cabal-install configureCompiler: configure progdb

We should configure unconfigured programs before serialising them
(using the Binary ProgramDb instance) in
Distribution.Client.ProjectPlanning.configureCompiler, as otherwise
we can accidentally discard information.

This isn't currently a live bug, because in practice we end up
re-running configuration steps when interfacing with the Cabal library.
However, in the bright future in which we avoid re-configuring things
when building a Cabal package that we already determined when invoking
cabal-install, this starts causing problems.

Author: sheaf

cabal-install/src/Distribution/Client/ProjectPlanning.hs

@@ -482,24 +482,28 @@ configureCompiler
         liftIO $ info verbosity "Compiler settings changed, reconfiguring..."
         progdb <- liftIO $ prependProgramSearchPath verbosity (fromNubList packageConfigProgramPathExtra) defaultProgramDb
         let progdb' = userSpecifyPaths (Map.toList (getMapLast packageConfigProgramPaths)) progdb
-        result@(_, _, progdb'') <-
+        (comp, plat, progdb'') <-
           liftIO $
             Cabal.configCompilerEx
               hcFlavor
               hcPath
               hcPkg
               progdb'
               verbosity
+        -- Configure the unconfigured programs in the program database,
+        -- as we can't serialise unconfigured programs.
+        -- See also #2241 and #9840.
+        finalProgDb <- liftIO $ configureAllKnownPrograms verbosity progdb''
 
         -- Note that we added the user-supplied program locations and args
         -- for /all/ programs, not just those for the compiler prog and
         -- compiler-related utils. In principle we don't know which programs
         -- the compiler will configure (and it does vary between compilers).
         -- We do know however that the compiler will only configure the
         -- programs it cares about, and those are the ones we monitor here.
-        monitorFiles (programsMonitorFiles progdb'')
+        monitorFiles (programsMonitorFiles finalProgDb)
 
-        return result
+        return (comp, plat, finalProgDb)
     where
       hcFlavor = flagToMaybe projectConfigHcFlavor
       hcPath = flagToMaybe projectConfigHcPath