On 1/19/2024 5:02 AM, Tomas Langer wrote:
Helidon currently has around 300 modules with module-info.java. In
general, this has improved our module structure and design.
Yet, we are now encountering some major issues related to extensibility.
I will put down a few points that are problematic, and explain each in
detail further in the e-mail (it is quite long, sorry about that).
1. provider implementations cannot be code generated without major problems
Annotation processing is designed to avoid mutating the elements, so it
would be a fundamental change to allow mutation of module elements in
the annotation processing API. It's on the framework to post-process
module-info.class so it has `provides` clauses. The framework can use
the ClassFile API to do this.
It's not "weird" for a framework to modify module-info.class to ensure
that code in the module has the right execution environment. Another
example would be a tool that injects calls to a logging API into user
code, then has to post-process module-info.class to add `requires
logging.lib;`.
2. the provider interface module MUST be on module path, even if it
could have `requires static`
Relaxing module resolution to allow a module to `provides` an interface
that it can't access is do-able, but the implications are unknown. It
would be unfortunate if resolution succeeded but then unforeseen
exceptions occur when faraway code tries to access the missing
interface. We'll leave JDK-8299504 open for now, but we would need
evidence that a large number of users are finding the current rules
unworkable before actively looking at `provides` again.
3. the provider implementation must be public with public constructor
4. duality of definition between module path and class path
These requests for ServiceLoader to (i) support package-private
providers and (ii) inspect module-info.class files for `provides`
clauses in JARs on the classpath both stem from insisting that modular
JARs can be deployed on the classpath without losing functionality. This
is a net-new requirement on the module system. It's relatively low risk,
but also low reward, so we aren't going to investigate it further.
Alex
