cmd/zlint-gtld-update/main.go
func renderGTLDMap(writer io.Writer) error {
	// Get all of ICANN's gTLDs including ones that haven't been delegated.
	allGTLDs, err := getGTLDData()
	if err != nil {
		return err
	}

	// Filter out the non-delegated gTLD entries
	delegatedGTLDs := delegatedGTLDs(allGTLDs)

	// Validate that all of the delegated gTLDs have correct dates
	if err := validateGTLDs(delegatedGTLDs); err != nil {
		return err
	}

	// Get all of the TLDs. This data source doesn't provide delegationDates and
	// so we only want to use it to populate missing entries in `delegatedGTLDs`,
	// not to replace any existing entries that have more specific information
	// about the validity period for the TLD.
	allTLDs, err := getTLDData()
	if err != nil {
		return err
	}

	tldMap := make(map[string]util.GTLDPeriod)

	// Deduplicate delegatedGTLDs into the tldMap first
	for _, tld := range delegatedGTLDs {
		tldMap[tld.GTLD] = tld
	}

	// Then populate any missing entries from the allTLDs list
	for _, tld := range allTLDs {
		if _, found := tldMap[tld.GTLD]; !found {
			tldMap[tld.GTLD] = tld
		}
	}

	templateData := struct {
		GTLDs map[string]util.GTLDPeriod
	}{
		GTLDs: tldMap,
	}

	// Render the gTLD map to a buffer with the delegated gTLD data
	var buf bytes.Buffer
	if err := gTLDMapTemplate.Execute(&buf, templateData); err != nil {
		return err
	}

	// format the buffer so it won't trip up the `gofmt_test.go` checks
	formatted, err := format.Source(buf.Bytes())
	if err != nil {
		return err
	}

	// Write the formatted buffer to the writer
	_, err = writer.Write(formatted)
	if err != nil {
		return err
	}
	return nil
}
func renderGTLDMap(writer io.Writer) error {
	// Get all of ICANN's gTLDs including ones that haven't been delegated.
	allGTLDs, err := getGTLDData()
	if err != nil {
		return err
	}

	// Filter out the non-delegated gTLD entries
	delegatedGTLDs := delegatedGTLDs(allGTLDs)

	// Validate that all of the delegated gTLDs have correct dates
	if err := validateGTLDs(delegatedGTLDs); err != nil {
		return err
	}

	// Get all of the TLDs. This data source doesn't provide delegationDates and
	// so we only want to use it to populate missing entries in `delegatedGTLDs`,
	// not to replace any existing entries that have more specific information
	// about the validity period for the TLD.
	allTLDs, err := getTLDData()
	if err != nil {
		return err
	}

	tldMap := make(map[string]util.GTLDPeriod)

	// Deduplicate delegatedGTLDs into the tldMap first
	for _, tld := range delegatedGTLDs {
		tldMap[tld.GTLD] = tld
	}

	// Then populate any missing entries from the allTLDs list
	for _, tld := range allTLDs {
		if _, found := tldMap[tld.GTLD]; !found {
			tldMap[tld.GTLD] = tld
		}
	}

	templateData := struct {
		GTLDs map[string]util.GTLDPeriod
	}{
		GTLDs: tldMap,
	}

	// Render the gTLD map to a buffer with the delegated gTLD data
	var buf bytes.Buffer
	if err := gTLDMapTemplate.Execute(&buf, templateData); err != nil {
		return err
	}

	// format the buffer so it won't trip up the `gofmt_test.go` checks
	formatted, err := format.Source(buf.Bytes())
	if err != nil {
		return err
	}

	// Write the formatted buffer to the writer
	_, err = writer.Write(formatted)
	if err != nil {
		return err
	}
	return nil
}
// renderGTLDMap fetches the ICANN gTLD data, filters out undelegated entries,
// validates the remaining entries have parseable dates, and renders the
// gTLDMapTemplate to the provided writer using the validated entries (or
// returns an error if any of the aforementioned steps fail). It then fetches
// the ICANN TLD data, and uses it to populate any missing entries for ccTLDs.
// These entries will have a default delegationDate because the data source is
// not specific enough to provide one. The produced output text is a Golang
// source code file in the `util` package that contains a single map variable
// containing GTLDPeriod objects created with the ICANN data.