Fix possible hanging while comparing regex (#102)

pytest_mypy_plugins/tests/test-regex_assertions.yml

@@ -15,6 +15,20 @@
   out: |
     main:2: note: .*str.*
 
+- case: regex_with_out_does_not_hang
+  expect_fail: yes
+  regex: yes
+  main: |
+    'abc'.split(4)
+  out: |
+    main:1: error: Argument 1 to "split" of "str" has incompatible type "int"; expected "Optional[str]"
+
+- case: regex_with_comment_does_not_hang
+  expect_fail: yes
+  regex: yes
+  main: |
+    a = 'abc'.split(4)  # E: Argument 1 to "split" of "str" has incompatible type "int"; expected "Optional[str]"
+
 - case: expected_single_message_regex
   regex: no
   main: |
@@ -34,7 +48,7 @@
     a = 'hello'
     reveal_type(a)  # N: .*str.*
 
-- case: regext_does_not_match
+- case: regex_does_not_match
   expect_fail: yes
   regex: no
   main: |

pytest_mypy_plugins/utils.py

@@ -144,6 +144,8 @@ def _add_aligned_message(s1: str, s2: str, error_message: str) -> str:
 
     error_message += "Alignment of first line difference:\n"
 
+    assert s1 != s2
+
     trunc = False
     while s1[:30] == s2[:30]:
         s1 = s1[10:]
@@ -260,7 +262,9 @@ def format_error_lines(lines: List[str]) -> str:
             format_error_lines(actual_message_lines), format_error_lines(expected_message_lines)
         )
 
-        if (
+        if expected_line and expected_line.regex:
+            error_message += "The actual output does not match the expected regex."
+        elif (
             first_diff_actual is not None
             and first_diff_expected is not None
             and (