[Git][ghc/ghc][wip/expand-do] Expand `do` blocks right before typechecking using the `HsExpansion` philosophy.

[Apoorv Ingle (@ani)]

Apoorv Ingle pushed to branch wip/expand-do at Glasgow Haskell Compiler / GHC


Commits:
f206c989 by Apoorv Ingle at 2023-11-05T23:02:09+01:00
Expand `do` blocks right before typechecking using the `HsExpansion` philosophy.

- A step towards killing `tcSyntaxOp`

- Fixes #18324 #20020 #23147 #22788 #15598 #22086 #21206

- Note [Expanding HsDo with HsExpansion] in `GHC.Tc.Gen.Do` explains change in detail

- Note Note [Doing HsExpansion in the Renamer vs Typechecker] in `GHC.Rename.Expr` expains the rational of doing expansions in type checker as opposed to in the renamer

- New datatype to make this expansion work `GHC.Hs.Expr.XXExprGhcRn`:
    1. Expansion bits for Expressions, Statements and Patterns in (`ExpandedThingRn`)
    2. `PopErrCtxt` a special GhcRn Phase only artifcat to pop the previous error message in the error context stack
- Kills `HsExpansion` and `HsExpanded` as we have inlined them in `XXExprGhcRn` and `XXExprGhcTc`

- `GHC.Basic.Origin` now tracks the reason for expansion in case of Generated
  This is useful for type checking cf. `GHC.Tc.Gen.Expr.tcExpr` case for `HsLam`

- Ensures warnings such as
  1. Pattern mach checks
  2. Failable patterns
  3. non-() return in body statements are preserved

- Expansions inside Template haskell also work without issues.

- Testcases:
  * T18324 T20020 T23147 T22788 T15598 T22086
  * T23147b (error message check),
  * DoubleMatch (match inside a match for pmc check)
  * pattern-fails (check pattern match with non-refutable pattern, eg. newtype)
  * Simple-rec (rec statements inside do statment)
  * T22788 (code snippet from #22788)
  * DoExpanion1 (Error messages for body statments)
  * DoExpansion2 (Error messages for bind statements)
  * DoExpansion3 (Error messages for let statements)

- - - - -


30 changed files:

- compiler/GHC/Hs/Expr.hs
- compiler/GHC/Hs/Instances.hs
- compiler/GHC/Hs/Pat.hs
- compiler/GHC/Hs/Syn/Type.hs
- compiler/GHC/Hs/Utils.hs
- compiler/GHC/HsToCore/Arrows.hs
- compiler/GHC/HsToCore/Expr.hs
- compiler/GHC/HsToCore/Match.hs
- compiler/GHC/HsToCore/Pmc.hs
- compiler/GHC/HsToCore/Quote.hs
- compiler/GHC/HsToCore/Ticks.hs
- compiler/GHC/Iface/Ext/Ast.hs
- compiler/GHC/Rename/Expr.hs
- compiler/GHC/Rename/Pat.hs
- compiler/GHC/Rename/Utils.hs
- compiler/GHC/Tc/Deriv/Generate.hs
- compiler/GHC/Tc/Errors/Ppr.hs
- compiler/GHC/Tc/Gen/App.hs
- + compiler/GHC/Tc/Gen/Do.hs
- compiler/GHC/Tc/Gen/Expr.hs
- compiler/GHC/Tc/Gen/Head.hs
- compiler/GHC/Tc/Gen/Match.hs
- compiler/GHC/Tc/Gen/Pat.hs
- compiler/GHC/Tc/Gen/Splice.hs
- compiler/GHC/Tc/TyCl/Instance.hs
- compiler/GHC/Tc/TyCl/PatSyn.hs
- compiler/GHC/Tc/TyCl/Utils.hs
- compiler/GHC/Tc/Types/ErrCtxt.hs
- compiler/GHC/Tc/Types/LclEnv.hs
- compiler/GHC/Tc/Types/Origin.hs


The diff was not included because it is too large.


View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/f206c989ce003ff2c57fdc7fb437d83219a244dd

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/f206c989ce003ff2c57fdc7fb437d83219a244dd
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