| Commit message (Collapse) | Author | Age | Files | Lines |
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Implements GHC Proposal #54: .../ghc-proposals/blob/master/proposals/0054-kind-signatures.rst
With this patch, a type constructor can now be given an explicit
standalone kind signature:
{-# LANGUAGE StandaloneKindSignatures #-}
type Functor :: (Type -> Type) -> Constraint
class Functor f where
fmap :: (a -> b) -> f a -> f b
This is a replacement for CUSKs (complete user-specified
kind signatures), which are now scheduled for deprecation.
User-facing changes
-------------------
* A new extension flag has been added, -XStandaloneKindSignatures, which
implies -XNoCUSKs.
* There is a new syntactic construct, a standalone kind signature:
type <name> :: <kind>
Declarations of data types, classes, data families, type families, and
type synonyms may be accompanied by a standalone kind signature.
* A standalone kind signature enables polymorphic recursion in types,
just like a function type signature enables polymorphic recursion in
terms. This obviates the need for CUSKs.
* TemplateHaskell AST has been extended with 'KiSigD' to represent
standalone kind signatures.
* GHCi :info command now prints the kind signature of type constructors:
ghci> :info Functor
type Functor :: (Type -> Type) -> Constraint
...
Limitations
-----------
* 'forall'-bound type variables of a standalone kind signature do not
scope over the declaration body, even if the -XScopedTypeVariables is
enabled. See #16635 and #16734.
* Wildcards are not allowed in standalone kind signatures, as partial
signatures do not allow for polymorphic recursion.
* Associated types may not be given an explicit standalone kind
signature. Instead, they are assumed to have a CUSK if the parent class
has a standalone kind signature and regardless of the -XCUSKs flag.
* Standalone kind signatures do not support multiple names at the moment:
type T1, T2 :: Type -> Type -- rejected
type T1 = Maybe
type T2 = Either String
See #16754.
* Creative use of equality constraints in standalone kind signatures may
lead to GHC panics:
type C :: forall (a :: Type) -> a ~ Int => Constraint
class C a where
f :: C a => a -> Int
See #16758.
Implementation notes
--------------------
* The heart of this patch is the 'kcDeclHeader' function, which is used to
kind-check a declaration header against its standalone kind signature.
It does so in two rounds:
1. check user-written binders
2. instantiate invisible binders a la 'checkExpectedKind'
* 'kcTyClGroup' now partitions declarations into declarations with a
standalone kind signature or a CUSK (kinded_decls) and declarations
without either (kindless_decls):
* 'kinded_decls' are kind-checked with 'checkInitialKinds'
* 'kindless_decls' are kind-checked with 'getInitialKinds'
* DerivInfo has been extended with a new field:
di_scoped_tvs :: ![(Name,TyVar)]
These variables must be added to the context in case the deriving clause
references tcTyConScopedTyVars. See #16731.
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The `Ix` class seems rather orthogonal to its original home in
`GHC.Arr`.
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Introduces a new flag `-fmax-pmcheck-deltas` to achieve that. Deprecates
the old `-fmax-pmcheck-iter` mechanism in favor of this new flag.
From the user's guide:
Pattern match checking can be exponential in some cases. This limit makes sure
we scale polynomially in the number of patterns, by forgetting refined
information gained from a partially successful match. For example, when
matching `x` against `Just 4`, we split each incoming matching model into two
sub-models: One where `x` is not `Nothing` and one where `x` is `Just y` but
`y` is not `4`. When the number of incoming models exceeds the limit, we
continue checking the next clause with the original, unrefined model.
This also retires the incredibly hard to understand "maximum number of
refinements" mechanism, because the current mechanism is more general
and should catch the same exponential cases like PrelRules at the same
time.
-------------------------
Metric Decrease:
T11822
-------------------------
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Enabling both DeriveAnyClass and GeneralizedNewtypeDeriving can cause
a warning when no explicit deriving strategy is in use. This change adds
an enable/suppress flag for it.
