        }
+
+        self.compile(tokenize, Grammar(rules))
+        self.assertNoParse("a b", message="expected 'b', got 'a'")
+        self.assertParse(
+            'b a',
+            ('goal', ('abs_2', 'b', 'a')))
+
+        # In simple cases like this, the lookahead restriction can even
+        # disambiguate a grammar that would otherwise be ambiguous.
+        rules['goal'].append(prod(['a'], 'goal_a'))
+        self.compile(tokenize, Grammar(rules))
+        self.assertParse('a', ('goal_a', 'a'))
+
+    def disabledNegativeLookaheadDisambiguation(self):
+        tokenize = lexer.LexicalGrammar(
+            '( ) { } ; function =',
+            IDENT=r'[A-Za-z_][A-Za-z_0-9]*')
+        grammar = Grammar({
+            'stmts': [
+                ['stmt'],
+                ['stmts', 'stmt'],
+            ],
+            'stmt': [
+                [LookaheadRule(set=frozenset({'function'}), positive=False),
+                 'expr', ';'],
+                ['fndecl'],
+            ],
+            'fndecl': [
+                ['function', 'IDENT', '(', ')', '{', Optional('stmt'), '}'],
+            ],
+            'expr': [
+                ['term'],
+                ['IDENT', '=', 'expr'],
+            ],
+            'term': [
+                ['(', 'expr', ')'],
+                ['fndecl'],
+                ['term', '(', 'expr', ')'],
+            ],
+        })
+        self.compile(tokenize, grammar)
+
+        # Test that without the lookahead restriction, we reject this grammar
+        # (it's ambiguous):
+        del grammar['stmt'][0][0]
+        self.assertRaisesRegex(ValueError,
+                               'banana',
+                               lambda: gen.compile(grammar))
+
+        self.assertParse(
+            'function f() { x = function y() {}; }',
+            ('stmt', 1,
+                ('fndecl',
+                    'function', 'f', '(', ')', '{',
+                    ('stmt', 0,
+                        ('expr', 1,
+                            'x',
+                            '=',
+                            ('expr', 0,
+                                ('term', 1,
+                                    ('fndecl',
+                                        'function', 'y', '(', ')',
+                                        '{', None, '}')))),
+                        ';'))))
+
+        self.assertParse(
+            '(function g(){});',
+            ('stmts', 0,
+                ('stmt', 0,
+                    ('term', 1,
+                        ('fndecl',
+                            'function', 'g', '(', ')', '{', None, '}')),
+                    ';')))
+
+    def testTrailingLookahead(self):
+        """Lookahead at the end of a production is banned."""
+        tokenize = lexer.LexicalGrammar('IF ( X ) ELSE OTHER ;')
+        grammar = gen.Grammar({
+            'goal': [['stmt']],
+            'stmt': [
+                ['OTHER', ';'],
+                ['IF', '(', 'X', ')', 'stmt',
+                 LookaheadRule(frozenset({'ELSE'}), False)],
+                ['IF', '(', 'X', ')', 'stmt', 'ELSE', 'stmt'],
+            ],
+        })
+
+        def stmt_0():
+            return ('stmt_0', 'OTHER', ';')
+
+        def stmt_1(t):
+            return ('stmt_1', 'IF', '(', 'X', ')', t)
+
+        def stmt_2(t, e):
+            return ('stmt_2', 'IF', '(', 'X', ')', t, 'ELSE', e)
+
+        self.compile(tokenize, grammar)
+        self.assertParse('IF(X) OTHER;', stmt_1(stmt_0()))
+        self.assertParse('IF(X) OTHER; ELSE OTHER;',
+                         stmt_2(stmt_0(), stmt_0()))
+        self.assertParse('IF(X) IF(X) OTHER; ELSE OTHER; ELSE OTHER;',
+                         stmt_2(stmt_2(stmt_0(), stmt_0()), stmt_0()))
+        self.assertParse('IF(X) OTHER; ELSE IF(X) OTHER; ELSE OTHER;',
+                         stmt_2(stmt_0(), stmt_2(stmt_0(), stmt_0())))
+        self.assertParse('IF(X) IF(X) OTHER; ELSE OTHER;',
+                         stmt_1(stmt_2(stmt_0(), stmt_0())))
+
+    def testLookaheadBeforeOptional(self):
+        self.compile(
+            lexer.LexicalGrammar(
+                '= : _',
+                PUBLIC=r'public\b',
+                IDENT=r'[a-z]+\b',
+                NUM=r'[0-9]\b'),
+            Grammar({
+                'decl': [
+                    [
+                        LookaheadRule(frozenset({'IDENT'}), True),
+                        Optional('attrs'),
+                        'pat', '=', 'NUM'
+                    ],
+                ],
+                'attrs': [
+                    ['attr'],
+                    ['attrs', 'attr'],
