Stack cannot build projects that require Alex with the LTS-7.x resolver

[Calvin-L]

General summary

One of my older projects uses an ancient resolver that no longer seems to work.

Steps to reproduce

Save this as repro.sh in an empty folder:

#!/bin/bash

set -e

cat >please-install-alex.cabal <<EOF
name:    please-install-alex
version: 0.0

executable Main
  main-is:
    Main.hs
  build-depends:
    base
  build-tools:
    alex
EOF

cat >stack.yaml <<EOF
require-stack-version: "==2.1.3"
resolver: lts-7.24
packages: [.]
EOF

cat >Main.hs <<EOF
module Main (main) where

main :: IO ()
main = do
    putStrLn "hello"
EOF

stack build

Then run it:

$ bash ./repro.sh

Expected

The project should build.

Actual

alex               > configure
alex               > [1 of 2] Compiling Main             ( /private/var/folders/d4/n6djsq8x5dv0jfx84hzl0v000000gn/T/stack-6accc37869a8dddd/alex-3.1.7/Setup.lhs, /private/var/folders/d4/n6djsq8x5dv0jfx84hzl0v000000gn/T/stack-6accc37869a8dddd/alex-3.1.7/.stack-work/dist/x86_64-osx/Cabal-1.24.0.0/setup/Main.o )
alex               > [2 of 2] Compiling StackSetupShim   ( /Users/loncaric/.stack/setup-exe-src/setup-shim-mPHDZzAJ.hs, /private/var/folders/d4/n6djsq8x5dv0jfx84hzl0v000000gn/T/stack-6accc37869a8dddd/alex-3.1.7/.stack-work/dist/x86_64-osx/Cabal-1.24.0.0/setup/StackSetupShim.o )

[...]

alex               > 9 warnings generated.
alex               > Configuring alex-3.1.7...
alex               > build
alex               > Building alex-3.1.7...
alex               > Preprocessing executable 'alex' for alex-3.1.7...
alex               > setup: The program 'happy' is required but it could not be found

--  While building package alex-3.1.7 using:
      /private/var/folders/d4/n6djsq8x5dv0jfx84hzl0v000000gn/T/stack-6accc37869a8dddd/alex-3.1.7/.stack-work/dist/x86_64-osx/Cabal-1.24.0.0/setup/setup --builddir=.stack-work/dist/x86_64-osx/Cabal-1.24.0.0 build --ghc-options ""
    Process exited with code: ExitFailure 1
Progress 1/2

I am happy to provide more verbose logs if they will be helpful.

Stack version

$ stack --version 
Version 2.1.3 x86_64
[...]

Method of installation

• On MacOS via Homebrew

[qrilka]

I guess you need to add happy as a dependency as well because alex doesn't list it as it's dependency.

[Calvin-L]

Adding happy to the build-tools section does not fix the problem. In fact, happy won't build either: https://gist.github.com/Calvin-L/ce1e40bde893de7eaa59738c6de7c342

I should clarify that this worked fine with an older version of Stack circa 2017/2018. I will try to reproduce that successful build; there might have been something about my environment that caused it to succeed back then when it shouldn't have.

[Calvin-L]

Sure enough, this project does build with Stack 1.1.2.

(Unrelated: to build with the older version of Stack I had to create a Setup.hs file with these contents:

import Distribution.Simple
main = defaultMain

It is possible that this is required for modern Stack as well, but the build didn't progress far enough to let me know. Obviously I also had to remove the require-stack-version line from stack.yaml.)

[mpilgrem]

I am closing given the passage of time and that the master branch of Stack does not support LTS < 12.0.