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Duplicate @Bean name inspection is silent when overriding is allowed but Spring silently drops one method #698
Description
Summary
With spring.main.allow-bean-definition-overriding=true, the duplicate @Bean name inspection reports nothing for two @Bean methods that declare the same bean name. Spring does not fail there, but it does not use both methods either: it registers one of them and silently never calls the other. The ignored method is dead code that looks like a working bean factory, and which one is ignored changes between Spring Framework versions.
Where (public/main 7d9574f)
modules/spring-core/src/main/kotlin/com/explyt/spring/core/inspections/SpringDuplicateBeanNameInspection.kt:36: checkClass returns null when overridingOf (:55-64) answers Overriding.ALLOWED for a known true value of spring.main.allow-bean-definition-overriding (ALLOW_OVERRIDING_KEY, :90). The same applies on the open stack #692 (#686) → #695 (#689), where the verdict is decided per collision but overriding allowed still yields no problem outside the Spring 7 rule.
What Spring does (probes on real spring-context jars, AnnotationConfigApplicationContext, overriding allowed)
| Pair | 5.3.31 / 6.0.11 / 6.1.13 | 6.2.0 | 6.2.1+ | 7.0.9 |
|---|---|---|---|---|
one class: @Bean A a() + @Bean("a") A b() |
starts, bean a from b(), a() never called |
starts, bean a from a(), b() never called |
starts, bean a from b() |
fails for a full @Configuration (#686) |
hierarchy: base @Bean a() + subclass @Bean("a") b() |
subclass method kept | base method kept | subclass method kept | fails for a full @Configuration |
lite class (@Component with @Bean methods) |
b() kept |
a() kept |
b() kept |
starts |
name is the primary name of one method and an alias of the other, @Bean({"a","svc"}) x() + @Bean("svc") y() |
5.3.31: only x() runs (both declaration orders); 6.0.11, 6.1.13: both run, svc points to y() |
both run | (not probed) | x() declared first: both run; y() declared first: only x() runs |
So for a pair of primary names the app starts and exactly one method is dropped, and the dropped method is not predictable from the source (6.2.0 drops the other one than 6.1 and 6.2.1). For a primary name that is also another method's alias, Spring 5.3 and 7.0 can drop one method depending on the declaration order, while 6.0–6.2 keep both and only move the alias.
Proposal
When overriding is allowed and the collision is between primary names (the first declared @Bean name, else the method name, of both methods), report a weak warning on the second method: "Bean ''a'' is also declared by ''…''; Spring registers only one of the two methods and never calls the other". Do not name the kept method. For a primary name that is another method's alias, use a hedged wording ("may never call") on versions where the probe shows a dropped method (before 6.0, and 7.x), and probe 6.2.1+ first. Skip it where #686 already reports an error (Spring 7, full @Configuration with enforceUniqueMethods, primary names).
Activity
test: Pin duplicate @bean names Spring silently drops with overriding…
test: Expect the overriding-allowed warning where Spring drops a @bean …
fix: Warn about a duplicate @bean name whose method Spring drops when…
test: Cover overriding-allowed duplicate @bean name branches (#698)
test: Name the overriding-allowed tests after the warning they expect (…
docs: State every case of the overriding-allowed duplicate @bean warn…
fix: Warn about a duplicate @bean name whose method Spring drops when…