[ruby-core:124361] [Ruby Bug#21805] Wrong "key not found" in NoMatchingPatternKeyError when destructuring Data

25 Dec 2025

      Issue #21805 has been reported by esad (Esad Hajdarevic).

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Bug #21805: Wrong "key not found" in NoMatchingPatternKeyError when destructuring Data
https://bugs.ruby-lang.org/issues/21805

* Author: esad (Esad Hajdarevic)
* Status: Open
* ruby -v: ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [arm64-darwin24]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
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Consider

```
Foo = Data.define(:x)
Foo.new(1) => {x:, z:}
```

It raises `#<data Foo x=1>: key not found: :x (NoMatchingPatternKeyError)`

Clearly the message is misleading, as it is key :z that is missing.

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