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## Summary _This is preview only feature and is available using the `--preview` command-line flag._ With the implementation of [PEP 701] in Python 3.12, f-strings can now be broken into multiple lines, can contain comments, and can re-use the same quote character. Currently, no other Python formatter formats the f-strings so there's some discussion which needs to happen in defining the style used for f-string formatting. Relevant discussion: https://github.com/astral-sh/ruff/discussions/9785 The goal for this PR is to add minimal support for f-string formatting. This would be to format expression within the replacement field without introducing any major style changes. ### Newlines The heuristics for adding newline is similar to that of [Prettier](https://prettier.io/docs/en/next/rationale.html#template-literals) where the formatter would only split an expression in the replacement field across multiple lines if there was already a line break within the replacement field. In other words, the formatter would not add any newlines unless they were already present i.e., they were added by the user. This makes breaking any expression inside an f-string optional and in control of the user. For example, ```python # We wouldn't break this aaaaaaaaaaa = f"asaaaaaaaaaaaaaaaa { aaaaaaaaaaaa + bbbbbbbbbbbb + ccccccccccccccc } cccccccccc" # But, we would break the following as there's already a newline aaaaaaaaaaa = f"asaaaaaaaaaaaaaaaa { aaaaaaaaaaaa + bbbbbbbbbbbb + ccccccccccccccc } cccccccccc" ``` If there are comments in any of the replacement field of the f-string, then it will always be a multi-line f-string in which case the formatter would prefer to break expressions i.e., introduce newlines. For example, ```python x = f"{ # comment a }" ``` ### Quotes The logic for formatting quotes remains unchanged. The existing logic is used to determine the necessary quote char and is used accordingly. Now, if the expression inside an f-string is itself a string like, then we need to make sure to preserve the existing quote and not change it to the preferred quote unless it's 3.12. For example, ```python f"outer {'inner'} outer" # For pre 3.12, preserve the single quote f"outer {'inner'} outer" # While for 3.12 and later, the quotes can be changed f"outer {"inner"} outer" ``` But, for triple-quoted strings, we can re-use the same quote char unless the inner string is itself a triple-quoted string. ```python f"""outer {"inner"} outer""" # valid f"""outer {'''inner'''} outer""" # preserve the single quote char for the inner string ``` ### Debug expressions If debug expressions are present in the replacement field of a f-string, then the whitespace needs to be preserved as they will be rendered as it is (for example, `f"{ x = }"`. If there are any nested f-strings, then the whitespace in them needs to be preserved as well which means that we'll stop formatting the f-string as soon as we encounter a debug expression. ```python f"outer { x = !s :.3f}" # ^^ # We can remove these whitespaces ``` Now, the whitespace doesn't need to be preserved around conversion spec and format specifiers, so we'll format them as usual but we won't be formatting any nested f-string within the format specifier. ### Miscellaneous - The [`hug_parens_with_braces_and_square_brackets`](https://github.com/astral-sh/ruff/issues/8279) preview style isn't implemented w.r.t. the f-string curly braces. - The [indentation](https://github.com/astral-sh/ruff/discussions/9785#discussioncomment-8470590) is always relative to the f-string containing statement ## Test Plan * Add new test cases * Review existing snapshot changes * Review the ecosystem changes [PEP 701]: https://peps.python.org/pep-0701/
88 lines
4.2 KiB
Rust
88 lines
4.2 KiB
Rust
//! Helpers to test if a specific preview style is enabled or not.
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//!
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//! The motivation for these functions isn't to avoid code duplication but to ease promoting preview styles
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//! to stable. The challenge with directly using [`is_preview`](PyFormatContext::is_preview) is that it is unclear
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//! for which specific feature this preview check is for. Having named functions simplifies the promotion:
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//! Simply delete the function and let Rust tell you which checks you have to remove.
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use crate::PyFormatContext;
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/// Returns `true` if the [`fix_power_op_line_length`](https://github.com/astral-sh/ruff/issues/8938) preview style is enabled.
