-
e0f3ff11
by Patrick at 2025-04-17T04:31:12-04:00
Refactor Handling of Multiple Default Declarations
Fixes: #25912, #25914, #25934
Previously, GHC discarded all loaded defaults (tcg_default) when local
defaults were encountered during typechecking. According to the
exportable-named-default proposal (sections 2.4.2 and 2.4.3), local
defaults should be merged into tcg_default, retaining any defaults
already present while overriding where necessary.
Key Changes:
* Introduce DefaultProvenance to track the origin of default declarations
(local, imported, or built-in), replacing the original cd_module
in ClassDefaults with cd_provenance :: DefaultProvenance.
* Rename tcDefaults to tcDefaultDecls, limiting its responsibility to only
converting renamed class defaults into ClassDefaults.
* Add extendDefaultEnvWithLocalDefaults to merge local defaults into the
environment, with proper duplication checks:
- Duplicate local defaults for a class trigger an error.
- Local defaults override imported or built-in defaults.
* Update and add related notes: Note [Builtin class defaults],
Note [DefaultProvenance].
* Add regression tests: T25912, T25914, T25934.
Thanks sam and simon for the help on this patch.
Co-authored-by: sheaf <sam.derbyshire@gmail.com>
-
386f1854
by Teo Camarasu at 2025-04-17T04:31:55-04:00
template-haskell: Remove `addrToByteArrayName` and `addrToByteArray`
These were part of the implementation of the `Lift ByteArray` instance and were errornously exported because this module lacked an explicit export list. They have no usages on Hackage.
Resolves #24782
-
1a6a4b1e
by Simon Peyton Jones at 2025-04-18T17:42:14+01:00
Track rewriter sets more accurately in constraint solving
The key change, which fixed #25440, is to call `recordRewriter` in
GHC.Tc.Solver.Rewrite.rewrite_exact_fam_app. This missing call meant
that we were secretly rewriting a Wanted with a Wanted, but not really
noticing; and that led to a very bad error message, as you can see
in the ticket.
But of course that led me into rabbit hole of other refactoring around
the RewriteSet code:
* Improve Notes [Wanteds rewrite Wanteds]
* Zonk the RewriterSet in `zonkCtEvidence` rather than only in GHC.Tc.Errors.
This is tidier anyway (e.g. de-clutters debug output), and helps with the
next point.
* In GHC.Tc.Solver.Equality.inertsCanDischarge, don't replace a constraint
with no rewriters with an equal constraint that has many. See
See (CE4) in Note [Combining equalities]
* Move zonkRewriterSet and friends from GHC.Tc.Zonk.Type into
GHC.Tc.Zonk.TcType, where they properly belong.
A handful of tests get better error messages.
For some reason T24984 gets 12% less compiler allocation -- good
Metric Decrease:
T24984