[Refactor] Refactor the build subcommand flagging process

[Zheaoli]

Checklist:

• Create a file in pkg/api/types/${cmd}_types.go, and define the CommandOption for this command
• Create some file in pkg/cmd/${cmd}, and move the command entry point in real into this package

Signed-off-by: Zheao.Li me@manjusaka.me

[Zheaoli]

Should be merged since #1793

[Zheaoli]

should be merged after #1797

[Zheaoli]

Since #1797 has been merged, I think this PR is ready to go.

cc @AkihiroSuda @djdongjin @ktock

[djdongjin]

I found multiple "assign an option to a local variable (noCache := option.GOptions.NoCache) and then only use it once" pattern. We should remove those redundant assignment code unless for convenience because it's used several times.

Thanks

[djdongjin]

move into if output == block, they're only used in if (also suggest use options.xxx directly (same for options.BuildKitHost below) if they're not used frequently, that makes it more clear where the variable comes from)

[Zheaoli]

Noop, I think it will be used outside the if ouput==, see https://github.com/containerd/nerdctl/pull/1792/files#diff-3d28f1d0455b7f054ebac7695bbbe3d9c758b44b12602f7365d404a86011a49eR287-R289

[djdongjin]

options.GOptions.Namespace and options.GOptions.Adress are only used within if output==. We can move these 2 inside.

(Although personally I will use options.Platform directly in line 285... 😅 it's so far away from its definition (line 185) and it's not changed in between)

[Zheaoli]

done

[djdongjin]

do we need this line var err error?

[Zheaoli]

It's a special scope trick

if we don't have var err error, the code should be

		if options.File == "-" {
			var err error
			dir, err  := buildkitutil.WriteTempDockerfile(stdin)
			if err != nil {
				return "", nil, false, "", nil, nil, err
			}
			cleanup = func() {
				os.RemoveAll(dir)
			}
		} else {
			dir, file = filepath.Split(options.File)
		}

It means that the new dir variable will be unavailable outside the condition block....

[djdongjin]

LGTM, thanks

[AkihiroSuda]

Thanks