fix(formatter): `BestFitting` doesn't exactly matches the `conditinalGroup` behavior in Prettier by Dunqing · Pull Request #14983 · oxc-project/oxc

Dunqing · 2025-10-27T08:13:48Z

I found a case where Oxfmt's output differs from Prettier. Honestly, I think the Oxfmt output is prettier than Prettier.
Anyway, I investigated this case to find the root cause.

Failed example

Input:

const defaultColorDecoratorsEnablement = accessor
  .get(IConfigurationService)
  .getValue<"auto" | "always" | "never">(
    "longlonglonglonglonglonglonglonglong",
  );

Oxfmt and Biome's output:

const defaultColorDecoratorsEnablement = accessor
  .get(IConfigurationService)
  .getValue<"auto" | "always" | "never">(
    "longlonglonglonglonglonglonglonglong",
  );

Prettier output:

const defaultColorDecoratorsEnablement = accessor
  .get(IConfigurationService)
  .getValue<
    "auto" | "always" | "never"
  >("longlonglonglonglonglonglonglonglong");

Investigating the cause

Initially, I think the problem is that we generate inconsistent IR, so the output is different, which is a reasonable suspicion because, so far, almost all issues are due to this reason. However, after carefully comparing both IR of Oxfmt and Prettier, they are essentially the same, so the problem is moved to the printing IR part.

After spending a few days on this case, I finally found the reason why they produce the same IR but print different outputs. The cause is inside the BestFitting, which is a graceful solution for Prettier's conditionalGroup.

Let's take a look at how Prettier handles conditionalGroup

Prettier implementation:

conditionalGroup
https://github.com/prettier/prettier/blob/7584432401a47a26943dd7a9ca9a8e032ead7285/src/document/builders.js#L99-L106

/**
 * @param {Doc[]} states
 * @param {object} [opts] - TBD ???
 * @returns Doc
 */
function conditionalGroup(states, opts) {
  return group(states[0], { ...opts, expandedStates: states });
}

handling of conditionalGroup
https://github.com/prettier/prettier/blob/7584432401a47a26943dd7a9ca9a8e032ead7285/src/document/printer.js#L408-L445

// Expanded states are a rare case where a document
// can manually provide multiple representations of
// itself. It provides an array of documents
// going from the least expanded (most flattened)
// representation first to the most expanded. If a
// group has these, we need to manually go through
// these states and find the first one that fits.
// eslint-disable-next-line no-lonely-if
if (doc.expandedStates) {
  const mostExpanded = doc.expandedStates.at(-1);

  if (doc.break) {
    cmds.push({ ind, mode: MODE_BREAK, doc: mostExpanded });

    break;
  } else {
    for (let i = 1; i < doc.expandedStates.length + 1; i++) {
      if (i >= doc.expandedStates.length) {
        cmds.push({ ind, mode: MODE_BREAK, doc: mostExpanded });

        break;
      } else {
        const state = doc.expandedStates[i];
        /** @type {Command} */
        const cmd = { ind, mode: MODE_FLAT, doc: state };

        if (fits(cmd, cmds, rem, hasLineSuffix, groupModeMap)) {
          cmds.push(cmd);

          break;
        }
      }
    }
  }
} else {
  cmds.push({ ind, mode: MODE_BREAK, doc: doc.contents });
}

Oxfmt implementation

oxc/crates/oxc_formatter/src/formatter/printer/mod.rs

Lines 366 to 418 in d9f7df8

    
           fn print_best_fitting( 
        
               &mut self, 
        
               best_fitting: &'a BestFittingElement, 
        
               queue: &mut PrintQueue<'a>, 
        
               stack: &mut PrintCallStack, 
        
               indent_stack: &mut PrintIndentStack, 
        
           ) -> PrintResult<()> { 
        
               let args = stack.top(); 
        
               if args.mode().is_flat() && self.state.measured_group_fits { 
        
                   queue.extend_back(best_fitting.most_flat()); 
        
                   self.print_entry(queue, stack, indent_stack, args) 
        
               } else { 
        
                   self.state.measured_group_fits = true; 
        
                   let normal_variants = &best_fitting.variants()[..best_fitting.variants().len() - 1]; 
        
                   for variant in normal_variants { 
        
                       // Test if this variant fits and if so, use it. Otherwise try the next 
        
                       // variant. 
        
