Support const assertions and unit type const variable references in constant expressions by ahejlsberg · Pull Request #59475 · microsoft/TypeScript

Anders Hejlsberg (ahejlsberg) · 2024-07-30T17:18:10Z

With this PR we permit constant expressions to contain const assertions and references to const variables with unit types:

const C00 = "a";
const C01 = "b" as const;
const C02: "c" = "c";
declare const C03: "d";

const enum E0 {
    A = C00,
    B = C01,  // Was error, now ok
    C = C02,  // Was error, now ok
    D = C03,  // Was error, now ok
}

const C10 = 1;
const C11 = 2 as const;
const C12: 3 = 3;
declare const C13: 4;

const enum E1 {
    A = C10,
    B = C11,  // Was error, now ok
    C = C12,  // Was error, now ok
    D = C13,  // Was error, now ok
}

Note that a const variable with a type annotation may be referenced in a constant expression only if the type annotation is a string or numeric literal. Other forms of types, such as named types or union types, are not supported.

Fixes #59346.

…pressions

Anders Hejlsberg (ahejlsberg) · 2024-07-30T17:18:24Z

TypeScript Bot (@typescript-bot) test it

TypeScript Bot (typescript-bot) · 2024-07-30T17:18:27Z

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 (typescript-bot) · 2024-07-30T17:39:37Z

Hey Anders Hejlsberg (@ahejlsberg), the results of running the DT tests are ready.

Everything looks the same!

You can check the log here.

TypeScript Bot (typescript-bot) · 2024-07-30T17:44:40Z

Anders Hejlsberg (@ahejlsberg) Here are the results of running the user tests with tsc comparing main and refs/pull/59475/merge:

Everything looks good!

