Add response metadata to slack response

[alyosha]

Summary of Changes

The Web API response represented by the SlackResponse struct can contain an additional JSON field "response_metadata" in such cases as block validation failure, etc. It would be helpful to include the field in the struct so that these extra descriptors can be returned in existing models like ViewResponse when something goes wrong.

Example

Below are two examples of what the ViewResponse looks like when dumped before/after the addition.

Before

(*slack.ViewResponse)(0xc000419320)({
   SlackResponse: (slack.SlackResponse) {
       Ok: (bool) false,
       Error: (string) (len=17) "invalid_arguments"
    },
    ...
}

After

(*slack.ViewResponse)(0xc000778500)({
    SlackResponse: (slack.SlackResponse) {
        Ok: (bool) false,                                                                                                                                            
        Error: (string) (len=17) "invalid_arguments",                                                                                                                
        ResponseMetadata: (slack.ResponseMetadata) {                                                                                                                 
           Cursor: (string) "",                                                                                                                                        
           Messages: ([]string) (len=3 cap=4) {                                                                                                                        
              (string) (len=64) "[ERROR] failed to match all allowed schemas [json-pointer:/view]",                                                                      
              (string) (len=70) "[ERROR] failed to match all allowed schemas [json-pointer:/view/title]",                                                                
              (string) (len=71) "[ERROR] must be less than 25 characters [json-pointer:/view/title/text]"                                                                
           },                                                                                                                                                          
           Warnings: ([]string) (len=1 cap=4) {                                                                                                                        
             (string) (len=15) "missing_charset"                                                                                                                        
           }                                                                                                                                                           
        } 
    },
    ...
}

[ollieparsley]

Hi @alyosha. Thank you for this. Is godebug actually used? I can't see any references to it other than in the modules and vendor list. If it isn't used (could be that I'm missing it), could you remove it please. Then I can get this merged.

[kanata2]

In addition to @ollieparsley's comments, I commented a bit :)

[kanata2]

Maybe you can use struct { Message []string } as the type of response_metadata instead of map[string]interface{}.

e.g. official Java Implementation: https://github.com/slackapi/java-slack-sdk/blob/main/slack-api-model/src/main/java/com/slack/api/model/ResponseMetadata.java

[alyosha]

hey @kanata2 thanks for your feedback! I would be open to using a struct instead of a map here, will update

[alyosha]

hey @ollieparsley it's used in test but this is purely a personal preference (just wanted to check all fields match in the expected/received struct, where before only a few were being checked)

I will drop in lieu of reflect though, just to avoid introducing new deps 👍

[alyosha]

@ollieparsley @kanata2

Thanks again for the reviews and sorry for the delay in updating 👋

I made the move to use a struct rather than map as @kanata2 suggested, but I noticed there are already multiple ResponseMetadata types floating around in the library. I decided to just add the new metadata fields (messages/warnings) to one of the existing structs, please let me know if you have any concerns here.

I confirmed the behavior using a personal project and updated the PR description with an example of what the metadata looks like following these changes

[stevekuznetsov]

Fixes #805

Would love to see this merge, otherwise errors are not debuggable :)