Add explanation of package name parsing commercialhaskell#1873

mgsloan · mgsloan · commit 4fa3b47d7fce · 2016-03-03T15:02:28.000-08:00
diff --git a/src/Stack/Types/PackageName.hs b/src/Stack/Types/PackageName.hs
@@ -164,4 +164,8 @@ packageNameArgument =
     p s =
         case parsePackageNameFromString s of
             Just x -> Right x
-            Nothing -> Left ("Expected valid package name, but got: " ++ s)
+            Nothing -> Left $ unlines
+                [ "Expected valid package name, but got: " ++ s
+                , "Package names consist of one or more alphanumeric words separated by hyphens."
+                , "To avoid ambiguity with version numbers, each of these words must contain at least one letter."
+                ]
