Artem K. created MCOMPILER-510:
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Summary: 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.
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=test.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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