Resolve environments case-insensitively on Windows

[ikedam]

Please have a look on docker/compose#9431 for details.

compose-go extracts environment variables to Environment map[string]string and reference that later with simply Environment[varname].
It works case-sensitively but environment variables should be treated case-insensitively on Windows.

This change handles environment variables case-insensitively on Windows, without changing data structures on compose-go.

This change also adds exposed utils.EnvResolver function. I plan to use that for additional changes in https://github.com/docker/compose/ , handling option args like --build-arg with build sub command and -e with run sub command.
(like this: https://github.com/ikedam/compose/pull/1/files)

[ndeloof]

Thanks for looking into this!
For legal reasons, all commits need to be signed-off. Please amend your commit and force push your branch:
git commit --amend --signoff && git push --force ...

[ndeloof]

as EnvResolver is not used in any other place, I'd prefer we keep things simple with EnvResolverWithCase logic being directly included here

[ndeloof]

No need to allocate a full lowercase map on each lookup, could just do

key := strings.ToLower(s)
for k, v := range environment {
   if key == strings.ToLower(k) {
      return v
   }
}

[ndeloof]

👍

[ikedam]

Thanks for looking into this! For legal reasons, all commits need to be signed-off. Please amend your commit and force push your branch: git commit --amend --signoff && git push --force ...

I've added signed-off line as described in https://github.com/compose-spec/compose-go/blob/master/CONTRIBUTING.md :

PS C:\workspace\compose-go> git log -n 1
commit 90f9d92dab00e1272c050960baeaaa8d8b15aaad (HEAD -> feature/9431_CaseInsensitiveEnv, ikedam/feature/9431_CaseInsensitiveEnv)
Author: ikedam <[email protected]>
Date:   Tue May 3 11:58:23 2022 +0900

    Resolve environments case-insensitively on Windows

    Signed-off-by: IKEDA Yasuyuki <[email protected]>
PS C:\workspace\compose-go>

But something might be wrong as this is the first time I wrote signed-off line.

Should I use the real name also in author line? Or should I add GPG signature? (git commit -S)

[ikedam]

Oh, I got it. I have to pass DCO action. I'll try that.

[ikedam]

Thanks for the review. I fixed problems you pointed.

[glours]

LGTM