Fix nlohman::json array list initializer broken on GCC

[elpaso]

the issue:

json j { something_returning_json_array_of_values() };

produces a json::array( json::array( values ) ) )

instead of json::array( values )

by using the assignment all is fine:

json j = something_returning_json_array_of_values();

produces a json::array( values ) as expected

[elpaso]

@m-kuhn I think you've already seen this this bug recently.

[m-kuhn]

Since this is a cosmetic one, can you use QStringLiteral on "features" and drop 238 in favor of qgis::as_const? ;)

[elpaso]

no literal here, it's a std::strings, ok for the as_const

[m-kuhn]

@signedav you looked into it in more detail, what do you think?

[signedav]

I confirm what @elpaso writes regarding the json.

Like the observation I made during debugging and wrote down here #30758:

Apparently { QgsJsonUtils::jsonFromVariant( value ) } returns an array containing one element and that's an object while = QgsJsonUtils::jsonFromVariant( value ) contains the object itself not nested in an array.

[elpaso]

@signedav just to be sure, which compiler are you using? Because I was not able to reproduce this on clang, but only on GCC.

[signedav]

GCC as well.

[backporting]

The backport to release-3_8 failed:

Commits ["3924625b9bd98186ec242c3541a075baeb5494e7","5549a4e397d026263cf012c1c9d7c5b998a93d49","69b1ba5c8364b578d1966bb8671e87648814abda"] could not be cherry-picked on top of release-3_8

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub.
git fetch
# Create new working tree.
git worktree add .worktrees/backport release-3_8
# Navigate to the new directory.
cd .worktrees/backport
# Cherry-pick all the commits of this pull request and resolve the likely conflicts.
git cherry-pick 3924625b9bd98186ec242c3541a075baeb5494e7 5549a4e397d026263cf012c1c9d7c5b998a93d49 69b1ba5c8364b578d1966bb8671e87648814abda
# Create a new branch with these backported commits.
git checkout -b backport-31293-to-release-3_8
# Push it to GitHub.
git push --set-upstream origin backport-31293-to-release-3_8
# Go back to the original working tree.
cd ../..
# Delete the working tree.
git worktree remove .worktrees/backport

Then, create a pull request where the base branch is release-3_8 and the compare/head branch is backport-31293-to-release-3_8.

[elpaso]

no need to backport