diff options
| -rw-r--r-- | compiler/rename/RnBinds.lhs | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/compiler/rename/RnBinds.lhs b/compiler/rename/RnBinds.lhs index 65df7ba196..75c49437c0 100644 --- a/compiler/rename/RnBinds.lhs +++ b/compiler/rename/RnBinds.lhs @@ -454,9 +454,18 @@ rnBind _ (L loc bind@(PatBind { pat_lhs = pat -- MonoLocalBinds test in TcBinds.decideGeneralisationPlan bndrs = collectPatBinders pat bind' = bind { pat_rhs = grhss', bind_fvs = fvs' } - + is_wild_pat = case pat of + L _ (WildPat {}) -> True + _ -> False + + -- Warn if the pattern binds no variables, except for the + -- entirely-explicit idiom _ = rhs + -- which (a) is not that different from _v = rhs + -- (b) is sometimes used to give a type sig for, + -- or an occurrence of, a variable on the RHS ; ifWOptM Opt_WarnUnusedBinds $ - when (null bndrs) (addWarn $ unusedPatBindWarn bind') + when (null bndrs && not is_wild_pat) $ + addWarn $ unusedPatBindWarn bind' ; fvs' `seq` -- See Note [Free-variable space leak] return (L loc bind', bndrs, all_fvs) } |