expr/file/error.go

package file

import (
	"fmt"
	"strings"
	"unicode/utf8"

	"golang.org/x/text/width"
)

type Error struct {
	Location
	Message string
}

const (
	dot = "."
	ind = "^"
)

var (
	wideDot = width.Widen.String(dot)
	wideInd = width.Widen.String(ind)
)

func (e *Error) Error() string {
	return e.Message
}

func (e *Error) Format(source *Source) error {
	if e.Location.Empty() {
		return fmt.Errorf(e.Message)
	}
	var result = fmt.Sprintf(
		"%s (%d:%d)",
		e.Message,
		e.Location.Line,
		e.Location.Column+1, // add one to the 0-based column for display
	)
	if snippet, found := source.Snippet(e.Location.Line); found {
		snippet := strings.Replace(snippet, "\t", " ", -1)
		srcLine := "\n | " + snippet
		var bytes = []byte(snippet)
		var indLine = "\n | "
		for i := 0; i < e.Location.Column && len(bytes) > 0; i++ {
			_, sz := utf8.DecodeRune(bytes)
			bytes = bytes[sz:]
			if sz > 1 {
				indLine += wideDot
			} else {
				indLine += dot
			}
		}
		if _, sz := utf8.DecodeRune(bytes); sz > 1 {
			indLine += wideInd
		} else {
			indLine += ind
		}
		result += srcLine + indLine
	}
	return fmt.Errorf(result)
}