+                ],
+                'attr': [
+                    ['PUBLIC', ':'],
+                    ['IDENT', ':'],
+                ],
+                'pat': [
+                    ['IDENT'],
+                    ['_'],
+                ],
+            })
+        )
+        self.assertEqual(
+            self.parse("x = 0"),
+            ("decl", None, "x", "=", "0"))
+        self.assertParse("thread: x = 0")
+        self.assertNoParse(
+            "public: x = 0",
+            message="expected 'IDENT', got 'public'")
+        self.assertNoParse("_ = 0", message="expected 'IDENT', got '_'")
+        self.assertParse("funny: public: x = 0")
+        self.assertParse("funny: _ = 0")
+
+    def testForLookahead(self):
+        grammar = Grammar({
+            'Stmt': [
+                [';'],
+                ['ForStmt'],
+            ],
+            'ForStmt': [
+                ["for", "(", LookaheadRule(frozenset({"let"}), False),
+                 "Expr", ";", ";", ")", "Stmt"],
+            ],
+            'Expr': [
+                ["0"],
+                ["let"],
+            ],
+        })
+        self.compile(lexer.LexicalGrammar("for ( let ; ) 0"), grammar)
+        self.assertParse("for (0;;) ;")
+        self.assertNoParse("for (let;;) ;", message="expected '0', got 'let'")
+
+    def testLookaheadDisambiguation(self):
+        """A lookahead restriction should be able to rule out certain nonterminals entirely."""
+
+        grammar = Grammar({
+            'Script': [
+                ['Statement'],
+                ['Statement', 'Statement'],
+            ],
+            'Statement': [
+                [LookaheadRule(frozenset({'function'}), False), 'Expression', ';'],
+                ['Function'],
+            ],
+            'Function': [
+                ['function', 'x', '(', ')', '{', '}'],
+            ],
+            'Expression': [
+                ['Primary'],
+                ['++', 'Primary'],
+                ['Primary', '++'],
+            ],
+            'Primary': [
+                ['Function'],
+                ['x'],
+            ],
+        })
+
+        self.compile(lexer.LexicalGrammar("function x ( ) { } ++ ;"), grammar)
+        self.assertParse("function x() {}")
+        self.assertParse("++function x() {};")
+        self.assertNoParse("++function x() {}", message="unexpected end")
+        # TODO: The parser generator fails to handle this case because it does
+        # not forward the restriction from producting a Function to the
+        # Primitive rule. Therefore, `Function [lookahead: ;]` is incorrectly
+        # reduced to a `Primitive [lookahead: ;]`
+        # self.assertNoParse("function x() {}++;", message="got ';'")
+        self.assertParse("function x() {} ++x;")
+
+    # XXX to test: combination of lookaheads, ++, +-, -+, --
+    # XXX todo: find an example where lookahead canonicalization matters
+
+    def testHugeExample(self):
+        grammar = Grammar(
+            {
+                'grammar': [['nt_def_or_blank_line'],
+                            ['grammar', 'nt_def_or_blank_line']],
+                'arg': [['sigil', 'NT']],
+                'args': [['arg'], ['args', ',', 'arg']],
+                'definite_sigil': [['~'], ['+']],
+                'exclusion': [['terminal'],
+                              ['nonterminal'],
+                              ['CHR', 'through', 'CHR']],
+                'exclusion_list': [['exclusion'],
+                                   ['exclusion_list', 'or', 'exclusion']],
+                'ifdef': [['[', 'definite_sigil', 'NT', ']']],
+                'line_terminator': [['NT'], ['NTALT']],
+                'lookahead_assertion': [
+                    ['==', 'terminal'],
+                    ['!=', 'terminal'],
+                    ['<!', 'NT'],
+                    ['<!', '{', 'lookahead_exclusions', '}']],
+                'lookahead_exclusion': [['lookahead_exclusion_element'],
+                                        ['lookahead_exclusion',
+                                         'lookahead_exclusion_element']],
+                'lookahead_exclusion_element': [['terminal'],
+                                                ['no_line_terminator_here']],
+                'lookahead_exclusions': [['lookahead_exclusion'],
+                                         ['lookahead_exclusions', ',',
+                                          'lookahead_exclusion']],
+                'no_line_terminator_here': [
+                    ['[', 'no', 'line_terminator', 'here', ']']],
+                'nonterminal': [['NT'], ['NTCALL', '[', 'args', ']']],
