ClangFormat takes over 1 minute to format any single file in a React Native Windows v0.73 Old Arch project

[shirakaba]

I do my native code in Visual Studio 2022 rather than Visual Studio Code, and rely on ClangFormat to format the C++.

However, the time it takes to run is just agony. No matter the library I'm working on, the size of the file, or the size of the code change made, it takes over a minute to run formatting on an M3 Max MacBook Pro. It affects all React Native Windows apps I've worked on. By comparison, fresh "vanilla" Windows apps format in an instant. It affects ClangFormat whether used through Visual Studio and Visual Studio Code, though the latter does feel a few seconds faster.

I'm not exaggerating – I have to sit through this for hours a day when working on native code:

clangformat_slow.mp4

I think my settings are pretty sane:

And my .clangformat file is based on rules I found in either the React Native Windows repo or Facebook's Hermes repo.

Show .clangformat

---
AccessModifierOffset: -1
AlignAfterOpenBracket: AlwaysBreak
AlignConsecutiveAssignments: false
AlignConsecutiveDeclarations: false
AlignEscapedNewlinesLeft: true
AlignOperands:   false
AlignTrailingComments: false
AllowAllParametersOfDeclarationOnNextLine: false
AllowShortBlocksOnASingleLine: false
AllowShortCaseLabelsOnASingleLine: false
AllowShortFunctionsOnASingleLine: Empty
AllowShortIfStatementsOnASingleLine: false
AllowShortLoopsOnASingleLine: false
AlwaysBreakAfterReturnType: None
AlwaysBreakBeforeMultilineStrings: true
AlwaysBreakTemplateDeclarations: true
BinPackArguments: false
BinPackParameters: false
BraceWrapping:
  AfterClass:      false
  AfterControlStatement: false
  AfterEnum:       false
  AfterFunction:   false
  AfterNamespace:  false
  AfterObjCDeclaration: false
  AfterStruct:     false
  AfterUnion:      false
  BeforeCatch:     false
  BeforeElse:      false
  IndentBraces:    false
BreakBeforeBinaryOperators: None
BreakBeforeBraces: Allman
BreakBeforeTernaryOperators: true
BreakConstructorInitializersBeforeComma: false
BreakAfterJavaFieldAnnotations: false
BreakStringLiterals: false
ColumnLimit:       120
CommentPragmas:  '^ IWYU pragma:'
ConstructorInitializerAllOnOneLineOrOnePerLine: true
ConstructorInitializerIndentWidth: 4
ContinuationIndentWidth: 4
Cpp11BracedListStyle: true
DerivePointerAlignment: false
DisableFormat:   false
ForEachMacros:   [ FOR_EACH_RANGE, FOR_EACH, TEST_CLASS, TEST_CLASS_EX ]
IncludeBlocks: Preserve
IncludeCategories:
  - Regex:           'pch.h'
    Priority:        -1
  - Regex:           '.*\.g\..*'
    Priority:        1
  - Regex:           '^<.*\.h(pp)?>'
    Priority:        2
  - Regex:           '^<.*'
    Priority:        3
  - Regex:           '.*'
    Priority:        4
IndentCaseLabels: true
IndentWidth:     2
IndentWrappedFunctionNames: false
KeepEmptyLinesAtTheStartOfBlocks: false
MacroBlockBegin: ''
MacroBlockEnd:   ''
MaxEmptyLinesToKeep: 1
NamespaceIndentation: None
ObjCBlockIndentWidth: 2
ObjCSpaceAfterProperty: true
ObjCSpaceBeforeProtocolList: true
PenaltyBreakBeforeFirstCallParameter: 1
PenaltyBreakComment: 300
PenaltyBreakFirstLessLess: 120
PenaltyBreakString: 1000
PenaltyExcessCharacter: 1000000
PenaltyReturnTypeOnItsOwnLine: 200
PointerAlignment: Right
ReflowComments:  true
SortIncludes:    true
SpaceAfterCStyleCast: false
SpaceBeforeAssignmentOperators: true
SpaceBeforeParens: ControlStatements
SpaceInEmptyParentheses: false
SpacesBeforeTrailingComments: 1
SpacesInAngles:  false
SpacesInContainerLiterals: true
SpacesInCStyleCastParentheses: false
SpacesInParentheses: false
SpacesInSquareBrackets: false
Standard:        Cpp11
TabWidth:        8
UseTab:          Never

Is there a trick to faster C++ formatting?

[chrisglein]

By chance is this trying to scan everything in \node_modules\? That would certainly add a ton of additional files for this to get tripped up on. See if you can make sure that's excluded?

We don't have a lot of material knowledge about how Visual Studio handles this. We don't have any default ClangFormat set up but do use ESLint, and sometimes Visual Studio does seem to get a little... occupied. Not sure how to debug.

And my .clangformat file is based on rules I found in either the React Native Windows repo or Facebook's Hermes repo.

Can you link what you used as sources?

[shirakaba]

Thanks for the response!

By chance is this trying to scan everything in \node_modules?

I suspect it might be, but no idea how to stop it. As possible evidence otherwise, though, I have a standalone Win32 library, that doesn't import React Native Windows at all, sitting inside the same monorepo that formats in under a second. So I think some aspect of importing React Native Windows causes it to either format or analyse the entire RNW codebase on each usage?

See if you can make sure that's excluded?

Unfortunately I've been unable to figure out via Visual Studio how to get any debug into that either. There might be some more debug on the Visual Studio Code side (which is similarly slow), but I'm generally working within Visual Studio.

Can you link what you used as sources?

I think I began with the Hermes one as-is, but then made this change because it was squeezing my lambdas into a narrow two-word column whilst leaving 100 characters of whitespace unused.

- BreakBeforeBraces: Attach
+ BreakBeforeBraces: Allman

It was slow both before and after that change, though.