                       // Try to fit only the first variant on a single line 
        
                       if !matches!(variant.first(), Some(&FormatElement::Tag(Tag::StartEntry))) { 
        
                           return invalid_start_tag(TagKind::Entry, variant.first()); 
        
                       } 
        
                       let entry_args = args.with_print_mode(PrintMode::Flat); 
        
                       // Skip the first element because we want to override the args for the entry and the 
        
                       // args must be popped from the stack as soon as it sees the matching end entry. 
        
                       let content = &variant[1..]; 
        
                       queue.extend_back(content); 
        
                       stack.push(TagKind::Entry, entry_args); 
        
                       let variant_fits = self.fits(queue, stack, indent_stack)?; 
        
                       stack.pop(TagKind::Entry)?; 
        
                       // Remove the content slice because printing needs the variant WITH the start entry 
        
                       let popped_slice = queue.pop_slice(); 
        
                       debug_assert_eq!(popped_slice, Some(content)); 
        
                       if variant_fits { 
        
                           queue.extend_back(variant); 
        
                           return self.print_entry(queue, stack, indent_stack, entry_args); 
        
                       } 
        
                   } 
        
                   // No variant fits, take the last (most expanded) as fallback 
        
                   let most_expanded = best_fitting.most_expanded(); 
        
                   queue.extend_back(most_expanded); 
        
                   self.print_entry(queue, stack, indent_stack, args.with_print_mode(PrintMode::Expanded)) 
        
               } 
        
           }

The difference between the implementations is in handling different expandedStates (Called as variants in Oxfmt).

In prettier, it will try to get all expandedStates to check whether they fit or not in the MODE_FLAT mode. If not, they will fall back to the mostExpanded and print it in MODE_BREAK mode.

In Oxfmt, it will try to get all variants except the last one (most expanded) to check whether they fit or not in the PrintMode::Flat mode. If not, they will fall back to the mostExpanded and print it in PrintMode::Expanded mode.

So the root cause is Oxfmt, which doesn't check the mostExpanded one, whether it fits in the PrintMode::Fit mode. After aligning this, the issue was solved.

Thinking

After understanding the use of conditionalGroup, although this issue is due to Oxfmt not exactly aligning with Prettier's behavior, I suspect this is a bug in Prettier because mostExpanded is expected to be printed in break mode, but Prettier prints it in flat mode if it fits. It's not intuitive, and it's not as if the variable names describe it. Additionally, this case is a little complex, and the Prettier tests don't include such cases, so the Prettier team probably wasn't aware of this case.

Dunqing · 2025-10-27T08:14:13Z

fix(formatter): correct calculating layout for ChainExpression in StaticMemberExpression #14986
fix(formatter): should not break when the parent of root of StaticMemberExpression is used as the Argument of NewExpression #14985
fix(formatter): align the short argument handling for UnaryExpression with Prettier #14984
fix(formatter): BestFitting doesn't exactly matches the conditinalGroup behavior in Prettier #14983 👈 (View in Graphite)
fix(formatter): align the logic of printing type parameters, parameters, and return type for functions with Prettier #14942
refactor(formatter): clean up unneeded implementations for printing comments #14935
refactor(formatter): improve printing trailing comments #14934
fix(formatter): non-nested static member expressions will never break #14929
fix(formatter): check whether a type alias is complex when its right hand side never break #14928
refactor(formatter): align printing trailing comments with Prettier #14927
fix(formatter): should not add a trailing comma for long curried calls when trailingComma is es5 #14913
main

How to use the Graphite Merge Queue

Add either label to this PR to merge it via the merge queue:

0-merge - adds this PR to the back of the merge queue
hotfix - for urgent hot fixes, skip the queue and merge this PR next

You must have a Graphite account in order to use the merge queue. Sign up using this link.

