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Value of a variable is forgotten in case where it ought to be known with certainty #11705

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Open
Value of a variable is forgotten in case where it ought to be known with certainty#11705
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bug
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Easy fixes

Description

@mind-bending-forks
mind-bending-forks
opened on Sep 17, 2024

Bug report

I have encountered a scenario where the value of a variable appears to be 'forgotten' by phpstan in a case where it ought to be known with certainty, and as a result, phpstan fails to narrow a type and so reports an incorrect error.

Code snippet that reproduces the problem

https://phpstan.org/r/f1aad144-7261-4e0b-ac2c-bba065431bcb

Expected output

No error reported by phpstan.

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Activity

  1. mind-bending-forks
    changed the title [-]Value and type of variable are forgotten in case where they ought to be known with certainty[/-] [+]Value of a variable is forgotten in case where it ought to be known with certainty[/+] on Sep 17, 2024

  2. ondrejmirtes commented on Sep 18, 2024

    @ondrejmirtes
    ondrejmirtes
    on Sep 18, 2024
    Member

    Problem simplified to: https://phpstan.org/r/d62a02ab-388d-4fb8-81c6-a246ff6d831b

    The problem lies in array_key_exists at the beginning, removing it fixes it: https://phpstan.org/r/1e120370-b233-467a-9eda-531745a0b920

  3. ondrejmirtes
    added
    bug
    on Sep 18, 2024
  4. ondrejmirtes
    added this to the Easy fixes milestone on Sep 18, 2024
  5. phpstan-bot
    added a commit that references this issue on Feb 27, 2026

    Fix array dim fetch type not reflecting narrowed variable key

    a39ffdc
  6. phpstan-bot
    added a commit that references this issue on Mar 10, 2026

    Fix phpstan/phpstan#11705: variable type forgotten for array dim fetc…

    2716e22

  7. staabm commented on Mar 12, 2026

    @staabm
    staabm
    on Mar 12, 2026
    Contributor

    the problem is that we have 2 different information for $theInput[$tag].

    in Scope we remembered $theInput[$tag] is string|array<int,string>
    while for $theInput-type we know array{name: string, owners: array<int, string>}

    see https://phpstan.org/r/4ebcaacf-37a1-4c65-ae95-a49c8fbc1cec

    I don't think we can fix this in ArrayKeyExistsFunctionTypeSpecifyingExtension because at that point we only know $tag will be 'name'|'owners'. via switch we later on narrow $tag to 'name'.

    I think the fix would be to foget the remembered expression for $theInput[$tag], as soon as $tag gets narrowed.
    that way scope-type-resolving would pickup the type from $theInput's constant array type.

    wdyt @ondrejmirtes ?

  8. phpstan-bot
    added a commit that references this issue on Mar 12, 2026

    Fix phpstan/phpstan#11705: move fix from MutatingScope to ArrayKeyExi…

    55773e6
  9. staabm
    added 2 commits that reference this issue on Mar 12, 2026

    Fix phpstan/phpstan#11705: variable type forgotten for array dim fetc…

    e3e9895

    Fix phpstan/phpstan#11705: move fix from MutatingScope to ArrayKeyExi…

    84f9914
  10. phpstan-bot
    added a commit that references this issue on Mar 12, 2026

    Fix phpstan/phpstan#11705: recompute ArrayDimFetch type in MutatingSc…

    75cffd0

  11. phpstan-bot commented on Apr 24, 2026

    @phpstan-bot
    phpstan-bot
    on Apr 24, 2026
    Contributor

    @staabm After the latest push in 2.2.x, PHPStan now reports different result with your code snippet:

