Change project style disabling from being a project load flag to a new project "capability"

[nyalldawson]

This avoids the unwanted cost of initialising a blank style database
whenever QgsProject::clear is called and project styles are not
required (eg. for server)

Hopefully fixes regression in server project load times

[nyalldawson]

Ping @dmarteau -- can you test if this fixes your server performance regression please?

[rldhont]

Thanks @nyalldawson

@dmarteau will test it

[dmarteau]

Hi, thx for the fix,

I'm trying to test the branch but I cannot figure how to pass '0' in python as capabilities value. I'm stuck with the error TypeError: QgsProject(): argument 'capabilities' has unexpected type 'int' if I try to execute QgsProject(capabilities=0)

[nyalldawson]

@dmarteau use the flags constructor

capabilities=Qgis.ProjectCapabilities()

[dmarteau]

@nyalldawson Tests are now ok,

From simple loading test I benchmarked approx 200ms for initialising QgsProject() the default flags and aroud 19ms with QgsProject(capabilities=Qgis.ProjectCapabilities()).

Benchmarks on other server tests have improved with the same ratio.

Thanks for the job !

[qgis-bot]

The backport to release-3_26 failed:

The process '/usr/bin/git' failed with exit code 1

stderr

error: could not apply fa7d424e69... Change project style disabling from being a project load flag
hint: After resolving the conflicts, mark them with
hint: "git add/rm <pathspec>", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".

stdout

Auto-merging python/core/auto_additions/qgis.py
CONFLICT (content): Merge conflict in python/core/auto_additions/qgis.py
Auto-merging python/core/auto_generated/qgis.sip.in
CONFLICT (content): Merge conflict in python/core/auto_generated/qgis.sip.in
Auto-merging src/app/browser/qgsinbuiltdataitemproviders.cpp
Auto-merging src/core/qgis.h
CONFLICT (content): Merge conflict in src/core/qgis.h

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release-3_26 release-3_26
# Navigate to the new working tree
cd .worktrees/backport-release-3_26
# Create a new branch
git switch --create backport-49266-to-release-3_26
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick fa7d424e692de536426caf719591692bb9ab769f
# Push it to GitHub
git push --set-upstream origin backport-49266-to-release-3_26
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release-3_26

Then, create a pull request where the base branch is release-3_26 and the compare/head branch is backport-49266-to-release-3_26.