ab93feae3f
This PR was merged into the 3.3-dev branch.
Discussion
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[BC BREAK][DI] Always autowire "by id" instead of using reflection against all existing services
| Q | A
| ------------- | ---
| Branch? | 3.3
| Bug fix? | no
| New feature? | yes
| BC breaks? | yes - compile time only
| Deprecations? | no
| Tests pass? | yes
| Fixed tickets | -
| License | MIT
| Doc PR | -
(patch best reviewed [ignoring whitespaces](https://github.com/symfony/symfony/pull/22295/files?w=1).)
"By-id" autowiring, as introduced in #22060 is free from all the issues that "by-type" autowiring has:
- it has no magic and requires explicit type<>id matching (*vs* using reflection on all services to cherry-pick *the* one that matches some type-hint *at that time*, which is fragile)
- it is free from any ambiguities (*vs* the Damocles' sword of breaking config just by enabling some unrelated bundle)
- it is easily introspected: just look at DI config files (*vs* inspecting the type-hierarchy of all services + their type-hints)
- ~~it is side-effect free, thus plain predictable (*vs* auto-registration of discovered types as services)~~
- it plays nice with deprecated services or classes (see #22282)
- *etc.*
Another consideration is that any "by-type" autowired configuration is either broken (because of future ambiguities) - or equivalent to a "by-id" configuration (because resolving ambiguities *means* adding explicit type<>id mappings.) For theoreticians, we could say that "by-id" autowiring is the asymptotic limit of "by-type" autowiring :-)
For all these reasons - and also because it reduces the complexity of the code base - I propose to change the behavior and only support "by-id" autowiring in 3.3. This will break some configurations relying on "by-type" autowiring. Yet the break will only happen at compile-time, which means this won't *silently* break any apps. For all core Symfony services, they will work out of the box thanks to #22098 *et al.* For the remaining services, fixing ones config should be pretty straightforward: just follow the suggestions provided by the exception messages. If they are fine to you, you'll end up with the exact same config in the end. And maybe you'll spot issues that were hidden previously.
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