Mention "skip news" label in CHANGELOG action (#2797)

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

diff --git a/src/black/__init__.py b/src/black/__init__.py
index fa918ce293172239fb87db2e0bfb600e836494d0..eaf72f9c2b3f4d12ae275d01472112931af331e9 100644 (file)
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -24,6 +24,7 @@ from typing import (
     MutableMapping,
     Optional,
     Pattern,
+    Sequence,
     Set,
     Sized,
     Tuple,
@@ -225,6 +226,16 @@ def validate_regex(
         "(useful when piping source on standard input)."
     ),
 )
+@click.option(
+    "--python-cell-magics",
+    multiple=True,
+    help=(
+        "When processing Jupyter Notebooks, add the given magic to the list"
+        f" of known python-magics ({', '.join(PYTHON_CELL_MAGICS)})."
+        " Useful for formatting cells with custom python magics."
+    ),
+    default=[],
+)
 @click.option(
     "-S",
     "--skip-string-normalization",
@@ -241,9 +252,14 @@ def validate_regex(
     "--experimental-string-processing",
     is_flag=True,
     hidden=True,
+    help="(DEPRECATED and now included in --preview) Normalize string literals.",
+)
+@click.option(
+    "--preview",
+    is_flag=True,
     help=(
-        "Experimental option that performs more normalization on string literals."
-        " Currently disabled because it leads to some crashes."
+        "Enable potentially disruptive style changes that will be added to Black's main"
+        " functionality in the next major release."
     ),
 )
 @click.option(
@@ -396,9 +412,11 @@ def main(
     fast: bool,
     pyi: bool,
     ipynb: bool,
+    python_cell_magics: Sequence[str],
     skip_string_normalization: bool,
     skip_magic_trailing_comma: bool,
     experimental_string_processing: bool,
+    preview: bool,
     quiet: bool,
     verbose: bool,
     required_version: Optional[str],
@@ -469,6 +487,8 @@ def main(
         string_normalization=not skip_string_normalization,
         magic_trailing_comma=not skip_magic_trailing_comma,
         experimental_string_processing=experimental_string_processing,
+        preview=preview,
+        python_cell_magics=set(python_cell_magics),
     )
 
     if code is not None:
@@ -974,7 +994,7 @@ def format_file_contents(src_contents: str, *, fast: bool, mode: Mode) -> FileCo
     return dst_contents
 
 
-def validate_cell(src: str) -> None:
+def validate_cell(src: str, mode: Mode) -> None:
     """Check that cell does not already contain TransformerManager transformations,
     or non-Python cell magics, which might cause tokenizer_rt to break because of
     indentations.
@@ -993,7 +1013,10 @@ def validate_cell(src: str) -> None:
     """
     if any(transformed_magic in src for transformed_magic in TRANSFORMED_MAGICS):
         raise NothingChanged
-    if src[:2] == "%%" and src.split()[0][2:] not in PYTHON_CELL_MAGICS:
+    if (
+        src[:2] == "%%"
+        and src.split()[0][2:] not in PYTHON_CELL_MAGICS | mode.python_cell_magics
+    ):
         raise NothingChanged
 
 
@@ -1013,7 +1036,7 @@ def format_cell(src: str, *, fast: bool, mode: Mode) -> str:
     could potentially be automagics or multi-line magics, which
     are currently not supported.
     """
-    validate_cell(src)
+    validate_cell(src, mode)
     src_without_trailing_semicolon, has_trailing_semicolon = remove_trailing_semicolon(
         src
     )
@@ -1305,7 +1328,10 @@ def assert_equivalent(src: str, dst: str, *, pass_num: int = 1) -> None:
         src_ast = parse_ast(src)
     except Exception as exc:
         raise AssertionError(
-            f"cannot use --safe with this file; failed to parse source file: {exc}"
+            f"cannot use --safe with this file; failed to parse source file AST: "
+            f"{exc}\n"
+            f"This could be caused by running Black with an older Python version "
+            f"that does not support new syntax used in your source file."
         ) from exc
 
     try: