RFE simplify usage of patched module [by Robert Scholte, from jdk-dev]

[Alex Buckley]

On 2/14/2020 9:34 PM, Christian Stein wrote:
> Assuming `--patch-module-descriptor` was already available, the
> org.astro test story would read:
> 
> - org.astro/main/module-info.java:
> 
> module org.astro {
>    exports org.astro;
>    requires java.logging;
> }
> 
> - org.astro/test/module-info.java:
> 
> open /*test*/ module org.astro /*extends main module org.astro*/ {
>    requires java.sql; // system-provided module needed by test code
>    requires org.junit.jupiter; // framework reflecting entry-points
>    requires org.assertj.core; // ...and more test-related modules
> }
> 
> A build tool now easily may detect that `--patch-module-descriptor`
> is required at test compile and run time. It could infer it from the
> same module name or simply by seeing a main and a test
> `module-info.java` compilation unit within the sources of the
> org.astro Maven-/Gradle-/pro-/Bach-/any-build-tool-"module".
> 
> Build tools could pass the following argument to javac/java
> while being in their test-scope tasks. Of course, implying that
> org.astro/test/module-info.java is the current "primary" module
> descriptor:
> 
> --patch-module-descriptor org.astro=org.astro/main/module-info.java
> 
> That's it.
> 
> The primary test-relevant modular directives are enriched by
> those of the main module as declared in org.astro/main/module-info.java
> resulting effectively in a synthetic in-module test module descriptor that
> resembles the inter-module test descriptor presented above:
> 
> - SYNTHETIC test module for org.astro
> 
> open /*test*/ module org.astro /*extends main module org.astro*/ {
>    requires java.sql; // system-provided module needed by test code
>    requires org.junit.jupiter; // framework reflecting entry-points
>    requires org.assertj.core; // ...and more test-related modules
>    //
>    exports org.astro; // patched from org.astro/main/module-info.java
>    requires java.logging; // patched from org.astro/main/module-info.java
> }

Good description of how the main module 
(org.astro/main/module-info.java) and the test module 
(org.astro/test/module-info.java) interact to form a test-scoped module. 
If a build tool has detected the presence of the test module, then the 
build tool can use javax.lang.model.element.ModuleElement to inspect the 
test module's declaration and infer what it requires, whether it's open, 
etc. Then, the build tool can enrich the main module by passing 
--add-modules, --add-reads, and --add-opens to javac/java while in a 
test scope. No need for --patch-module-descriptor in the JDK.

Alex