Compatibility with newest Lark parser

HypothesisWorks · Oct 14, 2020 · 2665393 · 2665393
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diff --git a/hypothesis-python/RELEASE.rst b/hypothesis-python/RELEASE.rst
@@ -0,0 +1,4 @@
+RELEASE_TYPE: patch
+
+This patch fixes :func:`~hypothesis.extra.lark.from_lark` with version
+0.10.1+ of the :pypi:`lark-parser` package.
diff --git a/hypothesis-python/src/hypothesis/extra/lark.py b/hypothesis-python/src/hypothesis/extra/lark.py
@@ -92,7 +92,14 @@ def __init__(self, grammar, start, explicit):
             start = [start]
         self.grammar = grammar
 
-        if "start" in getfullargspec(grammar.grammar.compile).args:
+        # This is a total hack, but working around the changes is a nicer user
+        # experience than breaking for anyone who doesn't instantly update their
+        # installation of Lark alongside Hypothesis.
+        compile_args = getfullargspec(grammar.grammar.compile).args
+        if "terminals_to_keep" in compile_args:
+            terminals, rules, ignore_names = grammar.grammar.compile(start, ())
+        elif "start" in compile_args:  # pragma: no cover
+            # Support lark <= 0.10.0, without the terminals_to_keep argument.
             terminals, rules, ignore_names = grammar.grammar.compile(start)
         else:  # pragma: no cover
             # This branch is to support lark <= 0.7.1, without the start argument.