_{An organization admin has enabled the Graphite Merge Queue in this repository.} _{Please do not merge from GitHub as this will restart CI on PRs being processed by the merge queue.}

This stack of pull requests is managed by Graphite. Learn more about stacking.

codspeed-hq · 2025-10-27T08:19:05Z

CodSpeed Performance Report

Merging #14983 will not alter performance

_{Comparing 10-27-fix_formatter_bestfitting_doesn_t_exactly_matches_the_conditinalgroup_behavior_in_prettier (54c509e) with 10-25-fix_formatter_lign_the_logic_of_printing_type_parameters_parameters_and_return_type_for_functions_with_prettier (63c324d)}

Summary

✅ 33 untouched
⏩ 4 skipped¹

4 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

graphite-app · 2025-10-27T09:32:28Z

Merge activity

Oct 27, 9:32 AM UTC: leaysgur added this pull request to the Graphite merge queue.
Oct 27, 9:48 AM UTC: Merged by the Graphite merge queue.

@param

…Group` behavior in Prettier (#14983) I found a case where Oxfmt's output differs from Prettier. Honestly, I think the `Oxfmt` output is prettier than `Prettier`. Anyway, I investigated this case to find the root cause. ### Failed example Input: ```ts const defaultColorDecoratorsEnablement = accessor .get(IConfigurationService) .getValue<"auto" | "always" | "never">( "longlonglonglonglonglonglonglonglong", ); ``` Oxfmt and Biome's output: ```ts const defaultColorDecoratorsEnablement = accessor .get(IConfigurationService) .getValue<"auto" | "always" | "never">( "longlonglonglonglonglonglonglonglong", ); ``` Prettier output: ```ts const defaultColorDecoratorsEnablement = accessor .get(IConfigurationService) .getValue< "auto" | "always" | "never" >("longlonglonglonglonglonglonglonglong"); ``` ### Investigating the cause Initially, I think the problem is that we generate inconsistent `IR`, so the output is different, which is a reasonable suspicion because, so far, almost all issues are due to this reason. However, after carefully comparing both IR of Oxfmt and Prettier, they are essentially the same, so the problem is moved to the printing IR part. After spending a few days on this case, I finally found the reason why they produce the same IR but print different outputs. The cause is inside the `BestFitting`, which is a graceful solution for Prettier's `conditionalGroup`. Let's take a look at how Prettier handles `conditionalGroup` #### Prettier implementation: **conditionalGroup** https://github.com/prettier/prettier/blob/7584432401a47a26943dd7a9ca9a8e032ead7285/src/document/builders.js#L99-L106 ```js /** * @param {Doc[]} states * @param {object} [opts] - TBD ??? * @returns Doc */ function conditionalGroup(states, opts) { return group(states[0], { ...opts, expandedStates: states }); } ``` **handling of conditionalGroup** https://github.com/prettier/prettier/blob/7584432401a47a26943dd7a9ca9a8e032ead7285/src/document/printer.js#L408-L445 ```js // Expanded states are a rare case where a document // can manually provide multiple representations of // itself. It provides an array of documents // going from the least expanded (most flattened) // representation first to the most expanded. If a // group has these, we need to manually go through // these states and find the first one that fits. // eslint-disable-next-line no-lonely-if if (doc.expandedStates) { const mostExpanded = doc.expandedStates.at(-1); if (doc.break) { cmds.push({ ind, mode: MODE_BREAK, doc: mostExpanded }); break; } else { for (let i = 1; i < doc.expandedStates.length + 1; i++) { if (i >= doc.expandedStates.length) { cmds.push({ ind, mode: MODE_BREAK, doc: mostExpanded }); break; } else { const state = doc.expandedStates[i]; /** @type {Command} */ const cmd = { ind, mode: MODE_FLAT, doc: state }; if (fits(cmd, cmds, rem, hasLineSuffix, groupModeMap)) { cmds.push(cmd); break; } } } } } else { cmds.push({ ind, mode: MODE_BREAK, doc: doc.contents }); } ``` #### Oxfmt implementation https://github.com/oxc-project/oxc/blob/d9f7df8bc6bf7e48c90ba99638502c87afba0e04/crates/oxc_formatter/src/formatter/printer/mod.rs#L366-L418 The difference between the implementations is in handling different `expandedStates` (Called as `variants` in Oxfmt). In prettier, they will try to get all `expandedStates` except the first one to check whether they fit or not in the `MODE_FLAT` mode. If not, they will fall back to the `mostExpanded` and print it in `MODE_BREAK` mode.

