Wolfgang Jeltsch pushed to branch wip/jeltsch/smaller-pit at Glasgow Haskell Compiler / GHC Commits: f8cfb1a5 by Hécate Kleidukos at 2026-10-04T19:36:39+02:00 [CLC 341] Strict variants of mutable types This commit is the implementation of CLC Proposal 341 https://github.com/haskell/core-libraries-committee/issues/341 - - - - - 575c4bc6 by Rodrigo Mesquita at 2026-10-05T12:32:02-04:00 ttg: HsModuleName in the AST, ModuleName in GHC This commit makes the AST fully independent from GHC by parsing a "module name" as an `HsModuleName (= HText)` rather than constructing an `ModuleName (= FastString)` straight away. In the GHC side, everything remains as a `ModuleName`. We turn AST `HsModuleName`s into fast strings with the cheap `mkFastStringShortText` when we process the AST for manipulation within the compiler. There are no performance regressions introduced by this approach. This is the final piece of #21592 Alternative plans were discussed in gitlab.haskell.org/ghc/ghc/-/merge_requests/16546#note_694647, but the Simon suggested one won in simplicity and performance when compared against my attempt at implementing my original plan of having a family `ModuleNameP`. - - - - - b3b89d32 by mangoiv at 2026-10-05T22:03:32-04:00 hadrian: Persist the used flavour name in the build root (#20650) This executes the idea proposed in #20650, teaching Hadrian to persist the flavour used to build a build root. This both makes use of multiple build roots more ergonomic (as the user no longer needs to repeat themselves) and avoids a tiresome foot-gun (forgetting to specify a flavour, often wholly invalidating a build root). Closes #20650. Co-authored-by: Sylvain Henry <sylvain@haskus.fr> - - - - - f977837b by mangoiv at 2026-10-05T22:04:21-04:00 configure: fix sed script and subst tooldir script Fixes #27672 Adds sanity checking for SUBST_TOOLDIR Metric Decrease: LinkableUsage01 MultiLayerModulesTH_OneShot T10547 T12234 T12425 T13035 T13820 T18140 T18730 T18923 T9198 TcPlugin_RewritePerf mhu-perf - - - - - f1cb08be by Hannes Siebenhandl at 2026-10-05T22:05:03-04:00 Prepend in-memory unit database for backpack The packageDbFlags are stored in reverse order. Thus, prepending will ensure that the in-memory unit database is the last item on the unit database stack. Further, the in-memory unit database needs to be able to shadow units from earlier unit databases in the unit database stack. Moreover, a `-clear-package-db` would remove the in-memory database if it weren't the last item on the stack. Closes #27835 - - - - - 8d49ed42 by Kazu Yamamoto at 2026-10-06T19:37:25-04:00 Do not leave standard file descriptors free at startup (#24450) A process may be started with stdout closed -- `prog >&-` from a shell does exactly that. Nothing then reserves descriptor 1, and open(), pipe() and socket() hand out the lowest free descriptor, so the next descriptor the runtime creates for itself takes it: the ticker's pipe, or a capability's IO manager control pipe. 'GHC.Internal.IO.StdHandles.stdout' is a CAF, built the first time the program writes to stdout, which is long after that has happened. It builds a 'Handle' over descriptor 1, which now belongs to the runtime, and nothing reports an error because the descriptor is perfectly good. The program then writes its output into the runtime's own plumbing. What that looks like from the outside is a hang. The descriptor the Handle has taken over is the read end of a pipe, so poll() for POLLOUT on it never says yes and epoll_ctl() accepts a registration for it; the thread waiting to write blocks for ever. Closing the Handle at exit closes the runtime's descriptor, which is worse: the ticker then fails on every tick. 'hs_init_ghc' now opens /dev/null onto whichever of descriptors 0, 1 and 2 are closed, before the runtime creates any descriptor of its own. Each is opened for the access that descriptor would normally have, read-only for 0 and write-only for 1 and 2, so that writing to 'stdin' or reading from 'stdout' still fails rather than quietly succeeding against /dev/null. See Note [Standard file descriptors must be open]. Moving only the descriptors the runtime opens would not do: the first file the program itself opened would land on the free number instead. The fix has to leave no free number. A program run this way therefore finds stdout connected to /dev/null rather than failing with EBADF on the first write, which is what such a program would get from most other language runtimes. