Simon Peyton Jones pushed to branch wip/spj-apporv-Oct24 at Glasgow Haskell Compiler / GHC

Commits:

4 changed files:

Changes:

  • compiler/GHC/Hs/Expr.hs
    ... ... @@ -662,9 +662,13 @@ type instance XXExpr GhcTc = XXExprGhcTc
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     -- See Note [Rebindable syntax and XXExprGhcRn]
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     -- See Note [Expanding HsDo with XXExprGhcRn] in `GHC.Tc.Gen.Do`
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    -data HsExpansion p = HSE { hs_ctxt :: HsCtxt -- The original source thing context to be used for error messages
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    -                         , expanded_expr :: LHsExpr p } -- The compiler generated, expanded expression
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    -                                                        -- This is located because of do statements (TODO ANI : Add Note)
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    +data HsExpansion p
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    +  = HSE { hse_ctxt :: HsCtxt      -- The original source thing context,
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    +                                  -- to be used for error messages
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    +        , hse_exp  :: LHsExpr p   -- The compiler generated expansion
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    +                                  -- This is located because of do statements
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    +                                  -- (TODO ANI : Add Note)
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    +        }
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     data XXExprGhcRn
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       = ExpandedThingRn (HsExpansion GhcRn)  -- ^ Renamed/Pre Typecheck expanded expression

  • compiler/GHC/Tc/Gen/Do.hs
    ... ... @@ -46,7 +46,10 @@ import Data.List ((\\))
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     --   See Note [Expanding HsDo with XXExprGhcRn] below for `HsDo` specific commentary
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     --   and Note [Handling overloaded and rebindable constructs] for high level commentary
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     expandDoStmts :: HsDoFlavour -> XRec GhcRn [ExprLStmt GhcRn] -> TcM (HsExpansion GhcRn)
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    -expandDoStmts doFlav lstmts@(L _ stmts) = HSE (ExprCtxt (HsDo noExtField doFlav lstmts)) <$> expand_do_stmts doFlav stmts
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    +expandDoStmts doFlav lstmts@(L _ stmts)
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    +  = do { exp <- expand_do_stmts doFlav stmts
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    +       ; return $ HSE { hse_ctxt = ExprCtxt (HsDo noExtField doFlav lstmts)
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    +                      , hse_exp  = exp } }
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     -- | The main work horse for expanding do block statements into applications of binds and thens
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     --   See Note [Expanding HsDo with XXExprGhcRn]

