curl build error when ngtcp2 is installed but nghttp3 is not

[chiouss]

Hi,

I installed ngtcp2 on Openwrt in order to build some small program with QUIC I wrote. But then I found curl will build failed after it finds ngtcp2 in system is usable but doesn't notice there's no nghttp3 in system.

I know I can add --without-ngtcp2 in configure, but I add --without-nghttp3 at the first time and found nothing changed. Then I realized that there's no checking of USE_NGHTTP3 in code.

I think in configure.ac we need to check nghttp3 first then check ngtcp2 maybe?

In file included from quic.h:29,
                 from urldata.h:142,
                 from altsvc.c:30:
vquic/ngtcp2.h:30:10: fatal error: nghttp3/nghttp3.h: No such file or directory
 #include <nghttp3/nghttp3.h>
          ^~~~~~~~~~~~~~~~~~~
compilation terminated.
Makefile:1670: recipe for target 'libcurl_la-altsvc.lo' failed

I did this

./configure --target=aarch64-openwrt-linux --host=aarch64-openwrt-linux --build=x86_64-pc-linux-gnu --program-prefix="" --program-suffix="" --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --libexecdir=/usr/lib --sysconfdir=/etc --datadir=/usr/share --localstatedir=/var --mandir=/usr/man --infodir=/usr/info --disable-nls --disable-debug --disable-ares --enable-shared --enable-static --disable-manual --without-nss --without-librtmp --without-libidn --without-ca-path --without-libpsl --without-zstd --with-ca-bundle=/etc/ssl/certs/ca-certificates.crt --enable-ipv6 --without-wolfssl --without-gnutls --with-ssl="/home/chiouss/galaxy-ap/release-655/mt7981/openwrt/staging_dir/target-aarch64-openwrt-linux_musl/usr" --without-mbedtls --without-libidn2 --without-libssh2 --without-zlib --without-zstd --without-nghttp2 --disable-dict --enable-file --enable-ftp --disable-gopher --enable-http --disable-imap --disable-ldap --disable-ldaps --disable-pop3 --disable-rtsp --disable-smb --disable-smtp --disable-telnet --disable-tftp --enable-cookies --disable-crypto-auth --disable-libcurl-option --enable-proxy --enable-threaded-resolver --disable-tls-srp --disable-unix-sockets --enable-verbose
then make

I expected the following

a success build of curl

curl/libcurl version

7.83.1

operating system

Ubuntu 18.04/Openwrt 21.02

[icing]

Proposed #10821 to fix this issue.

[chiouss]

@icing thank for fixing.

But I still think the wording and order of checking ngtcp2 & nghttp3 is wrong in configure.ac:

https://github.com/curl/curl/blob/master/configure.ac#L2824

# without HTTP, ngtcp2 is no use

https://github.com/curl/curl/blob/master/configure.ac#L3078

# without ngtcp2, nghttp3 is of no use for us

It should be "without HTTP, nghttp3 is no use" and "without nghttp3, ngtcp2 is of no use for us", since nghttp3 requires ngtcp2 to work. Do I miss something?