diff options
Diffstat (limited to 'compiler/GHC/Rename/Names.hs')
| -rw-r--r-- | compiler/GHC/Rename/Names.hs | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/compiler/GHC/Rename/Names.hs b/compiler/GHC/Rename/Names.hs index dbf1f88cba..b3360ad73b 100644 --- a/compiler/GHC/Rename/Names.hs +++ b/compiler/GHC/Rename/Names.hs @@ -690,7 +690,8 @@ extendGlobalRdrEnvRn :: [AvailInfo] -- see Note [Top-level Names in Template Haskell decl quotes] extendGlobalRdrEnvRn avails new_fixities - = do { (gbl_env, lcl_env) <- getEnvs + = checkNoErrs $ -- See Note [Fail fast on duplicate definitions] + do { (gbl_env, lcl_env) <- getEnvs ; stage <- getStage ; isGHCi <- getIsGHCi ; let rdr_env = tcg_rdr_env gbl_env @@ -767,7 +768,19 @@ extendGlobalRdrEnvRn avails new_fixities (False, True) -> isNoFieldSelectorGRE gre' (False, False) -> False -{- +{- Note [Fail fast on duplicate definitions] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If there are duplicate bindings for the same thing, we want to fail +fast. Having two bindings for the same thing can cause follow-on errors. +Example (test T9975a): + data Test = Test { x :: Int } + pattern Test wat = Test { x = wat } +This defines 'Test' twice. The second defn has no field-names; and then +we get an error from Test { x=wat }, saying "Test has no field 'x'". + +Easiest thing is to bale out fast on duplicate definitions, which +we do via `checkNoErrs` on `extendGlobalRdrEnvRn`. + Note [Reporting duplicate local declarations] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In general, a single module may not define the same OccName multiple times. This |