Problems with build-tools support in Stack

[qrilka]

It appears that Stack doesn't properly supports constraints in the build-tools stanza of Cabal. An example of this could be seen in the repo https://github.com/qrilka/hsc2hs-fail quoting:

---

It appears that lts-14.27 includes hsc2hs-0.68.6 and with the lines

#build-tools:
#- hsc2hs >= 0.68.6

commented out from the package.yaml we get a build failure because the version 0.68.5 from GHC-8.6.5 gets used. Uncommenting the constraint above gives a unsatisfied version failure from Cabal.

One could build hsc2hs manually with stack build hsc2hs and that adds the version 0.68.6 into the Stack's path:

$ stack exec -- hsc2hs --version
hsc2hs version 0.68.6
But it appears that stack build could only use hsc2hs shipped with GHC.

---

It appears that the documentation doesn't tell explicitly if build-tools stanza is fully supported.
Also it looks like the problem in #5242 should also come from incorrect handling of build-tools. My incomplete investigation showed that Stack sets --bindir when configuring Cabal project but that doesn't seem to be used for build tools and it looks like required tools should appear in the $PATH.

Stack version

$ stack --version
2.1.3.1 x86_64 hpack-0.33.0

Method of installation

• Other (please specify) - nixpkgs (not on NixOS)

[mpilgrem]

It has been suggested that sol/hpack#516 is also a manifestation of Stack not supporting build-tools correctly/fully. Other open issues mentioning build-tools include:

• Feature: include build-tools in list-dependencies #3195
• Move build-tool dependency logic earlier, into package promotion / snapshot loading  #3777
• Stack cannot build projects that require Alex with the LTS-7.x resolver #5242