lang: structs: Fix duplicate resource field bug

[adamsigal]

Add extra verification in Init() to prevent a resource with multiple instances of the same field from being validated.

Tips:

• please read the style guide before submitting your patch: docs/style-guide.md

• commit message titles must be in the form:

topic: Capitalized message with no trailing period

or:

topic, topic2: Capitalized message with no trailing period

• golang code must be formatted according to the standard, please run:

make gofmt      # formats the entire project correctly

or format a single golang file correctly:

gofmt -w yourcode.go

• please rebase your patch against current git master:

git checkout master
git pull origin master
git checkout your-feature
git rebase master
git push your-remote your-feature
hub pull-request    # or submit with the github web ui

• after a patch review, please ping @purpleidea so we know to re-review:

# make changes based on reviews...
git add -p      # add new changes
git commit --amend  # combine with existing commit
git push your-remote your-feature -f
# now ping @purpleidea in the github PR since it doesn't notify us automatically

Thanks for contributing to mgmt and welcome to the team!

[purpleidea]

@adamsigal FYI, this was never reviewed because the tests failed. The convention is that a PR will be ignored if the tests failed unless you leave a comment explaining why the failure is not your fault or you need help understanding it.

[adamsigal]

@adamsigal FYI, this was never reviewed because the tests failed. The convention is that a PR will be ignored if the tests failed unless you leave a comment explaining why the failure is not your fault or you need help understanding it.

I actually realised that the tests didn't pass, that's why I didn't mention it on IRC ¯_(ツ)_/¯

[purpleidea]

Heya, I've had to close this because I replaced it with a finished version.

I also added the meta dupes checking, so my version is a bit more complicated, but in case you're curious in the learning experience...

Here:

https://github.com/purpleidea/mgmt/commit/a45b7a1d8872d9fc3abbe8bccbb99df3aeea248f#diff-475d0aedee767145087b385c3ea097461792ffe83edac562c8263bb0e51e69b0R321

You can see how we look at the type of the thing, and switch into it before looking at it. We can't use foo.String() because:

1) That's a bigger representation that wouldn't guarantee us unique fields, and 2) We don't want to examine Edges for example.

If you have questions or want to jump back in, please LMK =D