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

@@ -483,7 +483,7 @@ configureCompiler
         let extraPath = fromNubList packageConfigProgramPathExtra
         progdb <- liftIO $ prependProgramSearchPath verbosity extraPath [] defaultProgramDb
         let progdb' = userSpecifyPaths (Map.toList (getMapLast packageConfigProgramPaths)) progdb
-        result@(_, _, progdb'') <-
+        (comp, plat, progdb'') <-
           liftIO $
             Cabal.configCompilerEx
               hcFlavor
@@ -500,7 +500,12 @@ configureCompiler
         -- programs it cares about, and those are the ones we monitor here.
         monitorFiles (programsMonitorFiles progdb'')
 
-        return result
+        -- 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''
+
+        return (comp, plat, finalProgDb)
     where
       hcFlavor = flagToMaybe projectConfigHcFlavor
       hcPath = flagToMaybe projectConfigHcPath