+                'nt_def': [['nt_lhs', 'EQ', 'NL', 'rhs_lines', 'NL'],
+                           ['nt_lhs', 'EQ', 'one', 'of', 'NL',
+                            't_list_lines', 'NL']],
+                'nt_def_or_blank_line': [['NL'], ['nt_def']],
+                'nt_lhs': [['NT'], ['NTCALL', '[', 'params', ']']],
+                'param': [['NT']],
+                'params': [['param'], ['params', ',', 'param']],
+                'rhs': [['symbols'], ['[', 'empty', ']']],
+                'rhs_line': [[Optional(inner='ifdef'), 'rhs',
+                              Optional(inner='PRODID'), 'NL'],
+                             ['PROSE', 'NL']],
+                'rhs_lines': [['rhs_line'], ['rhs_lines', 'rhs_line']],
+                'sigil': [['definite_sigil'], ['?']],
+                'symbol': [['terminal'],
+                           ['nonterminal'],
+                           ['nonterminal', '?'],
+                           ['nonterminal', 'but', 'not', 'exclusion'],
+                           ['nonterminal', 'but', 'not', 'one', 'of',
+                            'exclusion_list'],
+                           ['[', 'lookahead', 'lookahead_assertion', ']'],
+                           ['no_line_terminator_here'],
+                           ['WPROSE']],
+                'symbols': [['symbol'], ['symbols', 'symbol']],
+                't_list_line': [['terminal_seq', 'NL']],
+                't_list_lines': [['t_list_line'],
+                                 ['t_list_lines', 't_list_line']],
+                'terminal': [['T'], ['CHR']],
+                'terminal_seq': [['terminal'], ['terminal_seq', 'terminal']]
+            },
+            variable_terminals='EQ T CHR NTCALL NT NTALT '
+                               'PRODID PROSE WPROSE'.split()
+        )
+
+        # Note: This lexical grammar is not suitable for use with incremental
+        # parsing.
+        emu_grammar_lexer = lexer.LexicalGrammar(
+            # the operators and keywords:
+            "[ ] { } , ~ + ? <! == != "
+            "but empty here lookahead no not of one or through",
+            NL="\n",
+            # any number of colons together
+            EQ=r':+',
+            # terminals of the ES grammar, quoted with backticks
+            T=r'`[^` \n]+`|```',
+            # also terminals, denoting control characters
+            CHR=r'<[A-Z]+>|U\+[0-9A-f]{4}',
+            # nonterminals that will be followed by boolean parameters
+            NTCALL=r'(?:uri|[A-Z])\w*(?=\[)',
+            # nonterminals (also, boolean parameters)
+            NT=r'(?:uri|[A-Z])\w*',
+            # nonterminals wrapped in vertical bars for no apparent reason
+            NTALT=r'\|[A-Z]\w+\|',
+            # the spec also gives a few productions names
+            PRODID=r'#[A-Za-z]\w*',
+            # prose to the end of the line
+            PROSE=r'>.*',
+            # prose wrapped in square brackets
+            WPROSE=r'\[>[^]]*\]',
+        )
+
+        self.compile(emu_grammar_lexer, grammar)
+
+        source = """\
+        IdentifierReference[Yield, Await] :
+          Identifier
+          [~Yield] `yield`
+          [~Await] `await`
+
+        """
+
+        self.assertParse(source)
+
+    def testParameterizedProductions(self):
+        passthru = ('Yield', Var('Yield')),
+        name = Nt("name", passthru)
+        stmt = Nt("stmt", passthru)
+        stmts = Nt("stmts", passthru)
+        grammar = Grammar({
+            'script': [
+                ['def'],
+                ['script', 'def'],
+            ],
+            'def': [
+                [
+                    'function', 'IDENT', '(', ')', '{',
+                    Nt('stmts', (('Yield', False),)), '}'
+                ],
+                [
+                    'function', '*', 'IDENT', '(', ')', '{',
+                    Nt('stmts', (('Yield', True),)), '}'
+                ],
+            ],
+            'stmts': NtDef(('Yield',), [
+                [stmt],
+                [stmts, stmt],
+            ], None),
+            'stmt': NtDef(('Yield',), [
+                [name, "(", ")", ";"],
+                [name, "=", name, ";"],
+                Production(["yield", name, ";"],
+                           reducer=CallMethod("yield_stmt", [1]),
+                           condition=('Yield', True)),
+            ], None),
+            'name': NtDef(('Yield',), [
+                ["IDENT"],
+                # Specifically ask for a method here, because otherwise we
+                # wouldn't get one and then type checking would fail.
