notify.DeepCopyWithTemplate edge cases

[TheMeier]

What did you do?

Input like "{}:{alertname=\"test1\"}" trips up notify.DeepCopyWithTemplate

What did you expect to see?

passing "{}:{alertname=\"test1\"}" into notify.DeepCopyWithTemplate to just return the string

What did you see instead? Under which circumstances?

passing "{}:{alertname=\"test1\"}" into notify.DeepCopyWithTemplate returns interface{} nil

System information

Irrelevant

Alertmanager version

current main branch

Alertmanager configuration file

Irrelevant

Prometheus version

Irrelevant

Prometheus configuration file

Irrelevant

Logs

Irrelevant

[TheMeier]

It turns out the reason is https://github.com/prometheus/alertmanager/blob/main/template/template.go#L461

passing such a string into yaml.Unmarshal() returns no error and map[] this is unexpected. This might be a bug in the yaml library, need to check if the string is spec compliant. Here is a small test with different yaml libraries: https://go.dev/play/p/u_61B-yFQAF
only github.com/goccy/go-yaml reports an error.

Quick test in python also reports an error:

Error: expected '<document start>', but found '<scalar>'
  in "<unicode string>", line 1, column 3:
    {}/{foo="lbar"}:{alertname=" ... 
      ^

[TheMeier]

Some more tests:

            	Error:      	Not equal: 
            	            	expected: string("{env=\"testing\"}:{alertname=\"TestingAlert\", service=\"api\"}")
            	            	actual  : map[string]interface {}(map[string]interface {}{"env=\"testing\"":interface {}(nil)})

            	Error:      	Not equal: 
            	            	expected: string("{}/{env=\"testing\"}:{alertname=\"TestingAlert\", service=\"api\"}")
            	            	actual  : map[string]interface {}(map[string]interface {}{})