<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
<html lang="en">
<head>
<meta content="text/html; charset=US-ASCII" http-equiv="Content-Type">
<title>
GitLab
</title>
<style data-premailer="ignore" type="text/css">
a { color: #1068bf; }
</style>
<style>img {
max-width: 100%; height: auto;
}
body {
font-size: 0.875rem;
}
body {
-webkit-text-shadow: rgba(255,255,255,0.01) 0 0 1px;
}
body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Noto Sans", Ubuntu, Cantarell, "Helvetica Neue", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji"; font-size: inherit;
}
</style>
</head>
<body style='font-size: inherit; -webkit-text-shadow: rgba(255,255,255,0.01) 0 0 1px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Noto Sans", Ubuntu, Cantarell, "Helvetica Neue", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";'>
<div class="content">
<h3 style="margin-top: 20px; margin-bottom: 10px;">
Marge Bot pushed to branch master at <a href="https://gitlab.haskell.org/ghc/ghc" style="color: #1068bf;">Glasgow Haskell Compiler / GHC</a>
</h3>
<h4 style="margin-top: 10px; margin-bottom: 10px;">
Commits:
</h4>
<ul>
<li>
<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/aed1974e92366ab8e117734f308505684f70cddf" style="color: #1068bf;">aed1974e</a></strong>
<div>
<span> by Richard Eisenberg </span> <i> at 2023-01-11T08:30:42+00:00 </i>
</div>
<pre class="commit-message" style='white-space: pre-wrap; display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: #fafafa; border-radius: 2px; margin: 0; padding: 8px 12px; border: 1px solid #dbdbdb;'>Refactor the treatment of loopy superclass dicts
This patch completely re-engineers how we deal with loopy superclass
dictionaries in instance declarations. It fixes #20666 and #19690
The highlights are
* Recognise that the loopy-superclass business should use precisely
the Paterson conditions. This is much much nicer. See
Note [Recursive superclasses] in GHC.Tc.TyCl.Instance
* With that in mind, define "Paterson-smaller" in
Note [Paterson conditions] in GHC.Tc.Validity, and the new
data type `PatersonSize` in GHC.Tc.Utils.TcType, along with
functions to compute and compare PatsonSizes
* Use the new PatersonSize stuff when solving superclass constraints
See Note [Solving superclass constraints] in GHC.Tc.TyCl.Instance
* In GHC.Tc.Solver.Monad.lookupInInerts, add a missing call to
prohibitedSuperClassSolve. This was the original cause of #20666.
* Treat (TypeError "stuff") as having PatersonSize zero. See
Note [Paterson size for type family applications] in GHC.Tc.Utils.TcType.
* Treat the head of a Wanted quantified constraint in the same way
as the superclass of an instance decl; this is what fixes #19690.
See GHC.Tc.Solver.Canonical Note [Solving a Wanted forall-constraint]
(Thanks to Matthew Craven for this insight.)
This entailed refactoring the GivenSc constructor of CtOrigin a bit,
to say whether it comes from an instance decl or quantified constraint.
* Some refactoring way in which redundant constraints are reported; we
don't want to complain about the extra, apparently-redundant
constraints that we must add to an instance decl because of the
loopy-superclass thing. I moved some work from GHC.Tc.Errors to
GHC.Tc.Solver.
* Add a new section to the user manual to describe the loopy
superclass issue and what rules it follows.
</pre>
</li>
</ul>
<h4 style="margin-top: 10px; margin-bottom: 10px;">
30 changed files:
</h4>
<ul>
<li class="file-stats">
<a href="#5596bb0f228bd2a308c4391df97375ae879430a8" style="color: #1068bf;">
compiler/GHC/Core/InstEnv.hs
</a>
</li>
<li class="file-stats">
<a href="#039e8f5676356ef05c90af828aae48aac7296e47" style="color: #1068bf;">
compiler/GHC/Core/TyCo/FVs.hs
</a>
</li>
<li class="file-stats">
<a href="#b768fdf8e0594bf98104ef18145fc9f16550bc06" style="color: #1068bf;">
compiler/GHC/Tc/Deriv.hs
</a>
</li>
<li class="file-stats">
<a href="#1e112461bfd65ab9492f37fe37931c1d5ddc5c26" style="color: #1068bf;">
compiler/GHC/Tc/Deriv/Infer.hs
</a>
</li>
<li class="file-stats">
<a href="#e4b9d5e9d2de37561bfd06a2c97a5c924a1bab76" style="color: #1068bf;">
compiler/GHC/Tc/Errors.hs
</a>
</li>
<li class="file-stats">
<a href="#1dd9c7a6bbc222c976a6ec1c4b772232ae60f7e5" style="color: #1068bf;">
compiler/GHC/Tc/Errors/Ppr.hs
</a>
</li>
<li class="file-stats">
<a href="#9355bef855426caf5f526925edf351b20f9a86c4" style="color: #1068bf;">
compiler/GHC/Tc/Gen/HsType.hs
</a>
</li>
<li class="file-stats">
<a href="#54436e21ea530a66a8a71bcc01c836f4740b8f02" style="color: #1068bf;">