    @@ @@
 $theTags (Yes): non-empty-array<int, string>
 __phpstanParameterVariableOriginalValue(theTags) (Yes): array<int, string>
 $tag (Yes): 'name'|'owners'
+__phpstanOriginalForeachValue(tag) (Yes): string
 $theInput[$tag] (Yes): array<int, string>|string
 native $theInput (Yes): non-empty-array
 native __phpstanParameterVariableOriginalValue(theInput) (Yes): array
@@ @@
 native $theTags (Yes): non-empty-array
 native __phpstanParameterVariableOriginalValue(theTags) (Yes): array
 native $tag (Yes): 'name'|'owners'
+native __phpstanOriginalForeachValue(tag) (Yes): mixed
 native $theInput[$tag] (Yes): array<int, string>|string
 18: $theInput (Yes): array{name: string, owners: array<int, string>}
 __phpstanParameterVariableOriginalValue(theInput) (Yes): array{name: string, owners: array<int, string>}
@@ @@
 $theTags (Yes): non-empty-array<int, string>
 __phpstanParameterVariableOriginalValue(theTags) (Yes): array<int, string>
 $tag (Yes): 'name'
+__phpstanOriginalForeachValue(tag) (Yes): string
 $theInput[$tag] (Yes): array<int, string>|string
 native $theInput (Yes): non-empty-array
 native __phpstanParameterVariableOriginalValue(theInput) (Yes): array
@@ @@
 native $theTags (Yes): non-empty-array
 native __phpstanParameterVariableOriginalValue(theTags) (Yes): array
 native $tag (Yes): 'name'
+native __phpstanOriginalForeachValue(tag) (Yes): mixed
 native $theInput[$tag] (Yes): array<int, string>|string
 19: Dumped type: array{name: string, owners: array<int, string>}
 20: Parameter #1 (array<int, string>|string) of echo cannot be converted to string.
    Full report
    Line Error
    15 `$theInput (Yes): array{name: string, owners: array<int, string>}__phpstanParameterVariableOriginalValue(theInput) (Yes): array{name: string, owners: array<int, string>}$theTags (Yes): non-empty-array<int, string>__phpstanParameterVariableOriginalValue(theTags) (Yes): array<int, string>$tag (Yes): 'name'
    18 `$theInput (Yes): array{name: string, owners: array<int, string>}__phpstanParameterVariableOriginalValue(theInput) (Yes): array{name: string, owners: array<int, string>}$theTags (Yes): non-empty-array<int, string>__phpstanParameterVariableOriginalValue(theTags) (Yes): array<int, string>$tag (Yes): 'name'__phpstanOriginalForeachValue(tag) (Yes): string$theInput[$tag] (Yes): array<int, string>
    19 Dumped type: array{name: string, owners: array<int, string>}
    20 `Parameter #1 (array<int, string>

  12. phpstan-bot commented on Sep 20, 2026

    @phpstan-bot
    phpstan-bot
    on Sep 20, 2026
    Contributor

    @staabm After the latest push in 2.3.x, PHPStan now reports different result with your code snippet:

    @@ @@
 $theTags (Yes): non-empty-array<int, string>
 __phpstanParameterVariableOriginalValue(theTags) (Yes): array<int, string>
 $tag (Yes): 'name'|'owners'
+__phpstanOriginalForeachValue(tag) (Yes): string
 $theInput[$tag] (Yes): array<int, string>|string
+!\array_key_exists($tag, $theInput) (Yes): false
 native $theInput (Yes): non-empty-array
 native __phpstanParameterVariableOriginalValue(theInput) (Yes): array
 native $theTags (Yes): non-empty-array
 native __phpstanParameterVariableOriginalValue(theTags) (Yes): array
 native $tag (Yes): 'name'|'owners'
+native __phpstanOriginalForeachValue(tag) (Yes): mixed
 native $theInput[$tag] (Yes): array<int, string>|string
+native !\array_key_exists($tag, $theInput) (Yes): false
 18: $theInput (Yes): array{name: string, owners: array<int, string>}
 __phpstanParameterVariableOriginalValue(theInput) (Yes): array{name: string, owners: array<int, string>}
 $theTags (Yes): non-empty-array<int, string>
 __phpstanParameterVariableOriginalValue(theTags) (Yes): array<int, string>
 $tag (Yes): 'name'
+__phpstanOriginalForeachValue(tag) (Yes): string
 $theInput[$tag] (Yes): array<int, string>|string
+!\array_key_exists($tag, $theInput) (Yes): false
 native $theInput (Yes): non-empty-array
 native __phpstanParameterVariableOriginalValue(theInput) (Yes): array
 native $theTags (Yes): non-empty-array
 native __phpstanParameterVariableOriginalValue(theTags) (Yes): array
 native $tag (Yes): 'name'
+native __phpstanOriginalForeachValue(tag) (Yes): mixed
 native $theInput[$tag] (Yes): array<int, string>|string
+native !\array_key_exists($tag, $theInput) (Yes): false
 19: Dumped type: array{name: string, owners: array<int, string>}
 20: Parameter #1 (array<int, string>|string) of echo cannot be converted to string.
    Full report
    Line Error
    15 `$theInput (Yes): array{name: string, owners: array<int, string>}__phpstanParameterVariableOriginalValue(theInput) (Yes): array{name: string, owners: array<int, string>}$theTags (Yes): non-empty-array<int, string>__phpstanParameterVariableOriginalValue(theTags) (Yes): array<int, string>$tag (Yes): 'name'
    18 `$theInput (Yes): array{name: string, owners: array<int, string>}__phpstanParameterVariableOriginalValue(theInput) (Yes): array{name: string, owners: array<int, string>}$theTags (Yes): non-empty-array<int, string>__phpstanParameterVariableOriginalValue(theTags) (Yes): array<int, string>$tag (Yes): 'name'__phpstanOriginalForeachValue(tag) (Yes): string$theInput[$tag] (Yes): array<int, string>
    19 Dumped type: array{name: string, owners: array<int, string>}
    20 `Parameter #1 (array<int, string>
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