fix(template): helm template "--show-only" flag producing duplicates when flag used more than once

[lbontecou]

Issue

#7203

Summary

---

• While migrating from helm2 to helm3, we began switching --execute parameters to the new --show-only parameter that was listed as being equivalent.
• We found our helm template <name> <chart> --show-only template1.yaml --show-only template2.yaml --values values.yaml | kubectl replace --force -f - commands failing due to "Resource already exists" errors.
• Using grep, we were able to identify our issue, duplicated outputs when multiple --show-only were used.

$ helm template myapp myapp --show-only templates/job.yaml --values values.yaml | grep Source 
# Source: app/templates/job.yaml

$ helm template myapp myapp --show-only templates/configmap.yaml --values values.yaml | grep Source 
# Source: myapp/templates/configmap.yaml

$ helm template myapp myapp --show-only templates/configmap.yaml --show-only templates/job.yaml --values values.yaml  | grep Source   
# Source: myapp/templates/configmap.yaml
# Source: myapp/templates/configmap.yaml
# Source: myapp/templates/job.yaml

Solution

---

• Identified an incorrect looping logic.
• Tested using make and ./bin/helm

$ helm template myapp myapp --show-only templates/configmap.yaml --values values.yaml | grep Source 
# Source: myapp/templates/configmap.yaml

$ helm template myapp myapp --show-only templates/configmap.yaml --show-only templates/job.yaml --values values.yaml  | grep Source   
# Source: myapp/templates/configmap.yaml
# Source: myapp/templates/migrations-job.yaml

[bacongobbler]

Thanks! Would you mind writing some unit tests to cover this? Have a look at template_test.go for some examples. Let me know if you have any questions.

[bacongobbler]

testdata output can be generated by running

$ cd cmd/helm # this is important; seems to only work when in the cmd/helm directory
$ go test -update

Run this once the unit test is created, and the testdata output will be generated for you.

[hickeyma]

@hoboken515 Fix looks good, thanks for this. As suggested by @bacongobbler in #7204 (comment), I think unit test on this would be useful.

[lbontecou]

I want to create the tests for this, may take me awhile to find the time / get up to speed on how to do so in the code base. Thanks for the inputs on how to do that @bacongobbler

[lbontecou]

@bacongobbler @hickeyma unittests added

[hickeyma]

@hoboken515 Can you rebase to fix the conflicts?

[lbontecou]

rebased

[hickeyma]

LGTM, thanks for catching and fixing this @hoboken515