[gui] reenable fit panel testing and fix nullptr access

[ferdymercury]

This Pull request:

Changes or fixes:

initialize to null instead

Fixes #21881

Checklist:

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

[github-actions]

Test Results

    22 files      22 suites   3d 10h 11m 32s ⏱️
 3 834 tests  3 831 ✅  1 💤  2 ❌
75 673 runs  75 634 ✅ 18 💤 21 ❌

For more details on these failures, see this check.

Results for commit 522f4c3.

♻️ This comment has been updated with latest results.

[linev]

Checking of gVirtualX does not make big sense - it always present, also in batch mode

[ferdymercury]

It was null when i checked with the debugger. Note that TVirtualX::Instance can still return nullptr when on batch

[linev]

For changes in GUI classes we need ok from Bertrand @bellenot.
Can we combine this PR with enabling of gui test: #21891
Then we directly can see if our changes works/fails?

And finally we will be able to decide if such extra checks in GUI classes allows to use them in batch GUI tests.

[linev]

I checkout your branch and try to run test.
There are many issues with normal GUI mode.

1. Last two tests TestTree2D and TestTreeND do not work for me - while fit panel does not have entries like "gaus2d" or "gausND".
2. Also running test in batch possible only with root -b --web=off UnitTesting.cxx. Produced test executable crashed much earlier because TGClient::Instance() returns nullptr
3. When run inside root, one sees lot of errors about missing images.

[ferdymercury]

• Last two tests TestTree2D and TestTreeND do not work for me - while fit panel does not have entries like "gaus2d" or "gausND".

Yes, same here, I had deactivated (commented) locally those old tests for the moment and was focusing on whether it was running at all without crashing.

• Also running test in batch possible only with root -b --web=off UnitTesting.cxx. Produced test executable crashed much earlier because TGClient::Instance() returns nullptr

Weird, where? I see a different behavior on Linux. It just crashes when deleting the TGTooltip at shutdown for me.

• When run inside root, one sees lot of errors about missing images.

Same here, that's what I would say "expected", a lot of errors in batch mode of not being able to load icons, but no crashes.

[linev]

Weird, where? I see a different behavior on Linux. It just crashes when deleting the TGTooltip at shutdown for me.

I mean when I run compiled executable.

• When run inside root, one sees lot of errors about missing images.

Same here, that's what I would say "expected", a lot of errors in batch mode of not being able to load icons, but no crashes.

This is most challenging part - try to understand if there double deletion or just wrong pointer released.
Because of lot of errors I cannot exclude incomplete initialization of some GUI classes

[linev]

@ferdymercury @bellenot

I probably found the reason why it crashes.
Seems to be it is wrongly set flag TGLabel::fHasOwnFont.
In batch it is incorrect and TGLabel destructor tries to free TGGC object which does not belong to the label.

Also side problem is that in TGGC::TGGC(GCValues_t *values) constructor ref counter not always set correctly.

Fixing this two problems makes test running for me

[linev]

First step is #21907

@ferdymercury
Can you extract your changes in TASImage to separate PR.

After such two steps we will be able to enable this and may be other GUI tests in CI

[ferdymercury]

Probably these changes are no longer needed since I was trying out different things and you already found the culprit in TGGC