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* Add regression test for #18755.wip/T18755Richard Eisenberg2020-09-293-0/+6
| | | | Close #18755
* PmCheck: Desugar string literal patterns with -XRebindableSyntax correctly ↵Sebastian Graf2020-09-243-0/+27
| | | | | | (#18708) Fixes #18708.
* Improve kind generalisation, error messagesSimon Peyton Jones2020-09-24124-414/+592
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch does two things: * It refactors GHC.Tc.Errors a bit. In debugging Quick Look I was forced to look in detail at error messages, and ended up doing a bit of refactoring, esp in mkTyVarEqErr'. It's still quite a mess, but a bit better, I think. * It makes a significant improvement to the kind checking of type and class declarations. Specifically, we now ensure that if kind checking fails with an unsolved constraint, all the skolems are in scope. That wasn't the case before, which led to some obscure error messages; and occasional failures with "no skolem info" (eg #16245). Both of these, and the main Quick Look patch itself, affect a /lot/ of error messages, as you can see from the number of files changed. I've checked them all; I think they are as good or better than before. Smaller things * I documented the various instances of VarBndr better. See Note [The VarBndr tyep and its uses] in GHC.Types.Var * Renamed GHC.Tc.Solver.simpl_top to simplifyTopWanteds * A bit of refactoring in bindExplicitTKTele, to avoid the footwork with Either. Simpler now. * Move promoteTyVar from GHC.Tc.Solver to GHC.Tc.Utils.TcMType Fixes #16245 (comment 211369), memorialised as typecheck/polykinds/T16245a Also fixes the three bugs in #18640
* Implement Quick Look impredicativitySimon Peyton Jones2020-09-2458-258/+580
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch implements Quick Look impredicativity (#18126), sticking very closely to the design in A quick look at impredicativity, Serrano et al, ICFP 2020 The main change is that a big chunk of GHC.Tc.Gen.Expr has been extracted to two new modules GHC.Tc.Gen.App GHC.Tc.Gen.Head which deal with typechecking n-ary applications, and the head of such applications, respectively. Both contain a good deal of documentation. Three other loosely-related changes are in this patch: * I implemented (partly by accident) points (2,3)) of the accepted GHC proposal "Clean up printing of foralls", namely https://github.com/ghc-proposals/ghc-proposals/blob/ master/proposals/0179-printing-foralls.rst (see #16320). In particular, see Note [TcRnExprMode] in GHC.Tc.Module - :type instantiates /inferred/, but not /specified/, quantifiers - :type +d instantiates /all/ quantifiers - :type +v is killed off That completes the implementation of the proposal, since point (1) was done in commit df08468113ab46832b7ac0a7311b608d1b418c4d Author: Krzysztof Gogolewski <krzysztof.gogolewski@tweag.io> Date: Mon Feb 3 21:17:11 2020 +0100 Always display inferred variables using braces * HsRecFld (which the renamer introduces for record field selectors), is now preserved by the typechecker, rather than being rewritten back to HsVar. This is more uniform, and turned out to be more convenient in the new scheme of things. * The GHCi debugger uses a non-standard unification that allows the unification variables to unify with polytypes. We used to hack this by using ImpredicativeTypes, but that doesn't work anymore so I introduces RuntimeUnkTv. See Note [RuntimeUnkTv] in GHC.Runtime.Heap.Inspect Updates haddock submodule. WARNING: this patch won't validate on its own. It was too hard to fully disentangle it from the following patch, on type errors and kind generalisation. Changes to tests * Fixes #9730 (test added) * Fixes #7026 (test added) * Fixes most of #8808, except function `g2'` which uses a section (which doesn't play with QL yet -- see #18126) Test added * Fixes #1330. NB Church1.hs subsumes Church2.hs, which is now deleted * Fixes #17332 (test added) * Fixes #4295 * This patch makes typecheck/should_run/T7861 fail. But that turns out to be a pre-existing bug: #18467. So I have just made T7861 into expect_broken(18467)