+                Production(["yield"],
+                           CallMethod("yield_as_name", []),
+                           condition=('Yield', False)),
+            ], None),
+        }, variable_terminals=["IDENT"])
+        self.compile(lexer.LexicalGrammar("( ) { } ; * = function yield",
+                                          IDENT=r'[A-Za-z]\w*'),
+                     grammar)
+        self.assertParse("function* farm() { cow = pig; yield cow; }")
+        self.assertNoParse(
+            "function city() { yield toOncomingTraffic; }",
+            message="expected one of ['(', '='], got 'toOncomingTraffic'")
+        self.assertNoParse(
+            "function* farm() { yield = corn; yield yield; }",
+            message="expected 'IDENT', got '='")
+
+    def testMissingParameterError(self):
+        grammar = {
+            'Foo': [
+                ['Bar'],
+            ],
+            'Bar': NtDef(('Arg',), [
+                ['NUM'],
+                Production(['STR'],
+                           reducer=0,
+                           condition=('Arg', True)),
+            ], None),
+        }
+
+        self.assertRaisesRegex(ValueError, "missing parameters for 'Bar'",
+                               lambda: Grammar(grammar))
+
+    def testCanonicalLR(self):
+        """Example 4.39 (grammar 4.20) from the book."""
+
+        # Modified as marked below
+        grammar = Grammar({
+            "S": [
+                ["L", "=", "R"],
+                ["R"],
+            ],
+            "L": [
+                ["*", "R"],
+                ["id"],
+            ],
+            "R": [
+                ["L"],
+                # added so we can have a negative test, showing that
+                # `R = R` is not an S:
+                ["7"],
+            ],
+        })
+        self.compile(lexer.LexicalGrammar("id = * 7"), grammar)
+        self.assertParse("id = *id")
+        self.assertParse("*id = id")
+        self.assertParse("id = 7")
+        self.assertNoParse("7 = id",
+                           message="expected 'end of input', got '='")
+
+    def testLookaheadWithCanonicalLR(self):
+        """Only a lookahead assertion makes this grammar unambiguous."""
+        tokenize = lexer.LexicalGrammar("async => { } ;", Identifier=r'\w+')
+        grammar = Grammar({
+            "script": [
+                ["Expression", ";"],
+            ],
+            "Expression": [
+                ["PrimaryExpression"],
+                ["async", "Identifier", "=>", "AsyncConciseBody"],
+            ],
+            "AsyncConciseBody": [
+                [LookaheadRule(set=frozenset(["{"]), positive=False),
+                 "Expression"],
+                ["{", "}"],
+            ],
+            "PrimaryExpression": [
+                ["{", "}"],
+            ],
+        })
+
+        self.compile(tokenize, grammar)
+        self.assertParse("{};")
+        self.assertParse("async x => {};")
+        self.assertParse("async x => async y => {};")
+
+    def testMultiGoal(self):
+        tokenize = lexer.LexicalGrammar("WHILE DEF FN { } ( ) -> ;", ID=r'\w+')
+        grammar = Grammar({
+            "stmt": [
+                ["expr", ";"],
+                ["{", "stmts", "}"],
+                ["WHILE", "(", "expr", ")", "stmt"],
+                ["DEF", "ID", "(", "ID", ")", "{", Optional("stmts"), "}"],
+            ],
+            "stmts": [
+                ["stmt"],
+                ["stmts", "stmt"],
+            ],
+            "expr": [
+                ["FN", "ID", "->", "expr"],
+                ["call_expr"],
+            ],
+            "call_expr": [
+                ["ID"],
+                ["call_expr", "(", "expr", ")"],
+                ["(", "expr", ")"],
+            ],
+        }, goal_nts=["stmts", "expr"])
+        self.compile(tokenize, grammar)
+        self.assertParse("WHILE ( x ) { decx ( x ) ; }", goal="stmts")
+        self.assertNoParse(
+            "WHILE ( x ) { decx ( x ) ; }", goal="expr",
+            message="expected one of ['(', 'FN', 'ID'], got 'WHILE'")
+        self.assertParse("f(x);", goal="stmts")
+        self.assertNoParse("f(x);", goal="expr",
+                           message="expected 'end of input', got ';'")
+        self.assertParse("(FN x -> f ( x ))(x)", goal="expr")
+        self.assertNoParse("(FN x -> f ( x ))(x)", goal="stmts",
+                           message="unexpected end of input")
+
+    def testStaggeredItems(self):
+        """Items in a state can have different amounts of leading context."""
