Make localeResolver overridable via @ConditionalOnMissingBean

[codeconsole]

What

I18nAutoConfiguration.localeResolver() registers the localeResolver bean unconditionally. As a result, an application-supplied LocaleResolver overrides the framework default — a bean-definition override warning on startup by default, and a hard startup failure when spring.main.allow-bean-definition-overriding=false.

This adds @ConditionalOnMissingBean(name = "localeResolver") so the Grails default backs off cleanly when the application already defines one. This mirrors Spring Boot's own WebMvcAutoConfiguration.localeResolver(), which is @ConditionalOnMissingBean for exactly this reason — registering it unconditionally is the divergence.

@Bean(DispatcherServlet.LOCALE_RESOLVER_BEAN_NAME)
@ConditionalOnMissingBean(name = DispatcherServlet.LOCALE_RESOLVER_BEAN_NAME)
public LocaleResolver localeResolver() {
    return new SessionLocaleResolver();
}

Scope — what this covers

@ConditionalOnMissingBean is evaluated during auto-configuration, so it lets the Grails default back off in favor of a localeResolver bean that is already present at that point:

• an application @Bean localeResolver (user @Configuration is processed before auto-configuration),
• an @Imported configuration, or
• another auto-configuration ordered @AutoConfigureBefore grails-i18n.

It does not affect beans contributed after auto-configuration — e.g. a Grails plugin's doWithSpring, which is registered later and still overrides via the normal override mechanism. Silencing that case additionally requires the contributor to register its resolver during auto-config (e.g. an @AutoConfigureBefore(I18nAutoConfiguration) class) so this condition can see it and back off. This PR is the upstream half that makes such a clean backoff possible.

Behavior for a plain app (no competing localeResolver) is unchanged: the condition passes and the Grails default registers as before.

Why keyed on the name, not the type

DispatcherServlet resolves the locale resolver by the fixed bean name DispatcherServlet.LOCALE_RESOLVER_BEAN_NAME ("localeResolver"). A LocaleResolver bean registered under a different name is never the one actually used, so keying the condition on the bean name matches the real lookup semantics — a by-type condition could back off for an unrelated resolver bean that DispatcherServlet ignores.

Note

The sibling beans in the same class (localeChangeInterceptor, messageSource) are also registered unconditionally; this PR is intentionally scoped to localeResolver only. Happy to extend if maintainers prefer.

[testlens-app]

🚨 TestLens detected 5 failed tests 🚨

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1. Inspect the test failures carefully.
2. If you are convinced that some of the tests are flaky, you can mute them below.
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Test Summary

CI - Groovy Joint Validation Build / build_grails > :grails-test-examples-app1:integrationTest

Test	Runs
BookFunctionalSpec > Test that switching language results in correct encodings	❌

CI - Groovy Joint Validation Build / build_grails > :grails-test-examples-scaffolding:integrationTest

Test	Runs
UserControllerSpec > User list	❌

CI / Functional Tests (Java 21, indy=false) > :grails-test-examples-app1:integrationTest

Test	Runs
BookFunctionalSpec > Test that switching language results in correct encodings	❌

CI / Functional Tests (Java 21, indy=true) > :grails-test-examples-app1:integrationTest

Test	Runs
BookFunctionalSpec > Test that switching language results in correct encodings	❌

CI / Functional Tests (Java 25, indy=false) > :grails-test-examples-app1:integrationTest

Test	Runs
BookFunctionalSpec > Test that switching language results in correct encodings	❌

🏷️ Commit: dbee13e
▶️ Tests: 42030 executed
⚪️ Checks: 44/44 completed

Test Failures

BookFunctionalSpec > Test that switching language results in correct encodings (:grails-test-examples-app1:integrationTest in CI / Functional Tests (Java 21, indy=false))

