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Add BestFittingMode (#5184)
## Summary
Black supports for layouts when it comes to breaking binary expressions:
```rust
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
enum BinaryLayout {
/// Put each operand on their own line if either side expands
Default,
/// Try to expand the left to make it fit. Add parentheses if the left or right don't fit.
///
///```python
/// [
/// a,
/// b
/// ] & c
///```
ExpandLeft,
/// Try to expand the right to make it fix. Add parentheses if the left or right don't fit.
///
/// ```python
/// a & [
/// b,
/// c
/// ]
/// ```
ExpandRight,
/// Both the left and right side can be expanded. Try in the following order:
/// * expand the right side
/// * expand the left side
/// * expand both sides
///
/// to make the expression fit
///
/// ```python
/// [
/// a,
/// b
/// ] & [
/// c,
/// d
/// ]
/// ```
ExpandRightThenLeft,
}
```
Our current implementation only handles `ExpandRight` and `Default` correctly. `ExpandLeft` turns out to be surprisingly hard. This PR adds a new `BestFittingMode` parameter to `BestFitting` to support `ExpandLeft`.
There are 3 variants that `ExpandLeft` must support:
**Variant 1**: Everything fits on the line (easy)
```python
[a, b] + c
```
**Variant 2**: Left breaks, but right fits on the line. Doesn't need parentheses
```python
[
a,
b
] + c
```
**Variant 3**: The left breaks, but there's still not enough space for the right hand side. Parenthesize the whole expression:
```python
(
[
a,
b
]
+ ccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
)
```
Solving Variant 1 and 2 on their own is straightforward The printer gives us this behavior by nesting right inside of the group of left:
```
group(&format_args![
if_group_breaks(&text("(")),
soft_block_indent(&group(&format_args![
left,
soft_line_break_or_space(),
op,
space(),
group(&right)
])),
if_group_breaks(&text(")"))
])
```
The fundamental problem is that the outer group, which adds the parentheses, always breaks if the left side breaks. That means, we end up with
```python
(
[
a,
b
] + c
)
```
which is not what we want (we only want parentheses if the right side doesn't fit).
Okay, so nesting groups don't work because of the outer parentheses. Sequencing groups doesn't work because it results in a right-to-left breaking which is the opposite of what we want.
Could we use best fitting? Almost!
```
best_fitting![
// All flat
format_args![left, space(), op, space(), right],
// Break left
format_args!(group(&left).should_expand(true), space(), op, space(), right],
// Break all
format_args![
text("("),
block_indent!(&format_args![
left,
hard_line_break(),
op,
space()
right
])
]
]
```
I hope I managed to write this up correctly. The problem is that the printer never reaches the 3rd variant because the second variant always fits:
* The `group(&left).should_expand(true)` changes the group so that all `soft_line_breaks` are turned into hard line breaks. This is necessary because we want to test if the content fits if we break after the `[`.
* Now, the whole idea of `best_fitting` is that you can pretend that some content fits on the line when it actually does not. The way this works is that the printer **only** tests if all the content of the variant **up to** the first line break fits on the line (we insert that line break by using `should_expand(true))`. The printer doesn't care whether the rest `a\n, b\n ] + c` all fits on (multiple?) lines.
Why does breaking right work but not breaking the left? The difference is that we can make the decision whether to parenthesis the expression based on the left expression. We can't do this for breaking left because the decision whether to insert parentheses or not would depend on a lookahead: will the right side break. We simply don't know this yet when printing the parentheses (it would work for the right parentheses but not for the left and indent).
What we kind of want here is to tell the printer: Look, what comes here may or may not fit on a single line but we don't care. Simply test that what comes **after** fits on a line.
This PR adds a new `BestFittingMode` that has a new `AllLines` option that gives us the desired behavior of testing all content and not just up to the first line break.
## Test Plan
I added a new example to `BestFitting::with_mode`
This commit is contained in:
Micha Reiser
GitHub
parent
6929fcc55f
commit
d9e59b21cd
8 changed files with 329 additions and 120 deletions
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@ -6,7 +6,7 @@ use std::hash::{Hash, Hasher};
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use std::ops::Deref;
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use std::rc::Rc;
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use crate::format_element::tag::{LabelId, Tag};
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use crate::format_element::tag::{GroupMode, LabelId, Tag};
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use crate::source_code::SourceCodeSlice;
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use crate::TagKind;
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use ruff_text_size::TextSize;
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@ -57,7 +57,10 @@ pub enum FormatElement {
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/// A list of different variants representing the same content. The printer picks the best fitting content.
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/// Line breaks inside of a best fitting don't propagate to parent groups.
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BestFitting(BestFitting),
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BestFitting {
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variants: BestFittingVariants,
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mode: BestFittingMode,
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},
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/// A [Tag] that marks the start/end of some content to which some special formatting is applied.
