Transitive implicit aliases do not always work with @AliasFor in merged annotations [SPR-14069]

[spring-projects-issues]

Sam Brannen opened SPR-14069 and commented

Status Quo

For the most post, transitive implicit aliases for annotation attribute overrides configured via @AliasFor work. However, I have detected a corner case that fails.

Failing Example

Given the following three annotations, if an attempt is made to look up a merged @ContextConfig annotation via AnnotatedElementUtils (e.g., using getMergedAnnotation() or findMergedAnnotation()) on an element annotated with @TransitiveImplicitAliasesContextConfig then the look up will fail with an AnnotationConfigurationException stating something similar to the following:

attribute 'value' and its alias 'locations' are declared with values of [{}] and [{test.groovy}], but only one is permitted.

If the value attribute in ImplicitAliasesContextConfig declares attribute = "locations" via @AliasFor, the code then works as expected. Thus, there is obviously a bug in the lookup mechanism for names of overridden attributes in conjunction with transitive implicit aliases.

@Retention(RetentionPolicy.RUNTIME)
@interface ContextConfig {

	@AliasFor(attribute = "locations")
	String[] value() default {};

	@AliasFor(attribute = "value")
	String[] locations() default {};

	Class<?>[] classes() default {};
}

@ContextConfig
@Retention(RetentionPolicy.RUNTIME)
@interface ImplicitAliasesContextConfig {

	@AliasFor(annotation = ContextConfig.class, attribute = "locations")
	String[] groovyScripts() default {};

	@AliasFor(annotation = ContextConfig.class, attribute = "locations")
	String[] xmlFiles() default {};

	// intentionally omitted: attribute = "locations"
	@AliasFor(annotation = ContextConfig.class)
	String[] locations() default {};

	// intentionally omitted: attribute = "locations"
	@AliasFor(annotation = ContextConfig.class)
	String[] value() default {};
}

@ImplicitAliasesContextConfig
@Retention(RetentionPolicy.RUNTIME)
@interface TransitiveImplicitAliasesContextConfig {

	@AliasFor(annotation = ImplicitAliasesContextConfig.class, attribute = "xmlFiles")
	String[] xml() default {};

	@AliasFor(annotation = ImplicitAliasesContextConfig.class, attribute = "groovyScripts")
	String[] groovy() default {};
}

Deliverables

1. Determine why the aforementioned example fails and fix the bug.
   • See TODO in AnnotatedElementUtilsTests.

---

Affects: 4.2.2

Referenced from: commits d22480b, 2153d88

[spring-projects-issues]

Sam Brannen commented

Fixed as described in GitHub commit d22480b:

Ensure all aliased attributes in target annotation are overridden

Prior to this commit, it was possible that implicit aliases and
transitive implicit aliases (configured via @AliasFor) might not be
honored in certain circumstances, in particular if implicit aliases
were declared to override different attributes within an alias pair in
the target meta-annotation.

This commit addresses this issue by ensuring that all aliased
attributes in the target meta-annotation are overridden during the
merge process in AnnotatedElementUtils.

In addition, concrete default values for attributes in a
meta-annotation declaration can now be effectively shadowed by
transitive implicit aliases in composed annotations.