diff options
Diffstat (limited to 'compiler/GHC')
| -rw-r--r-- | compiler/GHC/Rename/Expr.hs | 41 |
1 files changed, 24 insertions, 17 deletions
diff --git a/compiler/GHC/Rename/Expr.hs b/compiler/GHC/Rename/Expr.hs index 0323998ecb..3b22e3ea73 100644 --- a/compiler/GHC/Rename/Expr.hs +++ b/compiler/GHC/Rename/Expr.hs @@ -1210,11 +1210,11 @@ rnStmt ctxt rnBody (L loc (RecStmt { recS_stmts = L _ rec_stmts })) thing_inside segs -- See Note [Deterministic ApplicativeDo and RecursiveDo desugaring] ; (thing, fvs_later) <- thing_inside bndrs - -- In interactive mode, assume that all variables are used later + -- In interactive mode, all variables could be used later. So we pass whether + -- we are in GHCi along to segmentRecStmts. See Note [What is "used later" in a rec stmt] ; is_interactive <- isInteractiveModule . tcg_mod <$> getGblEnv ; let - final_fvs_later = if is_interactive then Nothing else Just fvs_later - (rec_stmts', fvs) = segmentRecStmts (locA loc) ctxt empty_rec_stmt segs final_fvs_later + (rec_stmts', fvs) = segmentRecStmts (locA loc) ctxt empty_rec_stmt segs (fvs_later, is_interactive) -- We aren't going to try to group RecStmts with -- ApplicativeDo, so attaching empty FVs is fine. ; return ( ((zip rec_stmts' (repeat emptyNameSet)), thing) @@ -1567,16 +1567,19 @@ segmentRecStmts :: AnnoBody body => SrcSpan -> HsStmtContext GhcRn -> Stmt GhcRn (LocatedA (body GhcRn)) -> [Segment (LStmt GhcRn (LocatedA (body GhcRn)))] - -> Maybe FreeVars -- Nothing when in interactive mode, everything can be used later - -- Note [What is "used later" in a rec stmt] + -> (FreeVars, Bool) + -- ^ The free variables used in later statements. + -- If the boolean is 'True', this might be an underestimate + -- because we are in GHCi, and might thus be missing some "used later" + -- FVs. See Note [What is "used later" in a rec stmt] -> ([LStmt GhcRn (LocatedA (body GhcRn))], FreeVars) -segmentRecStmts loc ctxt empty_rec_stmt segs mfvs_later +segmentRecStmts loc ctxt empty_rec_stmt segs (fvs_later, might_be_more_fvs_later) | null segs = ([], final_fv_uses) | HsDoStmt (MDoExpr _) <- ctxt - = segsToStmts empty_rec_stmt grouped_segs later_ids + = segsToStmts empty_rec_stmt grouped_segs fvs_later -- Step 4: Turn the segments into Stmts -- Use RecStmt when and only when there are fwd refs -- Also gather up the uses from the end towards the @@ -1586,19 +1589,22 @@ segmentRecStmts loc ctxt empty_rec_stmt segs mfvs_later | otherwise = ([ L (noAnnSrcSpan loc) $ empty_rec_stmt { recS_stmts = noLocA ss - , recS_later_ids = nameSetElemsStable later_ids + , recS_later_ids = nameSetElemsStable final_fvs_later , recS_rec_ids = nameSetElemsStable (defs `intersectNameSet` uses) }] -- See Note [Deterministic ApplicativeDo and RecursiveDo desugaring] , uses `plusFV` final_fv_uses) where - final_fv_uses = case mfvs_later of - Nothing -> defs - Just later -> uses `plusFV` later - later_ids = case mfvs_later of - Nothing -> defs - Just fvs_later -> defs `intersectNameSet` fvs_later + (final_fv_uses, final_fvs_later) + | might_be_more_fvs_later + = (defs, defs) + -- If there might be more uses later (e.g. we are in GHCi and have not + -- yet seen the whole rec statement), conservatively assume that everything + -- will be used later (as is possible). + | otherwise + = ( uses `plusFV` fvs_later + , defs `intersectNameSet` fvs_later ) (defs_s, uses_s, _, ss) = unzip4 segs defs = plusFVs defs_s @@ -1677,7 +1683,7 @@ glom it together with the first two groups Note [What is "used later" in a rec stmt] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -We desugar a recursive Stmt to somethign like +We desugar a recursive Stmt to something like (a,_,c) <- mfix (\(a,b,_) -> do { ... ; return (a,b,c) }) ...stuff after the rec... @@ -1693,8 +1699,9 @@ after the `rec` (#20206). For example, we might have ghci> print y So we have to assume that *all* the variables bound in the `rec` are used -afterwards. We use `Nothing` in the argument to segmentRecStmts to signal -that all the variables are used. +afterwards. We pass a Boolean to segmentRecStmts to signal such a situation, +in which case that function conservatively assumes that everything might well +be used later. -} glomSegments :: HsStmtContext GhcRn |