## [0.9.0] - 2025-10-30 ### 🚀 Features - 8fe7e85 formatter: Support printing Formatter IR (#14855) (Dunqing) ### 🐛 Bug Fixes - a6b6ef8 formatter: Correct calculating layout for `TSNonNullExpression` in `StaticMemberExpression` (#15065) (Dunqing) - 99bd995 formatter: Print parenthesis for sequence expression in `ReturnStatement` and `ExpressionStatement` (#15062) (Dunqing) - f3fb998 formatter: Correct printing comments for `TSAsExpression` (#15061) (Dunqing) - 1e4a018 formatter: Correct checking of the short argument for `CallArguments` (#15055) (Dunqing) - c0dfd9b formatter: Print comments before fat arrow as-is for `ArrowFunctionExpression` (#15050) (Dunqing) - 206b519 formatter: Should hug parameter with `TSMappedType` type annotation (#15049) (Dunqing) - e48c604 formatter: Incorrect formatting of a function with `this` parameter (#15031) (Dunqing) - a9f0c45 formatter: Decorators and class method on the same line shouldn't be broken by a leading comment of the method (#15029) (Dunqing) - 43d74e4 formatter: Handle `<CRLF>` for `SourceText` (#15016) (leaysgur) - 34fab40 formatter: Correct calculating layout for `ChainExpression` in `StaticMemberExpression` (#14986) (Dunqing) - 68dc101 formatter: Should not break when the parent of root of `StaticMemberExpression` is used as the `Argument` of `NewExpression` (#14985) (Dunqing) - 071b739 formatter: Align the short argument handling for UnaryExpression with Prettier (#14984) (Dunqing) - 3940f3a formatter: `BestFitting` doesn't exactly matches the `conditinalGroup` behavior in Prettier (#14983) (Dunqing) - 4a84e44 formatter: Align the logic of printing type parameters, parameters, and return type for functions with Prettier (#14942) (Dunqing) - 68c1f2a formatter: Non-nested static member expressions will never break (#14929) (Dunqing) - 42adc47 formatter: Check whether a type alias is complex when its right hand side never break (#14928) (Dunqing) - e501f13 formatter: Should not add a trailing comma for long curried calls when `trailingComma` is es5 (#14913) (Dunqing) ### 🚜 Refactor - 7d64291 formatter: Simplify printing ClassElement with a semicolon (#15030) (Dunqing) - 5de99c2 formatter: Export unified way to get_parse_options (#15027) (leaysgur) - f6f22e2 formatter: Clean up unneeded implementations for printing comments (#14935) (Dunqing) - 7a2b9d1 formatter: Improve printing trailing comments (#14934) (Dunqing) - ba10caa formatter: Align printing trailing comments with Prettier (#14927) (Dunqing) - 597c9e8 formatter: Remove redundunt public API (#14915) (leaysgur) ### ⚡ Performance - 467b3a1 formatter: Optimize grouping logic for call arguments (#15033) (Dunqing) Co-authored-by: leaysgur <[email protected]>