  • compiler/GHC/Tc/Gen/Expr.hs
    ... ... @@ -798,8 +798,8 @@ Example: Typechecking the do expression. The typechecker looks (somewhat) like t
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     The `expandDoStmts` replaces the HsDo { x <- e1; return x }
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     with something like
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    -   HSE { hs_ctxt = e
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    -       , expanded_expr = e1 >>= \ x -> x }
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    +   HSE { hse_ctxt = ExprCtxt e
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    +       , hse_exp  = e1 >>= \ x -> x }
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     and we then typecheck the expression `e1 >>= \ x -> x`
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     See also Note [Handling overloaded and rebindable constructs]
    ... ... @@ -812,8 +812,8 @@ The rest of this Note explains how that is done.
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     * The expansion process typically takes a user written thing
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            L lspan ue
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       and returns
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    -       L lspan (XExpr (ExpandedThingRn (HSE { hs_ctxt = ue
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    -                                            , expanded_expr = ee } ))
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    +       L lspan (XExpr (ExpandedThingRn (HSE { hse_ctxt = ue
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    +                                            , hse_exp  = ee } ))
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       where `ee` is the expansion of the user written thing `ue`
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     * The type checker context has 3 key fields that describe the context:
    ... ... @@ -830,36 +830,32 @@ The rest of this Note explains how that is done.
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       The `tcl_in_gen_code` is a boolean that keeps track of whether
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       the current expression being typechecked is compiler generated
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       or user generated.
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    -  INVARIANT: `tcl_in_gen_code` is modified only in `setSrcSpan`.
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    +  INVARIANT: `tcl_loc` and `tcl_in_gen_code` are modified only in `setSrcSpan`.
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     * Now, when
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           tcMonoLExpr :: LHsExpr GhcRn -> ExpRhoType -> TcM (HsExpr GhcTc)
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       gets a located expression, it does 3 things:
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         (a) Calls `setSrcSpanA` to set the ambient source-code location
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    -    (b) Calls `addExprCtxt` to add a suitable `HsCtxt` on top of the `tcl_err_ctxt`.
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    +    (b) Calls `addExprCtxt` to push a suitable `HsCtxt` on top of the `tcl_err_ctxt`.
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         (c) Calls `tcExpr` to typecheck the expression.
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     * In these calls, if the `span` is generated  (see `isGeneratedSrcSpan`), then
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    -     - `setSrcSpanA` sets `tcl_in_gen_code` to `True`
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    -     - `addErrCtxt` is a no-op if `tcl_in_gen_code` is True
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    -  This is how we avoid populating the TcLclCtxt with generated code.
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    -
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    -* The type checker error-stack element `GHC.Tc.Types.ErrCtxt.HsCtxt`
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    -  just stores an error message
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    -
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    -           type ErrCtxtStack = [HsCtxt]
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    -
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    -  When called on an `XExpr`, `addLExprCtxt`, adds the user written thing
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    -  `ue`, and the error message provided by the caller on the `ErrCtxtStack` See
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    -  Note [ErrCtxtStack Manipulation] for more details.
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    -
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    +     - `setSrcSpanA` sets `tcl_in_gen_code` to `True`, and leaves `tcl_loc` unchanged
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    +     - `addExprCtxt` is a no-op if `tcl_in_gen_code` is True
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    +  The result is that `tcl_loc` has the span from the innermost /user/ tree node;
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    +  and the ErrCtxtStack in `tcl_err_ctxt` only has contexts arisign from user code.
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    +
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    +* Note that inside an expansion we have sub-expressions from the original program.
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    +  As soon as we enter one of those, identified by a /user/ span, `setSrcSpanA` will
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    +  sets the `tcl_loc` to reflect that span, and switch off `tcl_in_gen_code`.  Nice!
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     -}
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     tcHsExpansion :: HsExpansion GhcRn -> ExpRhoType -> TcM (HsExpr GhcTc)
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    -tcHsExpansion (HSE o e) res_ty
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    -   = do e' <- tcMonoLExpr e res_ty
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    -        return $ XExpr (ExpandedThingTc (HSE o e'))
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    +tcHsExpansion (HSE { hse_ctxt = o, hse_exp = e }) res_ty
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    +   = do { e' <- tcMonoLExpr e res_ty
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    +        ; return $ XExpr $ ExpandedThingTc $
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    +          HSE { hse_ctxt = o, hse_exp = e' } }
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     {-

  • compiler/GHC/Tc/Types/LclEnv.hs
    ... ... @@ -168,14 +168,12 @@ getLclEnvErrCtxt = tcl_err_ctxt . tcl_lcl_ctxt
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     setLclEnvErrCtxt :: ErrCtxtStack -> TcLclEnv -> TcLclEnv
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     setLclEnvErrCtxt ctxt = modifyLclCtxt (\env -> env { tcl_err_ctxt = ctxt })
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    --- See Note [ErrCtxtStack Manipulation]
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     addLclEnvErrCtxt :: HsCtxt -> TcLclEnv -> TcLclEnv
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     addLclEnvErrCtxt ec = setLclEnvHsCtxt ec
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     setLclEnvHsCtxt :: HsCtxt -> TcLclEnv -> TcLclEnv
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     setLclEnvHsCtxt ec = modifyLclCtxt (setLclCtxtHsCtxt ec)
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    178 
    --- See Note [ErrCtxtStack Manipulation]
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     setLclCtxtHsCtxt :: HsCtxt -> TcLclCtxt -> TcLclCtxt
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     setLclCtxtHsCtxt ec lclCtxt
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       -- Never stack 2 statement error contexts on top of each other

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