From 84b20a40168e469ebdbfc4e3cc23253d3955134a Mon Sep 17 00:00:00 2001
From: Anthony Sottile <asottile@umich.edu>
Date: Fri, 24 Jul 2020 15:13:35 -0700
Subject: [PATCH] fix highlighting hang with empty begin end rules

---
 babi/highlight.py       | 23 ++++++++++++++++++-----
 tests/highlight_test.py | 22 ++++++++++++++++++++++
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/babi/highlight.py b/babi/highlight.py
index e701e03..bcb937d 100644
--- a/babi/highlight.py
+++ b/babi/highlight.py
@@ -273,6 +273,7 @@ class CompiledRegsetRule(CompiledRule, Protocol):
 class Entry(NamedTuple):
     scope: Tuple[str, ...]
     rule: CompiledRule
+    start: Tuple[str, int]
     reg: _Reg = ERR_REG
     boundary: bool = False
 
@@ -284,7 +285,7 @@ def _inner_capture_parse(
         scope: Scope,
         rule: CompiledRule,
 ) -> Regions:
-    state = State.root(Entry(scope + rule.name, rule))
+    state = State.root(Entry(scope + rule.name, rule, (s, 0)))
     _, regions = highlight_line(compiler, state, s, first_line=False)
     return tuple(
         r._replace(start=r.start + start, end=r.end + start) for r in regions
@@ -440,7 +441,8 @@ class EndRule(NamedTuple):
 
         boundary = match.end() == len(match.string)
         reg = make_reg(expand_escaped(match, self.end))
-        state = state.push(Entry(next_scope, self, reg, boundary))
+        start = (match.string, match.start())
+        state = state.push(Entry(next_scope, self, start, reg, boundary))
         regions = _captures(compiler, scope, match, self.begin_captures)
         return state, True, regions
 
@@ -455,7 +457,16 @@ class EndRule(NamedTuple):
         if m.start() > pos:
             ret.append(Region(pos, m.start(), state.cur.scope))
         ret.extend(_captures(compiler, state.cur.scope, m, self.end_captures))
-        return state.pop(), m.end(), False, tuple(ret)
+        # this is probably a bug in the grammar, but it pushed and popped at
+        # the same position.
+        # we'll advance the highlighter by one position to get past the loop
+        # this appears to be what vs code does as well
+        if state.entries[-1].start == (m.string, m.end()):
+            ret.append(Region(m.end(), m.end() + 1, state.cur.scope))
+            end = m.end() + 1
+        else:
+            end = m.end()
+        return state.pop(), end, False, tuple(ret)
 
     def search(
             self,
@@ -501,7 +512,9 @@ class WhileRule(NamedTuple):
 
         boundary = match.end() == len(match.string)
         reg = make_reg(expand_escaped(match, self.while_))
-        state = state.push_while(self, Entry(next_scope, self, reg, boundary))
+        start = (match.string, match.start())
+        entry = Entry(next_scope, self, start, reg, boundary)
+        state = state.push_while(self, entry)
         regions = _captures(compiler, scope, match, self.begin_captures)
         return state, True, regions
 
@@ -541,7 +554,7 @@ class Compiler:
         self._rule_to_grammar: Dict[_Rule, Grammar] = {}
         self._c_rules: Dict[_Rule, CompiledRule] = {}
         root = self._compile_root(grammar)
-        self.root_state = State.root(Entry(root.name, root))
+        self.root_state = State.root(Entry(root.name, root, ('', 0)))
 
     def _visit_rule(self, grammar: Grammar, rule: _Rule) -> _Rule:
         self._rule_to_grammar[rule] = grammar
diff --git a/tests/highlight_test.py b/tests/highlight_test.py
index c2c3d84..8c825ef 100644
--- a/tests/highlight_test.py
+++ b/tests/highlight_test.py
@@ -637,3 +637,25 @@ def test_backslash_z(compiler_state):
     assert regions2 == (
         Region(0, 6, ('test', 'comment')),
     )
+
+
+def test_buggy_begin_end_grammar(compiler_state):
+    # before this would result in an infinite loop of start / end
+    compiler, state = compiler_state({
+        'scopeName': 'test',
+        'patterns': [
+            {
+                'begin': '(?=</style)',
+                'end': '(?=</style)',
+                'name': 'css',
+            },
+        ],
+    })
+
+    state, regions = highlight_line(compiler, state, 'test </style', True)
+
+    assert regions == (
+        Region(0, 5, ('test',)),
+        Region(5, 6, ('test', 'css')),
+        Region(6, 12, ('test',)),
+    )