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Tag(Tag),
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@ -84,9 +87,11 @@ impl std::fmt::Debug for FormatElement {
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.field(contains_newlines)
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.finish(),
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FormatElement::LineSuffixBoundary => write!(fmt, "LineSuffixBoundary"),
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FormatElement::BestFitting(best_fitting) => {
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fmt.debug_tuple("BestFitting").field(&best_fitting).finish()
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}
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FormatElement::BestFitting { variants, mode } => fmt
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.debug_struct("BestFitting")
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.field("variants", variants)
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.field("mode", &mode)
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.finish(),
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FormatElement::Interned(interned) => {
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fmt.debug_list().entries(interned.deref()).finish()
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}
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@ -134,6 +139,15 @@ impl PrintMode {
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}
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}
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impl From<GroupMode> for PrintMode {
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fn from(value: GroupMode) -> Self {
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match value {
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GroupMode::Flat => PrintMode::Flat,
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GroupMode::Expand | GroupMode::Propagated => PrintMode::Expanded,
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}
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}
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}
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#[derive(Clone)]
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pub struct Interned(Rc<[FormatElement]>);
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@ -256,7 +270,10 @@ impl FormatElements for FormatElement {
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FormatElement::Interned(interned) => interned.will_break(),
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// Traverse into the most flat version because the content is guaranteed to expand when even
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// the most flat version contains some content that forces a break.
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FormatElement::BestFitting(best_fitting) => best_fitting.most_flat().will_break(),
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FormatElement::BestFitting {
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variants: best_fitting,
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..
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} => best_fitting.most_flat().will_break(),
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FormatElement::LineSuffixBoundary
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| FormatElement::Space
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| FormatElement::Tag(_)
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@ -284,19 +301,36 @@ impl FormatElements for FormatElement {
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}
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}
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/// Provides the printer with different representations for the same element so that the printer
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/// can pick the best fitting variant.
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///
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/// Best fitting is defined as the variant that takes the most horizontal space but fits on the line.
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#[derive(Clone, Eq, PartialEq)]
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pub struct BestFitting {
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/// The different variants for this element.
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/// The first element is the one that takes up the most space horizontally (the most flat),
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/// The last element takes up the least space horizontally (but most horizontal space).
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variants: Box<[Box<[FormatElement]>]>,
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/// Mode used to determine if any variant (except the most expanded) fits for [`BestFittingVariants`].
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#[repr(u8)]
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#[derive(Copy, Clone, Debug, Eq, PartialEq, Default)]
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pub enum BestFittingMode {
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/// The variant fits if the content up to the first hard or a soft line break inside a [`Group`] with
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/// [`PrintMode::Expanded`] fits on the line. The default mode.
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///
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/// [`Group`]: tag::Group
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#[default]
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FirstLine,
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/// A variant fits if all lines fit into the configured print width. A line ends if by any
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/// hard or a soft line break inside a [`Group`] with [`PrintMode::Expanded`].
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/// The content doesn't fit if there's any hard line break outside a [`Group`] with [`PrintMode::Expanded`]
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/// (a hard line break in content that should be considered in [`PrintMode::Flat`].
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///
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/// Use this mode with caution as it requires measuring all content of the variant which is more
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/// expensive than using [`BestFittingMode::FirstLine`].
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///
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/// [`Group`]: tag::Group
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AllLines,
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}
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impl BestFitting {
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/// The different variants for this element.
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/// The first element is the one that takes up the most space horizontally (the most flat),
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/// The last element takes up the least space horizontally (but most horizontal space).
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#[derive(Clone, Eq, PartialEq, Debug)]
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pub struct BestFittingVariants(Box<[Box<[FormatElement]>]>);
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impl BestFittingVariants {
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/// Creates a new best fitting IR with the given variants. The method itself isn't unsafe
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/// but it is to discourage people from using it because the printer will panic if
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/// the slice doesn't contain at least the least and most expanded variants.
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@ -312,33 +346,42 @@ impl BestFitting {
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"Requires at least the least expanded and most expanded variants"
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);
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Self {
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variants: variants.into_boxed_slice(),
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}
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Self(variants.into_boxed_slice())
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}
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/// Returns the most expanded variant
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pub fn most_expanded(&self) -> &[FormatElement] {
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self.variants.last().expect(
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self.0.last().expect(
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"Most contain at least two elements, as guaranteed by the best fitting builder.",
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)
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}
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pub fn variants(&self) -> &[Box<[FormatElement]>] {
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&self.variants
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pub fn as_slice(&self) -> &[Box<[FormatElement]>] {
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&self.0
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}
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/// Returns the least expanded variant
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pub fn most_flat(&self) -> &[FormatElement] {
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self.variants.first().expect(
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self.0.first().expect(
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"Most contain at least two elements, as guaranteed by the best fitting builder.",
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)
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}
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}
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impl std::fmt::Debug for BestFitting {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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f.debug_list().entries(&*self.variants).finish()
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impl Deref for BestFittingVariants {
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type Target = [Box<[FormatElement]>];
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fn deref(&self) -> &Self::Target {
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self.as_slice()
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}
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}
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impl<'a> IntoIterator for &'a BestFittingVariants {
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type Item = &'a Box<[FormatElement]>;
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type IntoIter = std::slice::Iter<'a, Box<[FormatElement]>>;
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fn into_iter(self) -> Self::IntoIter {
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self.as_slice().iter()
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}
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}
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@ -397,7 +440,7 @@ mod sizes {
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assert_eq_size!(ruff_text_size::TextRange, [u8; 8]);
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assert_eq_size!(crate::prelude::tag::VerbatimKind, [u8; 8]);
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assert_eq_size!(crate::prelude::Interned, [u8; 16]);
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assert_eq_size!(crate::format_element::BestFitting, [u8; 16]);
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assert_eq_size!(crate::format_element::BestFittingVariants, [u8; 16]);
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#[cfg(not(debug_assertions))]
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assert_eq_size!(crate::SourceCodeSlice, [u8; 8]);
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