fix: Restore case-insensitive search in File Open for PySide2 with QtCore5

[kikeda-falcons]

Summary

Restores case-insensitive search behavior in the File Open dialog when running under PySide2 with Qt5 (e.g., Maya 2022).

This resolves Issue #173.

The fix corrects version detection and aligns regex construction with the appropriate Qt API for each major version.

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Problem

Case-insensitive search stopped working in Maya environments that ship with PySide2 + Qt5. Filters behaved inconsistently depending on the Qt binding, particularly under newer Maya versions.

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Root Cause

The regex creation logic attempted to infer API behavior by checking for the presence of QtCore.QRegularExpression.

This approach is unreliable because:

• QRegularExpression exists in Qt5, but its flag handling differs from Qt6.
• Qt6 removed QRegExp entirely and reorganized QRegularExpression flag enums.
• The previous implementation did not properly distinguish between Qt major versions, leading to incorrect case-insensitivity handling.

As documented in Qt 5.15 (QRegularExpression API reference), Qt5 exposes QRegularExpression and its flag enums via QtCore, but its behavior and preferred usage differ from Qt6.

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Solution

Use the Qt major version to determine which regex API to construct, instead of checking for attribute existence.

• Qt5

  • Prefer QRegExp
  • Use FixedString syntax
  • Apply Qt.CaseInsensitive
  • Treat patterns as literal strings (not regex)

• Qt6+

  • Use QRegularExpression
  • Apply CaseInsensitiveOption via setPatternOptions
  • Align with Qt6-only API surface (no QRegExp)

This makes the behavior explicit, version-correct, and stable across Maya 2022–2026.

---

Changes

• Replace attribute-based detection with Qt major version check
• Normalize regex construction logic per Qt version
• Add inline documentation explaining Qt5 vs Qt6 differences

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 32.38%. Comparing base (195a0f1) to head (c96184f).

Files with missing lines	Patch %	Lines
python/tk_multi_workfiles/util.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #174      +/-   ##
==========================================
+ Coverage   32.36%   32.38%   +0.01%     
==========================================
  Files          68       68              
  Lines        7671     7671              
==========================================
+ Hits         2483     2484       +1     
+ Misses       5188     5187       -1     

Flag	Coverage Δ
Linux	32.38% <75.00%> (+0.01%)	⬆️
Python-3.10	?
Python-3.11	32.38% <75.00%> (+<0.01%)	⬆️
Python-3.13	32.36% <75.00%> (+<0.01%)	⬆️
Python-3.9	?
Windows	19.27% <75.00%> (+0.01%)	⬆️
macOS	32.36% <75.00%> (ø)

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