diff options
| -rw-r--r-- | compiler/rename/RnBinds.hs | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/compiler/rename/RnBinds.hs b/compiler/rename/RnBinds.hs index d7790ca419..79b55029a1 100644 --- a/compiler/rename/RnBinds.hs +++ b/compiler/rename/RnBinds.hs @@ -470,9 +470,10 @@ rnBind _ bind@(PatBind { pat_lhs = pat ok_nobind_pat = -- See Note [Pattern bindings that bind no variables] case pat of - L _ (WildPat {}) -> True - L _ (BangPat {}) -> True -- #9127, #13646 - _ -> False + L _ (WildPat {}) -> True + L _ (BangPat {}) -> True -- #9127, #13646 + L _ (SplicePat {}) -> True + _ -> False -- Warn if the pattern binds no variables -- See Note [Pattern bindings that bind no variables] @@ -518,7 +519,7 @@ rnBind _ b = pprPanic "rnBind" (ppr b) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Generally, we want to warn about pattern bindings like Just _ = e -because they don't do anything! But we have two exceptions: +because they don't do anything! But we have three exceptions: * A wildcard pattern _ = rhs @@ -532,6 +533,12 @@ because they don't do anything! But we have two exceptions: Moreover, Trac #13646 argues that even for single constructor types, you might want to write the constructor. See also #9127. +* A splice pattern + $(th-lhs) = rhs + It is impossible to determine whether or not th-lhs really + binds any variable. We should disable the warning for any pattern + which contain splices, but that is a more expensive check. + Note [Free-variable space leak] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We have |