dig cannot display ACE query if locale is not unicode

Summary

If system has no locales built or current language does not allow conversion from ACE, dig currently fails with fatal error.

Reported to RH Bugzilla Bug #1647829.

BIND version used

BIND 9.13.5 (Development Release) <id:14d48a9b69>
running on Linux x86_64 4.20.3-200.fc29.x86_64 #1 SMP Thu Jan 17 15:19:35 UTC 2019
built by make with '--enable-exportlib' '--with-libtool' '--with-dlopen' '--with-libidn2' '--without-lmdb' '--with-atf=/usr' '--enable-threads' 'CFLAGS=-ggdb -O0'
compiled by GCC 8.2.1 20181215 (Red Hat 8.2.1-6)
compiled with OpenSSL version: OpenSSL 1.1.1a FIPS  20 Nov 2018
linked to OpenSSL version: OpenSSL 1.1.1a FIPS  20 Nov 2018
compiled with libxml2 version: 2.9.8
linked to libxml2 version: 20908
compiled with libjson-c version: 0.13.1
linked to libjson-c version: 0.13.1
compiled with zlib version: 1.2.11
linked to zlib version: 1.2.11
threads support is enabled

Steps to reproduce

LANG=C bin/dig/dig -t NS $(idn2 háčkyčárky.cz)
LANG=C dig NS xn--cg4bki.

What is the current bug behavior?

dig: Cannot represent 'xn--hkyrky-ptac70bc.cz' in the current locale (string encoding error), use +noidnout or a different locale

What is the expected correct behavior?

Dig should output any valid form. ACE is not user friendly, but far better than fatal error and usage of custom parameter.

; <<>> DiG 9.13.5 <<>> -t NS xn--hkyrky-ptac70bc.cz
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51221
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;xn--hkyrky-ptac70bc.cz.		IN	NS

;; ANSWER SECTION:
xn--hkyrky-ptac70bc.cz.	695	IN	NS	b.ns.xn--hkyrky-ptac70bc.cz.
xn--hkyrky-ptac70bc.cz.	695	IN	NS	a.ns.xn--hkyrky-ptac70bc.cz.

;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Tue Jan 29 18:17:50 CET 2019
;; MSG SIZE  rcvd: 86

;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 9699
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 8, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;xn--cg4bki.			IN	NS

;; ANSWER SECTION:
xn--cg4bki.		86383	IN	NS	ns1.xn--cg4bki.centralnic-dns.com.
xn--cg4bki.		86383	IN	NS	ns2.xn--cg4bki.centralnic-dns.com.
xn--cg4bki.		86383	IN	NS	ns3.xn--cg4bki.centralnic-dns.com.
xn--cg4bki.		86383	IN	NS	c.xn--cg4bki.dyntld.net.
xn--cg4bki.		86383	IN	NS	ns4.xn--cg4bki.centralnic-dns.com.
xn--cg4bki.		86383	IN	NS	d.xn--cg4bki.dyntld.net.
xn--cg4bki.		86383	IN	NS	a.xn--cg4bki.dyntld.net.
xn--cg4bki.		86383	IN	NS	b.xn--cg4bki.dyntld.net.

;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Tue Jan 29 18:43:59 CET 2019
;; MSG SIZE  rcvd: 225

Relevant configuration files

Just compile --with-libidn2

Possible fixes

dig would just fall back to ASCII, which he already verified is working. Preserves compatibility with disabled IDN in this case, no matter what locale is used.