compiler/GHC/Tc/Solver.hs
</a>
</li>
<li class="file-stats">
<a href="#f018e77421f495c6f75733fee4a511cfe57bebe8" style="color: #1068bf;">
compiler/GHC/Tc/Solver/Canonical.hs
</a>
</li>
<li class="file-stats">
<a href="#b97557795e2f14fc492ff8c685b149c247b5e480" style="color: #1068bf;">
compiler/GHC/Tc/Solver/InertSet.hs
</a>
</li>
<li class="file-stats">
<a href="#f639b0b31b7245cb7d34ac190b798f5ec1c7da2e" style="color: #1068bf;">
compiler/GHC/Tc/Solver/Interact.hs
</a>
</li>
<li class="file-stats">
<a href="#0c6b585a8a21f8340a85ca2cef89c4b1bf5a8953" style="color: #1068bf;">
compiler/GHC/Tc/Solver/Monad.hs
</a>
</li>
<li class="file-stats">
<a href="#e63425e031ffe9350ee6b1687e506aaea75d11e1" style="color: #1068bf;">
compiler/GHC/Tc/TyCl/Instance.hs
</a>
</li>
<li class="file-stats">
<a href="#3b6d78a50c8462304f843b952a88e531718dbbd2" style="color: #1068bf;">
compiler/GHC/Tc/Types/Constraint.hs
</a>
</li>
<li class="file-stats">
<a href="#93bba9b9e0195db135fec54160523a427ea042fd" style="color: #1068bf;">
compiler/GHC/Tc/Types/Origin.hs
</a>
</li>
<li class="file-stats">
<a href="#5d7c5ef0541bd4c1c950ecc95edf95171d20f538" style="color: #1068bf;">
compiler/GHC/Tc/Utils/Backpack.hs
</a>
</li>
<li class="file-stats">
<a href="#59d42d45d27a766c3ef299d73c226697153b7f6e" style="color: #1068bf;">
compiler/GHC/Tc/Utils/Instantiate.hs
</a>
</li>
<li class="file-stats">
<a href="#94c96afe1bb3b771ffbcfeeca34ce43ebbe76ccb" style="color: #1068bf;">
compiler/GHC/Tc/Utils/TcMType.hs
</a>
</li>
<li class="file-stats">
<a href="#5461e7beeb7ae73d7c01f720cbaa3fa2c5333590" style="color: #1068bf;">
compiler/GHC/Tc/Utils/TcType.hs
</a>
</li>
<li class="file-stats">
<a href="#74295edeac870ee7f2f3484ebaffab5c948b735a" style="color: #1068bf;">
compiler/GHC/Tc/Utils/Unify.hs
</a>
</li>
<li class="file-stats">
<a href="#1db07ed8cd9bab6b217a8f5a140176d3cb8672fd" style="color: #1068bf;">
compiler/GHC/Tc/Validity.hs
</a>
</li>
<li class="file-stats">
<a href="#ed75822e0b6142f196a6abeb623c7669d31b4711" style="color: #1068bf;">
docs/users_guide/exts/instances.rst
</a>
</li>
<li class="file-stats">
<a href="#b0e39b425004e8e88ff63a5562223eb6e82325ae" style="color: #1068bf;">
testsuite/tests/deriving/should_compile/T14339.hs
</a>
</li>
<li class="file-stats">
<a href="#954a33372babe74b69a36772689c12e24eb84915" style="color: #1068bf;">
testsuite/tests/deriving/should_fail/T21302.hs
</a>
</li>
<li class="file-stats">
<a href="#08cbbf76060fdb412dcf50a3c7f1691dd34b8ca0" style="color: #1068bf;">
testsuite/tests/deriving/should_fail/T8165_fail2.stderr
</a>
</li>
<li class="file-stats">
<a href="#f195a235a4af149d74d2298281faa95ce16ded2e" style="color: #1068bf;">
testsuite/tests/impredicative/T17332.stderr
</a>
</li>
<li class="file-stats">
<a href="#7fd6e34ea6c265f0c7f4b1268abbd347d66e32b8" style="color: #1068bf;">
testsuite/tests/indexed-types/should_fail/NotRelaxedExamples.stderr
</a>
</li>
<li class="file-stats">
<a href="#827c2d444eb1045452bfcd712c92fc5e56f28f2e" style="color: #1068bf;">
testsuite/tests/indexed-types/should_fail/T10817.stderr
</a>
</li>
<li class="file-stats">
<a href="#dc7ecdb350f44d7c1363b499bb8806fba600ea76" style="color: #1068bf;">
testsuite/tests/indexed-types/should_fail/T13271.stderr
</a>
</li>
<li class="file-stats">
<a href="#2b29e234970943795624c1885e7c51896dae6578" style="color: #1068bf;">
testsuite/tests/indexed-types/should_fail/T15172.stderr
</a>
</li>
</ul>
<h5 style="margin-top: 10px; margin-bottom: 10px; font-size: 0.875rem;">
The diff was not included because it is too large.
</h5>
</div>
<div class="footer" style="margin-top: 10px;">
<p style="font-size: small; color: #666;">
—
<br>
<a href="https://gitlab.haskell.org/ghc/ghc/-/commit/aed1974e92366ab8e117734f308505684f70cddf" style="color: #1068bf;">View it on GitLab</a>.
<br>
You're receiving this email because of your account on <a target="_blank" rel="noopener noreferrer" href="https://gitlab.haskell.org" style="color: #1068bf;">gitlab.haskell.org</a>. <a href="https://gitlab.haskell.org/-/profile/notifications" target="_blank" rel="noopener noreferrer" class="mng-notif-link" style="color: #1068bf;">Manage all notifications</a> · <a href="https://gitlab.haskell.org/help" target="_blank" rel="noopener noreferrer" class="help-link" style="color: #1068bf;">Help</a>
<script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","action":{"@type":"ViewAction","name":"View Commit","url":"https://gitlab.haskell.org/ghc/ghc/-/commit/aed1974e92366ab8e117734f308505684f70cddf"}}</script>
</p>
</div>
</body>
</html>