+        # In this example grammar, after "A" "B", we're in a state that
+        # contains these two items (ignoring lookahead):
+        #       goal ::= "A" "B" · y
+        #       x ::= "B" · stars "X"
+        #
+        # Likewise, after `"A" "B" stars`, we have:
+        #       x ::= "B" stars · "X"
+        #       y ::= stars · "Y"
+        #       stars ::= stars · "*"
+        tokenize = lexer.LexicalGrammar("A B * X Y")
+        grammar = Grammar({
+            "goal": [
+                ["A", "x"],
+                ["A", "B", "y"],
+            ],
+            "x": [
+                ["B", "stars", "X"],
+            ],
+            "y": [
+                ["stars", "Y"],
+            ],
+            "stars": [
+                ["*"],
+                ["stars", "*"],
+            ],
+        })
+        self.compile(tokenize, grammar)
+        self.assertParse("A B * * * X")
+        self.assertParse("A B * * * Y")
+
+    def testCheckCycleFree(self):
+        tokenize = lexer.LexicalGrammar("!")
+        grammar = Grammar({
+            "problem": [
+                ["one", "two"],
+            ],
+            "one": [
+                ["!"],
+            ],
+            "two": [
+                [Optional("problem")],
+            ],
+        })
+        self.compile(tokenize, grammar)
+        self.assertParse("! ! ! ! !")
+
+    def testReduceActions(self):
+        tokenize = lexer.LexicalGrammar("+ - * / ( )",
+                                        NUM=r'[0-9]\w*',
+                                        VAR=r'[A-Za-z]\w*')
+        grammar = Grammar({
+            "expr": [
+                ["term"],
+                prod(["expr", "+", "term"], "add"),
+                prod(["expr", "-", "term"], "sub"),
+            ],
+            "term": [
+                ["unary"],
+                prod(["term", "*", "unary"], "mul"),
+                prod(["term", "/", "unary"], "div"),
+            ],
+            "unary": [
+                ["prim"],
+                prod(["-", "prim"], "neg"),
+            ],
+            "prim": [
+                prod(["(", "expr", ")"], "parens"),
+                prod(["NUM"], "num"),
+                prod(["VAR"], "var"),
+            ],
+        }, goal_nts=['expr'])
+
+        self.compile(tokenize, grammar)
+        self.assertParse("X", ('var', 'X'))
+        self.assertParse("3 + 4", ('add', ('num', '3'), '+', ('num', '4')))
+        self.assertParse(
+            "2 * 3 + 4 * (5 + 7)",
+            (
+                'add',
+                ('mul', ('num', '2'), '*', ('num', '3')),
+                '+',
+                (
+                    'mul',
+                    ('num', '4'),
+                    '*',
+                    ('parens', '(',
+                        ('add', ('num', '5'), '+', ('num', '7')), ')'))))
+        self.assertParse(
+            "1 / (1 + 1 / (1 + 1 / (1 + 1)))",
+            (
+                'div', ('num', '1'), '/', (
+                    'parens', '(', (
+                        'add', ('num', '1'), '+', (
+                            'div', ('num', '1'), '/', (
+                                'parens', '(', (
+                                    'add', ('num', '1'), '+', (
+                                        'div', ('num', '1'), '/', (
+                                            'parens', '(', (
+                                                'add', ('num', '1'), '+',
+                                                ('num', '1')),
+                                            ')'))),
+                                ')'))),
+                    ')')))
+
+    def testConvenienceMethodTypeInference(self):
+        """A method can be called only in an intermediate reduce expression."""
+
+        # The reduce expression `f(g($0))`.
+        reducer = CallMethod("f", [CallMethod("g", [0])])
+
+        # The grammar `goal ::= NAME => f(g($1))`.
+        grammar = Grammar(
+            {
+                'goal': [Production(['NAME'], reducer)],
+            },
+            variable_terminals=['NAME'])
+
+        # Since the return value of f() is used as the value of a `goal`,
+        # we infer that f() returns a goal.
