fix: add ViewerComparator compatibility workaround for Outline view

[iloveeclipse]

CommonViewerComparator was introduced in Eclipse 4.39 and so Outline can't use this class on older Eclipse versions. Let use old CommonViewerSorter for compatibility with older Eclipse releases.

See eclipse-platform/eclipse.platform.ui#3621
Fixes #1515

[iloveeclipse]

@rubenporras : I have to validate the fix with older SDK, just quickly coded that without testing for now.

[travkin79]

I've created a target platform for Eclipse 4.38 and LSP4E (unfortunately, GitHub doesn't accept *.target files, so I added the code below). @iloveeclipse, your code doesn't compile using that target since org.eclipse.ui.navigator.CommonViewerComparator cannot be resolved.

target-platform-438.target

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<?pde version="3.8"?>
<target name="LSP4E Target-platform Eclipse 4.38">
  <locations>
    <location includeAllPlatforms="false" includeConfigurePhase="false" includeMode="planner" includeSource="true" type="InstallableUnit">
      <unit id="org.eclipse.lsp4j" version="0.0.0"/>
      <unit id="org.eclipse.lsp4j.jsonrpc" version="0.0.0"/>
      <unit id="org.eclipse.lsp4j.debug" version="0.0.0"/>
      <unit id="org.eclipse.lsp4j.jsonrpc.debug" version="0.0.0"/>
      <unit id="com.google.gson" version="0.0.0"/>
      <repository location="https://download.eclipse.org/lsp4j/updates/releases/1.0.0/"/>
    </location>
    <location includeAllPlatforms="false" includeConfigurePhase="false" includeMode="planner" includeSource="true" type="InstallableUnit">
      <unit id="org.eclipse.sdk.ide" version="0.0.0"/>
      <repository location="https://download.eclipse.org/releases/2025-12/"/>
    </location>
    <location includeAllPlatforms="false" includeConfigurePhase="false" includeMode="planner" includeSource="true" type="InstallableUnit">
      <unit id="org.eclipse.ui.tests.harness" version="0.0.0"/>
      <repository location="https://download.eclipse.org/eclipse/updates/4.38/"/>
    </location>
    <location includeAllPlatforms="false" includeConfigurePhase="false" includeMode="planner" includeSource="true" type="InstallableUnit">
      <repository location="https://download.eclipse.org/tools/orbit/simrel/orbit-aggregation/2025-12/"/>
      <unit id="org.commonmark" version="0.0.0"/>
      <unit id="org.commonmark.ext-gfm-tables" version="0.0.0"/>
      <unit id="com.google.guava" version="0.0.0"/>
      <unit id="com.google.guava.failureaccess" version="0.0.0"/>
    </location>
    <location includeAllPlatforms="false" includeConfigurePhase="false" includeMode="planner" includeSource="true" type="InstallableUnit">
      <unit id="org.eclipse.tm4e.feature.feature.group" version="0.0.0"/>
      <repository location="https://download.eclipse.org/tm4e/releases/0.17.2/"/>
    </location>
    <location includeDependencyDepth="none" includeDependencyScopes="compile" missingManifest="error" type="Maven">
      <dependencies>
        <dependency>
          <groupId>com.vegardit.no-npe</groupId>
          <artifactId>no-npe-eea-all</artifactId>
          <version>1.3.9</version>
          <type>jar</type>
        </dependency>
      </dependencies>
    </location>
  </locations>
  <targetJRE path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-21"/>
</target>

[iloveeclipse]

your code doesn't compile using that target since org.eclipse.ui.navigator.CommonViewerComparator cannot be resolved

Sure, it is a workaround, but it compiles with current lsp4e target (whatever it is). The point is, it should work at runtime but not force lsp4e to change the target (for now). Whatever lsp4e decides regarding target handling is not part of this change / ticket.

[travkin79]

@iloveeclipse, what I mean is, it doesn't work with Eclipse 4.38. I created an Eclipse 4.38 target to check your work-around and it doesn't work (doesn't compile), since the class CommonViewerComparator is not available in Eclipse 4.38.

If we just roll back the original PR #1512, the code compiles / works with Eclipse 4.38 and with Eclipse 4.39 (the current LSP4E target).

[iloveeclipse]

If we just roll back the original PR #1512, the code compiles / works with Eclipse 4.38 and with Eclipse 4.39 (the current LSP4E target).

That is clear, but this is not my goal here, because it will cause troubles later once the CommonViewerSorter code will be removed from platform.

[travkin79]

Ok, now I understand your approach. You still compile against Eclipse 4.39 (having CommonViewerComparator) and if someone using an older Eclipse version gets a NoClassDefFoundError, you catch that and fall back to CommonViewerSorter. So in that case it's ok that the code doesn't compile with Eclipse 4.38 (for now).

[iloveeclipse]

Unfortunately current fix doesn't work. I still see the same error, looks like the class name is stored in the constant pool of the class even if it is only used in the method. I will try to provide something better.

[iloveeclipse]

Unfortunately current fix doesn't work.

Something strange happens here. In Eclipse patches work, but binaries produced by lsp4e Jenkins build don't work, looks like different compiler settings. This makes testing extremely hard...

[iloveeclipse]

Finally, last build works on 4.38.

[rubenporras]

Hi @iloveeclipse ,

thank you for the work. I will merge and do a new release.