frontend/dockerfile: BFlags.Parse: include flag with "--" prefix in errors

[thaJeztah]

• addresses Dockerfile: improve error-messages for invalid flags or flags without required value #5368

frontend/dockerfile: BFlags.Parse: return earlier on "--" terminator

Minor optimization; put the check for a literal "--" first, instead of
matching for "--" as prefix. Also add some documentation to the code,
to outline why we return early.

from the POSIX Utility Syntax Guidelines;
https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html#tag_12_02

The first -- argument that is not an option-argument should be accepted
as a delimiter indicating the end of options. Any following arguments
should be treated as operands, even if they begin with the '-' character.

frontend/dockerfile: BFlags.Parse: include flag with "--" prefix in errors

Before this change, only the name of the flag would be printed as part
of errors. Change the errors to include the flag-name including the
"--" prefix to make it more clear the error is about a flag that was
provided but invalid.

Before this change:

Dockerfile:2
--------------------
1 |     FROM alpine
2 | >>> COPY --nosuchflag . .
3 |
--------------------
ERROR: failed to solve: dockerfile parse error on line 2: unknown flag: nosuchflag

Dockerfile:4
--------------------
2 |     FROM alpine
3 |     WORKDIR /test
4 | >>> COPY --exclude /.git . .
5 |
--------------------
ERROR: failed to solve: dockerfile parse error on line 4: missing a value on flag: exclude

With this change;

Dockerfile:2
--------------------
1 |     FROM alpine
2 | >>> COPY --nosuchflag . .
3 |
--------------------
ERROR: failed to solve: dockerfile parse error on line 2: unknown flag: --nosuchflag

Dockerfile:4
--------------------
2 |     FROM alpine
3 |     WORKDIR /test
4 | >>> COPY --exclude /.git . .
5 |
--------------------
ERROR: failed to solve: dockerfile parse error on line 4: missing a value on flag: --exclude

[thaJeztah]

We should probably also look at this one to say did you mean --mount?, but I think the same error-type is used in multiple situations, so it probably needs some changes to make it preserve --, but that not to affect the "matching";

buildkit/util/suggest/error.go

Lines 58 to 70 in 185751b

	type suggestError struct {
	err error
	match string
	}
	func (e *suggestError) Error() string {
	return e.err.Error() + " (did you mean " + e.match + "?)"
	}
	// Unwrap returns the underlying error.
	func (e *suggestError) Unwrap() error {
	return e.err
	}

Maybe the -- could be trimmed as part of the Search (not sure), but then it would have to be added again when printing, so this needs a slightly more deeper dive into how this all works;

buildkit/util/suggest/error.go

Line 47 in 185751b

match, ok := Search(val, options, caseSensitive)

[thaJeztah]

Failure is unrelated; opened a PR to fix it;

• util/archutil: re-generate to fix validation for mips64 #5370

[thaJeztah]

Hm... looks like I broke something here;

   sandbox.go:138: time="2024-09-30T12:49:03Z" level=error msg="/moby.buildkit.v1.Control/Solve returned error: rpc error: code = Unknown desc = dockerfile parse error on line 2: unknown flag: --platform" spanID=3b196da4ac85c2c4 traceID=7e2abcd2600868353a504108e50183ae
    sandbox.go:138: dockerfile parse error on line 2: unknown flag: --platform
    sandbox.go:138: 63105 8fad595 buildkitd --containerd-worker-gc=false --containerd-worker=true --containerd-worker-addr /tmp/bktest_containerd2334226698/containerd.sock --containerd-worker-labels=org.mobyproject.buildkit.worker.sandbox=true --oci-worker=false --

[tonistiigi]

^ this line seems to be the bug

[thaJeztah]

DOH!!! I see what I did there; was originally taking a slightly different approach 🙈 . Let me fix that

[thaJeztah]

OK; mistake was fixed, and CI is happy now, so this should be ready for review 🤗