Whole file

lark-parser/lark

The author described this change as “Fix types for tree_templates, better error messages”. It counts as a record because the check below fails on the code as it stood at 66c22d001 and passes on 242c4a574, with nothing else changed between the two runs.

Projectlark-parser/lark

Fix saved2022-05-24

Sharing licenceMIT · LICENSE

Change size+15 −5

What the code was meant to do, written into the code itself as a save note

Fix types for tree_templates, better error messages

The change

9	9		from lark import Tree, Transformer
10	10		from lark.exceptions import MissingVariableError
11	11
	12	+	Branch = Union[Tree[str], str]
12	13		TreeOrCode = Union[Tree[str], str]
	14	+	MatchResult = Dict[str, Tree]
13	15		_TEMPLATE_MARKER = '$'
14	16
15	17
⋯
17	19		"""Template Configuration
18	20
19	21		Allows customization for different uses of Template
	22	+
	23	+	parse() must return a Tree instance.
20	24		"""
21	25
22	26		def __init__(self, parse=None):
⋯
49	53		assert self._parse
50	54		template = self._parse(template)
51	55
52		-	assert isinstance(template, Tree)
	56	+	if not isinstance(template, Tree):
	57	+	raise TypeError("template parser must return a Tree instance")
	58	+
53	59		return template
54	60
55	61		def __call__(self, template: Tree[str]) -> 'Template':
56	62		return Template(template, conf=self)
57	63
58		-	def _match_tree_template(self, template: TreeOrCode, tree: TreeOrCode) -> Optional[Dict[str, TreeOrCode]]:
	64	+	def _match_tree_template(self, template: TreeOrCode, tree: Branch) -> Optional[MatchResult]:
	65	+	"""Returns dict of {var: match} if found a match, else None
	66	+	"""
59	67		template_var = self.test_var(template)
60	68		if template_var:
	69	+	if not isinstance(tree, Tree):
	70	+	raise TypeError(f"Template variables can only match Tree instances. Not {tree}")
61	71		return {template_var: tree}
62	72
63	73		if isinstance(template, str):
⋯
100	110
101	111
102	112		class Template:
103		-	"""Represents a tree templates, tied to a specific configuration
	113	+	"""Represents a tree template, tied to a specific configuration
104	114
105	115		A tree template is a tree that contains nodes that are template variables.
106	116		Those variables will match any tree.
⋯
111	121		self.conf = conf
112	122		self.tree = conf._get_tree(tree)
113	123
114		-	def match(self, tree: TreeOrCode) -> Optional[Dict[str, TreeOrCode]]:
	124	+	def match(self, tree: TreeOrCode) -> Optional[MatchResult]:
115	125		"""Match a tree template to a tree.
116	126
117	127		A tree template without variables will only match ``tree`` if it is equal to the template.
⋯
127	137		tree = self.conf._get_tree(tree)
128	138		return self.conf._match_tree_template(self.tree, tree)
129	139
130		-	def search(self, tree: TreeOrCode) -> Iterator[Tuple[Tree[str], Dict[str, TreeOrCode]]]:
	140	+	def search(self, tree: TreeOrCode) -> Iterator[Tuple[Tree[str], MatchResult]]:
131	141		"""Search for all occurances of the tree template inside ``tree``.
132	142		"""
133	143		tree = self.conf._get_tree(tree)

The check that tells the two apart

fail→pass·tests/test_tree_templates.py::TestTreeTemplatesConf::test_template_match__only_tree

Check file tests/test_tree_templates.py, taken without changes from the fix and copied onto the older code, so the exact same check runs against both versions.

Origin and history

The fix242c4a5741efff3beffa8f60fb5da09e42dd07d1

The code before it66c22d0019170ad4d6bfb45e881776e0dad32625

Broken version dated2022-05-24

Modulelark.tree_templates

Units changedTemplate, TemplateConf

Fingerprint83d9d0d77f91583e

Checked2026-08-18 by goldset/0.1

Every field above is generated by our program. None of it is written by hand.

Other bugs found in lark-parser/lark

2026-07-08Fix lexer_callbacks silently dropped for keyword terminals
2026-06-24Transformer_NonRecursive
2026-06-04Raise GrammarError for non-terminal names in %declare
2026-06-02Fix empty SPPF node from xearley ignore carry-over (fixes #1598)
2026-05-24fix: raise GrammarError for template usage inside terminals
2024-10-25Adjust behaviour in #1481 to raise a NotImplementedError