Dedup go errors

[VenelinMartinov]

The muxer previously de-duplicated CheckFailures but not go errors. This PR should add that and address #1418 but not the original issue in pulumi/pulumi-aws#2285 (comment). See #1418 (comment)

This fixes duplicated error messages in the aws-provider when no aws region is specified.

Before:

    error: rpc error: code = Unknown desc = 2 errors occurred:
    	* unable to validate AWS credentials.
    Details: validating provider credentials: retrieving caller identity from STS: operation error STS: GetCallerIdentity, failed to resolve service endpoint, endpoint rule error, Invalid Configuration: Missing Region
    Make sure you have set your AWS region, e.g. `pulumi config set aws:region us-west-2`.

    	* unable to validate AWS credentials.
    Details: validating provider credentials: retrieving caller identity from STS: operation error STS: GetCallerIdentity, failed to resolve service endpoint, endpoint rule error, Invalid Configuration: Missing Region
    Make sure you have set your AWS region, e.g. `pulumi config set aws:region us-west-2`.

After:

    error: rpc error: code = Unknown desc = unable to validate AWS credentials.
    Details: validating provider credentials: retrieving caller identity from STS: operation error STS: GetCallerIdentity, failed to resolve service endpoint, endpoint rule error, Invalid Configuration: Missing Region
    Make sure you have set your AWS region, e.g. `pulumi config set aws:region us-west-2`.

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (0ac62de) 62.02% compared to head (ff6ec62) 57.96%.
Report is 6 commits behind head on master.

Files	Patch %	Lines
x/muxer/muxer.go	0.00%	6 Missing ⚠️
testing/x/replay.go	0.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1496      +/-   ##
==========================================
- Coverage   62.02%   57.96%   -4.06%     
==========================================
  Files         185      286     +101     
  Lines       32895    39695    +6800     
==========================================
+ Hits        20402    23009    +2607     
- Misses      11353    15344    +3991     
- Partials     1140     1342     +202     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[iwahbe]

This code looks good. There is code on L154 that does almost the same thing. I would probably change the comment on L154 to say "failures" instead of "errors" to help disambiguate.

Can you add a test for this?

[iwahbe]

entry.Errors is a JSON list that is user provided, but we still assert that it should have a length of 1. What happens if we want to test that we have multiple errors?

[VenelinMartinov]

It doesn't look like the provider can return multiple errors as far as I can see. It seems to combine all the errors into one. The CheckConfig method can only return one error value.

[iwahbe]

If we can't have multiple errors, when why do we unmarshal entry.Errors into a list. I think we can simplify this whole block into

if err != nil && entry.Error != nil {
	assert.Equal(t, entry.Error, err.Error())
	return
}

This would involve changing the field Errors json.RawMessage to Error *string. We would then represent the error from fmt.Errorf("my-error") as &"my-error". No error would be represented as nil.

[iwahbe]

I still don't understand the complexity for one of the tests, but otherwise this looks great! LGTM

[iwahbe]

If we can't have multiple errors, when why do we unmarshal entry.Errors into a list. I think we can simplify this whole block into

if err != nil && entry.Error != nil {
	assert.Equal(t, entry.Error, err.Error())
	return
}

This would involve changing the field Errors json.RawMessage to Error *string. We would then represent the error from fmt.Errorf("my-error") as &"my-error". No error would be represented as nil.