[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:
3a55f5f1 by Apoorv Ingle at 2024-02-02T08:53:51-06:00
Expand `do` blocks right before typechecking using the `HsExpansion` philosophy.

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

- The change is detailed in
  - Note [Expanding HsDo with HsExpansion] in `GHC.Tc.Gen.Do`
  - 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

- Adds new datatypes:
  - `GHC.Hs.Expr.XXExprGhcRn`: new datatype makes this expansion work easier
    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

  - `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`

  - Kills `HsExpansion` and `HsExpanded` as we have inlined them in `XXExprGhcRn` and `XXExprGhcTc`

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

- Kill `HsMatchCtxt` in favor of `TcMatchAltChecker`

- 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)

Also repoint haddock to the right submodule so that the test (haddockHypsrcTest) pass

Metric Increase 'compile_time/bytes allocated':
    T9020

The testcase is a pathalogical example of a `do`-block with many statements that do nothing.
Given that we are expanding the statements into function binds, we will have to bear
a (small) 2% cost upfront in the compiler to unroll the 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/Arrow.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


The diff was not included because it is too large.


View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/3a55f5f1a8bf4830b78a16eee153c64d308cba45

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