TypeScript Bot (typescript-bot) · 2024-07-30T17:55:50Z

Anders Hejlsberg (@ahejlsberg)
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	₃₀	₃₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_62,153	_62,153	_~	_~	_~	_{p=1.000 n=6}
_Types	_50,242	_50,242	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{192,882k (± 0.74%)}	_{194,182k (± 0.97%)}	_{+1,301k (+ 0.67%)}	_192,303k	_196,019k	_{p=0.031 n=6}
_{Parse Time}	_{1.57s (± 0.52%)}	_{1.57s (± 1.02%)}	_~	_1.54s	_1.58s	_{p=0.796 n=6}
_{Bind Time}	_{0.86s (± 0.95%)}	_{0.85s (± 1.21%)}	_~	_0.84s	_0.87s	_{p=0.546 n=6}
_{Check Time}	_{11.36s (± 0.30%)}	_{11.39s (± 0.65%)}	_~	_11.31s	_11.50s	_{p=0.573 n=6}
_{Emit Time}	_{3.26s (± 1.09%)}	_{3.26s (± 0.93%)}	_~	_3.21s	_3.30s	_{p=1.000 n=6}
_{Total Time}	_{17.06s (± 0.15%)}	_{17.08s (± 0.55%)}	_~	_16.95s	_17.23s	_{p=0.687 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₇	₇	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_945,532	_945,532	_~	_~	_~	_{p=1.000 n=6}
_Types	_409,507	_409,507	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{1,221,116k (± 0.00%)}	_{1,221,146k (± 0.00%)}	_~	_1,221,115k	_1,221,202k	_{p=0.066 n=6}
_{Parse Time}	_{7.86s (± 0.76%)}	_{7.85s (± 0.63%)}	_~	_7.80s	_7.93s	_{p=0.686 n=6}
_{Bind Time}	_{2.22s (± 0.72%)}	_{2.21s (± 0.74%)}	_~	_2.19s	_2.24s	_{p=0.625 n=6}
_{Check Time}	_{36.35s (± 0.43%)}	_{36.36s (± 0.49%)}	_~	_36.22s	_36.68s	_{p=1.000 n=6}
_{Emit Time}	_{17.75s (± 0.62%)}	_{17.78s (± 0.97%)}	_~	_17.51s	_18.00s	_{p=0.748 n=6}
_{Total Time}	_{64.17s (± 0.36%)}	_{64.20s (± 0.39%)}	_~	_63.81s	_64.43s	_{p=1.000 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,439,121	_2,439,121	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,004,407	_1,004,407	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{2,410,535k (± 0.00%)}	_{2,410,556k (± 0.00%)}	_~	_2,410,517k	_2,410,630k	_{p=0.471 n=6}
_{Parse Time}	_{9.94s (± 0.21%)}	_{9.94s (± 0.20%)}	_~	_9.91s	_9.96s	_{p=0.807 n=6}
_{Bind Time}	_{2.49s (± 0.65%)}	_{2.49s (± 0.22%)}	_~	_2.48s	_2.49s	_{p=0.228 n=6}
_{Check Time}	_{89.24s (± 2.12%)}	_{89.04s (± 1.51%)}	_~	_88.06s	_91.61s	_{p=0.630 n=6}
_{Emit Time}	_{0.33s (± 2.29%)}	_{0.32s (± 2.79%)}	_~	_0.31s	_0.33s	_{p=0.149 n=6}
_{Total Time}	_{102.00s (± 1.85%)}	_{101.79s (± 1.32%)}	_~	_100.77s	_104.37s	_{p=0.689 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,227,815	_1,227,818	_{+3 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_265,152	_265,153	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,464,884k (± 7.42%)}	_{2,347,114k (± 0.03%)}	_~	_2,345,986k	_2,347,910k	_{p=0.936 n=6}
_{Parse Time}	_{5.97s (± 0.75%)}	_{5.91s (± 0.50%)}	_{-0.05s (- 0.92%)}	_5.88s	_5.96s	_{p=0.031 n=6}
_{Bind Time}	_{2.27s (± 0.66%)}	_{2.26s (± 1.03%)}	_~	_2.25s	_2.31s	_{p=0.120 n=6}
_{Check Time}	_{40.54s (± 0.54%)}	_{40.61s (± 0.27%)}	_~	_40.43s	_40.76s	_{p=0.689 n=6}
_{Emit Time}	_{3.93s (± 0.84%)}	_{3.94s (± 0.88%)}	_~	_3.88s	_3.98s	_{p=0.872 n=6}
_{Total Time}	_{52.73s (± 0.50%)}	_{52.74s (± 0.17%)}	_~	_52.66s	_52.89s	_{p=0.575 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,227,815	_1,227,818	_{+3 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_265,152	_265,153	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,420,353k (± 0.03%)}	_{2,420,621k (± 0.01%)}	_~	_2,420,189k	_2,421,053k	_{p=0.810 n=6}
_{Parse Time}	_{6.20s (± 0.83%)}	_{6.22s (± 0.67%)}	_~	_6.15s	_6.27s	_{p=0.520 n=6}
_{Bind Time}	_{2.04s (± 0.91%)}	_{2.03s (± 1.16%)}	_~	_1.98s	_2.04s	_{p=0.324 n=6}
_{Check Time}	_{41.24s (± 0.78%)}	_{41.19s (± 0.15%)}	_~	_41.11s	_41.28s	_{p=0.936 n=6}
_{Emit Time}	_{4.05s (± 1.53%)}	_{4.04s (± 2.54%)}	_~	_3.95s	_4.24s	_{p=0.421 n=6}
_{Total Time}	_{53.55s (± 0.54%)}	_{53.51s (± 0.36%)}	_~	_53.25s	_53.82s	_{p=0.936 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_255,990	_255,993	_{+3 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_104,965	_104,966	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{427,919k (± 0.02%)}	_{428,058k (± 0.05%)}	_~	_427,848k	_428,334k	_{p=0.471 n=6}
_{Parse Time}	_{3.35s (± 0.93%)}	_{3.37s (± 0.68%)}	_~	_3.34s	_3.39s	_{p=0.222 n=6}
_{Bind Time}	_{1.32s (± 0.57%)}	_{1.30s (± 1.33%)}	_{-0.02s (- 1.77%)}	_1.28s	_1.32s	_{p=0.036 n=6}
_{Check Time}	_{17.97s (± 0.27%)}	_{18.02s (± 0.34%)}	_~	_17.94s	_18.09s	_{p=0.335 n=6}
_{Emit Time}	_{1.64s (± 1.30%)}	_{1.66s (± 0.98%)}	_~	_1.64s	_1.68s	_{p=0.106 n=6}
_{Total Time}	_{24.29s (± 0.34%)}	_{24.34s (± 0.25%)}	_~	_24.27s	_24.41s	_{p=0.336 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₃₅	₃₅	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_224,931	_224,931	_~	_~	_~	_{p=1.000 n=6}
_Types	_94,146	_94,146	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{370,075k (± 0.02%)}	_{370,113k (± 0.05%)}	_~	_369,912k	_370,329k	_{p=0.936 n=6}
_{Parse Time}	_{3.45s (± 0.79%)}	_{3.43s (± 0.66%)}	_~	_3.40s	_3.45s	_{p=0.120 n=6}
_{Bind Time}	_{1.92s (± 0.71%)}	_{1.92s (± 0.51%)}	_~	_1.91s	_1.93s	_{p=0.611 n=6}
_{Check Time}	_{19.36s (± 0.30%)}	_{19.32s (± 0.50%)}	_~	_19.23s	_19.49s	_{p=0.261 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{24.74s (± 0.26%)}	_{24.67s (± 0.36%)}	_~	_24.57s	_24.82s	_{p=0.128 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₁₁	₁₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,989,199	_2,989,199	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,028,388	_1,028,428	_{+40 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{3,113,698k (± 0.00%)}	_{3,113,665k (± 0.00%)}	_~	_3,113,608k	_3,113,733k	_{p=0.230 n=6}
_{Parse Time}	_{13.82s (± 0.50%)}	_{13.81s (± 0.27%)}	_~	_13.78s	_13.87s	_{p=0.806 n=6}
_{Bind Time}	_{4.36s (± 2.67%)}	_{4.32s (± 2.22%)}	_~	_4.26s	_4.51s	_{p=0.464 n=6}
_{Check Time}	_{79.40s (± 0.35%)}	_{79.65s (± 0.50%)}	_~	_79.16s	_80.11s	_{p=0.378 n=6}
_{Emit Time}	_{20.57s (± 0.97%)}	_{20.60s (± 0.41%)}	_~	_20.44s	_20.68s	_{p=0.297 n=6}
_{Total Time}	_{118.16s (± 0.35%)}	_{118.39s (± 0.38%)}	_~	_117.69s	_118.96s	_{p=0.378 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_267,994	_267,994	_~	_~	_~	_{p=1.000 n=6}
_Types	_109,192	_109,192	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{412,899k (± 0.02%)}	_{412,944k (± 0.03%)}	_~	_412,849k	_413,149k	_{p=0.810 n=6}
_{Parse Time}	_{3.81s (± 0.59%)}	_{3.81s (± 0.45%)}	_~	_3.79s	_3.84s	_{p=0.806 n=6}
_{Bind Time}	_{1.72s (± 0.30%)}	_{1.71s (± 0.37%)}	_~	_1.70s	_1.72s	_{p=0.091 n=6}
_{Check Time}	_{16.87s (± 0.63%)}	_{16.91s (± 0.56%)}	_~	_16.81s	_17.08s	_{p=0.574 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{22.40s (± 0.47%)}	_{22.43s (± 0.41%)}	_~	_22.35s	_22.60s	_{p=0.423 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_535,921	_535,921	_~	_~	_~	_{p=1.000 n=6}
_Types	_176,733	_176,733	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{477,642k (± 0.06%)}	_{477,474k (± 0.09%)}	_~	_477,065k	_477,930k	_{p=0.378 n=6}
_{Parse Time}	_{2.80s (± 0.79%)}	_{2.79s (± 0.70%)}	_~	_2.76s	_2.81s	_{p=0.190 n=6}
_{Bind Time}	_{1.04s (± 0.50%)}	_{1.03s (± 1.13%)}	_~	_1.01s	_1.04s	_{p=0.523 n=6}
_{Check Time}	_{15.17s (± 0.25%)}	_{15.18s (± 0.53%)}	_~	_15.11s	_15.31s	_{p=0.871 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{19.01s (± 0.25%)}	_{19.00s (± 0.54%)}	_~	_18.89s	_19.15s	_{p=0.748 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 (typescript-bot) · 2024-07-30T19:03:22Z

