output

$ runhaskell TestAddTopDecls.hs 

TestAddTopDecls.hs:5:14:
    GHC internal error: ‘one_a2M1’ is not in scope during type checking, but it passed the renamer
    tcl_env of environment: []
    In the first argument of ‘print’, namely ‘one_a2M1’
    In the expression: print one_a2M1
    In an equation for ‘main’: main = print one_a2M1

TestAddTopDecls.hs

{-# LANGUAGE TemplateHaskell #-}

import AddTopDecls

main = print $testAddTopDecls

AddTopDecls.hs

{-# LANGUAGE TemplateHaskell #-}

module AddTopDecls where

import Language.Haskell.TH.Syntax

-- Causes a GHC internal error.
testAddTopDecls = do
    n <- newName "one"
    addTopDecls [FunD n [Clause [] (NormalB (LitE (IntegerL 1))) []]]
    return (VarE n)

-- This is a separate issue.  I would expect this one to work, but I'm
-- guessing that 'addTopDecls' doesn't erase the uniqueness of names,
-- or something along those lines.
testAddTopDecls' = do
    addTopDecls =<< [d| one = 1 |]
    return (VarE (mkName "one"))