chore: only mention cabal.project issue for parser errors

nix/haskell-parsers/default.nix

@@ -1,6 +1,7 @@
 { pkgs
 , lib
 , throwError ? builtins.throw
+, throwErrorOnCabalProjectParseError ? builtins.throw
 , ...
 }:
 
@@ -49,13 +50,13 @@ in
                 if isSelfPath path
                 then projectRoot
                 else if lib.strings.hasInfix "*" path
-                then throwError "Found a path with glob (${path}) in ${cabalProjectFile}, which is not supported"
+                then throwErrorOnCabalProjectParseError "Found a path with glob (${path}) in ${cabalProjectFile}, which is not supported"
                 else if lib.strings.hasSuffix ".cabal" path
-                then throwError "Expected a directory but ${path} (in ${cabalProjectFile}) is a .cabal filepath"
+                then throwErrorOnCabalProjectParseError "Expected a directory but ${path} (in ${cabalProjectFile}) is a .cabal filepath"
                 else "${projectRoot}/${path}"
               )
               res.value
-          else throwError "Failed to parse ${cabalProjectFile}: ${builtins.toJSON res}"
+          else throwErrorOnCabalProjectParseError "Failed to parse ${cabalProjectFile}: ${builtins.toJSON res}"
         else
           [ projectRoot ];
     in

nix/modules/project/defaults.nix

@@ -41,6 +41,12 @@ in
               A default value for `packages` cannot be auto-determined:
 
                 ${msg}
+            '';
+            throwErrorOnCabalProjectParseError = msg: config.log.throwError ''
+
+              A default value for `packages` cannot be auto-determined:
+
+                ${msg}
 
               haskell-flake's `cabal.project` parser is limited; see #307.
               Please specify the `packages` option manually or modify your