MGS4010: target keys on a file its own run generates

A target finished successfully and magus did not cache it. A file its key read changed while it ran, and that file is a declared output: something in the target's own run generated it after the key was taken.

[MGS4010] .:test is never cached: its key reads 1 file its own run generates after the key is taken: gen/api.json. Generate them before this target's key, as a skip_cache target it composes or a target it depends on

The run stays green, and the next one runs in full again, every time. Nothing else says so: each run looks like an ordinary miss.

Why only generated files

One invocation runs a file's writer before its readers, so a declared output that moves under a step moved inside that step's own run. A moved file no target declares is a concurrent writer instead, an editor or another magus, and magus reports it as a plain notice: the next run hashes the new bytes and caches normally.

Resolution

The generator has to finish before the key is taken. Two ways do that:

• Compose it as a skip_cache target. A skip_cache target a composer reaches through ctx.needs runs ahead of the composer's key, once its dependencies have finished, and the body does not run it again.
• Depend on it. A target in another project that the composer's project depends on runs, and finishes, before the composer starts.

If the target does not actually need the file, drop it from the target's inputs instead.

Distinct from MGS4007

MGS4007 is a declared source the run changed, and it fails the run. This code is a generated file the key reads, and it only declines to cache.