## [0.9.0] - 2025-10-30 ### 🚀 Features - 8fe7e85 formatter: Support printing Formatter IR (#14855) (Dunqing) ### 🐛 Bug Fixes - a6b6ef8 formatter: Correct calculating layout for `TSNonNullExpression` in `StaticMemberExpression` (#15065) (Dunqing) - 99bd995 formatter: Print parenthesis for sequence expression in `ReturnStatement` and `ExpressionStatement` (#15062) (Dunqing) - f3fb998 formatter: Correct printing comments for `TSAsExpression` (#15061) (Dunqing) - 1e4a018 formatter: Correct checking of the short argument for `CallArguments` (#15055) (Dunqing) - c0dfd9b formatter: Print comments before fat arrow as-is for `ArrowFunctionExpression` (#15050) (Dunqing) - 206b519 formatter: Should hug parameter with `TSMappedType` type annotation (#15049) (Dunqing) - e48c604 formatter: Incorrect formatting of a function with `this` parameter (#15031) (Dunqing) - a9f0c45 formatter: Decorators and class method on the same line shouldn't be broken by a leading comment of the method (#15029) (Dunqing) - 43d74e4 formatter: Handle `<CRLF>` for `SourceText` (#15016) (leaysgur) - 34fab40 formatter: Correct calculating layout for `ChainExpression` in `StaticMemberExpression` (#14986) (Dunqing) - 68dc101 formatter: Should not break when the parent of root of `StaticMemberExpression` is used as the `Argument` of `NewExpression` (#14985) (Dunqing) - 071b739 formatter: Align the short argument handling for UnaryExpression with Prettier (#14984) (Dunqing) - 3940f3a formatter: `BestFitting` doesn't exactly matches the `conditinalGroup` behavior in Prettier (#14983) (Dunqing) - 4a84e44 formatter: Align the logic of printing type parameters, parameters, and return type for functions with Prettier (#14942) (Dunqing) - 68c1f2a formatter: Non-nested static member expressions will never break (#14929) (Dunqing) - 42adc47 formatter: Check whether a type alias is complex when its right hand side never break (#14928) (Dunqing) - e501f13 formatter: Should not add a trailing comma for long curried calls when `trailingComma` is es5 (#14913) (Dunqing) ### 🚜 Refactor - 7d64291 formatter: Simplify printing ClassElement with a semicolon (#15030) (Dunqing) - 5de99c2 formatter: Export unified way to get_parse_options (#15027) (leaysgur) - f6f22e2 formatter: Clean up unneeded implementations for printing comments (#14935) (Dunqing) - 7a2b9d1 formatter: Improve printing trailing comments (#14934) (Dunqing) - ba10caa formatter: Align printing trailing comments with Prettier (#14927) (Dunqing) - 597c9e8 formatter: Remove redundunt public API (#14915) (leaysgur) ### ⚡ Performance - 467b3a1 formatter: Optimize grouping logic for call arguments (#15033) (Dunqing) ### 💼 Other - aceff66 oxfmt: V0.9.0 (#15088) (Boshen)

## [0.9.0] - 2025-10-30 ### 🚀 Features - 8fe7e85 formatter: Support printing Formatter IR (#14855) (Dunqing) ### 🐛 Bug Fixes - a6b6ef8 formatter: Correct calculating layout for `TSNonNullExpression` in `StaticMemberExpression` (#15065) (Dunqing) - 99bd995 formatter: Print parenthesis for sequence expression in `ReturnStatement` and `ExpressionStatement` (#15062) (Dunqing) - f3fb998 formatter: Correct printing comments for `TSAsExpression` (#15061) (Dunqing) - 1e4a018 formatter: Correct checking of the short argument for `CallArguments` (#15055) (Dunqing) - c0dfd9b formatter: Print comments before fat arrow as-is for `ArrowFunctionExpression` (#15050) (Dunqing) - 206b519 formatter: Should hug parameter with `TSMappedType` type annotation (#15049) (Dunqing) - e48c604 formatter: Incorrect formatting of a function with `this` parameter (#15031) (Dunqing) - a9f0c45 formatter: Decorators and class method on the same line shouldn't be broken by a leading comment of the method (#15029) (Dunqing) - 43d74e4 formatter: Handle `<CRLF>` for `SourceText` (#15016) (leaysgur) - 34fab40 formatter: Correct calculating layout for `ChainExpression` in `StaticMemberExpression` (#14986) (Dunqing) - 68dc101 formatter: Should not break when the parent of root of `StaticMemberExpression` is used as the `Argument` of `NewExpression` (#14985) (Dunqing) - 071b739 formatter: Align the short argument handling for UnaryExpression with Prettier (#14984) (Dunqing) - 3940f3a formatter: `BestFitting` doesn't exactly matches the `conditinalGroup` behavior in Prettier (#14983) (Dunqing) - 4a84e44 formatter: Align the logic of printing type parameters, parameters, and return type for functions with Prettier (#14942) (Dunqing) - 68c1f2a formatter: Non-nested static member expressions will never break (#14929) (Dunqing) - 42adc47 formatter: Check whether a type alias is complex when its right hand side never break (#14928) (Dunqing) - e501f13 formatter: Should not add a trailing comma for long curried calls when `trailingComma` is es5 (#14913) (Dunqing) ### 🚜 Refactor - 7d64291 formatter: Simplify printing ClassElement with a semicolon (#15030) (Dunqing) - 5de99c2 formatter: Export unified way to get_parse_options (#15027) (leaysgur) - f6f22e2 formatter: Clean up unneeded implementations for printing comments (#14935) (Dunqing) - 7a2b9d1 formatter: Improve printing trailing comments (#14934) (Dunqing) - ba10caa formatter: Align printing trailing comments with Prettier (#14927) (Dunqing) - 597c9e8 formatter: Remove redundunt public API (#14915) (leaysgur) ### ⚡ Performance - 467b3a1 formatter: Optimize grouping logic for call arguments (#15033) (Dunqing) ### 💼 Other - 6368793 oxfmt: V0.9.0 (#15091) (Boshen) - aceff66 oxfmt: V0.9.0 (#15088) (Boshen)

