Fix #489

Report an error when attempting to create a submodule or type with the
same name as an existing submodule or type.

Author: pschachte

src/Normalise.hs

@@ -55,18 +55,18 @@ normalise items = do
 normaliseItem :: Item -> Compiler ()
 normaliseItem (TypeDecl vis (TypeProto name params) mods
               (TypeRepresentation rep) items pos) = do
-    validateModuleName "type" pos name
+    validateNewModuleName "type" pos name
     let items' = RepresentationDecl params mods rep pos : items
     unless (List.null params)
       $ errmsg pos "types defined by representation cannot have type parameters"
     normaliseSubmodule name vis pos items'
 normaliseItem (TypeDecl vis (TypeProto name params) mods
               (TypeCtors ctorVis ctors) items pos) = do
-    validateModuleName "type" pos name
+    validateNewModuleName "type" pos name
     let items' = ConstructorDecl ctorVis params mods ctors pos : items
     normaliseSubmodule name vis pos items'
 normaliseItem (ModuleDecl vis name items pos) = do
-    validateModuleName "module" pos name
+    validateNewModuleName "module" pos name
     normaliseSubmodule name vis pos items
 normaliseItem (RepresentationDecl params mods rep pos) = do
     updateTypeModifiers mods
@@ -301,7 +301,19 @@ completeTypeSCC (CyclicSCC modTypeDefs) = do
     mapM_ (uncurry completeType) modTypeDefs
 
 
--- |Check that the specified module name is valid, reporting and error if not.
+-- |Check that the specified name is a valid name for a new module of the
+-- current module.  Report an error if it's an invalid module name component or
+-- is the name of an existing submodule.
+validateNewModuleName :: String -> OptPos -> Ident -> Compiler ()
+validateNewModuleName what pos name = do
+    validateModuleName what pos name
+    subModSpec <- (++[name]) <$> getModuleSpec
+    alreadyExists <- isJust <$> getLoadingModule subModSpec
+    when alreadyExists
+      $ errmsg pos $ "module " ++ showModSpec subModSpec ++ " already exists"
+
+
+-- |Check that the specified module name is valid, reporting an error if not.
 validateModuleName :: String -> OptPos -> Ident -> Compiler ()
 validateModuleName what pos name =
     unless (validModuleName name)

test-cases/final-dump/dup_submodule.exp

@@ -0,0 +1,2 @@
+Error detected during preliminary processing of module dup_submodule
+final-dump/dup_submodule.wybe:6:1: module dup_submodule.again already exists

test-cases/final-dump/dup_submodule.wybe

@@ -0,0 +1,11 @@
+module again {
+   pub def answer:int = 42
+}
+
+# should be an error:
+module again {
+   pub def foo:int = answer
+}
+
+!println "answer = $answer"
+!println "foo = $foo"