+        self.assertEqual(
+            grammar.methods['f'].return_type,
+            jsparagus.types.Type('goal'))
+
+        # Since the return value of g() isn't used except as an argument, we
+        # just give it the type `g`.
+        self.assertEqual(
+            grammar.methods['g'].return_type,
+            jsparagus.types.Type('g'))
+
+        # Since g() is passed to f(), we infer this:
+        self.assertEqual(
+            grammar.methods['f'].argument_types,
+            [jsparagus.types.Type('g')])
+
+    def testEpsilonFreeTransform(self):
+        tokenize = lexer.LexicalGrammar('{ } X')
+        grammar = Grammar({
+            'goal': [
+                ['{', 'xlist', '}'],
+            ],
+            'xlist': [
+                [],
+                ['xlist', 'X'],
+            ],
+        })
+        self.compile(tokenize, grammar)
+        self.assertParse("{}", ('goal', '{', ('xlist_0',), '}'))
+
+    def compile_as_js(
+            self,
+            grammar_source: str,
+            goals: typing.Optional[typing.Iterable[str]] = None,
+            verbose: bool = False,
+    ) -> None:
+        """Like self.compile(), but generate a parser from ESGrammar,
+        with ASI support, using the JS lexer.
+        """
+        from js_parser.lexer import JSLexer
+        from js_parser import load_es_grammar
+        from js_parser import generate_js_parser_tables
+
+        grammar = parse_esgrammar(
+            grammar_source,
+            filename="es-simplified.esgrammar",
+            extensions=[],
+            goals=goals,
+            synthetic_terminals=load_es_grammar.ECMASCRIPT_SYNTHETIC_TERMINALS,
+            terminal_names=load_es_grammar.TERMINAL_NAMES_FOR_SYNTACTIC_GRAMMAR)
+        grammar = generate_js_parser_tables.hack_grammar(grammar)
+        base_parser_class = gen.compile(grammar, verbose=verbose)
+
+        # "type: ignore" because poor mypy can't cope with the runtime codegen
+        # we're doing here.
+        class JSParser(base_parser_class):  # type: ignore
+            def __init__(self, goal='Script', builder=None):
+                super().__init__(goal, builder)
+                self._goal = goal
+                # self.debug = True
+
+            def clone(self):
+                return JSParser(self._goal, self.methods)
+
+            def on_recover(self, error_code, lexer, stv):
+                """Check that ASI error recovery is really acceptable."""
+                if error_code == 'asi':
+                    if not self.closed and stv.term != '}' and not lexer.saw_line_terminator():
+                        lexer.throw("missing semicolon")
+                else:
+                    assert error_code == 'do_while_asi'
+
+        self.tokenize = JSLexer
+        self.parser_class = JSParser
+
+    def testExtraGoal(self):
+
+        grammar_source = """
+StuffToIgnore_ThisWorksAroundAnUnrelatedBug:
+  Identifier
+  IdentifierName
+
+Hat :
+  `^`
+
+ArrowFunction :
+  `^` `=>`
+  Hat `*` `=>`
+
+Script :
+  `?` `?` ArrowFunction
+  `?` `?` [lookahead <! {`async`} ] Hat `of`
+
+LazyArrowFunction :
+  ArrowFunction
+            """
+
+        def try_it(goals):
+            self.compile_as_js(grammar_source, goals=goals)
+            self.assertParse("? ? ^ =>", goal='Script')
+            self.assertParse("? ? ^ of", goal='Script')
+
+        try_it(['Script', 'LazyArrowFunction'])
+        try_it(['Script'])
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/third_party/rust/jsparagus/tests/test_js.py b/third_party/rust/jsparagus/tests/test_js.py
new file mode 100644
index 0000000000..571232f77a
--- /dev/null
+++ b/third_party/rust/jsparagus/tests/test_js.py
@@ -0,0 +1,207 @@
+""" Tests for the JS parser. """
+
+import unittest
+import jsparagus.lexer
+from js_parser.parser import parse_Script, JSParser
+from js_parser.lexer import JSLexer
+
+
+class ESTestCase(unittest.TestCase):
+    def parse(self, s):
+        if isinstance(s, list):
+            f = JSLexer(JSParser())
+            for chunk in s:
+                f.write(chunk)
+            return f.close()
+        else:
+            return parse_Script(s)
+
+    def assert_parses(self, s):
+        self.parse(s)
+
+    def assert_incomplete(self, s):
+        """Assert that s fails to parse with UnexpectedEndError.