* PmCheck: Rewrite inhabitation testSebastian Graf2020-09-223-0/+58
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | We used to produce inhabitants of a pattern-match refinement type Nabla in the checker in at least two different and mostly redundant ways: 1. There was `provideEvidence` (now called `generateInhabitingPatterns`) which is used by `GHC.HsToCore.PmCheck` to produce non-exhaustive patterns, which produces inhabitants of a Nabla as a sub-refinement type where all match variables are instantiated. 2. There also was `ensure{,All}Inhabited` (now called `inhabitationTest`) which worked slightly different, but was whenever new type constraints or negative term constraints were added. See below why `provideEvidence` and `ensureAllInhabited` can't be the same function, the main reason being performance. 3. And last but not least there was the `nonVoid` test, which tested that a given type was inhabited. We did use this for strict fields and -XEmptyCase in the past. The overlap of (3) with (2) was always a major pet peeve of mine. The latter was quite efficient and proven to work for recursive data types, etc, but could not handle negative constraints well (e.g. we often want to know if a *refined* type is empty, such as `{ x:[a] | x /= [] }`). Lower Your Guards suggested that we could get by with just one, by replacing both functions with `inhabitationTest` in this patch. That was only possible by implementing the structure of φ constraints as in the paper, namely the semantics of φ constructor constraints. This has a number of benefits: a. Proper handling of unlifted types and strict fields, fixing #18249, without any code duplication between `GHC.HsToCore.PmCheck.Oracle.instCon` (was `mkOneConFull`) and `GHC.HsToCore.PmCheck.checkGrd`. b. `instCon` can perform the `nonVoid` test (3) simply by emitting unliftedness constraints for strict fields. c. `nonVoid` (3) is thus simply expressed by a call to `inhabitationTest`. d. Similarly, `ensureAllInhabited` (2), which we called after adding type info, now can similarly be expressed as the fuel-based `inhabitationTest`. See the new `Note [Why inhabitationTest doesn't call generateInhabitingPatterns]` why we still have tests (1) and (2). Fixes #18249 and brings nice metric decreases for `T17836` (-76%) and `T17836b` (-46%), as well as `T18478` (-8%) at the cost of a few very minor regressions (< +2%), potentially due to the fact that `generateInhabitingPatterns` does more work to suggest the minimal COMPLETE set. Metric Decrease: T17836 T17836b
* Fix the occurrence analyserSimon Peyton Jones2020-09-222-0/+30
| | | | | | | | | | | | | | | | | | | Ticket #18603 demonstrated that the occurrence analyser's handling of local RULES for imported Ids (which I now call IMP-RULES) was inadequate. It led the simplifier into an infnite loop by failing to label a binder as a loop breaker. The main change in this commit is to treat IMP-RULES in a simple and uniform way: as extra rules for the local binder. See Note [IMP-RULES: local rules for imported functions] This led to quite a bit of refactoring. The result is still tricky, but it's much better than before, and better documented I think. Oh, and it fixes the bug.
