[Bug]: Attempting to configure for HTTP3 without other required options results in disabled HTTP3, not an error.

[Kangie]

I did this

./configure --prefix=/usr --build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu --mandir=/usr/share/man --infodir=/usr/share/info --datadir=/usr/share --sysconfdir=/etc --localstatedir=/var/lib --datarootdir=/usr/share --disable-dependency-tracking --disable-silent-rules --disable-static --docdir=/usr/share/doc/curl-9999 --htmldir=/usr/share/doc/curl-9999/html --with-sysroot=/ --libdir=/usr/lib64 --without-ca-fallback --with-ca-bundle=/etc/ssl/certs/ca-certificates.crt --without-gnutls --without-mbedtls --without-rustls --with-ssl --with-ca-path=/etc/ssl/certs --with-default-ssl-backend=openssl --enable-alt-svc --with-nghttp3
. . .
configure: Configured to build curl/libcurl:

  Host setup:       x86_64-pc-linux-gnu
  Install prefix:   /usr
  Compiler:         x86_64-pc-linux-gnu-gcc
   CFLAGS:          -Werror-implicit-function-declaration -O2 -Wno-system-headers
   CPPFLAGS:        
   LDFLAGS:         
   LIBS:            -lnghttp3 -lnghttp2 -lidn2 -lpsl -lssl -lcrypto -lssl -lcrypto -lldap -llber -lzstd -lbrotlidec -lz

  curl version:     8.9.0-DEV
  SSL:              enabled (OpenSSL v3+)
  SSH:              no      (--with-{libssh,libssh2})
  zlib:             enabled
  brotli:           enabled (libbrotlidec)
  zstd:             enabled (libzstd)
  GSS-API:          no      (--with-gssapi)
  GSASL:            no      (libgsasl not found)
  TLS-SRP:          enabled
  resolver:         POSIX threaded
  IPv6:             enabled
  Unix sockets:     enabled
  IDN:              enabled (libidn2)
  Build docs:       enabled (--disable-docs)
  Build libcurl:    Shared=yes, Static=no
  Built-in manual:  enabled
  --libcurl option: enabled (--disable-libcurl-option)
  Verbose errors:   enabled (--disable-verbose)
  Code coverage:    disabled
  SSPI:             no      (--enable-sspi)
  ca cert bundle:   /etc/ssl/certs/ca-certificates.crt
  ca cert path:     /etc/ssl/certs
  ca fallback:      no
  LDAP:             enabled (OpenLDAP)
  LDAPS:            enabled
  RTSP:             enabled
  RTMP:             no      (--with-librtmp)
  PSL:              enabled
  Alt-svc:          enabled (--disable-alt-svc)
  Headers API:      enabled (--disable-headers-api)
  HSTS:             enabled (--disable-hsts)
  HTTP1:            enabled (internal)
  HTTP2:            enabled (nghttp2)
  HTTP3:            no      (--with-ngtcp2 --with-nghttp3, --with-quiche, --with-openssl-quic, --with-msh3)
  ECH:              no      (--enable-ech)
  WebSockets:       no      (--enable-websockets)
  Protocols:        DICT FILE FTP FTPS GOPHER GOPHERS HTTP HTTPS IMAP IMAPS IPFS IPNS LDAP LDAPS MQTT POP3 POP3S RTSP SMB SMBS SMTP SMTPS TELNET TFTP
  Features:         AsynchDNS HSTS HTTP2 HTTPS-proxy IDN IPv6 Largefile NTLM PSL SSL TLS-SRP UnixSockets alt-svc brotli libz threadsafe zstd

Time: 0h:00m:12s                                                                                                                                                                                                                
kangie@monolith /data/development/temp/curl (pkg-conf-lib-names) $ echo $?
0

I expected the following

Configure to fail if an explicitly requested feature cannot be configured.

curl/libcurl version

current master - fa0b1d9209850f523159a332c00cbe2f1e6ab3ab

operating system

Linux monolith 6.9.2-gentoo--bouncy-mouse #1 SMP PREEMPT_DYNAMIC Fri May 31 07:50:55 AEST 2024 x86_64 AMD Ryzen 9 5950X 16-Core Processor AuthenticAMD GNU/Linux