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pub(crate) const fn is_fix_power_op_line_length_enabled(context: &PyFormatContext) -> bool {
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context.is_preview()
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}
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/// Returns `true` if the [`hug_parens_with_braces_and_square_brackets`](https://github.com/astral-sh/ruff/issues/8279) preview style is enabled.
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pub(crate) const fn is_hug_parens_with_braces_and_square_brackets_enabled(
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context: &PyFormatContext,
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) -> bool {
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context.is_preview()
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}
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/// Returns `true` if the [`prefer_splitting_right_hand_side_of_assignments`](https://github.com/astral-sh/ruff/issues/6975) preview style is enabled.
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pub(crate) const fn is_prefer_splitting_right_hand_side_of_assignments_enabled(
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context: &PyFormatContext,
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) -> bool {
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context.is_preview()
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}
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/// Returns `true` if the [`parenthesize_long_type_hints`](https://github.com/astral-sh/ruff/issues/8894) preview style is enabled.
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pub(crate) const fn is_parenthesize_long_type_hints_enabled(context: &PyFormatContext) -> bool {
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context.is_preview()
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}
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/// Returns `true` if the [`no_blank_line_before_class_docstring`] preview style is enabled.
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///
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/// [`no_blank_line_before_class_docstring`]: https://github.com/astral-sh/ruff/issues/8888
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pub(crate) const fn is_no_blank_line_before_class_docstring_enabled(
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context: &PyFormatContext,
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) -> bool {
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context.is_preview()
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}
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/// Returns `true` if the [`wrap_multiple_context_managers_in_parens`](https://github.com/astral-sh/ruff/issues/8889) preview style is enabled.
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///
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/// Unlike Black, we re-use the same preview style feature flag for [`improved_async_statements_handling`](https://github.com/astral-sh/ruff/issues/8890)
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pub(crate) const fn is_wrap_multiple_context_managers_in_parens_enabled(
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context: &PyFormatContext,
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) -> bool {
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context.is_preview()
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}
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/// Returns `true` if the [`blank_line_after_nested_stub_class`](https://github.com/astral-sh/ruff/issues/8891) preview style is enabled.
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pub(crate) const fn is_blank_line_after_nested_stub_class_enabled(
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context: &PyFormatContext,
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) -> bool {
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context.is_preview()
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}
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/// Returns `true` if the [`module_docstring_newlines`](https://github.com/astral-sh/ruff/issues/7995) preview style is enabled.
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pub(crate) const fn is_module_docstring_newlines_enabled(context: &PyFormatContext) -> bool {
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context.is_preview()
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}
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/// Returns `true` if the [`dummy_implementations`](https://github.com/astral-sh/ruff/issues/8357) preview style is enabled.
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pub(crate) const fn is_dummy_implementations_enabled(context: &PyFormatContext) -> bool {
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context.is_preview()
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}
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/// Returns `true` if the [`hex_codes_in_unicode_sequences`](https://github.com/psf/black/pull/2916) preview style is enabled.
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pub(crate) const fn is_hex_codes_in_unicode_sequences_enabled(context: &PyFormatContext) -> bool {
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context.is_preview()
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}
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/// Returns `true` if the [`multiline_string_handling`](https://github.com/astral-sh/ruff/issues/8896) preview style is enabled.
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pub(crate) const fn is_multiline_string_handling_enabled(context: &PyFormatContext) -> bool {
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context.is_preview()
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}
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/// Returns `true` if the [`multiline_string_handling`](https://github.com/astral-sh/ruff/pull/9725) preview style is enabled.
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/// Black does not [`format docstrings`](https://github.com/psf/black/issues/3493) so we keep this
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/// preview for compatibility with Black.
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pub(crate) const fn is_format_module_docstring_enabled(context: &PyFormatContext) -> bool {
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context.is_preview()
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}
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/// Returns `true` if the [`f-string formatting`](https://github.com/astral-sh/ruff/issues/7594) preview style is enabled.
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pub(crate) fn is_f_string_formatting_enabled(context: &PyFormatContext) -> bool {
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context.is_preview()
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}
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