field.path: make squash-aware

[coxley]

Summary

(previous PR based from master vs. my branch)

Since fig relies on mapstructure, fields can be annotated with ",squash" to flatten the config. It's super helpful for base settings that are embedded.

However, because the environment variable resolution relies on field.path(), it doesn't match the config-file structure.

This makes field.path() omit squashed fields.

Example config that's affected:

env: prod
logging:
  level: info

Example structs:

type Base struct {
  Env string `fig:"env"`
  Logging struct {
    Level string `fig:"level"`
  } `fig:"logging"`
}

type Config struct {
  Base `fig:",squash"`
}

Overriding with env var before and after this change:

BASE_ENV=staging # before
ENV=staging      # after

Test Plan

> go test ./... -count=1
ok      github.com/kkyr/fig     0.238s
ok      github.com/kkyr/fig/examples/config     0.388s
ok      github.com/kkyr/fig/examples/custom     0.693s
ok      github.com/kkyr/fig/examples/env        0.861s
ok      github.com/kkyr/fig/examples/required   0.529s

[kkyr]

Code change LGTM - thank you!

Can u please document in doc.go? Right after the environment section seems like a good place to add it.

[coxley]

@kkyr Done!

[coxley]

@kkyr Friendly ping here when you have time. :)

[kkyr]

Merged! Apologies for getting to this so late

[kkyr]

Available on v0.5.0

[coxley]

@kkyr All good! You're already way better at replying to PRs and issues than I am. :)

Thanks a bunch ❤️