Elaborate on Python support policy (#2819)

[etc/vim.git] / src / black / __init__.py

diff --git a/src/black/__init__.py b/src/black/__init__.py
index 7024c9d52b059f5dd8b7db94c2c5655619afe706..769e693ed2386659522f2f2fdda6e5516f8883fb 100644 (file)
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -968,17 +968,7 @@ def check_stability_and_equivalence(
     content differently.
     """
     assert_equivalent(src_contents, dst_contents)
-
-    # Forced second pass to work around optional trailing commas (becoming
-    # forced trailing commas on pass 2) interacting differently with optional
-    # parentheses.  Admittedly ugly.
-    dst_contents_pass2 = format_str(dst_contents, mode=mode)
-    if dst_contents != dst_contents_pass2:
-        dst_contents = dst_contents_pass2
-        assert_equivalent(src_contents, dst_contents, pass_num=2)
-        assert_stable(src_contents, dst_contents, mode=mode)
-    # Note: no need to explicitly call `assert_stable` if `dst_contents` was
-    # the same as `dst_contents_pass2`.
+    assert_stable(src_contents, dst_contents, mode=mode)
 
 
 def format_file_contents(src_contents: str, *, fast: bool, mode: Mode) -> FileContent:
@@ -1108,7 +1098,7 @@ def format_ipynb_string(src_contents: str, *, fast: bool, mode: Mode) -> FileCon
         raise NothingChanged
 
 
-def format_str(src_contents: str, *, mode: Mode) -> FileContent:
+def format_str(src_contents: str, *, mode: Mode) -> str:
     """Reformat a string and return new contents.
 
     `mode` determines formatting options, such as how many characters per line are
@@ -1138,6 +1128,16 @@ def format_str(src_contents: str, *, mode: Mode) -> FileContent:
         hey
 
     """
+    dst_contents = _format_str_once(src_contents, mode=mode)
+    # Forced second pass to work around optional trailing commas (becoming
+    # forced trailing commas on pass 2) interacting differently with optional
+    # parentheses.  Admittedly ugly.
+    if src_contents != dst_contents:
+        return _format_str_once(dst_contents, mode=mode)
+    return dst_contents
+
+
+def _format_str_once(src_contents: str, *, mode: Mode) -> str:
     src_node = lib2to3_parse(src_contents.lstrip(), mode.target_versions)
     dst_contents = []
     future_imports = get_future_imports(src_node)
@@ -1367,7 +1367,10 @@ def assert_equivalent(src: str, dst: str, *, pass_num: int = 1) -> None:
 
 def assert_stable(src: str, dst: str, mode: Mode) -> None:
     """Raise AssertionError if `dst` reformats differently the second time."""
-    newdst = format_str(dst, mode=mode)
+    # We shouldn't call format_str() here, because that formats the string
+    # twice and may hide a bug where we bounce back and forth between two
+    # versions.
+    newdst = _format_str_once(dst, mode=mode)
     if dst != newdst:
         log = dump_to_file(
             str(mode),