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> - - - - - 65bcf9e9 by Simon Jakobi at 2026-10-06T19:38:09-04:00 changelog: Repair the sentence describing #27477 The description read "programs using could crash", the object of "using" having been lost. The synopsis already says which programs are affected, so drop the dangling word. Assisted-by: Claude Fable 5.1 - - - - - 15ece296 by mangoiv at 2026-10-08T15:14:56-04:00 ci: move hadrian/ghci into the lint category so it can be picked up by more runners Fixes #27817 - - - - - c0823135 by mangoiv at 2026-10-08T15:14:56-04:00 ci: make lint-adjacent jobs into platform independent - move lint jobs into lint-anyarch tag - unify lint jobs under the same platform independent container - - - - - f76464cf by Zubin Duggal at 2026-10-08T15:15:39-04:00 DmdAnal: Make AbsDmd neutral in maxDmd fixes #27845 - - - - - ffa56ae4 by sheaf at 2026-10-09T17:15:59+02:00 Preserve sign of zero when parsing -0.0# This commit leverages the recently added GHC.Types.Literal.Floating module in order to preserve the sign of negative zero from source-written floating-point literals. Fixes #27545 - - - - - d538cac9 by Facundo Domínguez at 2026-10-09T20:26:38-04:00 Propagate annotations to simple interfaces This allows annotations to be visible to plugins when run by haddock. The LiquidHaskell plugin needs the annotations, in particular. Fixes #26761 - - - - - 32c4f4ab by meooow25 at 2026-10-09T20:27:28-04:00 Bump containers submodule to 0.8.1 And fix affected tests. * T4086a: containers depends on template-haskell-lift now instead of template-haskell. * T22611: Updated to be less dependent on containers internals. - - - - - c786065e by sheaf at 2026-10-09T20:28:20-04:00 Use an explicit pattern match in toIfaceIdDetails The old wildcard pattern let this code bit rot: it did not properly account for recently added 'IdDetails' such as 'RepPolyId', which resulted in spurious 'pprTrace' messages that could even pollute HLS sessions. Fixes #23785 - - - - - e7cacf59 by sheaf at 2026-10-09T20:29:09-04:00 Take into account ifKind in freeNamesIfDecl Commit 3c2f4bb4 added the 'ifKind' field to various constructors of 'IfaceDecl', which preserves the original kind (before type synonym expansion) for better error messages. However, that commit forgot to update 'freeNamesIfDecl' correspondingly. This could result in a "urk! lookup local fingerpring" crash when e.g. a type's kind uses a type synonym defined later, as we failed to add a dependency on the type synonym during dependency analysis. Fixes #27916 - - - - - 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. - - - - - 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> - - - - - 8511ab91 by Wolfgang Jeltsch at 2026-10-13T01:18:33+03:00 Make Haddock avoid the PIT To this end, Haddock has been using `loadSysInterface` to fetch module interfaces. The `loadSysInterface` operation is very complex, containing many bits that do not seem to be needed by Haddock. In particular, storing interface data in and potentially retrieving it from the PIT seems to be superfluous. This interaction with the PIT limits how much we can statically shrink the amount of information that is stored in the PIT. Therefore, we drop the use of `loadSysInterface` and implement the necessary bits of interface fetching directly in `loadHiFile`, where `loadSysInterface` use to be invoked. - - - - - 41381402 by Wolfgang Jeltsch at 2026-10-13T01:18:33+03:00 Statically enforce module interface reduction for the PIT `GHC.Iface.Load.loadInterface` used to replace certain fields of each fetched module interface by `panic` applications before storing it in the PIT. With the present change, the absence of those fields in the PIT is guaranteed statically. See #27044 for the bigger picture. - - - - - 46029e3b by Wolfgang Jeltsch at 2026-10-13T01:18:33+03:00 Make `IfaceBinHandle` a type synonym family This brings the handling of `IfaceBinHandle` somewhat in line with how other phase-dependent