Unify mult-error handling

[MrAlias]

Currently, when multiple errors are desired to be rolled into a single error we have not standard way of doing this. In fact, there are three separate ways:

opentelemetry-go/sdk/metric/pipeline.go

Lines 479 to 482 in 7a60bc7

	type multierror struct {
	wrapped error
	errors []string
	}

opentelemetry-go/exporters/otlp/otlpmetric/internal/transform/error.go

Lines 48 to 54 in 7a60bc7

	// multiErr is used by the data-type transform functions to wrap multiple
	// errors into a single return value. The error message will show all errors
	// as a list and scope them by the datatype name that is returning them.
	type multiErr struct {
	datatype string
	errs []error
	}

opentelemetry-go/sdk/metric/config.go

Lines 51 to 57 in 7a60bc7

	var errs []error
	for _, f := range funcs {
	if err := f(ctx); err != nil {
	errs = append(errs, err)
	}
	}
	return unifyErrors(errs)

With the last example being replicated in a variety of formats in multiple packages.

Possible Solutions

github.com/hashicorp/go-multierror

• This package has a clean interface designed around a well designed Error type. It does not have as many "helper" functions as github.com/uber-go/multierr, but it seems to be able to do the same features.
• Can unwrap and wrap errors. Supports errors.As and errors.Is.
• It has an ErrorOrNil method which we use in the metric SDK already.
• Fine tuned error string with a function.
• Versioning: stable v1.X
• Dependencies: 1 direct
• Popularity: 20919 packages depend on this (direct and indirect)
• License: MPL-2.0
  • This license is not ideal for users planning to make their own distributions. They will be required to include a notice that portions of the source code use this license and they will need to link to github.com/hashicorp/go-multierror

github.com/uber-go/multierr

• The clean Error design of github.com/hashicorp/go-multierror is missing, but instead there are a good set of "helper" functions to combine function output.
• Can unwrap and wrap errors. Supports errors.As and errors.Is.
• There is no ErrorOrNil method which we use in the metric SDK.
• Error string is clear, but not customizable.
• Versioning: stable v1.X
• Dependencies: 2 direct, 3 indirect
• Popularity: 1152 packages depend on this (direct and indirect)
• License: MIT
  • There are no patent guarantees, though I'm not sure this matters given this project is licensed with an Apache 2.0 license.

Build our own

• I'm not sure we can improve on the multi-error design, but we would be able to ensure features we want are there.
• Licensing: Apache 2.0 (like the rest of the project)
  • It will be really hard to ensure our implementation doesn't borrow from the prior two packages. Which means they would need to be attributed anyways.

[MrAlias]

Also, it looks like multiple error wrapping will be added in Go 1.20.

[Omkar-Waingankar]

^An early draft of Go release notes also confirms this - https://tip.golang.org/doc/go1.20#errors

If the Go OTEL project is going to upgrade to v1.20, and there is a decision made to use the standard multi err implementation, then I think a good approach to consolidate this type of error handling might be to simply refactor the functions in opentelemetry-go/sdk/metric/config.go pointed out above

[MrAlias]

The multiErr types in the OTLP transform packages annotate the error with additional information. Leaving them.