XO1318: a module's tree cannot be read for the effect, escape hatch, or tidy scan

The effect audit (XO1317) and the escape hatch audit (XO1316) read every .xo file of each selected module version. When a directory or file of the tree fails to read with an I/O error, what it holds cannot be checked, so the build stops with this error instead of passing on a partial tree. The content hash of a module tree (core 4.3) fails the same way rather than hash a partial tree, which a command recording hashes would write to xo.lock. xo mod tidy stops the same way when its scan of the main module’s imports cannot read a directory or file, rather than drop the requirements of what it did not see. A directory that does not exist is not an error.

Fix

Run the command again: a transient error (no file descriptors or memory left) does not recur. If it persists, check the files under the module cache, or empty it with `xo mod clean` so the next build fetches the versions again.

Run xo explain XO1318 for this text in a terminal, or see section 10.6 of the specification.