…16028) Revert the change made in #14983. Even though Prettier doesn't fix the bug yet, Prettier at least confirms that this is a bug in Prettier, so it would be better to revert it to avoid introducing weird formatting

…xc-project#16028) Revert the change made in oxc-project#14983. Even though Prettier doesn't fix the bug yet, Prettier at least confirms that this is a bug in Prettier, so it would be better to revert it to avoid introducing weird formatting

This was referenced Oct 27, 2025

fix(formatter): should not add a trailing comma for long curried calls when trailingComma is es5 #14913

Merged

refactor(formatter): align printing trailing comments with Prettier #14927

Merged

github-actions bot added the A-formatter Area - Formatter label Oct 27, 2025

Dunqing mentioned this pull request Oct 27, 2025

fix(formatter): check whether a type alias is complex when its right hand side never break #14928

Merged

github-actions bot added the C-bug Category - Bug label Oct 27, 2025

This was referenced Oct 27, 2025

fix(formatter): non-nested static member expressions will never break #14929

Merged

refactor(formatter): improve printing trailing comments #14934

Merged

refactor(formatter): clean up unneeded implementations for printing comments #14935

Merged

Dunqing changed the title ~~fix(formatter): BestFitting doesn't exactly matches the conditinalGroup behavior in Prettier~~ fix(formatter): BestFitting doesn't exactly matches the conditinalGroup behavior in Prettier Oct 27, 2025

Dunqing marked this pull request as ready for review October 27, 2025 08:46

graphite-app bot added the 0-merge Merge with Graphite Merge Queue label Oct 27, 2025

graphite-app bot force-pushed the 10-25-fix_formatter_lign_the_logic_of_printing_type_parameters_parameters_and_return_type_for_functions_with_prettier branch from 63c324d to 4a84e44 Compare October 27, 2025 09:36

graphite-app bot requested a review from overlookmotel as a code owner October 27, 2025 09:36

graphite-app bot force-pushed the 10-27-fix_formatter_bestfitting_doesn_t_exactly_matches_the_conditinalgroup_behavior_in_prettier branch from 54c509e to 3940f3a Compare October 27, 2025 09:36

graphite-app bot removed the 0-merge Merge with Graphite Merge Queue label Oct 27, 2025

Base automatically changed from 10-25-fix_formatter_lign_the_logic_of_printing_type_parameters_parameters_and_return_type_for_functions_with_prettier to main October 27, 2025 09:47

graphite-app bot merged commit 3940f3a into main Oct 27, 2025
21 checks passed

graphite-app bot deleted the 10-27-fix_formatter_bestfitting_doesn_t_exactly_matches_the_conditinalgroup_behavior_in_prettier branch October 27, 2025 09:48

