poc: embed nb-javac compiler into the javac plugin

[robstryker]

No description provided.

[datho7561]

Something's up, the CI job isn't finishing in the usual amount of time.

[robstryker]

● nb-javac Shading Project Report

Work Completed

Successfully created a Maven-based shading solution for nb-javac to prevent OSGi/Equinox classloader conflicts
in Eclipse extensions. The repository at https://github.com/nb-javac-shaded/nb-javac-shaded publishes two shaded
artifacts via JitPack.

Shading Implementation

Complete package relocation of all nb-javac classes to shaded.* prefix:

• com.sun.tools.* → shaded.com.sun.tools.*
• com.sun.source.* → shaded.com.sun.source.*
• javax.annotation.processing.* → shaded.javax.annotation.processing.*
• javax.lang.* → shaded.javax.lang.*
• javax.tools.* → shaded.javax.tools.*

Multi-release JAR support - Critical discovery and fix:

• Maven Shade plugin rewrites bytecode in META-INF/versions/* but doesn't relocate directory structure
• Created relocate-mrjar-classes.sh post-processing script to move versioned classes from
  META-INF/versions//com/sun/tools/ to META-INF/versions//shaded/com/sun/tools/
• Preserves Java 16+ language features (records, sealed classes, pattern matching) - 691 versioned classes
  properly relocated
• Without this fix, JVM would fail to load Java 16+ optimized classes due to path/package mismatch

Service file transformation:

• Added ServicesResourceTransformer to relocate META-INF/services/ entries
• Both filenames and contents updated: javax.tools.JavaCompiler → shaded.javax.tools.JavaCompiler
• Enables ServiceLoader to find services using shaded package names

Source JAR generation for IDE debugging:

• Enabled createSourcesJar=true and shadeSourcesContent=true in Maven Shade plugin
• Created relocate-source-dirs.sh to reorganize source directories (Maven Shade rewrites package declarations
  but not directory structure)
• Flattened OpenJDK module structure (src/MODULE/share/classes/* → direct package paths) for IDE compatibility
• Preserved nbjavac package sources: nb-javac stores these in OpenJDK directory structure but with package
  nbjavac; declarations - script now extracts from make/ and relocates files based on package declarations
• Final structure: shaded/com/sun/tools/javac/Main.java with package shaded.com.sun.tools.javac; - directories
  and package declarations perfectly aligned

Build hygiene:

• Changed sources dependency scope from compile to provided to prevent source files being bundled into main JARs
• Aligned Maven version with Git tag (jdk-26-35 using dashes, not plus signs, for JitPack compatibility)

Outstanding Issue: DocLint Service Loading

Problem Statement

Eclipse plugin cannot receive JCDiagnostic objects for Javadoc validation. The root cause is that DocLint
service lookup fails when using shaded nb-javac JARs.

Technical Details

Current behavior:

• nb-javac contains com.sun.tools.doclint.DocLint (interface) and DocLint$NoDocLint (fallback implementation)
• We shaded these to shaded.com.sun.tools.doclint.DocLint
• nb-javac code calls: ServiceLoader.load(DocLint.class, ClassLoader.getSystemClassLoader())
• After shading, this becomes: ServiceLoader.load(shaded.com.sun.tools.doclint.DocLint.class, ...)
• ServiceLoader looks for providers of shaded.com.sun.tools.doclint.DocLint
• But the JDK's jdk.javadoc module provides com.sun.tools.doclint.DocLint (unshaded)
• Mismatch → service not found → falls back to NoDocLint → no Javadoc diagnostics

Challenges Preventing Resolution

Option 1: Exclude DocLint from shading

• Keep com.sun.tools.doclint.* at original package name
• Problem: Recreates the original ClassCastException issue
  • Eclipse/Equinox might load DocLint from system JDK's javadoc module (via parent classloader)
  • Plugin bundles its own version from nb-javac JAR
  • When types are loaded by different classloaders: ClassCastException
  • This is the exact problem shading was meant to solve

Option 2: Programmatic service registration (adapter pattern)

• Create adapter in Eclipse plugin: implements shaded.com.sun.tools.doclint.DocLint, delegates to unshaded JDK
  version
• Register adapter as service provider for shaded interface
• Problem: ServiceLoader limitations
  • No runtime API to register services programmatically
  • Would need META-INF/services/shaded.com.sun.tools.doclint.DocLint in plugin JAR
  • nb-javac code uses ClassLoader.getSystemClassLoader() which won't see plugin's services
  • Would require modifying nb-javac to accept different classloader (defeats purpose of using upstream
    nb-javac)