* Better eta-expansion (again) and don't specilise DFunsSimon Peyton Jones2020-09-227-127/+111
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch fixes #18223, which made GHC generate an exponential amount of code. There are three quite separate changes in here 1. Re-engineer eta-expansion (again). The eta-expander was generating lots of intermediate stuff, which could be optimised away, but which choked the simplifier meanwhile. Relatively easy to kill it off at source. See Note [The EtaInfo mechanism] in GHC.Core.Opt.Arity. The main new thing is the use of pushCoArg in getArg_maybe. 2. Stop Specialise specalising DFuns. This is the cause of a huge (and utterly unnecessary) blowup in program size in #18223. See Note [Do not specialise DFuns] in GHC.Core.Opt.Specialise. I also refactored the Specialise monad a bit... it was silly, because it passed on unchanging values as if they were mutable state. 3. Do an extra Simplifer run, after SpecConstra and before late-Specialise. I found (investigating perf/compiler/T16473) that failing to do this was crippling *both* SpecConstr *and* Specialise. See Note [Simplify after SpecConstr] in GHC.Core.Opt.Pipeline. This change does mean an extra run of the Simplifier, but only with -O2, and I think that's acceptable. T16473 allocates *three* times less with this change. (I changed it to check runtime rather than compile time.) Some smaller consequences * I moved pushCoercion, pushCoArg and friends from SimpleOpt to Arity, because it was needed by the new etaInfoApp. And pushCoValArg now returns a MCoercion rather than Coercion for the argument Coercion. * A minor, incidental improvement to Core pretty-printing This does fix #18223, (which was otherwise uncompilable. Hooray. But there is still a big intermediate because there are some very deeply nested types in that program. Modest reductions in compile-time allocation on a couple of benchmarks T12425 -2.0% T13253 -10.3% Metric increase with -O2, due to extra simplifier run T9233 +5.8% T12227 +1.8% T15630 +5.0% There is a spurious apparent increase on heap residency on T9630, on some architectures at least. I tried it with -G1 and the residency is essentially unchanged. Metric Increase T9233 T12227 T9630 Metric Decrease T12425 T13253
* Disallow constraints in KindSigCtxtRyan Scott2020-09-213-0/+19
| | | | | | | | | | | | | | | | | | | This patch cleans up how `GHC.Tc.Validity` classifies `UserTypeCtxt`s that can only refer to kind-level positions, which is important for rejecting certain classes of programs. In particular, this patch: * Introduces a new `TypeOrKindCtxt` data type and `typeOrKindCtxt :: UserTypeCtxt -> TypeOrKindCtxt` function, which determines whether a `UserTypeCtxt` can refer to type-level contexts, kind-level contexts, or both. * Defines the existing `allConstraintsAllowed` and `vdqAllowed` functions in terms of `typeOrKindCtxt`, which avoids code duplication and ensures that they stay in sync in the future. The net effect of this patch is that it fixes #18714, in which it was discovered that `allConstraintsAllowed` incorrectly returned `True` for `KindSigCtxt`. Because `typeOrKindCtxt` now correctly classifies `KindSigCtxt` as a kind-level context, this bug no longer occurs.
* testsuite: Mark TH_spliceE5_prof as broken on WindowsGHC GitLab CI2020-09-201-1/+2
| | | | Due to #18721.
* testsuite: Mark some GHCi/Makefile tests as broken on WindowsBen Gamari2020-09-204-0/+5
| | | | See #18718.
* testsuite: Update expected output for outofmem on WindowsBen Gamari2020-09-201-1/+1
| | | | The error originates from osCommitMemory rather than getMBlocks.
* testsuite: Unmark T5975[ab] as broken on WindowsBen Gamari2020-09-201-2/+2
| | | | | | Sadly it's unclear *why* they have suddenly started working. Closes #7305.
* testsuite: Unmark T12971 as broken on WindowsBen Gamari2020-09-201-1/+1
| | | | | | It's unclear why, but this no longer seems to fail. Closes #17945.
* Remove GADT self-reference check (#11554, #12081, #12174, fixes #15942)Artyom Kuznetsov2020-09-1910-22/+43
| | | | Reverts 430f5c84dac1eab550110d543831a70516b5cac8
* Added explicit fixity to (~).HaskellMouse2020-09-175-0/+25
| | | | Solves #18252
* Do absence analysis on stable unfoldingsSimon Peyton Jones2020-09-173-0/+56
| | | | | | | | | Ticket #18638 showed that Very Bad Things happen if we fail to do absence analysis on stable unfoldings. It's all described in Note [Absence analysis for stable unfoldings and RULES]. I'm a bit surprised this hasn't bitten us before. Fortunately the fix is pretty simple.
