Add warnings for file header pragmas that appear in the body of a module (#20385)wip/parse-errs

Once we are done parsing the header of a module to obtain the options, we
look through the rest of the tokens in order to determine if they contain any
misplaced file header pragmas that would usually be ignored, potentially
resulting in bad error messages.

The warnings are reported immediately so that later errors don't shadow
over potentially helpful warnings.

Metric Increase:
  T13719

1 files changed, 5 insertions, 4 deletions

diff --git a/compiler/GHC/Driver/Pipeline.hs b/compiler/GHC/Driver/Pipeline.hs
index 415bb5e38f..d8b9bfa8af 100644
--- a/compiler/GHC/Driver/Pipeline.hs
+++ b/compiler/GHC/Driver/Pipeline.hs
@@ -663,13 +663,13 @@ preprocessPipeline pipe_env hsc_env input_fn = do
       use (T_Unlit pipe_env hsc_env input_fn)
 
 
-  (dflags1, warns1) <- use (T_FileArgs hsc_env unlit_fn)
+  (dflags1, p_warns1, warns1) <- use (T_FileArgs hsc_env unlit_fn)
   let hsc_env1 = hscSetFlags dflags1 hsc_env
 
   (cpp_fn, hsc_env2)
     <- runAfterFlag hsc_env1 (Cpp HsSrcFile) (xopt LangExt.Cpp) (unlit_fn, hsc_env1) $ do
           cpp_fn <- use (T_Cpp pipe_env hsc_env1 unlit_fn)
-          (dflags2, _) <- use (T_FileArgs hsc_env1 cpp_fn)
+          (dflags2, _, _) <- use (T_FileArgs hsc_env1 cpp_fn)
           let hsc_env2 = hscSetFlags dflags2 hsc_env1
           return (cpp_fn, hsc_env2)
 
@@ -677,15 +677,16 @@ preprocessPipeline pipe_env hsc_env input_fn = do
   pp_fn <- runAfterFlag hsc_env2 (HsPp HsSrcFile) (gopt Opt_Pp) cpp_fn $
             use (T_HsPp pipe_env hsc_env2 input_fn cpp_fn)
 
-  (dflags3, warns3)
+  (dflags3, p_warns3, warns3)
     <- if pp_fn == unlit_fn
           -- Didn't run any preprocessors so don't need to reparse, would be nicer
           -- if `T_FileArgs` recognised this.
-          then return (dflags1, warns1)
+          then return (dflags1, p_warns1, warns1)
           else do
             -- Reparse with original hsc_env so that we don't get duplicated options
             use (T_FileArgs hsc_env pp_fn)
 
+  liftIO (printOrThrowDiagnostics (hsc_logger hsc_env) (initDiagOpts dflags3) (GhcPsMessage <$> p_warns3))
   liftIO (handleFlagWarnings (hsc_logger hsc_env) (initDiagOpts dflags3) warns3)
   return (dflags3, pp_fn)