Dunqing mentioned this pull request Oct 28, 2025

Weird formatting when the options of conditionalGroup includes multiple breakable groups prettier/prettier#18136

Closed

Boshen mentioned this pull request Oct 30, 2025

release(oxfmt): v0.9.0 #15088

Merged

Boshen mentioned this pull request Oct 30, 2025

release(oxfmt): v0.9.0 #15091

Merged

Boshen mentioned this pull request Oct 30, 2025

release(oxfmt): v0.9.0 #15096

Merged

Dunqing mentioned this pull request Nov 24, 2025

fix(formatter): revert FormatElement::BestFitting printing logic #16028

Merged

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Comments

fix(formatter): `BestFitting` doesn't exactly matches the `conditinalGroup` behavior in Prettier#14983

fix(formatter): `BestFitting` doesn't exactly matches the `conditinalGroup` behavior in Prettier#14983
graphite-app[bot] merged 1 commit intomainfrom
10-27-fix_formatter_bestfitting_doesn_t_exactly_matches_the_conditinalgroup_behavior_in_prettier

Dunqing commented Oct 27, 2025 •

edited

Loading

Uh oh!

Dunqing commented Oct 27, 2025 •

edited

Loading

Uh oh!

codspeed-hq bot commented Oct 27, 2025

Uh oh!

graphite-app bot commented Oct 27, 2025 •

edited

Loading

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant

	fn print_best_fitting(
	&mut self,
	best_fitting: &'a BestFittingElement,
	queue: &mut PrintQueue<'a>,
	stack: &mut PrintCallStack,
	indent_stack: &mut PrintIndentStack,
	) -> PrintResult<()> {
	let args = stack.top();

	if args.mode().is_flat() && self.state.measured_group_fits {
	queue.extend_back(best_fitting.most_flat());
	self.print_entry(queue, stack, indent_stack, args)
	} else {
	self.state.measured_group_fits = true;

	let normal_variants = &best_fitting.variants()[..best_fitting.variants().len() - 1];

	for variant in normal_variants {
	// Test if this variant fits and if so, use it. Otherwise try the next
	// variant.

	// Try to fit only the first variant on a single line
	if !matches!(variant.first(), Some(&FormatElement::Tag(Tag::StartEntry))) {
	return invalid_start_tag(TagKind::Entry, variant.first());
	}

	let entry_args = args.with_print_mode(PrintMode::Flat);

	// Skip the first element because we want to override the args for the entry and the
	// args must be popped from the stack as soon as it sees the matching end entry.
	let content = &variant[1..];

	queue.extend_back(content);
	stack.push(TagKind::Entry, entry_args);
	let variant_fits = self.fits(queue, stack, indent_stack)?;
	stack.pop(TagKind::Entry)?;

	// Remove the content slice because printing needs the variant WITH the start entry
	let popped_slice = queue.pop_slice();
	debug_assert_eq!(popped_slice, Some(content));

	if variant_fits {
	queue.extend_back(variant);
	return self.print_entry(queue, stack, indent_stack, entry_args);
	}
	}

	// No variant fits, take the last (most expanded) as fallback
	let most_expanded = best_fitting.most_expanded();
	queue.extend_back(most_expanded);
	self.print_entry(queue, stack, indent_stack, args.with_print_mode(PrintMode::Expanded))
	}
	}

Uh oh!

Comments

Conversation

Dunqing commented Oct 27, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Failed example

Investigating the cause

Prettier implementation:

Oxfmt implementation

Thinking

Uh oh!

Dunqing commented Oct 27, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

How to use the Graphite Merge Queue

Uh oh!

codspeed-hq bot commented Oct 27, 2025

CodSpeed Performance Report

Merging #14983 will not alter performance

Summary

Footnotes

Uh oh!

graphite-app bot commented Oct 27, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Merge activity

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant

Dunqing commented Oct 27, 2025 •

edited

Loading

Dunqing commented Oct 27, 2025 •

edited

Loading

graphite-app bot commented Oct 27, 2025 •

edited

Loading