The ArcanistGeneratedLinter calls stopAllLinters(), which should prevent other linters from raising lint messages in generated files. Have you explicitly disabled/prevented this? Are the projects in question not using the Generated linter?

I didn't notice that. Yeah let me check.

One trick (which caught @mroch, at least) is that we made linter priority explicit some time September-ish. Before the change, we ran linters in the order you added them in the Engine. Now, each linter has an explicit priority (given by getLinterPriority()), and we sort linters by their priority instead.

This makes it easier to get things right in the common case (where you're just adding a bunch of normal linters and don't want to have to go look up their sequencing rules) but might have changed the behavior of existing Engines which relied on implicit sequencing. Similarly, if any linters have been set to a priority smaller than 0.25 explicitly, they'll run before the GeneratedLinter.

Finally, linters can sometimes raise messages in files other than the file they're linting. We might not be handling or excluding these messages correctly.