Provide nice output of plural form not found error

[d2r2]

Rational:

If you run code example:

package main

import (
	"fmt"

	"github.com/BurntSushi/toml"
	"github.com/nicksnyder/go-i18n/v2/i18n"
	"golang.org/x/text/language"
)

func main() {
	bundle := &i18n.Bundle{DefaultLanguage: language.English}
	bundle.RegisterUnmarshalFunc("toml", toml.Unmarshal)
	// No need to load active.en.toml since we are providing default translations.

	bundle.ParseMessageFileBytes([]byte(`

[Test1]
one = "One"
other = "Other"

		`),
		"active.en.toml")

	bundle.ParseMessageFileBytes([]byte(`

[Test1]
one = "Один"
other = "Другой"
#few = "Несколько"
#many = "Много"

		`), "active.ru.toml")

	localizer := i18n.NewLocalizer(bundle, "en")
	fmt.Println(fmt.Sprintf("en: %s", localizer.MustLocalize(
		&i18n.LocalizeConfig{MessageID: "Test1", PluralCount: 100})))

	localizer = i18n.NewLocalizer(bundle, "ru")
	fmt.Println(fmt.Sprintf("ru: %s", localizer.MustLocalize(
		&i18n.LocalizeConfig{MessageID: "Test1", PluralCount: 100})))
}

You will get output, which looks like a bug:

en: Other
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x539ba6]

goroutine 1 [running]:
github.com/nicksnyder/go-i18n/v2/internal.(*Template).parse(0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x5936f4, 0x4)
	/home/ddyakov/Documents/gocode/src/github.com/nicksnyder/go-i18n/v2/internal/template.go:16 +0x26
github.com/nicksnyder/go-i18n/v2/internal.(*MessageTemplate).Execute(0xc00007e7d0, 0x5936f4, 0x4, 0x566ac0, 0xc0000f6840, 0x0, 0x4, 0xc00007e7d0, 0x20, 0x571420)
	/home/ddyakov/Documents/gocode/src/github.com/nicksnyder/go-i18n/v2/internal/message_template.go:44 +0xa2
github.com/nicksnyder/go-i18n/v2/i18n.(*Localizer).LocalizeWithTag(0xc0000894a0, 0xc0000cbf08, 0x20, 0x571420, 0xc000089401, 0xc0000894a0, 0xc0000cbe08, 0x53b30f, 0x571420)
	/home/ddyakov/Documents/gocode/src/github.com/nicksnyder/go-i18n/v2/i18n/localizer.go:142 +0x3c2
github.com/nicksnyder/go-i18n/v2/i18n.(*Localizer).Localize(0xc0000894a0, 0xc0000cbf08, 0x1, 0x1, 0x1, 0xc000089480)
	/home/ddyakov/Documents/gocode/src/github.com/nicksnyder/go-i18n/v2/i18n/localizer.go:106 +0x35
github.com/nicksnyder/go-i18n/v2/i18n.(*Localizer).MustLocalize(0xc0000894a0, 0xc0000cbf08, 0x1, 0x1)
	/home/ddyakov/Documents/gocode/src/github.com/nicksnyder/go-i18n/v2/i18n/localizer.go:205 +0x35
main.main()
	/home/ddyakov/Documents/gocode/src/github.com/nicksnyder/go-i18n/v2/example2/main.go:40 +0x456
exit status 2

Fix proposed by me resolve this and gives nice output (easy to understand what plural form is missed):

en: Other
panic: message "Test1" has no plural form "many" defined

goroutine 1 [running]:
github.com/nicksnyder/go-i18n/v2/i18n.(*Localizer).MustLocalize(0xc00000b500, 0xc0000b5f08, 0x1, 0x1)
	/home/ddyakov/Documents/gocode/src/github.com/nicksnyder/go-i18n/v2/i18n/localizer.go:207 +0x79
main.main()
	/home/ddyakov/Documents/gocode/src/github.com/nicksnyder/go-i18n/v2/example2/main.go:40 +0x456
exit status 2

[codecov]

Codecov Report

Merging #147 into master will increase coverage by 0.08%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #147      +/-   ##
==========================================
+ Coverage   67.58%   67.66%   +0.08%     
==========================================
  Files          28       28              
  Lines        2298     2304       +6     
==========================================
+ Hits         1553     1559       +6     
  Misses        663      663              
  Partials       82       82

Impacted Files	Coverage Δ
v2/internal/message_template.go	68.75% <66.66%> (+7.21%)	⬆️

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[nicksnyder]

Thanks for finding and fixing this! Can you add a test for this?

[d2r2]

Hi @nicksnyder ! Sure, I'll try to figure out how to make the appropriate test and get back with update to commit.

[d2r2]

@nicksnyder, test added to the message_template_test.go.

[nicksnyder]

Thanks! I pushed a commit to use an error struct which makes testing easier. I will merge once CI passes.