Anders Hejlsberg (@ahejlsberg) Here are the results of running the top 400 repos with tsc comparing main and refs/pull/59475/merge:

Everything looks good!

Daniele Orlando (daniele-orlando) · 2025-01-24T16:59:04Z

Ryan Cavanaugh (@RyanCavanaugh) Hi dear TypeScript maintainers, this MR is pending since 6 months and it is blocking the resolution of issue #59346, which had a milestone of TypeScript 5.7.0, which has been clearly missed.

Can we get it merged?

Grigorii Lutkov (grigorii-lutkov) · 2025-01-28T17:18:33Z

I also would love to see this merged

P.S.: looks like all tests have successfully passed loooong time ago... Can someone review this MR already, please?

Daniele Orlando (daniele-orlando) · 2025-02-19T19:12:34Z

Ryan Cavanaugh (@RyanCavanaugh) Is there any hope to see this merge request merged sooner or later? 6 months have passed and it is blocked for no explained reason.

cc: Jake Bailey (@jakebailey) Andrew Branch (@andrewbranch) Daniel Rosenwasser (@DanielRosenwasser)

IainSAP (IainSAP) · 2025-04-02T09:07:14Z

Please approve and merge...thx!

Juliane Lehmann (strooooke) · 2025-05-07T15:25:56Z

Please, please, please, move this along... please!

TypeScript Bot (typescript-bot) · 2026-03-24T21:19:41Z

With 6.0 out as the final release vehicle for this codebase, we're closing all PRs that don't fit the merge criteria for post-6.0 patches. If you think this was a mistake and this PR fits the post-6.0 patch criteria, please post to the 6.0 iteration issue with details (specifically, which PR and which patch criteria it satisfies).

