## 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/
This PR splits the string formatting code in the formatter to be handled
by the respective nodes.
Previously, the string formatting was done through a single
`FormatString` interface. Now, the nodes themselves are responsible for
formatting.
The following changes were made:
1. Remove `StringLayout::ImplicitStringConcatenationInBinaryLike` and
inline the call to `FormatStringContinuation`. After the refactor, the
binary like formatting would delegate to `FormatString` which would then
delegate to `FormatStringContinuation`. This removes the intermediary
steps.
2. Add formatter implementation for `FStringPart` which delegates it to
the respective string literal or f-string node.
3. Add `ExprStringLiteralKind` which is either `String` or `Docstring`.
If it's a docstring variant, then the string expression would not be
implicitly concatenated. This is guaranteed by the
`DocstringStmt::try_from_expression` constructor.
4. Add `StringLiteralKind` which is either a `String`, `Docstring` or
`InImplicitlyConcatenatedFString`. The last variant is for when the
string literal is implicitly concatenated with an f-string (`"foo" f"bar
{x}"`).
5. Remove `FormatString`.
6. Extract the f-string quote detection as a standalone function which
is public to the crate. This is used to detect the quote to be used for
an f-string at the expression level (`ExprFString` or
`FormatStringContinuation`).
### Formatter ecosystem result
**This PR**
| project | similarity index | total files | changed files |
|----------------|------------------:|------------------:|------------------:|
| cpython | 0.75804 | 1799 | 1648 |
| django | 0.99984 | 2772 | 34 |
| home-assistant | 0.99955 | 10596 | 214 |
| poetry | 0.99905 | 321 | 15 |
| transformers | 0.99967 | 2657 | 324 |
| twine | 1.00000 | 33 | 0 |
| typeshed | 0.99980 | 3669 | 18 |
| warehouse | 0.99976 | 654 | 14 |
| zulip | 0.99958 | 1459 | 36 |
**main**
| project | similarity index | total files | changed files |
|----------------|------------------:|------------------:|------------------:|
| cpython | 0.75804 | 1799 | 1648 |
| django | 0.99984 | 2772 | 34 |
| home-assistant | 0.99955 | 10596 | 214 |
| poetry | 0.99905 | 321 | 15 |
| transformers | 0.99967 | 2657 | 324 |
| twine | 1.00000 | 33 | 0 |
| typeshed | 0.99980 | 3669 | 18 |
| warehouse | 0.99976 | 654 | 14 |
| zulip | 0.99958 | 1459 | 36 |
A follow-up to auto-generate the `FormatNodeRule` implementation for the
string part nodes. This is just a dummy implementation that is
unreachable because it's handled by the parent nodes.
## Summary
The motivating code here was:
```python
with test as (
# test
foo):
pass
```
Which we were formatting as:
```python
with test as
# test
(foo):
pass
```
`with` statements are oddly difficult. This PR makes a bunch of subtle
modifications and adds a more extensive test suite. For example, we now
only preserve parentheses if there's more than one `WithItem` _or_ a
trailing comma; before, we always preserved.
Our formatting is_not_ the same as Black, but here's a diff of our
formatted code vs. Black's for the `with.py` test suite. The primary
difference is that we tend to break parentheses when they contain
comments rather than move them to the end of the life (this is a
consistent difference that we make across the codebase):
```diff
diff --git a/crates/ruff_python_formatter/foo.py b/crates/ruff_python_formatter/foo.py
index 85e761080..31625c876 100644
--- a/crates/ruff_python_formatter/foo.py
+++ b/crates/ruff_python_formatter/foo.py
@@ -1,6 +1,4 @@
-with (
- aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
-), aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa:
+with aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa, aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa:
...
# trailing
@@ -16,28 +14,33 @@ with (
# trailing
-with a, b: # a # comma # c # colon
+with (
+ a, # a # comma
+ b, # c
+): # colon
...
with (
- a as # a # as
- # own line
- b, # b # comma
+ a as ( # a # as
+ # own line
+ b
+ ), # b # comma
c, # c
): # colon
... # body
# body trailing own
-with (
- a as # a # as
+with a as ( # a # as
# own line
- bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb # b
-):
+ bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
+): # b
pass
-with (a,): # magic trailing comma
+with (
+ a,
+): # magic trailing comma
...