+
+        (This should be the case if `s` is a prefix of a valid Script.)
+        """
+        self.assertRaises(jsparagus.lexer.UnexpectedEndError,
+                          lambda: parse_Script(s))
+
+    def assert_syntax_error(self, s):
+        """Assert that s fails to parse."""
+        with self.assertRaises(jsparagus.lexer.SyntaxError):
+            parse_Script(s)
+
+    def assert_can_close_after(self, s):
+        parser = JSParser()
+        lexer = JSLexer(parser)
+        if isinstance(s, list):
+            for chunk in s:
+                lexer.write(chunk)
+        else:
+            lexer.write(s)
+        self.assertTrue(lexer.can_close())
+
+    # === Tests!
+
+    def test_asi_at_end(self):
+        self.assert_parses("3 + 4")
+        self.assert_syntax_error("3 4")
+        self.assert_incomplete("3 +")
+        self.assert_incomplete("{")
+        self.assert_incomplete("{;")
+
+    def test_asi_at_block_end(self):
+        self.assert_parses("{ doCrimes() }")
+        self.assert_parses("function f() { ok }")
+
+    def test_asi_after_line_terminator(self):
+        self.assert_parses('''\
+           switch (value) {
+             case 1: break
+             case 2: console.log('2');
+           }
+        ''')
+        self.assert_syntax_error(
+            "switch (value) { case 1: break case 2: console.log('2'); }")
+
+    def test_asi_after_no_line_terminator_here(self):
+        self.assert_parses('''\
+           function f() {
+             return
+               x;
+           }
+        ''')
+
+    def test_asi_suppressed(self):
+        # The specification says ASI does not happen in the production
+        # EmptyStatement : `;`.
+        self.assert_syntax_error("if (true)")
+        self.assert_syntax_error("{ for (;;) }")
+
+        # ASI does not happen in for(;;) loops.
+        self.assert_syntax_error("for ( \n ; ) {}")
+        self.assert_syntax_error("for ( ; \n ) {}")
+        self.assert_syntax_error("for ( \n \n ) {}")
+        self.assert_syntax_error("for (var i = 0 \n i < 9;   i++) {}")
+        self.assert_syntax_error("for (var i = 0;   i < 9 \n i++) {}")
+        self.assert_syntax_error("for (i = 0     \n i < 9;   i++) {}")
+        self.assert_syntax_error("for (i = 0;       i < 9 \n i++) {}")
+        self.assert_syntax_error("for (let i = 0 \n i < 9;   i++) {}")
+
+        # ASI is suppressed in the production ClassElement[Yield, Await] : `;`
+        # to prevent an infinite loop of ASI. lol
+        self.assert_syntax_error("class Fail { \n +1; }")
+
+    def test_if_else(self):
+        self.assert_parses("if (x) f();")
+        self.assert_incomplete("if (x)")
+        self.assert_parses("if (x) f(); else g();")
+        self.assert_incomplete("if (x) f(); else")
+        self.assert_parses("if (x) if (y) g(); else h();")
+        self.assert_parses("if (x) if (y) g(); else h(); else j();")
+
+    def test_lexer_decimal(self):
+        self.assert_parses("0.")
+        self.assert_parses(".5")
+        self.assert_syntax_error(".")
+
+    def test_arrow(self):
+        self.assert_parses("x => x")
+        self.assert_parses("f = x => x;")
+        self.assert_parses("(x, y) => [y, x]")
+        self.assert_parses("f = (x, y) => {}")
+        self.assert_syntax_error("(x, y) => {x: x, y: y}")
+
+    def test_invalid_character(self):
+        self.assert_syntax_error("\0")
+        self.assert_syntax_error("—x;")
+        self.assert_syntax_error("const ONE_THIRD = 1 ÷ 3;")
+
+    def test_regexp(self):
+        self.assert_parses(r"/\w/")
+        self.assert_parses("/[A-Z]/")
+        self.assert_parses("/[//]/")
+        self.assert_parses("/a*a/")
+        self.assert_parses("/**//x*/")
+        self.assert_parses("{} /x/")
+        self.assert_parses("of / 2")
+
+    def test_incomplete_comments(self):
+        self.assert_syntax_error("/*")
+        self.assert_syntax_error("/* hello world")
+        self.assert_syntax_error("/* hello world *")
+        self.assert_parses(["/* hello\n", " world */"])
+        self.assert_parses(["// oawfeoiawj", "ioawefoawjie"])
+        self.assert_parses(["// oawfeoiawj", "ioawefoawjie\n ok();"])
+        self.assert_parses(["// oawfeoiawj", "ioawefoawjie", "jiowaeawojefiw"])
+        self.assert_parses(["// oawfeoiawj", "ioawefoawjie", "jiowaeawojefiw\n ok();"])
+
+    def test_awkward_chunks(self):
+        self.assert_parses(["let", "ter.head = 1;"])
+        self.assert_parses(["let", " x = 1;"])
+
+        # `list()` here explodes the string into a list of one-character strings.