* Care with implicit-parameter superclassesSimon Peyton Jones2020-09-156-0/+52
| | | | | | | | | | | | | | | | | | | | | | Two bugs, #18627 and #18649, had the same cause: we were not account for the fact that a constaint tuple might hide an implicit parameter. The solution is not hard: look for implicit parameters in superclasses. See Note [Local implicit parameters] in GHC.Core.Predicate. Then we use this new function in two places * The "short-cut solver" in GHC.Tc.Solver.Interact.shortCutSolver which simply didn't handle implicit parameters properly at all. This fixes #18627 * The specialiser, which should not specialise on implicit parameters This fixes #18649 There are some lingering worries (see Note [Local implicit parameters]) but things are much better.
* Make `tcCheckSatisfiability` incremental (#18645)Sebastian Graf2020-09-124-0/+122
| | | | | | | | | | | | | | | | | By taking and returning an `InertSet`. Every new `TcS` session can then pick up where a prior session left with `setTcSInerts`. Since we don't want to unflatten the Givens (and because it leads to infinite loops, see !3971), we introduced a new variant of `runTcS`, `runTcSInerts`, that takes and returns the `InertSet` and makes sure not to unflatten the Givens after running the `TcS` action. Fixes #18645 and #17836. Metric Decrease: T17977 T18478
* PmCheck: Disattach COMPLETE pragma lookup from TyConsSebastian Graf2020-09-127-13/+39
| | | | | | | | | | | | | | | | | | | By not attaching COMPLETE pragmas with a particular TyCon and instead assume that every COMPLETE pragma is applicable everywhere, we can drastically simplify the logic that tries to initialise available COMPLETE sets of a variable during the pattern-match checking process, as well as fixing a few bugs. Of course, we have to make sure not to report any of the ill-typed/unrelated COMPLETE sets, which came up in a few regression tests. In doing so, we fix #17207, #18277 and #14422. There was a metric decrease in #18478 by ~20%. Metric Decrease: T18478
* PmCheck: Handle ⊥ and strict fields correctly (#18341)wip/T18341Sebastian Graf2020-09-1014-0/+220
| | | | | | | | | | | | | | | | | | | | | In #18341, we discovered an incorrect digression from Lower Your Guards. This MR changes what's necessary to support properly fixing #18341. In particular, bottomness constraints are now properly tracked in the oracle/inhabitation testing, as an additional field `vi_bot :: Maybe Bool` in `VarInfo`. That in turn allows us to model newtypes as advertised in the Appendix of LYG and fix #17725. Proper handling of ⊥ also fixes #17977 (once again) and fixes #18670. For some reason I couldn't follow, this also fixes #18273. I also added a couple of regression tests that were missing. Most of them were already fixed before. In summary, this patch fixes #18341, #17725, #18273, #17977 and #18670. Metric Decrease: T12227
* PmCheck: Big refactor using guard tree variants more closely following ↵Sebastian Graf2020-09-105-4/+16
| | | | | | | | | | | | | | | | | | | | | | | | source syntax (#18565) Previously, we desugared and coverage checked plain guard trees as described in Lower Your Guards. That caused (in !3849) quite a bit of pain when we need to partially recover tree structure of the input syntax to return covered sets for long-distance information, for example. In this refactor, I introduced a guard tree variant for each relevant source syntax component of a pattern-match (mainly match groups, match, GRHS, empty case, pattern binding). I made sure to share as much coverage checking code as possible, so that the syntax-specific checking functions are just wrappers around the more substantial checking functions for the LYG primitives (`checkSequence`, `checkGrds`). The refactoring payed off in clearer code and elimination of all panics related to assumed guard tree structure and thus fixes #18565. I also took the liberty to rename and re-arrange the order of functions and comments in the module, deleted some dead and irrelevant Notes, wrote some new ones and gave an overview module haddock.
* Add long-distance info for pattern bindings (#18572)Sebastian Graf2020-09-103-2/+32
| | | | | | | | We didn't consider the RHS of a pattern-binding before, which led to surprising warnings listed in #18572. As can be seen from the regression test T18572, we get the expected output now.
