Add a preference to ignore the unnamed module for split packages

[jdneo]

Signed-off-by: Sheng Chen sheche@microsoft.com

Hi team! 👋

I was trying to make a draft to illustrate the idea mentioned in #415. It will be great and helpful if anyone from the team can take a look and let me know if this idea is acceptable, thanks!

What it does

Add a preference to control whether the unnamed module should be ignored when it comes to a split package.

In https://openjdk.org/projects/jigsaw/spec/sotms/#the-unnamed-module says

If a package is defined in both a named module and the unnamed module then
the package in the unnamed module is ignored. This preserves reliable configuration
even in the face of the chaos of the class path, ensuring that every module still reads
at most one module defining a given package.

How to test

Sample: test1.zip

In .settings/org.eclipse.jdt.core.prefs, if org.eclipse.jdt.core.compiler.ignoreUnnamedModuleForSplitPackage is set to enabled. After import the sample project, everything looks fine. If the preference is set to disabled, The package xxx is accessible from more than one module can be observed.

Author checklist

• I have thoroughly tested my changes
• The change is following the coding conventions
• I have signed the Eclipse Contributor Agreement (ECA)

[stephan-herrmann]

please find some nitpicks inline.

[stephan-herrmann]

We're getting closer, great!

With more diligence applied, here's the next round of comments

[jdneo]

Hi @stephan-herrmann, I've updated the PR, would you have time to take a look? :)

[stephan-herrmann]

All looks well now. Thanks!

[jdneo]

Thank you @stephan-herrmann :)

[laeubi]

@stephan-herrmann @jdneo I just came across the preference

org.eclipse.jdt.core.compiler.ignoreUnnamedModuleForSplitPackage=enabled

but it is quite hard to discover and I was not aware about this only after some google-search with a lot of unhelpful results.

Do you think it would be useful to enhance the error message with a hint to the property? e.g

The package xxx is accessible from more than one module, if you want to allow this use org.eclipse.jdt.core.compiler.ignoreUnnamedModuleForSplitPackage=enabled in your org.eclipse.jdt.core preferences.

[xnhp]

Can this option also be set when using eclipsec the Eclipse compiler but not the Eclipse IDE? For instance, IntelliJ comes with it. I've tried putting some variations in the compiler CLI arguments in IntelliJ but none were recognised.

[stephan-herrmann]

Can this option also be set when using eclipsec but not the Eclipse IDE? For instance, IntelliJ comes with eclipsec. I've tried putting some variations in the compiler CLI arguments in IntelliJ but none were recognised.

I've never heard the name "eclipsec" 😄 but ecj should understand the option via -properties <file> (haven't tried it myself, though).

[xnhp]

Thank you 🙏 It does not complain about some unknown option, but it does not seem to help with the split package error either. I think I'm having the same issue as here.

[laeubi]

@xnhp You should ask at the supportforum of your tool (IntelliJ) how to set compiler settings for the Eclipse Compiler there.

[stephan-herrmann]

public class Test {
	javax.xml.transform.Transformer transformer;
}

Here's a transcript of how to make the error appear and then disappear again:

$ ecj -23 Test.java
$ ecj -23 -classpath xml-apis-1.4.01.jar Test.java
----------
1. ERROR in /tmp/Test.java (at line 2)
        javax.xml.transform.Transformer transformer;
        ^^^^^^^^^^^^^^^^^^^
The package javax.xml.transform is accessible from more than one module: <unnamed>, java.xml
----------
1 problem (1 error)
$ cat > ecj.prefs
org.eclipse.jdt.core.compiler.ignoreUnnamedModuleForSplitPackage=enabled
^D
$ ecj -23 -classpath xml-apis-1.4.01.jar -properties ecj.prefs Test.java
$