CI: Nightly Docker builds broken due to change in alex-3.5.0.0's command-line flags

[RyanGlScott]

Recent nightly CI jobs are failing to build Dockerfiles, which attempt to install the latest version of alex (3.5.0.0). Here is an example from a recent CI job:

#13 137.2 checking for version of alex... Option '--verbose' not yet implementedUsage: alex [OPTION...] file
#13 137.2 
#13 137.2   -o FILE    --outfile=FILE     write the output to FILE (default: file.hs)
#13 137.2   -i[FILE]   --info[=FILE]      put detailed state-machine info in FILE (or file.info)
#13 137.2   -t DIR     --template=DIR     look in DIR for template files
#13 137.2   -g         --ghc              use GHC extensions
#13 137.2   -l         --latin1           generated lexer will use the Latin-1 encoding instead of UTF-8
#13 137.2   -s NUMBER  --tab-size=NUMBER  set tab size to be used in the generated lexer (default: 8)
#13 137.2   -d         --debug            produce a debugging scanner
#13 137.2   -v         --verbose          be verbose (not yet implemented)
#13 137.2   -?         --help             display this help and exit
#13 137.2   -V         --version          output version information and exit
#13 137.2              --numeric-version  output the version number and exit
#13 137.2 
#13 137.2 configure: error: Alex >= 3.2.6 && < 4 is required to compile GHC.
#13 ERROR: process "/bin/sh -c if ${PORTABILITY}; then         ghcup install ghc ${GHCVER_BOOTSTRAP} &&         ghcup set ghc ${GHCVER_BOOTSTRAP} &&         cabal v2-update &&         cabal v2-install alex happy-1.20.1.1 &&         git clone --recurse-submodules --depth 1 --branch ghc-${GHCVER}-release https://gitlab.haskell.org/ghc/ghc.git &&         cd ./ghc &&         git apply ../ghc-portability.patch &&         ./boot &&         ./configure &&         make -j &&         make install &&         cd .. &&         rm -rf ./ghc &&         ghcup rm ghc ${GHCVER_BOOTSTRAP};     else         ghcup install ghc ${GHCVER} &&         ghcup set ghc ${GHCVER};     fi" did not complete successfully: exit code: 1

The problem is that alex-3.5.0.0 changed the meaning of the -v flag from "return the version" to "dump verbose output", but the version of GHC that is built in this Dockerfile still assumes that -v means the former. See also this related GHC issue.

The most straightforward solution would be to explicitly pin the version of alex that the Dockerfile builds, much like we currently pin the version of happy that we build.