* gitlab-ci: Bump Docker imagesBen Gamari2020-09-091-0/+1
| | | | | | | We now generate our Docker images via Dhall definitions, as described in ghc/ci-images!52. Additionally, we are far more careful about where tools come from, using the ALEX, HAPPY, HSCOLOR, and GHC environment variables (set in the Dockerfiles) to find bootstrapping tools.
* Remove GENERATED pragma, as it is not being usedAlan Zimmerman2020-09-099-17/+1
| | | | | | | | | | | | | | | | | | | | | @alanz pointed out on ghc-devs that the payload of this pragma does not appear to be used anywhere. I (@bgamari) did some digging and traced the pragma's addition back to d386e0d2 (way back in 2006!). It appears that it was intended to be used by code generators for use in informing the code coveraging checker about generated code provenance. When it was added it used the pragma's "payload" fields as source location information to build an "ExternalBox". However, it looks like this was dropped a year later in 55a5d8d9. At this point it seems like the pragma serves no useful purpose. Given that it also is not documented, I think we should remove it. Updates haddock submodule Closes #18639
* DynFlags: add UnfoldingOpts and SimpleOptsSylvain Henry2020-09-091-1/+1
| | | | | Milestone: after this patch, we only use 'unsafeGlobalDynFlags' for the state hack and for debug in Outputable.
* Postpone associated tyfam default checks until after typecheckingRyan Scott2020-09-0912-9/+34
| | | | | | | | | | | | Previously, associated type family defaults were validity-checked during typechecking. Unfortunately, the error messages that these checks produce run the risk of printing knot-tied type constructors, which will cause GHC to diverge. In order to preserve the current error message's descriptiveness, this patch postpones these validity checks until after typechecking, which are now located in the new function `GHC.Tc.Validity.checkValidAssocTyFamDeflt`. Fixes #18648.
* Make the forall-or-nothing rule only apply to invisible foralls (#18660)Ryan Scott2020-09-082-0/+8
| | | | | | | | This fixes #18660 by changing `isLHsForAllTy` to `isLHsInvisForAllTy`, which is sufficient to make the `forall`-or-nothing rule only apply to invisible `forall`s. I also updated some related documentation and Notes while I was in the neighborhood.
* [macOS] improved runpath handlingMoritz Angermann2020-09-071-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In b592bd98ff25730bbe3c13d6f62a427df8c78e28 we started using -dead_strip_dylib on macOS when lining dynamic libraries and binaries. The underlying reason being the Load Command Size Limit in macOS Sierra (10.14) and later. GHC will produce @rpath/libHS... dependency entries together with a corresponding RPATH entry pointing to the location of the libHS... library. Thus for every library we produce two Load Commands. One to specify the dependent library, and one with the path where to find it. This makes relocating libraries and binaries easier, as we just need to update the RPATH entry with the install_name_tool. The dynamic linker will then subsitute each @rpath with the RPATH entries it finds in the libraries load commands or the environement, when looking up @rpath relative libraries. -dead_strip_dylibs intructs the linker to drop unused libraries. This in turn help us reduce the number of referenced libraries, and subsequently the size of the load commands. This however does not remove the RPATH entries. Subsequently we can end up (in extreme cases) with only a single @rpath/libHS... entry, but 100s or more RPATH entries in the Load Commands. This patch rectifies this (slighly unorthodox) by passing *no* -rpath arguments to the linker at link time, but -headerpad 8000. The headerpad argument is in hexadecimal and the maxium 32k of the load command size. This tells the linker to pad the load command section enough for us to inject the RPATHs later. We then proceed to link the library or binary with -dead_strip_dylibs, and *after* the linking inspect the library to find the left over (non-dead-stripped) dependencies (using otool). We find the corresponding RPATHs for each @rpath relative dependency, and inject them into the library or binary using the install_name_tool. Thus achieving a deadstripped dylib (and rpaths) build product. We can not do this in GHC, without starting to reimplement a dynamic linker as we do not know which symbols and subsequently libraries are necessary. Commissioned-by: Mercury Technologies, Inc. (mercury.com)
* testsuite: Mark T5975[ab] as broken on WindowsBen Gamari2020-09-051-2/+5
| | | | Due to #7305.
