HPC: Error out on multi-package when coverage is enabled (haskell#9493)

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

@@ -69,6 +69,8 @@ import Distribution.Client.Errors
 import GHC.Environment
   ( getFullArgs
   )
+import Distribution.Client.ProjectConfig.Types (ProjectConfig(projectConfigLocalPackages))
+import Distribution.Client.ProjectConfig (PackageConfig(packageConfigCoverage))
 
 testCommand :: CommandUI (NixStyleFlags ())
 testCommand =
@@ -125,6 +127,10 @@ testAction :: NixStyleFlags () -> [String] -> GlobalFlags -> IO ()
 testAction flags@NixStyleFlags{..} targetStrings globalFlags = do
   baseCtx <- establishProjectBaseContext verbosity cliConfig OtherCommand
 
+  -- Multi package coverage is not supported (see cabal#9493)
+  when (length (localPackages baseCtx) > 1 && fromFlagOrDefault False (packageConfigCoverage (projectConfigLocalPackages $ projectConfig baseCtx))) $
+    dieWithException verbosity MultiPackageCoverageUnsupported
+
   targetSelectors <-
     either (reportTargetSelectorProblems verbosity) return
       =<< readTargetSelectors (localPackages baseCtx) (Just TestKind) targetStrings

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

@@ -184,6 +184,7 @@ data CabalInstallException
   | CorruptedIndexCache String
   | UnusableIndexState RemoteRepo Timestamp Timestamp
   | MissingPackageList RemoteRepo
+  | MultiPackageCoverageUnsupported
   deriving (Show, Typeable)
 
 exceptionCodeCabalInstall :: CabalInstallException -> Int
@@ -334,6 +335,7 @@ exceptionCodeCabalInstall e = case e of
   CorruptedIndexCache{} -> 7158
   UnusableIndexState{} -> 7159
   MissingPackageList{} -> 7160
+  MultiPackageCoverageUnsupported -> 7161
 
 exceptionMessageCabalInstall :: CabalInstallException -> String
 exceptionMessageCabalInstall e = case e of
@@ -849,6 +851,9 @@ exceptionMessageCabalInstall e = case e of
     "The package list for '"
       ++ unRepoName (remoteRepoName repoRemote)
       ++ "' does not exist. Run 'cabal update' to download it."
+  MultiPackageCoverageUnsupported ->
+    "--enable-coverage was specified, but program coverage is not supported in "
+      ++ "multiple package projects because of a HPC limitation (see cabal#9493)."
 
 instance Exception (VerboseException CabalInstallException) where
   displayException :: VerboseException CabalInstallException -> [Char]