Support error types

[akutuev]

This is an enhancement related to that discussion: #238

The purpose of this PR is to make a possibility convert an error to its specific type.

Since the errors aggregation has been added before (#233), user should convert an error result to AggregateError first and then iterate over accumulated errors, example:

        err := Parse(&config{})
	if e, ok := err.(*AggregateError); ok {
		for _, er := range e.Errors {
			switch v := er.(type) {
			case ParseError:
				// handle it
			case NotStructPtrError:
				// handle it
			case NoParserError:
				// handle it
			case NoSupportedTagOptionError:
				// handle it
			default:
				fmt.Printf("Unknown type %v", v)
			}
		}
	}

[codecov]

Codecov Report

Base: 100.00% // Head: 99.74% // Decreases project coverage by -0.25% ⚠️

Coverage data is based on head (d9976c3) compared to base (da848aa).
Patch coverage: 98.41% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##              main     #240      +/-   ##
===========================================
- Coverage   100.00%   99.74%   -0.26%     
===========================================
  Files            2        3       +1     
  Lines          356      386      +30     
===========================================
+ Hits           356      385      +29     
- Misses           0        1       +1     

Impacted Files	Coverage Δ
env.go	99.70% <94.44%> (-0.30%)	⬇️
error.go	100.00% <100.00%> (ø)

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[akutuev]

@caarlos0 @jurajkulich please feel free to review and validate it

Any comments appreciated

Thanks

[caarlos0]

a few comments, but looking good so far!
thanks for the PR :D

[caarlos0]

seems like this can be simplified to something like:

var ErrNotAStructPtr = errors.New("expected a pointer to a Struct")

as the message is always the same, right?

[akutuev]

that's definitely true, but I did it deliberately to follow the same error pattern like other errors (struct + func to create and error) do you recommend to make it simpler?

[caarlos0]

yes, simpler is usually better :)

[akutuev]

I came to realize we are loosing a possibility to check the error type using a errors.New(). But anyway, I have updated this error, can you please check

[caarlos0]

I usually do something like this:

Suggested change

	type NoParserError struct {
	msg string
	}
	func newNoParserError(sf reflect.StructField) error {
	return NoParserError{fmt.Sprintf(`no parser found for field "%s" of type "%s"`, sf.Name, sf.Type)}
	}
	func (e NoParserError) Error() string {
	return e.msg
	}
	// NoParserError happens when etc...
	type NoParserError struct {
	Name string
	Type string
	}
	func newNoParserError(sf reflect.StructField) error {
	return NoParserError{sf.Name, sf.Type}
	}
	func (e NoParserError) Error() string {
	return fmt.Sprintf("no parser found for field %q of type %q", e.Name, e.Type)
	}

That way, internally, we can still get the "unparsed" name and type...

I would do this, and the same with the other similar errors bellow...

Also, we should add a comment to the error type saying when it should be raised and what it means.

[akutuev]

fair comment, I wanted to make all errors generic: the same structure (msg only), but your comment makes sense:

• User converts error to specific type of the error
• User now has access to all error fields +message string

Let me improve it

[akutuev]

Updated as discussed

[akutuev]

Hello @caarlos0. Can you please take a look at the changes when you have time

[akutuev]

Hello @caarlos0, any updates on this? Do you need my help to clarify/review it?

[caarlos0]

sorry, got caught up in some personal issues, will review it when I get some peace time