Properly disallow `yield` in bodyless arrows by Andarist · Pull Request #61976 · microsoft/TypeScript

Andarist · 2025-06-30T12:52:29Z

No description provided.

typescript-bot · 2025-06-30T12:52:35Z

This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.

typescript-bot · 2025-06-30T12:52:35Z

This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.

Copilot

Pull Request Overview

This PR ensures that yield expressions are disallowed in concise (bodyless) arrow function bodies as required by the ES6 spec and adds a corresponding test case.

Disable the yield parsing context when parsing arrow expression bodies
Add a conformance test and update baselines to validate that yield in a bodyless arrow yields an error
Update .types, .symbols, .js, and .errors.txt baselines to reflect the new error

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/compiler/parser.ts	Disable `yield` context around arrow body parsing and restore afterward
tests/cases/conformance/es6/yieldExpressions/YieldExpression20_es6.ts	New test case verifying `yield` is disallowed in a concise arrow
tests/baselines/reference/YieldExpression20_es6.types	Updated type-checking baseline for the new test
tests/baselines/reference/YieldExpression20_es6.symbols	Updated symbol baseline for the new test
tests/baselines/reference/YieldExpression20_es6.js	Updated transpiled JS baseline for the new test
tests/baselines/reference/YieldExpression20_es6.errors.txt	Updated error-message baseline for the new test

Comments suppressed due to low confidence (2)

src/compiler/parser.ts:5562

[nitpick] Add a brief comment explaining that we temporarily disable the yield parsing context here to enforce the ES6 rule that concise arrow bodies are not generator bodies.

        const savedYieldContext = inYieldContext();

src/compiler/parser.ts:5563

[nitpick] Consider using a doOutsideOfContext(NodeFlags.YieldContext, ...) helper (similar to await) to encapsulate context toggling, improving consistency and readability.

        setYieldContext(false);

jakebailey · 2025-06-30T17:24:15Z

Pretty sure this is correct but

@typescript-bot test it

typescript-bot · 2025-06-30T17:24:20Z

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`test top400`	✅ Started	✅ Results
`user test this`	✅ Started	✅ Results
`run dt`	✅ Started	✅ Results
`perf test this faster`	✅ Started	👀 Results

typescript-bot · 2025-06-30T17:45:30Z

Hey @jakebailey, the results of running the DT tests are ready.

Everything looks the same!

You can check the log here.

typescript-bot · 2025-06-30T18:02:03Z

@jakebailey Here are the results of running the user tests with tsc comparing main and refs/pull/61976/merge:

Everything looks good!

typescript-bot · 2025-06-30T18:25:19Z

@jakebailey
The results of the perf run you requested are in!

Here they are:

