Stability fixup: interaction between newlines and comments (#1975)

* Add test case to illustrate the issue

* Accept carriage returns as valid separators while enumerating comments

Without this acceptance, escaped multi-line statments that use carriage returns will not be counted into the 'ignored_lines' variable since the emitted line values will end with a CR and not an escape character.  That leads to comments associated with the line being incorrectly labeled with the STANDALONE_COMMENT type, affecting comment placement and line space management.

* Remove comment linking to ephemeral build log

src/black/__init__.py

@@ -2635,7 +2635,7 @@ def list_comments(prefix: str, *, is_endmarker: bool) -> List[ProtoComment]:
     consumed = 0
     nlines = 0
     ignored_lines = 0
-    for index, line in enumerate(prefix.split("\n")):
+    for index, line in enumerate(re.split("\r?\n", prefix)):
         consumed += len(line) + 1  # adding the length of the split '\n'
         line = line.lstrip()
         if not line:

tests/test_black.py

@@ -1793,6 +1793,11 @@ def test_bpo_33660_workaround(self) -> None:
         finally:
             os.chdir(str(old_cwd))
 
+    def test_newline_comment_interaction(self) -> None:
+        source = "class A:\\\r\n# type: ignore\n pass\n"
+        output = black.format_str(source, mode=DEFAULT_MODE)
+        black.assert_stable(source, output, mode=DEFAULT_MODE)
+
 
 with open(black.__file__, "r", encoding="utf-8") as _bf:
     black_source_lines = _bf.readlines()