@@ -47,6 +50,7 @@ with a: # should remove brackets
with aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa + bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb as c:
...
+
with (
# leading comment
a
@@ -74,8 +78,7 @@ with (
with (
a # trailing same line comment
# trailing own line comment
- as b
-):
+) as b:
...
with (
@@ -87,7 +90,9 @@ with (
with (
a
# trailing own line comment
-) as b: # trailing as same line comment # trailing b same line comment
+) as ( # trailing as same line comment
+ b
+): # trailing b same line comment
...
with (
@@ -124,18 +129,24 @@ with ( # comment
...
with ( # outer comment
- CtxManager1() as example1, # inner comment
+ ( # inner comment
+ CtxManager1()
+ ) as example1,
CtxManager2() as example2,
CtxManager3() as example3,
):
...
-with CtxManager() as example: # outer comment
+with ( # outer comment
+ CtxManager()
+) as example:
...
with ( # outer comment
CtxManager()
-) as example, CtxManager2() as example2: # inner comment
+) as example, ( # inner comment
+ CtxManager2()
+) as example2:
...
with ( # outer comment
@@ -145,7 +156,9 @@ with ( # outer comment
...
with ( # outer comment
- (CtxManager1()), # inner comment
+ ( # inner comment
+ CtxManager1()
+ ),
CtxManager2(),
) as example:
...
@@ -179,7 +192,9 @@ with (
):
pass
-with a as (b): # foo
+with a as ( # foo
+ b
+):
pass
with f(
@@ -209,17 +224,13 @@ with f(
) as b, c as d:
pass
-with (
- aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa + bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
-) as b:
+with aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa + bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb as b:
pass
with aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa + bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb as b:
pass
-with (
- aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa + bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
-) as b, c as d:
+with aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa + bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb as b, c as d:
pass
with (
@@ -230,6 +241,8 @@ with (
pass
with (
- aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa + bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
-) as b, c as d:
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+ + bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb as b,
+ c as d,
+):
pass
```
Closes https://github.com/astral-sh/ruff/issues/6600.
## Test Plan
Before:
| project | similarity index |
|--------------|------------------|
| cpython | 0.75473 |
| django | 0.99804 |
| transformers | 0.99618 |
| twine | 0.99876 |
| typeshed | 0.74292 |
| warehouse | 0.99601 |
| zulip | 0.99727 |
After:
| project | similarity index |
|--------------|------------------|
| cpython | 0.75473 |
| django | 0.99804 |
| transformers | 0.99618 |
| twine | 0.99876 |
| typeshed | 0.74292 |
| warehouse | 0.99601 |
| zulip | 0.99727 |
`cargo test`
## Summary
This PR leverages the `Arguments` AST node introduced in #6259 in the
formatter, which ensures that we correctly handle trailing comments in
calls, like:
```python
f(
1,
# comment
)
pass
```
(Previously, this was treated as a leading comment on `pass`.)
This also allows us to unify the argument handling across calls and
class definitions.
## Test Plan
A bunch of new fixture tests, plus improved Black compatibility.
## Summary
This PR renames a few AST nodes for clarity:
- `Arguments` is now `Parameters`
- `Arg` is now `Parameter`
- `ArgWithDefault` is now `ParameterWithDefault`
For now, the attribute names that reference `Parameters` directly are
changed (e.g., on `StmtFunctionDef`), but the attributes on `Parameters`
itself are not (e.g., `vararg`). We may revisit that decision in the
future.
For context, the AST node formerly known as `Arguments` is used in
function definitions. Formally (outside of the Python context),
"arguments" typically refers to "the values passed to a function", while
"parameters" typically refers to "the variables used in a function
definition". E.g., if you Google "arguments vs parameters", you'll get
some explanation like:
> A parameter is a variable in a function definition. It is a
placeholder and hence does not have a concrete value. An argument is a
value passed during function invocation.
We're thus deviating from Python's nomenclature in favor of a scheme
that we find to be more precise.
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## Summary
This PR removes the type ignore node from the AST because our parser doesn't support it, and just having it around is confusing.
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## Test Plan
`cargo build`
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## Summary
This PR upgrade RustPython to pull in the changes to `Arguments` (zip
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