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41e80f41
by Simon Peyton Jones at 2026-10-11T14:38:51-04:00
Simplify the error-suppression mechanism in GHC.Tc.Errors
In `GHC.Tc.Errors.reportWanteds` we suppress some errors in favour of
others. But the mechanism had grown crufty, and #27331 exposed a bug.
This MR makes it simpler and more uniform, by doing everything via
the `ei_suppress` field of the ErrorItem.
Claude then found another closely-related bug (see the review linked
on !16564). That bug is immortalised in new test T18851d.
I'm still not happy with `ignoreConstraint` but we can worry about
that another day; I have not touched it.
Main changes
* Instead of /predicting/ when an error will be reported, we set
`cec_error_reported` when an error is /actually/ reported. (I renamed
it from `cec_suppress` to reflect this change.)
Now errors are suppressed only when a preceding error has actually been
reported. Simpler and more robust.
See `Note [cec_error_reported: suppressing less-serious errors]`
The big changes are in `reportWanteds` which looks very different.
* New `Note [ei_suppress: suppressing confusing errors]` describes the
(quite separate) `ei_suppress` mechanism for suppressing confusing
errors, mainly arising from non-empty rewriter sets
* In `tryTypeClassDefaulting`, instead of switching off type-class defaulting
if there is an insoluble /anywhere/, we just switch it off locally when
we find an insoluble sub-tree. See Note [When to do type-class defaulting]
and (W5) in Note [ApproximateWC]
* Greatly simplify `insolubleWantedCt`.
* I made type-class-defaulting be a bit more eager, only switched off when
a peer or ancestor (but not child) constraint is insoluble. See
Note [When to do type-class defaulting].
Small refactorings
* Rename `askNoErrs` to `askErrsFound` and flip its polarity
* The code for "check if ei_suppress is true of all items" code is
moved to `mkErrorItems` rather than in the large `reportWanteds`.
* Code for `has_gadt_match` moves to `mkGivenErrorReporter`, rather than
polluting the large `reportWanteds`.
* Many tests with `-fdefer-type-errors` get more warnings, especially
about ambiguous (Num a) constraints. This is by-design: see
Note [Always warn with -fdefer-type-errors]. Previously GHC was not
honouring this Note but now it is, hence the extra errors.
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f217fc31
by Cheng Shao at 2026-10-11T14:39:33-04:00
compiler: ensure cross ghc --info output target unit ids
Previously, for cross ghcs, the base/ghc/ghc-internal unit ids in
--info output do not match the target unit ids reported by ghc-pkg,
breaking cross ghc release builds with hash-unit-ids when being used
with cabal 3.18. This patch fixes it by making --info output target
unit ids. Fixes #27919.
Co-authored-by: Codex <codex@openai.com>
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e8f40ee0
by Alan Zimmerman at 2026-10-12T18:05:10+01:00
EPA: Start using vocurly as basis for AnnListLayout
For the existing cases that populate AnnList.
This uses AnnListBraces when braces are explicitly supplied, and
AnnListLayout when vocurly is used
The change also shows up AnnList usages that can never capture layout,
these are cleared up later.