+        self.assert_parses(list("function f() { ok(); }"))
+
+        self.assertEqual(
+            self.parse(["/xyzzy/", "g;"]),
+            ('script',
+             ('script_body',
+              ('statement_list_single',
+               ('expression_statement',
+                ('regexp_literal', '/xyzzy/g'))))))
+
+        self.assertEqual(
+            self.parse(['x/', '=2;']),
+            ('script',
+             ('script_body',
+              ('statement_list_single',
+               ('expression_statement',
+                ('compound_assignment_expr',
+                 ('identifier_expr', ('identifier_reference', 'x')),
+                 ('box_assign_op', ('div_assign_op', '/=')),
+                 ('numeric_literal', '2')))))))
+
+    def test_can_close(self):
+        self.assert_can_close_after([])
+        self.assert_can_close_after("")
+        self.assert_can_close_after("2 + 2;\n")
+        self.assert_can_close_after("// seems ok\n")
+
+    def test_can_close_with_asi(self):
+        self.assert_can_close_after("2 + 2\n")
+
+    def test_conditional_keywords(self):
+        # property names
+        self.assert_parses("let obj = {if: 3, function: 4};")
+        self.assert_parses("assert(obj.if == 3);")
+
+        # method names
+        self.assert_parses("""
+            class C {
+                if() {}
+                function() {}
+            }
+        """)
+
+        self.assert_parses("var let = [new Date];")    # let as identifier
+        self.assert_parses("let v = let;")             # let as keyword, then identifier
+        # Next line would fail because the multitoken `let [` lookahead isn't implemented yet.
+        # self.assert_parses("let.length;")            # `let .` -> ExpressionStatement
+        self.assert_syntax_error("let[0].getYear();")  # `let [` -> LexicalDeclaration
+
+        self.assert_parses("""
+            var of = [1, 2, 3];
+            for (of of of) console.log(of);  // logs 1, 2, 3
+        """)
+        self.assert_parses("var of, let, private, target;")
+        self.assert_parses("class X { get y() {} }")
+        self.assert_parses("async: { break async; }")
+        self.assert_parses("var get = { get get() {}, set get(v) {}, set: 3 };")
+        self.assert_parses("for (async of => {};;) {}")
+        # self.assert_parses("for (async of []) {}")  # would fail
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/third_party/rust/jsparagus/tests/test_parse_pgen.py b/third_party/rust/jsparagus/tests/test_parse_pgen.py
new file mode 100644
index 0000000000..5052f9069c
--- /dev/null
+++ b/third_party/rust/jsparagus/tests/test_parse_pgen.py
@@ -0,0 +1,33 @@
+import unittest
+
+import jsparagus.gen
+from jsparagus import parse_pgen, parse_pgen_generated
+
+
+class ParsePgenTestCase(unittest.TestCase):
+    def test_self(self):
+        import os
+        filename = os.path.join(os.path.dirname(parse_pgen.__file__), "..",
+                                "pgen.pgen")
+        grammar = parse_pgen.load_grammar(filename)
+        self.maxDiff = None
+        pgen_grammar = parse_pgen.pgen_grammar
+        self.assertEqual(pgen_grammar.nonterminals, grammar.nonterminals)
+        self.assertEqual(pgen_grammar.variable_terminals,
+                         grammar.variable_terminals)
+        self.assertEqual(pgen_grammar.goals(), grammar.goals())
+
+        with open(parse_pgen_generated.__file__) as f:
+            pre_generated = f.read()
+
+        import io
+        out = io.StringIO()
+        jsparagus.gen.generate_parser(out, grammar)
+        generated_from_file = out.getvalue()
+
+        self.maxDiff = None
+        self.assertEqual(pre_generated, generated_from_file)
+
+
+if __name__ == '__main__':
+    unittest.main()