data is handled. Note that `mi_hi_bytes_` now includes the `Strict.Maybe` layer itself, independently of the phase. This is necessary, because with a type family instead of a GADT `clear_mi_hi_bytes` cannot determine the phase at runtime anymore and thus has to set `mi_hi_bytes_` to `Strict.Nothing` for every phase. - - - - - 8869f526 by Wolfgang Jeltsch at 2026-10-14T18:08:05+03:00 Improve the error message about non-found interfaces - - - - - 236 changed files: - .gitlab-ci.yml - .gitlab/hello.hs - + changelog.d/24450 - + changelog.d/26761 - + changelog.d/27845 - + changelog.d/T23785 - + changelog.d/T27545 - + changelog.d/T27731 - + changelog.d/T27916 - + changelog.d/clc-341-strict-mutable-data-types - + changelog.d/fix-cross-ghc-info-unit-id - changelog.d/fix-parallel-gc-selector-race-27477 - + changelog.d/hadrian-persist-flavour - changelog.d/unit-index - compiler/GHC.hs - compiler/GHC/Builtin/Modules.hs - compiler/GHC/Builtin/WiredIn/Ids.hs - compiler/GHC/ByteCode/Asm.hs - compiler/GHC/ByteCode/Show.hs - compiler/GHC/Core/DataCon.hs - compiler/GHC/Core/Make.hs - compiler/GHC/Core/Opt/CallerCC/Types.hs - compiler/GHC/CoreToIface.hs - compiler/GHC/Driver/Backpack.hs - compiler/GHC/Driver/Downsweep.hs - compiler/GHC/Driver/Env.hs - compiler/GHC/Driver/Main/Compile.hs - compiler/GHC/Driver/Main/Interactive.hs - compiler/GHC/Driver/Main/Passes.hs - compiler/GHC/Driver/Pipeline.hs-boot - compiler/GHC/Driver/Pipeline/Execute.hs - compiler/GHC/Driver/Pipeline/Phases.hs - compiler/GHC/Driver/Plugins.hs - compiler/GHC/Driver/Session.hs - compiler/GHC/Driver/Session/Inspect.hs - compiler/GHC/Hs/Doc.hs - compiler/GHC/Hs/Dump.hs - compiler/GHC/Hs/Expr.hs - compiler/GHC/Hs/ImpExp.hs - compiler/GHC/Hs/Lit.hs - compiler/GHC/HsToCore/Docs.hs - compiler/GHC/HsToCore/Match/Literal.hs - compiler/GHC/HsToCore/Quote.hs - compiler/GHC/HsToCore/Usage.hs - compiler/GHC/Iface/Binary.hs - compiler/GHC/Iface/Decl.hs - compiler/GHC/Iface/Errors/Types.hs - compiler/GHC/Iface/Ext/Ast.hs - compiler/GHC/Iface/Ext/Debug.hs - compiler/GHC/Iface/Ext/Types.hs - compiler/GHC/Iface/Load.hs - compiler/GHC/Iface/Load.hs-boot - compiler/GHC/Iface/Make.hs - compiler/GHC/Iface/Recomp.hs - compiler/GHC/Iface/Syntax.hs - compiler/GHC/Iface/Tidy.hs - compiler/GHC/Parser.y - compiler/GHC/Parser/Errors/Types.hs - compiler/GHC/Parser/Header.hs - compiler/GHC/Parser/Lexer.x - compiler/GHC/Parser/PostProcess.hs - compiler/GHC/Parser/String.hs - compiler/GHC/Rename/Env.hs - compiler/GHC/Rename/Module.hs - compiler/GHC/Rename/Names.hs - compiler/GHC/Rename/Unbound.hs - compiler/GHC/Rename/Utils.hs - compiler/GHC/Runtime/Loader.hs - compiler/GHC/Settings.hs - compiler/GHC/Settings/IO.hs - compiler/GHC/StgToJS/Linker/Linker.hs - compiler/GHC/Tc/Deriv/Generics.hs - compiler/GHC/Tc/Errors.hs - compiler/GHC/Tc/Errors/Ppr.hs - compiler/GHC/Tc/Errors/Types.hs - compiler/GHC/Tc/Gen/Export.hs - compiler/GHC/Tc/Gen/Splice.hs - compiler/GHC/Tc/Instance/Family.hs - compiler/GHC/Tc/Module.hs - compiler/GHC/Tc/Solver/Default.hs - compiler/GHC/Tc/Solver/Equality.hs - compiler/GHC/Tc/Types.hs - compiler/GHC/Tc/Types/Constraint.hs - compiler/GHC/Tc/Types/ErrCtxt.hs - compiler/GHC/Tc/Utils/Monad.hs - compiler/GHC/ThToHs.hs - compiler/GHC/Types/Demand.hs - compiler/GHC/Types/Unique.hs - compiler/GHC/Types/UnresolvedImport.hs - compiler/GHC/Unit/External.hs - compiler/GHC/Unit/Home.hs - compiler/GHC/Unit/Module.hs - compiler/GHC/Unit/Module/Env.hs - compiler/GHC/Unit/Module/ModIface.hs - + compiler/GHC/Unit/Module/Name.hs - compiler/GHC/Unit/Parser.hs - compiler/GHC/Unit/Types.hs - compiler/GHC/Unit/Types.hs-boot - compiler/GHC/Utils/Binary.hs - compiler/GHC/Utils/Outputable.hs - compiler/Language/Haskell/Syntax.hs - compiler/Language/Haskell/Syntax/Expr.hs - compiler/Language/Haskell/Syntax/ImpExp.hs - compiler/Language/Haskell/Syntax/Lit.hs - compiler/Language/Haskell/Syntax/Module/Name.hs - compiler/Language/Haskell/Syntax/Text.hs - compiler/ghc.cabal.in - distrib/configure.ac.in - ghc/GHCi/UI.hs - ghc/GHCi/UI/Info.hs - ghc/Main.hs - hadrian/bindist/Makefile - hadrian/bindist/config.mk.in - hadrian/doc/flavours.md - hadrian/src/Rules.hs - hadrian/src/Rules/BinaryDist.hs - 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