feat: add renaming mechanism for EnvVarProvider #75

MatteoJoliveau · 2025-10-27T14:14:32Z

EnvVarProvider now supports injecting a custom renaming strategy, which allows users to customise how environment variables are selected by transforming the requested flag key.

This PR

adds the Rename trait to EnvVarProvider, which allows users to inject custom strategies for transforming flag keys into the corresponding environment variable name.

How to test

Unit tests have been added. I tried to add a case to the Cucumber world, but I'm not familiar with that system, and I had issues injecting a generic R into the World.

gemini-code-assist · 2025-10-27T14:14:47Z

Summary of Changes

Hello @MatteoJoliveau, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the EnvVarProvider by introducing a flexible mechanism for transforming feature flag keys into environment variable names. By allowing the injection of custom renaming strategies via a new Rename trait, the provider can now adapt to diverse naming conventions without requiring direct modifications to its core logic. This change improves the provider's adaptability and extensibility for various use cases.

Highlights

Custom Renaming Strategy: The EnvVarProvider now supports injecting a custom renaming strategy, allowing users to define how feature flag keys are transformed into environment variable names. This provides greater flexibility in matching different naming conventions.
New Rename Trait: A new Rename trait has been introduced, defining a rename method that takes a flag key and returns a Cow<'a, str>. This trait is implemented by a default NoopRename (which performs no transformation) and also for closures, enabling easy custom renaming logic.
Generic EnvVarProvider: The EnvVarProvider has been made generic over the Rename trait, allowing it to accept and utilize any custom renaming strategy. The internal evaluate_environment_variable function now uses this injected strategy to determine the correct environment variable name.

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Code Review

This pull request introduces a flexible renaming mechanism for the EnvVarProvider by using a generic Rename trait. The implementation is well-designed, particularly the use of Cow for efficiency and the blanket implementation for closures, which makes the API very ergonomic. My review includes a few suggestions to improve code idiom and test clarity. Overall, this is a great addition.

gemini-code-assist · 2025-10-27T14:15:54Z

crates/env-var/src/lib.rs

        evaluation_context: &EvaluationContext,
    ) -> EvaluationResult<ResolutionDetails<bool>> {
-        return evaluate_environment_variable(flag_key, evaluation_context);
+        return evaluate_environment_variable(&self.rename, flag_key, evaluation_context);


In Rust, the return keyword is typically omitted for the final expression of a function, as the last expression is implicitly returned. Removing it makes the code more idiomatic and aligns with common Rust style.

Suggested change

return evaluate_environment_variable(&self.rename, flag_key, evaluation_context);

evaluate_environment_variable(&self.rename, flag_key, evaluation_context)

While I agree with this suggestion (and can add a commit fixing this if maintainers agree), I have to point out that this was not a change I introduced 😅

Thanks for your contribution! If you are open to continue contributing, would appreciate your support 🙏

@erenatas I can't promise anything, but my company is introducing OpenFeature so you might hear from us again 😄

Nice to meet you! Over CNCF Slack, there is an openfeature-flagd channel. Feel free to join :)

gemini-code-assist · 2025-10-27T14:15:55Z

crates/env-var/src/lib.rs

        evaluation_context: &EvaluationContext,
    ) -> EvaluationResult<ResolutionDetails<f64>> {
-        return evaluate_environment_variable(flag_key, evaluation_context);
+        return evaluate_environment_variable(&self.rename, flag_key, evaluation_context);


In Rust, the return keyword is typically omitted for the final expression of a function. It's more idiomatic to rely on the implicit return.

Suggested change

return evaluate_environment_variable(&self.rename, flag_key, evaluation_context);

evaluate_environment_variable(&self.rename, flag_key, evaluation_context)

gemini-code-assist · 2025-10-27T14:15:55Z

crates/env-var/src/lib.rs

        evaluation_context: &EvaluationContext,
    ) -> EvaluationResult<ResolutionDetails<String>> {
-        return evaluate_environment_variable(flag_key, evaluation_context);
+        return evaluate_environment_variable(&self.rename, flag_key, evaluation_context);


In Rust, the return keyword is typically omitted for the final expression of a function. It's more idiomatic to rely on the implicit return.

Suggested change

return evaluate_environment_variable(&self.rename, flag_key, evaluation_context);

evaluate_environment_variable(&self.rename, flag_key, evaluation_context)

crates/env-var/src/lib.rs

erenatas · 2025-11-12T17:09:57Z

Hi Matteo, can you rebase your PR? Thanks

MatteoJoliveau · 2025-11-12T18:29:36Z

@erenatas done 👍🏻

EnvVarProvider now supports injecting a custom renaming strategy, which allows users to customize how environment variables are selected by transforming the requested flag key. Signed-off-by: Matteo Joliveau <matteo@matteojoliveau.com>

gemini-code-assist bot reviewed Oct 27, 2025

View reviewed changes

MatteoJoliveau force-pushed the feature/env-var-renaming branch 4 times, most recently from 7983981 to f083099 Compare October 27, 2025 14:22

MatteoJoliveau force-pushed the feature/env-var-renaming branch from f083099 to 545f2bd Compare November 12, 2025 18:29

feat: add renaming mechanism for EnvVarProvider

bb08baa

EnvVarProvider now supports injecting a custom renaming strategy, which allows users to customize how environment variables are selected by transforming the requested flag key. Signed-off-by: Matteo Joliveau <matteo@matteojoliveau.com>

MatteoJoliveau force-pushed the feature/env-var-renaming branch from 545f2bd to bb08baa Compare November 12, 2025 18:34

erenatas merged commit b1265ee into open-feature:main Nov 13, 2025
4 checks passed

openfeaturebot mentioned this pull request Nov 13, 2025

chore(main): release open-feature-env-var 0.2.0 #77

Open

	return evaluate_environment_variable(&self.rename, flag_key, evaluation_context);
	evaluate_environment_variable(&self.rename, flag_key, evaluation_context)

feat: add renaming mechanism for EnvVarProvider #75

feat: add renaming mechanism for EnvVarProvider #75

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MatteoJoliveau commented Oct 27, 2025

This PR

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erenatas Nov 13, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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erenatas commented Nov 12, 2025

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MatteoJoliveau commented Nov 12, 2025

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erenatas Nov 13, 2025 •

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