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https://issues.apache.org/jira/browse/MCOMPILER-510?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17780799#comment-17780799
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Artem K. commented on MCOMPILER-510:
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Ok, I will need a few days to get organized for the ticket about the warning.
However, in the meantime I discovered another issue which I think would be
considered part of this fix. The pull request addressed the initialization of
`pathElements` in `CompilerMojo`. The same initialization is missing from
`TestCompilerMojo`. So with the latest nightly, I can use the patch module for
the compiling of the main classes but not of the test classes. It still
produces a `NullPointerException`.
> NullPointerException when using --patch-module compiler argument
> ----------------------------------------------------------------
>
> Key: MCOMPILER-510
> URL: https://issues.apache.org/jira/browse/MCOMPILER-510
> Project: Maven Compiler Plugin
> Issue Type: Bug
> Affects Versions: 3.10.1
> Reporter: Artem K.
> Priority: Major
> Attachments: poc.zip
>
>
> h2. Summary
> When using {{--patch-module}} compiler argument, there is a
> {{NullPointerException}} due to field {{pathElements}} not being initialized
> in {{{}CompilerMojo{}}}.
> h2. Description
> The method {{preparePaths}} in {{CompilerMojo}} has two code paths:
> {code:java}
> @Override
> protected void preparePaths( Set<File> sourceFiles )
> {
> boolean hasModuleDescriptor = false;
> // ...
> if ( hasModuleDescriptor )
> {
> modulepathElements = new ArrayList<>( compilePath.size() );
> classpathElements = new ArrayList<>( compilePath.size() );
> pathElements = new LinkedHashMap<>( compilePath.size() );
> }
> else
> {
> classpathElements = new ArrayList<>();
> modulepathElements = Collections.emptyList();
> // ...
> }
> }{code}
> Notice that in the else part, {{pathElements}} is not initialized. This field
> is used when the compiler arguments contain {{--patch-module}} switch. So
> whenever the compiler is used with this switch and there is no module
> descriptor in the project, NPE occurs.
> h2. Proof-of-concept
> Attached is a simple proof-of-concept to illustrate the issue. The project
> consists of a single class with raises {{NullPointerException}} using a new
> constructor {{{}NullPointerException(Throwable){}}}, which does not exist in
> base JDK.
> * When executing {{{}javac{}}}{{{{}} src\main\java\poc\Main.java{}}}, the
> compilation fails as expected.
> * Using a replacement {{NullPointerException}} class in {{java_base.jar}}
> with the added constructor, the compilation works fine:{{{{}} javac
> --patch-module java.base=java_base.jar src\main\java\poc\Main.java{}}}.
> * Attempting to do the same using Maven compiler plugin results in
> NullPointerException: {{mvn -X compile}}
> h2. Walkaround
> I was able to fix the problem by adding the line
> {code:java}
> pathElements = Collections.emptyMap(); {code}
> to the else part of the {{{}CompilerMojo.preparePaths{}}}.
> The compilation started working, it does however produce a warning
> {noformat}
> [WARNING] Can't locate java_base.jar{noformat}
> every single time. I did not investigate much the cause of this message.
> Also note that while similar, this issues is not the same as MCOMPILER-311.
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