tsc

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Compiler-Unions - node (v18.15.0, x64)}
_Errors	₃₄	₃₄	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_62,370	_62,370	_~	_~	_~	_{p=1.000 n=6}
_Types	_50,386	_50,386	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{196,418k (± 0.23%)}	_{195,371k (± 0.93%)}	_~	_193,005k	_196,675k	_{p=0.230 n=6}
_{Parse Time}	_{1.61s (± 1.24%)}	_{1.61s (± 0.64%)}	_~	_1.59s	_1.62s	_{p=0.744 n=6}
_{Bind Time}	_{0.88s (± 1.73%)}	_{0.87s (± 1.18%)}	_~	_0.86s	_0.89s	_{p=0.737 n=6}
_{Check Time}	_{11.80s (± 0.47%)}	_{11.77s (± 0.70%)}	_~	_11.68s	_11.90s	_{p=0.295 n=6}
_{Emit Time}	_{3.32s (± 2.10%)}	_{3.31s (± 3.89%)}	_~	_3.23s	_3.57s	_{p=0.423 n=6}
_{Total Time}	_{17.60s (± 0.65%)}	_{17.55s (± 0.97%)}	_~	_17.36s	_17.81s	_{p=0.422 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₅₆	₅₆	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_948,753	_948,753	_~	_~	_~	_{p=1.000 n=6}
_Types	_410,846	_410,846	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{1,225,046k (± 0.01%)}	_{1,225,044k (± 0.00%)}	_~	_1,225,006k	_1,225,102k	_{p=0.872 n=6}
_{Parse Time}	_{6.57s (± 0.81%)}	_{6.56s (± 0.76%)}	_~	_6.47s	_6.61s	_{p=0.517 n=6}
_{Bind Time}	_1.88s	_1.88s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{31.85s (± 0.25%)}	_{31.96s (± 0.52%)}	_~	_31.80s	_32.17s	_{p=0.335 n=6}
_{Emit Time}	_{14.80s (± 0.26%)}	_{14.85s (± 0.43%)}	_~	_14.77s	_14.94s	_{p=0.199 n=6}
_{Total Time}	_{55.11s (± 0.18%)}	_{55.25s (± 0.30%)}	_~	_54.99s	_55.45s	_{p=0.109 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,509,183	_2,509,183	_~	_~	_~	_{p=1.000 n=6}
_Types	_892,716	_892,716	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,804,461k (± 0.00%)}	_{2,804,500k (± 0.00%)}	_~	_2,804,361k	_2,804,603k	_{p=0.378 n=6}
_{Parse Time}	_{10.52s (± 0.28%)}	_{10.48s (± 0.38%)}	_~	_10.43s	_10.52s	_{p=0.148 n=6}
_{Bind Time}	_{2.74s (± 0.68%)}	_{2.74s (± 0.30%)}	_~	_2.74s	_2.76s	_{p=0.275 n=6}
_{Check Time}	_{101.07s (± 0.50%)}	_{101.64s (± 1.20%)}	_~	_100.74s	_103.40s	_{p=0.689 n=6}
_{Emit Time}	_{0.37s (± 2.04%)}	_{0.36s (± 2.29%)}	_~	_0.36s	_0.38s	_{p=0.432 n=6}
_{Total Time}	_{114.70s (± 0.46%)}	_{115.24s (± 1.04%)}	_~	_114.36s	_116.93s	_{p=0.689 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,227,080	_1,227,081	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_267,443	_267,443	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,362,966k (± 0.05%)}	_{2,363,185k (± 0.02%)}	_~	_2,362,212k	_2,363,762k	_{p=0.689 n=6}
_{Parse Time}	_{5.19s (± 1.13%)}	_{5.17s (± 0.85%)}	_~	_5.10s	_5.23s	_{p=0.470 n=6}
_{Bind Time}	_{1.79s (± 0.96%)}	_{1.80s (± 0.83%)}	_~	_1.79s	_1.83s	_{p=0.218 n=6}
_{Check Time}	_{35.24s (± 0.31%)}	_{35.33s (± 0.68%)}	_~	_35.15s	_35.80s	_{p=0.936 n=6}
_{Emit Time}	_{2.94s (± 2.36%)}	_{2.99s (± 1.52%)}	_~	_2.96s	_3.08s	_{p=0.295 n=6}
_{Total Time}	_{45.16s (± 0.35%)}	_{45.32s (± 0.48%)}	_~	_45.15s	_45.74s	_{p=0.149 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,227,080	_1,227,081	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_267,443	_267,443	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,821,659k (±13.31%)}	_{2,917,494k (±12.91%)}	_~	_2,430,770k	_3,162,038k	_{p=1.000 n=6}
_{Parse Time}	_{6.78s (± 1.34%)}	_{6.81s (± 1.59%)}	_~	_6.66s	_6.91s	_{p=0.423 n=6}
_{Bind Time}	_{2.16s (± 1.64%)}	_{2.17s (± 1.07%)}	_~	_2.13s	_2.19s	_{p=0.628 n=6}
_{Check Time}	_{42.69s (± 0.91%)}	_{42.89s (± 0.30%)}	_~	_42.68s	_43.05s	_{p=0.378 n=6}
_{Emit Time}	_{3.52s (± 2.18%)}	_{3.55s (± 3.58%)}	_~	_3.39s	_3.72s	_{p=0.810 n=6}
