I didn't see this clearly documented so reporting as an issue.

When using the new COPY --parents option (in labs), it will silently skip over files that do not exist.

Compare the following:

Without --parents:

# syntax=docker/dockerfile:1.7-labs
FROM scratch
COPY ./nonexistent-file /

results in:

ERROR: failed to solve: failed to compute cache key: failed to calculate checksum of ref 520ef390-e014-48a2-bdd5-b7fb3e850763::43brx8ibsmqfjzdxft4n7es8p: "/nonexistent-file": not found

With --parents:

# syntax=docker/dockerfile:1.7-labs
FROM scratch AS parents
COPY --parents ./nonexistent-file /

Is successful even though the file doesn't exist.

From a quick read of the code, it appears to treat every source as a wildcard pattern with --parents even if it doesn't contain any wildcard characters. Wildcard paths that don't match anything are silently accepted with our without the --parents option. I do see a lot of historical issues and confusion relating to wildcards that don't match anything, but it seems like that aspect is intended behavior.