Error whether or not project has packages

Guard against triggering an assertion if targets are null

Author: philderbeast

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

@@ -292,9 +292,9 @@ replAction flags@NixStyleFlags{extraFlags = replFlags@ReplFlags{..}, configFlags
 
     baseCtx <- case targetCtx of
       ProjectContext -> do
-        let pkgs = projectPackages $ projectConfig ctx
-        when (null targetSelectors && not (null pkgs)) $ do
+        when (null targetSelectors) $ do
           let projectFile = projectConfigProjectFile . projectConfigShared $ projectConfig ctx
+          let pkgs = projectPackages $ projectConfig ctx
           dieWithException verbosity $
             RenderReplTargetProblem [render (reportProjectNoTarget projectFile pkgs)]
         return ctx
@@ -396,10 +396,15 @@ replAction flags@NixStyleFlags{extraFlags = replFlags@ReplFlags{..}, configFlags
 
         let
           elaboratedPlan' =
-            pruneInstallPlanToTargets
-              TargetActionRepl
-              targets
-              elaboratedPlan
+            -- Guard against pruning with empty targets and failing an assertion
+            -- within pruneInstallPlanToTargets.
+            if null targets
+              then elaboratedPlan
+              else
+                pruneInstallPlanToTargets
+                  TargetActionRepl
+                  targets
+                  elaboratedPlan
           includeTransitive = fromFlagOrDefault True (envIncludeTransitive replEnvFlags)
 
         pkgsBuildStatus <-