_{Total Time}	_{55.15s (± 0.76%)}	_{55.43s (± 0.25%)}	_~	_55.18s	_55.58s	_{p=0.230 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_262,529	_262,530	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_107,150	_107,150	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{441,786k (± 0.01%)}	_{441,824k (± 0.01%)}	_~	_441,767k	_441,911k	_{p=0.295 n=6}
_{Parse Time}	_{3.52s (± 1.01%)}	_{3.54s (± 0.99%)}	_~	_3.50s	_3.59s	_{p=0.259 n=6}
_{Bind Time}	_{1.32s (± 1.31%)}	_{1.33s (± 0.74%)}	_~	_1.32s	_1.34s	_{p=0.154 n=6}
_{Check Time}	_{18.92s (± 0.38%)}	_{18.84s (± 0.38%)}	_~	_18.78s	_18.95s	_{p=0.127 n=6}
_{Emit Time}	_{1.52s (± 1.31%)}	_{1.51s (± 0.90%)}	_~	_1.49s	_1.53s	_{p=0.564 n=6}
_{Total Time}	_{25.29s (± 0.24%)}	_{25.23s (± 0.25%)}	_~	_25.12s	_25.31s	_{p=0.167 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₇₁	₇₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_225,367	_225,367	_~	_~	_~	_{p=1.000 n=6}
_Types	_94,290	_94,290	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{371,109k (± 0.01%)}	_{371,095k (± 0.03%)}	_~	_370,995k	_371,277k	_{p=0.336 n=6}
_{Parse Time}	_{2.90s (± 0.92%)}	_{2.88s (± 0.93%)}	_~	_2.83s	_2.91s	_{p=0.222 n=6}
_{Bind Time}	_{1.60s (± 0.92%)}	_{1.59s (± 0.65%)}	_~	_1.58s	_1.61s	_{p=0.616 n=6}
_{Check Time}	_{16.34s (± 0.15%)}	_{16.38s (± 0.37%)}	_~	_16.32s	_16.49s	_{p=0.196 n=6}
_{Emit Time}	_0.00s	_{0.00s (±154.76%)}	_~	_0.00s	_0.01s	_{p=0.174 n=6}
_{Total Time}	_{20.83s (± 0.15%)}	_{20.84s (± 0.25%)}	_~	_20.78s	_20.93s	_{p=0.568 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₃₃	₃₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_3,498,707	_3,498,707	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,176,728	_1,176,728	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{3,548,757k (± 0.00%)}	_{3,548,727k (± 0.00%)}	_~	_3,548,639k	_3,548,803k	_{p=0.575 n=6}
_{Parse Time}	_{15.01s (± 0.92%)}	_{15.06s (± 0.59%)}	_~	_14.95s	_15.20s	_{p=0.148 n=6}
_{Bind Time}	_{4.89s (± 0.59%)}	_{4.90s (± 0.61%)}	_~	_4.85s	_4.94s	_{p=0.627 n=6}
_{Check Time}	_{96.25s (± 3.01%)}	_{94.93s (± 1.75%)}	_~	_93.90s	_98.29s	_{p=0.378 n=6}
_{Emit Time}	_{30.01s (± 2.40%)}	_{31.10s (± 7.96%)}	_~	_29.54s	_35.98s	_{p=0.689 n=6}
_{Total Time}	_{146.17s (± 2.50%)}	_{145.99s (± 2.09%)}	_~	_143.29s	_150.27s	_{p=1.000 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_318,019	_318,019	_~	_~	_~	_{p=1.000 n=6}
_Types	_137,705	_137,705	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{472,210k (± 0.02%)}	_{472,126k (± 0.02%)}	_~	_471,931k	_472,229k	_{p=0.173 n=6}
_{Parse Time}	_{4.36s (± 0.45%)}	_{4.35s (± 0.57%)}	_~	_4.32s	_4.39s	_{p=0.519 n=6}
_{Bind Time}	_{1.78s (± 1.49%)}	_{1.76s (± 1.26%)}	_~	_1.73s	_1.78s	_{p=0.166 n=6}
_{Check Time}	_{20.79s (± 0.45%)}	_{20.78s (± 0.44%)}	_~	_20.65s	_20.85s	_{p=0.936 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{26.92s (± 0.36%)}	_{26.89s (± 0.35%)}	_~	_26.76s	_27.01s	_{p=0.574 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₃₀	₃₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_665,978	_665,978	_~	_~	_~	_{p=1.000 n=6}
_Types	_199,345	_199,345	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{570,384k (± 0.01%)}	_{570,349k (± 0.03%)}	_~	_569,999k	_570,510k	_{p=0.936 n=6}
_{Parse Time}	_{4.25s (± 0.58%)}	_{4.27s (± 0.64%)}	_~	_4.23s	_4.30s	_{p=0.124 n=6}
_{Bind Time}	_{1.33s (± 1.02%)}	_{1.33s (± 1.32%)}	_~	_1.31s	_1.36s	_{p=1.000 n=6}
_{Check Time}	_{19.94s (± 0.46%)}	_{19.92s (± 0.43%)}	_~	_19.81s	_20.03s	_{p=0.747 n=6}
_{Emit Time}	_0.00s	_{0.00s (±244.70%)}	_~	_0.00s	_0.01s	_{p=0.405 n=6}
_{Total Time}	_{25.52s (± 0.41%)}	_{25.53s (± 0.40%)}	_~	_25.39s	_25.66s	_{p=0.936 n=6}