Next steps for PRs:

For crash bugfixes or language service improvements, PRs are currently accepted at the typescript-go repo
Changes to type system behavior should wait until after 7.0, at which point mainline TypeScript development will resume in this repository with the Go codebase
Library file updates (lib.d.ts etc) continue to live in this repo or the DOM Generator repo as appropriate

Anders Hejlsberg (ahejlsberg) added 4 commits July 30, 2024 09:28

Allow const assertions in constant expressions

e0036e6

Allow references to const variables with literal types in constant ex…

2e0d0fc

…pressions

Add tests

4a6d9fd

Include declaration emit in tests

e713577

TypeScript Bot (typescript-bot) assigned Anders Hejlsberg (ahejlsberg) Jul 30, 2024

TypeScript Bot (typescript-bot) added Author: Team For Uncommitted Bug PR for untriaged, rejected, closed or missing bug labels Jul 30, 2024

Anders Hejlsberg (ahejlsberg) requested a review from Ryan Cavanaugh (RyanCavanaugh) July 30, 2024 17:18

Martin Johns (MartinJohns) mentioned this pull request Jan 28, 2025

Not possible to use const string as enum value #61064

Closed

TypeScript Bot (typescript-bot) closed this Mar 24, 2026

github-project-automation Bot moved this from Not started to Done in PR Backlog Mar 24, 2026

Jake Bailey (jakebailey) deleted the fix59346 branch August 28, 2026 20:08

Navigation Menu

Repository navigation

Support const assertions and unit type const variable references in constant expressions - #59475

Support const assertions and unit type const variable references in constant expressions#59475
Anders Hejlsberg (ahejlsberg) wants to merge 4 commits into
mainfrom
fix59346

Anders Hejlsberg (ahejlsberg) commented Jul 30, 2024 •

edited

Loading

Uh oh!

Anders Hejlsberg (ahejlsberg) commented Jul 30, 2024

Uh oh!

TypeScript Bot (typescript-bot) commented Jul 30, 2024 •

edited

Loading

Uh oh!

TypeScript Bot (typescript-bot) commented Jul 30, 2024

Uh oh!

TypeScript Bot (typescript-bot) commented Jul 30, 2024

Uh oh!

TypeScript Bot (typescript-bot) commented Jul 30, 2024

tsc

Uh oh!

TypeScript Bot (typescript-bot) commented Jul 30, 2024

Uh oh!

Daniele Orlando (daniele-orlando) commented Jan 24, 2025 •

edited

Loading

Uh oh!

Grigorii Lutkov (grigorii-lutkov) commented Jan 28, 2025

Uh oh!

Daniele Orlando (daniele-orlando) commented Feb 19, 2025 •

edited

Loading

Uh oh!

IainSAP (IainSAP) commented Apr 2, 2025 •

edited

Loading

Uh oh!

Juliane Lehmann (strooooke) commented May 7, 2025

Uh oh!

TypeScript Bot (typescript-bot) commented Mar 24, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

7 participants

Conversation

Anders Hejlsberg (ahejlsberg) commented Jul 30, 2024 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Anders Hejlsberg (ahejlsberg) commented Jul 30, 2024

Uh oh!

TypeScript Bot (typescript-bot) commented Jul 30, 2024 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

TypeScript Bot (typescript-bot) commented Jul 30, 2024

Uh oh!

TypeScript Bot (typescript-bot) commented Jul 30, 2024

Uh oh!

TypeScript Bot (typescript-bot) commented Jul 30, 2024

tsc

Uh oh!

TypeScript Bot (typescript-bot) commented Jul 30, 2024

Uh oh!

Daniele Orlando (daniele-orlando) commented Jan 24, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Grigorii Lutkov (grigorii-lutkov) commented Jan 28, 2025

Uh oh!

Daniele Orlando (daniele-orlando) commented Feb 19, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

IainSAP (IainSAP) commented Apr 2, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Juliane Lehmann (strooooke) commented May 7, 2025

Uh oh!

TypeScript Bot (typescript-bot) commented Mar 24, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

7 participants

Anders Hejlsberg (ahejlsberg) commented Jul 30, 2024 •

edited

Loading

TypeScript Bot (typescript-bot) commented Jul 30, 2024 •

edited

Loading

Daniele Orlando (daniele-orlando) commented Jan 24, 2025 •

edited

Loading

Daniele Orlando (daniele-orlando) commented Feb 19, 2025 •

edited

Loading

IainSAP (IainSAP) commented Apr 2, 2025 •

edited

Loading