Topic
Compiler-default changes that turn previously accepted code into build errors, and the per-declaration migration work they imply.
Polars 2.0.0 runs lazy queries on the streaming engine by default, and a left join on that engine no longer keeps row order. A dev.to author's repro shows the change raising no error and leaving every value correct.
Reality
Feodor Fitsner rebuilt Flet's internals before attaching a stable version number, so the release that arrived on September 15 is also the one that stops running the 0.28 code his users already wrote.
Reality
The release candidate keeps collect's signature and changes what its default resolves to. Group_by, joins and unpivot can now return rows in a different order, and explain() still prints the plan that was not run.
Perspective Coverage
3 publishersReality
The maintainer removed holistic "looks good" verdicts, moved planning to a separate cheap model, and left the gate closed when verification cannot run. Breaking for embedders.
Reality
A dev.to post says strictFunctionTypes goes on by default in TypeScript 6.0. If it does, the upgrade cost is per-declaration, and casting your way out swaps compile errors for crashes.
Reality