System info unknown

Hosts

node (v18.15.0, x64)

Scenarios

Compiler-Unions - node (v18.15.0, x64)
angular-1 - node (v18.15.0, x64)
mui-docs - node (v18.15.0, x64)
self-build-src - node (v18.15.0, x64)
self-build-src-public-api - node (v18.15.0, x64)
self-compiler - node (v18.15.0, x64)
ts-pre-modules - node (v18.15.0, x64)
vscode - node (v18.15.0, x64)
webpack - node (v18.15.0, x64)
xstate-main - node (v18.15.0, x64)

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

Developer Information:

Download Benchmarks

typescript-bot · 2025-06-30T19:20:54Z

@jakebailey Here are the results of running the top 400 repos with tsc comparing main and refs/pull/61976/merge:

Everything looks good!

Properly disallow yield in bodyless arrows

f84debf

Copilot AI review requested due to automatic review settings June 30, 2025 12:52

github-project-automation bot added this to PR Backlog Jun 30, 2025

github-project-automation bot moved this to Not started in PR Backlog Jun 30, 2025

typescript-bot added the For Uncommitted Bug PR for untriaged, rejected, closed or missing bug label Jun 30, 2025

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jakebailey approved these changes Jun 30, 2025

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github-project-automation bot moved this from Not started to Needs merge in PR Backlog Jun 30, 2025

jakebailey merged commit 1ea1809 into microsoft:main Jun 30, 2025
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github-project-automation bot moved this from Needs merge to Done in PR Backlog Jun 30, 2025

Andarist deleted the fix/disallow-yield-in-arrows branch June 30, 2025 22:11

Andarist mentioned this pull request Oct 5, 2025

Port "Properly disallow yield in bodyless arrows" microsoft/typescript-go#1825

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Properly disallow `yield` in bodyless arrows#61976

Properly disallow `yield` in bodyless arrows#61976
jakebailey merged 1 commit intomicrosoft:mainfrom
Andarist:fix/disallow-yield-in-arrows

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