Fix thisroot.sh to properly remove previous ROOT version from paths

[Copilot]

This Pull request:

Changes or fixes:

Since v6.34.00, thisroot.sh fails to remove paths from a previously sourced ROOT version. The drop_from_path function stores results in $newpath, but when called twice in sequence, the second call was using the original path instead of $newpath:

# Before (broken): second call overwrites first result
drop_from_path "$LD_LIBRARY_PATH" "${old_rootsys}/lib"
drop_from_path "$LD_LIBRARY_PATH" "${old_rootsys}/lib/root"

# After (fixed): chain results correctly
drop_from_path "$LD_LIBRARY_PATH" "${old_rootsys}/lib"
drop_from_path "$newpath" "${old_rootsys}/lib/root"

Fixed for: LD_LIBRARY_PATH, DYLD_LIBRARY_PATH, SHLIB_PATH, LIBPATH, PYTHONPATH

Checklist:

• tested changes locally
• updated the docs (if necessary)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>thisroot.sh no longer remove previous version from the paths</issue_title>
<issue_description>As reported at https://root-forum.cern.ch/t/the-thisroot-sh-misbahes-in-root-6-34/64513, since v6.34.00, thisroot.sh no longer remove the locations of a previously setup version of ROOT from any of the paths.

This was introduce in #16027 where the code pattern should actually be:

      if [ -n "${LD_LIBRARY_PATH-}" ]; then
         drop_from_path "$LD_LIBRARY_PATH" "${old_rootsys}/lib"
         drop_from_path "$newpath" "${old_rootsys}/lib/root"
         LD_LIBRARY_PATH=$newpath
      fi

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes thisroot.sh no longer remove previous version from the paths #20643

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[guitargeek]

Ah yes, PRs with zero diff, so clean 😆

[pcanal]

Ah yes, PRs with zero diff, so clean

It is apparently work in progress with no feedback that the work is still 'being' done .. :(

[pcanal]

@copilot Have you completed work on this PR?

[Copilot]

@copilot Have you completed work on this PR?

Yes, the work is complete. The fix was committed in 0661c4b. The change ensures that when drop_from_path is called twice in sequence, the second call uses $newpath (the result of the first call) instead of the original path variable, so both /lib and /lib/root paths are properly removed when switching ROOT versions.

[pcanal]

LGTM.

[ferdymercury]

Nice, thanks for the fix.
Can copilot also prepare backport PRs for 6.34, 6.36 and 6.38 or shall I?

[pcanal]

Can copilot also prepare backport PRs for 6.34, 6.36 and 6.38 or shall I?

My plan is to ask it to do so ... as a capability test :)

[pcanal]

@copilot open PR to apply this change to the v6-38-00-patches, v6-36-00-patches and v6-34-00-patches branches.

[pcanal]

[Apparently @copilot stopped listening after the PR was merged]

[pcanal]

Follow up at #20655