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Extraneous control flow error #37480

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#37965
Closed
Extraneous control flow error#37480
#37965
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ahejlsberg
Labels
BugA bug in TypeScriptFix AvailableA PR has been opened for this issue
Milestone
TypeScript 3.9.1

Description

@sandersn
Nathan Shively-Sanders (sandersn)
opened on Mar 19, 2020

From vscode: src/vs/workbench/contrib/search/common/searchModel.ts

Code

interface F {
    d(): void
}
export function doRemove(dds: F | F[]) {
    if (!Array.isArray(dds)) {
        dds = [dds]
    }
    for (let n of dds) {
        n.d()
    }
    return dds
}

Expected behavior:

No error, and n: F at all locations, and dds: F[] at all locations.

Actual behavior:

Types are correct; bogus error: 'F | F[]' must have a 'Symbol.iterator' method that returns an iterator.

Looks like narrowing works as expected, except for errors.

Activity

  1. Nathan Shively-Sanders (sandersn)
    added
    BugA bug in TypeScript
    on Mar 19, 2020
  2. Nathan Shively-Sanders (sandersn)
    added this to the TypeScript 3.9.0 milestone on Mar 19, 2020

  3. sandersn commented on Mar 19, 2020

    @sandersn
    Nathan Shively-Sanders (sandersn)
    on Mar 19, 2020
    MemberAuthor

    For future bisecting: Doesn't repro on a commit from March 2: dd6811f

  4. Matt Bierner (mjbvz)
    added a commit that references this issue on Mar 27, 2020

    Pick up latest TypeScript@next

    2b9e8b4
  5. Daniel Rosenwasser (DanielRosenwasser)
    modified the milestones: TypeScript 3.9.0, TypeScript 3.9.1 on Apr 7, 2020
  6. Anders Hejlsberg (ahejlsberg)
    self-assigned this
    on Apr 14, 2020
  7. Anders Hejlsberg (ahejlsberg)
    added
    Fix AvailableA PR has been opened for this issue
    on Apr 14, 2020
  8. Anders Hejlsberg (ahejlsberg)
    closed this as completedin #37965on Apr 15, 2020
  9. microsoft
    locked as resolved and limited conversation to collaborators on Oct 21, 2025
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