Option 3: OSGi Import-Package control

• Keep com.sun.tools.doclint unshaded
• Configure Eclipse bundle to NOT import com.sun.tools.doclint from system
• Force bundle classloader to load it locally from nb-javac JAR
• Unknown: Whether Eclipse/Equinox allows preventing system JDK package imports for com.sun.tools.* packages
  • Need to investigate Equinox classloader delegation rules for JDK-internal packages
  • May require specific OSGi framework properties or bundle manifest configuration
• Risk: May still hit parent classloader delegation depending on Equinox configuration

Open Questions

1. Can Eclipse/Equinox be configured to prevent loading com.sun.tools.doclint.* from the system classloader?
2. Is the DocLint interface in nb-javac identical to the JDK's javadoc module version (would help assess safety
   of Option 1)?
3. What is the actual classloader hierarchy in the Eclipse plugin when nb-javac code executes?
4. Does Equinox have boot delegation rules that force certain com.sun.* packages to load from the system?

[robstryker]

We are down to 20 regressions, which is pretty solid.

364a365
> org.eclipse.jdt.core.tests.javac.RegressionTests testlombok
515,516d515
< org.eclipse.jdt.ui.tests.quickfix.AssistQuickFixTest15 testConcatToTextBlock7
< org.eclipse.jdt.ui.tests.quickfix.AssistQuickFixTest15 testNoConcatToTextBlock8
528,531d526
< org.eclipse.jdt.ui.tests.quickfix.AssistQuickFixTest1d8 testConvertToLambda15
< org.eclipse.jdt.ui.tests.quickfix.AssistQuickFixTest1d8 testConvertToLambda31
< org.eclipse.jdt.ui.tests.quickfix.AssistQuickFixTest1d8 testNoRedundantNonNullInConvertIterableForLoop
< org.eclipse.jdt.ui.tests.quickfix.AssistQuickFixTest21 testDoNotConvertPatternInstanceofToSwitch1
589d583
< org.eclipse.jdt.ui.tests.quickfix.ConvertIterableLoopQuickFixTest testWrongIteratorMethod_bug411588
608d601
< org.eclipse.jdt.ui.tests.quickfix.JavadocQuickFixTest9 testMissingModuleComment
640d632
< org.eclipse.jdt.ui.tests.quickfix.LocalCorrectionsQuickFixTest testCastMissingInFieldDecl
664,665d655
< org.eclipse.jdt.ui.tests.quickfix.LocalCorrectionsQuickFixTest testTypeParametersToRawTypeReference09
< org.eclipse.jdt.ui.tests.quickfix.LocalCorrectionsQuickFixTest testUncaughtException
667d656
< org.eclipse.jdt.ui.tests.quickfix.LocalCorrectionsQuickFixTest testUncaughtExceptionOnSuper1
670d658
< org.eclipse.jdt.ui.tests.quickfix.LocalCorrectionsQuickFixTest testUnimplementedMethodsExtendingGenericType1
790d777
< org.eclipse.jdt.ui.tests.quickfix.NullAnnotationsQuickFixTest1d8 testBug531511_unconfigurable_decl
844d830
< org.eclipse.jdt.ui.tests.quickfix.NullAnnotationsQuickFixTest testRemoveRedundantAnnotation6
848d833
< org.eclipse.jdt.ui.tests.quickfix.QuickFixTest14 testAddDefaultCaseSwitchStatement1
853d837
< org.eclipse.jdt.ui.tests.quickfix.QuickFixTest15 testTextBlockGetNeedHigherComplianceProposal
858a843
> org.eclipse.jdt.ui.tests.quickfix.QuickFixTest17 testAddSealedAsDirectSuperTypeProposal1
883d867
< org.eclipse.jdt.ui.tests.quickfix.QuickFixTest22 testRenameToUnnamedProposal5
970,971d953
< org.eclipse.jdt.ui.tests.quickfix.UnresolvedMethodsQuickFixTest testMethodAssignedToWildcard2
< org.eclipse.jdt.ui.tests.quickfix.UnresolvedMethodsQuickFixTest testMethodInAnonymousCovering3
975d956
< org.eclipse.jdt.ui.tests.quickfix.UnresolvedMethodsQuickFixTest testSuperMethodInvocation
984d964
< org.eclipse.jdt.ui.tests.quickfix.UnresolvedVariablesQuickFixTest testVarInConstructurInvocation

[datho7561]

If it's built locally it should be installed locally as well, so it won't need to be set up as a repo I think?