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Enum members aren't subtype reduced in unions #35867

Closed
#49675
Closed
Enum members aren't subtype reduced in unions#35867
#49675
Labels
BugA bug in TypeScriptGood First IssueWell scoped, documented and has the green lightHas ReproThis issue has compiler-backed repros: https://aka.ms/ts-reprosHelp WantedYou can do thisInfrastructureIssue relates to TypeScript team infrastructure
Milestone
Backlog

Description

@DanielRosenwasser
Daniel Rosenwasser (DanielRosenwasser)
opened on Dec 27, 2019
enum E {
    A,
    B,
    C,
}

function f(x: E | undefined) {
    return x ?? E.C;
}

Expected f to have type E, but instead it has type E | E.C

Playground

Doesn't have anything to do with ?? - can reproduce it with ||.

enum E {
    A = 1,
    B,
    C,
}

function f(x: E | undefined) {
    return x || E.C;
}

Activity

  1. jack-williams commented on Dec 27, 2019

    @jack-williams
    Jack Williams (jack-williams)
    on Dec 27, 2019
    Collaborator

    Related: #32621?

  2. Ryan Cavanaugh (RyanCavanaugh)
    added
    BugA bug in TypeScript
    on Jan 13, 2020
  3. Ryan Cavanaugh (RyanCavanaugh)
    added this to the Backlog milestone on Jan 13, 2020

  4. DanielRosenwasser commented on Jul 16, 2020

    @DanielRosenwasser
    Daniel Rosenwasser (DanielRosenwasser)
    on Jul 16, 2020
    MemberAuthor
    enum E {
    A,
    B,
    C,
}

function f(x: E | undefined) {
//       ^?
    return x ?? E.C;
}

    Workbench Repro

  5. TypeScript Bot (typescript-bot)
    added
    Has ReproThis issue has compiler-backed repros: https://aka.ms/ts-repros
    on Apr 12, 2022

  6. DanielRosenwasser commented on Apr 12, 2022

    @DanielRosenwasser
    Daniel Rosenwasser (DanielRosenwasser)
    on Apr 12, 2022
    MemberAuthor

    I think this is fixed now. Would we have any volunteers willing to add a test case to prevent regressions?

  7. Daniel Rosenwasser (DanielRosenwasser)
    added
    Help WantedYou can do this
    Good First IssueWell scoped, documented and has the green light
    InfrastructureIssue relates to TypeScript team infrastructure
    on Apr 12, 2022

  8. typescript-bot commented on Apr 13, 2022

    @typescript-bot
    TypeScript Bot (typescript-bot)
    on Apr 13, 2022
    Contributor

    👋 Hi, I'm the Repro bot. I can help narrow down and track compiler bugs across releases! This comment reflects the current state of the repro in the issue body running against the nightly TypeScript.

    Issue body code block by Daniel Rosenwasser (@DanielRosenwasser)

    ‼️ Exception: Error - Did not find a source file for /home/runner/work/TypeScript/TypeScript/index.ts 

    Error: Did not find a source file for /home/runner/work/TypeScript/TypeScript/index.ts
    at Object.updateFile (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:6876:15)
    at _loop3 (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:1738:9)
    at twoslasher (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:1744:17)
    at /home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:777:44
    at runTwoslashRequests (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:744:56)
    at run (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:2169:75)
    at runMicrotasks (<anonymous>)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)

    Historical Information
    Version Reproduction Outputs Time
    4.2.2, 4.3.2, 4.4.2, 4.5.2, 4.6.2

    👍 Compiled

    		 ⚠️ Way slower

  9. typescript-bot commented on Apr 14, 2022

    @typescript-bot
    TypeScript Bot (typescript-bot)
    on Apr 14, 2022
    Contributor

    👋 Hi, I'm the Repro bot. I can help narrow down and track compiler bugs across releases! This comment reflects the current state of this repro running against the nightly TypeScript.

    Comment by Daniel Rosenwasser (@DanielRosenwasser)

    ‼️ Exception: TypeError - Cannot read properties of undefined (reading 'getPositionOfLineAndCharacter') 

    TypeError: Cannot read properties of undefined (reading 'getPositionOfLineAndCharacter')
    at Object.getPositionOfLineAndCharacter (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/ts/nightly/lib/typescript.js:10384:27)
    at /home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:1679:25
    at Array.map (<anonymous>)
    at _loop3 (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:1677:40)
    at twoslasher (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:1744:17)
    at /home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:777:44
    at runTwoslashRequests (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:744:56)
    at run (/home/runner/work/_actions/microsoft/TypeScript-Twoslash-Repro-Action/master/dist/index.js:2169:75)
    at runMicrotasks (<anonymous>)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)

    Historical Information
    Version Reproduction Outputs Time
    4.2.2, 4.3.2, 4.4.2, 4.5.2, 4.6.2

    ⚠️ Assertions:

    • function f(x: E | undefined): E

    		 ⚠️ Way slower
  10. Lawrence Craft (lawrencecraft)
    added 2 commits that reference this issue on Jun 16, 2022

    Add case to capture enum subtype reduction (addresses microsoft#35867)

    d3076fa

    Add case to capture enum subtype reduction (addresses microsoft#35867)

    c710b96
  11. Ashley Claymore (acutmore)
    added a commit that references this issue on Jun 16, 2022

    Add case to capture enum subtype reduction (addresses microsoft#35867) (

    bdf99c4
  12. Ryan Cavanaugh (RyanCavanaugh)
    closed this as completedin #49675on Jun 24, 2022
  13. microsoft
    locked as resolved and limited conversation to collaborators on Oct 21, 2025
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