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

[Apoorv Ingle (@ani)]

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


Commits:
b94a213d by Apoorv Ingle at 2023-10-02T10:46:23-05:00
Expands `do` blocks before typechecking using the `HsExpansion` philosophy

- Fixes #18324 #20020 #23147 #22788 #15598 #22086
- Note [Expanding HsDo with HsExpansion] in `GHC.Tc.Gen.Match` explains change in detail
- New datatypes to make this expansion work:
    `GHC.Hs.Expr.XXExprGhcRn`: It contains
    1. Expansion bits for Statements (`ExpansionStmt`) and Patterns (`ExpansionPat`)
    2. `PopErrCtxt` a special GhcRn Phase only artifcat to pop the previous error message in the error context stack
- `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/Utils.hs
- compiler/GHC/Tc/Deriv/Generate.hs
- compiler/GHC/Tc/Gen/App.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/Origin.hs
- compiler/GHC/Tc/Utils/Instantiate.hs
- compiler/GHC/Tc/Utils/Monad.hs
- compiler/GHC/Tc/Zonk/Type.hs
- compiler/GHC/Types/Basic.hs


The diff was not included because it is too large.


View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/b94a213d6451eb444afc1884852c3729fff2374f

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/b94a213d6451eb444afc1884852c3729fff2374f
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