* testsuite: Drop Windows-specific output for parseTreeBen Gamari2020-09-051-160/+0
| | | | The normalise_slashes normaliser should handle this.
* Introduce isBoxedTupleDataCon and use it to fix #18644Ryan Scott2020-09-043-0/+8
| | | | | | | | | | | | | | | | | | | | The code that converts promoted tuple data constructors to `IfaceType`s in `GHC.CoreToIface` was using `isTupleDataCon`, which conflates boxed and unboxed tuple data constructors. To avoid this, this patch introduces `isBoxedTupleDataCon`, which is like `isTupleDataCon` but only works for _boxed_ tuple data constructors. While I was in town, I was horribly confused by the fact that there were separate functions named `isUnboxedTupleCon` and `isUnboxedTupleTyCon` (similarly, `isUnboxedSumCon` and `isUnboxedSumTyCon`). It turns out that the former only works for data constructors, despite its very general name! I opted to rename `isUnboxedTupleCon` to `isUnboxedTupleDataCon` (similarly, I renamed `isUnboxedSumCon` to `isUnboxedSumDataCon`) to avoid this potential confusion, as well as to be more consistent with the naming convention I used for `isBoxedTupleDataCon`. Fixes #18644.
* testsuite: Add broken test for #18302Ben Gamari2020-09-013-0/+13
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* Fix FastString lexicographic ordering (fix #18562)Sylvain Henry2020-09-013-0/+8
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* Add additional tests for #18172 (Followup MR 3543)Roland Senn2020-08-313-0/+22
| | | | | | | There was still one active discussion [thread](https://gitlab.haskell.org/ghc/ghc/-/merge_requests/3543#note_284325) when MR !3543 got merged. This MR adds the requested tests exercising the changes in `compiler/GHC/HsToCore/Match/Literal.hs:warnAboutEmptyEnumerations` and its sub-functions.
* Add tests for #15617.Roland Senn2020-08-313-0/+9
| | | | Avoid a similar regression in the future.
* Make {hsExpr,hsType,pat}NeedsParens aware of boxed 1-tuplesRyan Scott2020-08-273-0/+28
| | | | | | | | | | | | `hsExprNeedsParens`, `hsTypeNeedsParens`, and `patNeedsParens` previously assumed that all uses of explicit tuples in the source syntax never need to be parenthesized. This is true save for one exception: boxed one-tuples, which use the `Solo` data type from `GHC.Tuple` instead of special tuple syntax. This patch adds the necessary logic to the three `*NeedsParens` functions to handle `Solo` correctly. Fixes #18612.
* Consolidate imports in getMinimalImports (#18264)Aditya Gupta2020-08-274-0/+32
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* Bignum: fix BigNat subtraction (#18604)Sylvain Henry2020-08-263-0/+12
| | | | | | There was a confusion between the boolean expected by withNewWordArrayTrimedMaybe and the boolean returned by subtracting functions.
* Add a test for #18585Krzysztof Gogolewski2020-08-252-0/+49
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* Add a test for #18397Krzysztof Gogolewski2020-08-242-0/+24
| | | | The bug was fixed by !3421.
* Fix types in silly shifts (#18589)Krzysztof Gogolewski2020-08-242-0/+13
| | | | Patch written by Simon. I have only added a testcase.
* Do not print synonyms in :i (->), :i Type (#18594)Krzysztof Gogolewski2020-08-237-4/+26
| | | | | This adds a new printing flag `sdocPrintTypeAbbreviations` that is used specifically to avoid ghci printing 'type (->) = (->)' and 'type Type = Type'.
