I'm getting a build failure doing the cabal install hdevtools command snippet from the manual.
Using the current versions of GHC and cabal from homebrew (GHC 8.10.1/cabal 3.2.0.0).

The install gives the following error messages:

Could not load module ‘HsExpr’
    It is a member of the hidden package ‘ghc-lib-parser-8.8.4.20200716’.
   Perhaps you need to add ‘ghc-lib-parser’ to the build-depends in your .cabal file.
   ..

I toyed around a bit and unfortunately following the suggestion created a new error: Ambiguous module name ‘HscTypes’.