Expression Completer: speedup property completion

[Lgt2x]

Cache object property list in expression completer, so it is not rebuilt for every requested index. This helps with performance when an object has a large number of properties.

Before this change, getCachedPropertyNamedList was called for every index property of the object, creating a new list every time. This had a significative impact on completion speed when the number of properties is in the thousands.

A new ExpressionCompleterModel object is created every time the expression dialog is brought up, so there should not be cache invalidation issues (feel free to confirm that).

mutable keyword is required for const-correctness.

Issues

Fix #5644 (originally opened almost 10 years ago!)

Before and After Images

On this statefile, open an expression dialog:

prop_complete.FCStd.zip

This file has an object with 10k props.

Before change (real time):

After change:

[freecad-ci-runner]

Successfully created backport PR for releases/FreeCAD-1-1:

• [Backport releases/FreeCAD-1-1] Expression Completer: speedup property completion #27182

[galou]

@Lgt2x this is great! Now that you are a completion expert, I'd like to try and implement a FreeCAD setting to switch between only listing Labels in the expression editor (but still allowing Names even if not proposed) and listing both Names and Labels (current behavior). Where should I start?

[Lgt2x]

Hey @galou , I suggest you open a dedicated issue, to get feedback from the design working group. Once the design has been validated, implementation should be pretty straightforward