* mkUnique refactoring (#18362)Aditya Gupta2020-08-221-0/+1
| | | | | Move uniqFromMask from Unique.Supply to Unique. Move the the functions that call mkUnique from Unique to Builtin.Uniques
* Fix -ddump-stg flagSylvain Henry2020-08-212-2/+2
| | | | | | | -ddump-stg was dumping the initial STG (just after Core-to-STG pass) which was misleading because we want the final STG to know if a function allocates or not. Now we have a new flag -ddump-stg-from-core for this and -ddump-stg is deprecated.
* NCG: Dwarf configurationSylvain Henry2020-08-211-2/+2
| | | | | | * remove references to DynFlags in GHC.CmmToAsm.Dwarf * add specific Dwarf options in NCGConfig instead of directly querying the debug level
* Put CFG weights into their own module (#17957)Sylvain Henry2020-08-212-3/+2
| | | | It avoids having to query DynFlags to get them
* Add right-to-left rule for pattern bindingsSimon Peyton Jones2020-08-197-23/+54
| | | | | | | | | | | | | | | | | | | | | | | Fix #18323 by adding a few lines of code to handle non-recursive pattern bindings. see GHC.Tc.Gen.Bind Note [Special case for non-recursive pattern bindings] Alas, this confused the pattern-match overlap checker; see #18323. Note that this patch only affects pattern bindings like that for (x,y) in this program combine :: (forall a . [a] -> a) -> [forall a. a -> a] -> ((forall a . [a] -> a), [forall a. a -> a]) breaks = let (x,y) = combine head ids in x y True We need ImpredicativeTypes for those [forall a. a->a] types to be valid. And with ImpredicativeTypes the old, unprincipled "allow unification variables to unify with a polytype" story actually works quite well. So this test compiles fine (if delicatedly) with old GHCs; but not with QuickLook unless we add this patch
* Implement -Wredundant-bang-patterns (#17340)nineonine2020-08-193-0/+104
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Add new flag '-Wredundant-bang-patterns' that enables checks for "dead" bangs. Dead bangs are the ones that under no circumstances can force a thunk that wasn't already forced. Dead bangs are a form of redundant bangs. The new check is performed in Pattern-Match Coverage Checker along with other checks (namely, redundant and inaccessible RHSs). Given f :: Bool -> Int f True = 1 f !x = 2 we can detect dead bang patterns by checking whether @x ~ ⊥@ is satisfiable where the PmBang appears in 'checkGrdTree'. If not, then clearly the bang is dead. Such a dead bang is then indicated in the annotated pattern-match tree by a 'RedundantSrcBang' wrapping. In 'redundantAndInaccessibles', we collect all dead bangs to warn about. Note that we don't want to warn for a dead bang that appears on a redundant clause. That is because in that case, we recommend to delete the clause wholly, including its leading pattern match. Dead bang patterns are redundant. But there are bang patterns which are redundant that aren't dead, for example f !() = 0 the bang still forces the match variable, before we attempt to match on (). But it is redundant with the forcing done by the () match. We currently don't detect redundant bangs that aren't dead.
* DynFlags: refactor GHC.CmmToAsm (#17957, #10143)Sylvain Henry2020-08-181-1/+2
| | | | | | | | | | | | | | | | | This patch removes the use of `sdocWithDynFlags` from GHC.CmmToAsm.*.Ppr To do that I've had to make some refactoring: * X86' and PPC's `Instr` are no longer `Outputable` as they require a `Platform` argument * `Instruction` class now exposes `pprInstr :: Platform -> instr -> SDoc` * as a consequence, I've refactored some modules to avoid .hs-boot files * added (derived) functor instances for some datatypes parametric in the instruction type. It's useful for pretty-printing as we just have to map `pprInstr` before pretty-printing the container datatype.
* testsuite: Add test for #18291Ben Gamari2020-08-182-0/+8
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