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Fix Dagger multibinding duplicate tracking for Maps #5167

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copybara-service merged 1 commit into from
May 14, 2026
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Fix Dagger multibinding duplicate tracking for Maps #5167

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17 changes: 17 additions & 0 deletions dev-guide/compiler-options.md
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Expand Up @@ -170,6 +170,23 @@ especially true when dealing with Kotlin sources, where wildcards must be
interpreted indirectly from a number of factors other than the explicit variance
at the use site.

## Detect duplicate map multibinding contributions across component boundaries {#map-multibinding-duplicate-detection-fix}

The `dagger.mapMultibindingDuplicateDetectionFix` flag fixes a bug in Dagger
where duplicate multibinding map keys were allowed in certain situations.
When the flag is enabled Dagger should enforce strict duplicate checking of map
multibinding contributions (e.g., identical `@IntoMap` bindings) across
component boundaries.

By default, this flag is disabled, meaning Dagger preserves the legacy lenient
behavior and ignores duplicate map key contributions across component
boundaries.

To opt-in to strict duplicate detection at compile time (for Maps), enable the
flag by passing the following compiler option:

`-Adagger.mapMultibindingDuplicateDetectionFix=ENABLED`

<!-- References -->

[`@Component`]: https://dagger.dev/api/latest/dagger/Component.html
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