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Support semaphore-compat 2.0.0 #6934
Description
Related resources:
- https://well-typed.com/blog/2026/06/haskell-ecosystem-report-march-may-2026/#semaphores-and--jsem
- https://gitlab.haskell.org/ghc/ghc/-/merge_requests/15729
- https://gitlab.haskell.org/ghc/semaphore-compat/-/merge_requests/8
- Cabal (the tool) Update semaphore-compat to 2.0.0.0 to fix #9993 haskell/cabal#11628
Stack no longer compiles with semaphore-compat 2.0.0 (GHC 9.12.5-rc2):
[155 of 217] Compiling Stack.Build.ExecuteEnv ( src/Stack/Build/ExecuteEnv.hs, dist/build/Stack/Build/ExecuteEnv.o, dist/build/Stack/Build/ExecuteEnv.dyn_o )
src/Stack/Build/ExecuteEnv.hs:122:22: error: [GHC-61689]
Module ‘System.Semaphore’ does not export ‘Semaphore’.
|
122 | ( Semaphore, destroySemaphore, freshSemaphore )
| ^^^^^^^^^
src/Stack/Build/ExecuteEnv.hs:122:33: error: [GHC-61689]
Module ‘System.Semaphore’ does not export ‘destroySemaphore’.
|
122 | ( Semaphore, destroySemaphore, freshSemaphore )
| ^^^^^^^^^^^^^^^^
Activity
mpilgrem commentedon Jun 23, 2026
@sternenseemann, that is correct. That is because Stack is built against GHC 9.10.3 and its boot package is
semaphore-compat-1.0.0. That is also true of all released versions of GHC that have a dependency onsemaphore-compat.As you may know (see: https://docs.haskellstack.org/en/stable/commands/build_command/#-no-semaphore-flag), semaphore may appear broken on non-musl Linux distributions. The 'solution', I believe, is to build the Stack tool from source. That is relatively straightforward to do:
(
--git-branchaccepts version tags as well as branch names. A wrinkle, I have discovered is that you can only build a more recent version of Stack than the currently one on your PATH. So, you may have to first downgrade Stack to build Stack.)Depending on what dependencies have been built in the past, that process may take between about 3 and 20 mins.
EDIT: I see from the NixOS project that a minor version bump of GHC 9.12 may depend on
semaphore-2.0.0. So, I am assuming that backwards compatibility has been considered. If that is the case, I think the sequence of events will be this:semaphore-compat >= 2.0.0; and[-]Support semaphore-compat 2.0.0 / new semaphore protocol[/-][+]Support semaphore-compat 2.0.0[/+]mpilgrem commentedon Jun 24, 2026
@sternenseemann, having discussed things in the GHC room on matrix and elsewhere, my current plan is this:
semaphore-compat-2.0.0as a boot package (likely GHC 9.12.5 and then GHC 9.10.4 - although perhaps the order may be switched);If the Stackage project adopts such a GHC version as a Nightly, I will then start the process of getting Stack ready for
semaphore-compat-2.0.0. I think that will be straightfoward except, perhaps, in having an intelligent Stack error message if semaphore is specified but the specified version of GHC does not support semaphore version 2.Re #6934 Add ghc --info "Semaphore version" to CompilerPaths
Re #6934 Update when GHC supports semaphore
Fix #6934 Depend on `semaphore-compat-2.0.0`
Re #6934 Update when GHC supports semaphore
Fix #6934 Depend on `semaphore-compat-2.0.0`
Re #6934 Add ghc --info "Semaphore version" to CompilerPaths
Re #6934 Update when GHC supports semaphore
Fix #6934 Depend on `semaphore-compat-2.0.0`
Re #6934 Add ghc --info "Semaphore version" to CompilerPaths
Re #6934 Update when GHC supports semaphore
Fix #6934 Depend on `semaphore-compat-2.0.0`
Fix #6934 Depend on `semaphore-compat-2.0.0`
mpilgrem commentedon Jun 26, 2026
@sternenseemann, I now have a draft pull request that builds Stack with GHC 9.12.5-rc2 and supports
semaphore-compat-2.0.0:semaphore-compat-2.0.0#6935Re #6934 Update to semaphore-compat-2.0.0 types and functions
Re #6934 Add ghc --info "Semaphore version" to CompilerPaths
Re #6934 Update when GHC supports semaphore
Fix #6934 Depend on `semaphore-compat-2.0.0`
Re #6934 Update to semaphore-compat-2.0.1 types and functions
Re #6934 Add ghc --info "Semaphore version" to CompilerPaths
Re #6934 Update when GHC supports semaphore
Fix #6934 Depend on `semaphore-compat-2.0.1`