Parser improvements (#45)

Author: gf712

integration/tests/left_recursive_rules.py

@@ -0,0 +1,57 @@
+# The parser seeds a left-recursion sentinel only for the rules that can re-enter themselves
+# at the same position, which after the precedence-climbing and postfix-loop rewrites is just
+# two: dotted_name (`import a.b.c`) and t_primary (the target side of an assignment).
+#
+# Those two are the reason the sentinel and grow_lr still exist, and this file is what proves
+# they still work. If a rule is dropped from is_left_recursive it will recurse without
+# terminating, and if a newly left-recursive rule is added without an entry the same happens
+# there - so a hang here is as much a failure as a wrong answer.
+
+# dotted_name: dotted_name '.' NAME | NAME
+import os.path
+
+assert os.path.sep == "/"
+
+import os.path as shortcut
+
+assert shortcut.sep == "/"
+
+from os.path import sep
+
+assert sep == "/"
+
+
+# t_primary: the left-recursive part of an assignment target. The parser matches the longest
+# prefix that is still followed by a postfix operator, and the enclosing rule takes the last
+# one, so each extra link here exercises another turn of the seed-growing loop.
+nested = {"x": {"y": [1, 2]}}
+nested["x"]["y"][0] = 9
+assert nested["x"]["y"][0] == 9
+assert nested["x"]["y"][1] == 2
+
+
+class Holder:
+    def __init__(self):
+        self.d = {"k": [0, 0]}
+        self.child = None
+
+
+h = Holder()
+h.d["k"][0] = 5
+assert h.d["k"][0] == 5
+
+# attribute target reached through another attribute
+h.child = Holder()
+h.child.d["k"][1] = 7
+assert h.child.d["k"][1] == 7
+
+# a longer chain: attribute, attribute, subscript, subscript
+h.child.child = Holder()
+h.child.child.d["k"][0] = 11
+assert h.child.child.d["k"][0] == 11
+
+# plain attribute targets still work alongside the chained ones
+h.child.child.d = {"k": [1]}
+assert h.child.child.d["k"][0] == 1
+
+print("left_recursive_rules: ok")