Document known lambda formatting deviations from Black #21954
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Summary -- Following #8179, we now format long lambda expressions a bit more like Black, preferring to keep long parameter lists on a single line, but we go one step further to break the body itself across multiple lines and parenthesize it if it's still too long. This PR documents both the stable deviation that breaks parameters across multiple lines, and the new preview deviation that breaks the body instead. I also fixed a couple of typos in the section immediately above my addition. Test Plan -- I tested all of the snippets here against `main` for the preview behavior, our playground for the stable behavior, and Black's playground for their behavior
MichaReiser
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Dec 12, 2025
dcreager
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Dec 13, 2025
* origin/main: (22 commits) [ty] Allow gradual lower/upper bounds in a constraint set (#21957) [ty] disallow explicit specialization of type variables themselves (#21938) [ty] Improve diagnostics for unsupported binary operations and unsupported augmented assignments (#21947) [ty] update implicit root docs (#21955) [ty] Enable even more goto-definition on inlay hints (#21950) Document known lambda formatting deviations from Black (#21954) [ty] fix hover type on named expression target (#21952) Bump benchmark dependencies (#21951) Keep lambda parameters on one line and parenthesize the body if it expands (#21385) [ty] Improve resolution of absolute imports in tests (#21817) [ty] Support `__all__ += submodule.__all__` [ty] Change frequency of invalid `__all__` debug message [ty] Add `KnownUnion::to_type()` (#21948) [ty] Classify `cls` as class parameter (#21944) [ty] Stabilize rename (#21940) [ty] Ignore `__all__` for document and workspace symbol requests [ty] Attach db to background request handler task (#21941) [ty] Fix outdated version in publish diagnostics after `didChange` (#21943) [ty] avoid fixpoint unioning of types containing current-cycle Divergent (#21910) [ty] improve bad specialization results & error messages (#21840) ...
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Summary
Following #8179, we now format long lambda expressions a bit more like Black, preferring to keep long parameter lists on a single line, but we go one step further to break the body itself across multiple lines and parenthesize it if it's still too long. This PR documents both the stable deviation that breaks parameters across multiple lines, and the new preview deviation that breaks the body instead.
I also fixed a couple of typos in the section immediately above my addition.
Test Plan
I tested all of the snippets here against
mainfor the preview behavior, our playground for the stable behavior, and Black's playground for their behavior