Condition not satisfied:

page.createButton.text() == 'Book anlegen'
|    |            |      |
|    |            |      false
|    |            |      11 differences (8% similarity)
|    |            |      (New-) (Book---)
|    |            |      (Book) (anlegen)
|    |            New Book
|    functionaltests.pages.BookShowPage -> createButton: geb.navigator.DefaultNavigator
functionaltests.pages.BookShowPage

	at functionaltests.BookFunctionalSpec.Test that switching language results in correct encodings(BookFunctionalSpec.groovy:48)

expected	actual
Book anlegen	New Book

BookFunctionalSpec > Test that switching language results in correct encodings (:grails-test-examples-app1:integrationTest in CI / Functional Tests (Java 21, indy=true))

Condition not satisfied:

page.createButton.text() == 'Book anlegen'
|    |            |      |
|    |            |      false
|    |            |      11 differences (8% similarity)
|    |            |      (New-) (Book---)
|    |            |      (Book) (anlegen)
|    |            New Book
|    functionaltests.pages.BookShowPage -> createButton: geb.navigator.DefaultNavigator
functionaltests.pages.BookShowPage

	at functionaltests.BookFunctionalSpec.Test that switching language results in correct encodings(BookFunctionalSpec.groovy:48)

expected	actual
Book anlegen	New Book

BookFunctionalSpec > Test that switching language results in correct encodings (:grails-test-examples-app1:integrationTest in CI / Functional Tests (Java 25, indy=false))

Condition not satisfied:

page.createButton.text() == 'Book anlegen'
|    |            |      |
|    |            |      false
|    |            |      11 differences (8% similarity)
|    |            |      (New-) (Book---)
|    |            |      (Book) (anlegen)
|    |            New Book
|    functionaltests.pages.BookShowPage -> createButton: geb.navigator.DefaultNavigator
functionaltests.pages.BookShowPage

	at functionaltests.BookFunctionalSpec.Test that switching language results in correct encodings(BookFunctionalSpec.groovy:48)

expected	actual
Book anlegen	New Book

BookFunctionalSpec > Test that switching language results in correct encodings (:grails-test-examples-app1:integrationTest in CI - Groovy Joint Validation Build / build_grails)

Condition not satisfied:

page.createButton.text() == 'Book anlegen'
|    |            |      |
|    |            |      false
|    |            |      11 differences (8% similarity)
|    |            |      (New-) (Book---)
|    |            |      (Book) (anlegen)
|    |            New Book
|    functionaltests.pages.BookShowPage -> createButton: geb.navigator.DefaultNavigator
functionaltests.pages.BookShowPage

	at functionaltests.BookFunctionalSpec.Test that switching language results in correct encodings(BookFunctionalSpec.groovy:48)

expected	actual
Book anlegen	New Book

UserControllerSpec > User list (:grails-test-examples-scaffolding:integrationTest in CI - Groovy Joint Validation Build / build_grails)

geb.waiting.WaitTimeoutException: condition did not pass in 30 seconds (failed with exception)
	at geb.waiting.Wait.waitFor(Wait.groovy:128)
	at geb.waiting.DefaultWaitingSupport.doWaitFor(DefaultWaitingSupport.groovy:55)
	at geb.waiting.DefaultWaitingSupport.waitFor(DefaultWaitingSupport.groovy:45)
	at geb.Page.waitFor(Page.groovy:120)
	at com.example.pages.LoginPage.login(LoginPage.groovy:39)
	at com.example.UserControllerSpec.setup(UserControllerSpec.groovy:33)
Caused by: Assertion failed: 

title != pageTitle
|     |  |
|     |  'Please sign in'
|     false
'Please sign in'

	at com.example.pages.LoginPage.login_closure1(LoginPage.groovy:39)
	at com.example.pages.LoginPage.login_closure1(LoginPage.groovy)
	at geb.waiting.Wait.waitFor(Wait.groovy:117)
	... 5 more

Muted Tests

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• BookFunctionalSpec > Test that switching language results in correct encodings
• UserControllerSpec > User list

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