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Due to #16555.
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Add a new optional failure handling for upsweep which continues
the compilation on other modules if any of them has errors.
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The pattern match oracle can now cope with the abundance of information
that ViewPatterns, NPlusKPats, overloaded lists, etc. provide.
No need to have PmFake anymore!
Also got rid of a spurious call to `allCompleteMatches`, which we used to call
*for every constructor* match. Naturally this blows up quadratically for
programs like `ManyAlternatives`.
-------------------------
Metric Decrease:
ManyAlternatives
Metric Increase:
T11822
-------------------------
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Issue #17056 revealed that we were sometimes building a case
expression whose type field (in the Case constructor) was bogus.
Consider a phantom type synonym
type S a = Int
and we want to form the case expression
case x of K (a::*) -> (e :: S a)
We must not make the type field of the Case constructor be (S a)
because 'a' isn't in scope. We must instead expand the synonym.
Changes in this patch:
* Expand synonyms in the new function CoreUtils.mkSingleAltCase.
* Use mkSingleAltCase in MkCore.wrapFloat, which was the proximate
source of the bug (when called by exprIsConApp_maybe)
* Use mkSingleAltCase elsewhere
* Documentation
CoreSyn new invariant (6) in Note [Case expression invariants]
CoreSyn Note [Why does Case have a 'Type' field?]
CoreUtils Note [Care with the type of a case expression]
* I improved Core Lint's error reporting, which was pretty
confusing in this case, because it didn't mention that the offending
type was the return type of a case expression.
* A little bit of cosmetic refactoring in CoreUtils
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Add GHC.Hs module hierarchy replacing hsSyn.
Metric Increase:
haddock.compiler
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The particular test is already fixed, but the issue seems to have
multiple different test cases lumped together.
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This fixes #15809, and is covered in
Note [Use level numbers for quantification] in TcMType.
This patch removes the "global tyvars" from the
environment, a nice little win.
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This commit should have no change in behavior.(*)
The observation was that Note [Recipe for checking a signature]
says that every metavariable in a type-checked type must either
(A) be generalized
(B) be promoted
(C) be zapped.
Yet the code paths for doing these were all somewhat separate.
This led to some steps being skipped. This commit shores this
all up. The key innovation is TcHsType.kindGeneralizeSome, with
appropriate commentary.
This commit also sets the stage for #15809, by turning the
WARNing about bad level-numbers in generalisation into an
ASSERTion. The actual fix for #15809 will be in a separate
commit.
Other changes:
* zonkPromoteType is now replaced by kindGeneralizeNone.
This might have a small performance degradation, because
zonkPromoteType zonked and promoted all at once. The new
code path promotes first, and then zonks.
* A call to kindGeneralizeNone was added in tcHsPartialSigType.
I think this was a lurking bug, because it did not follow
Note [Recipe for checking a signature]. I did not try to
come up with an example showing the bug. This is the (*)
above.
Because of this change, there is an error message regression
in partial-sigs/should_fail/T14040a. This problem isn't really
a direct result of this refactoring, but is a symptom of
something deeper. See #16775, which addresses the deeper
problem.
* I added a short-cut to quantifyTyVars, in case there's
nothing to quantify.
* There was a horribly-outdated Note that wasn't referred
to. Gone now.
* While poking around with T14040a, I discovered a small
mistake in the Coercion.simplifyArgsWorker. Easy to fix,
happily.
* See new Note [Free vars in coercion hole] in TcMType.
Previously, we were doing the wrong thing when looking
at a coercion hole in the gather-candidates algorithm.
Fixed now, with lengthy explanation.
Metric Decrease:
T14683
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In simplCast I totally failed to keep the sc_hole_ty field of
ApplyToTy (see Note [The hole type in ApplyToTy]) up to date.
When a cast goes by, of course the hole type changes.
Amazingly this has not bitten us before, but #16312 finally
triggered it. Fortunately the fix is simple.
Fixes #16312.
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As #13834 and #17150 report, we get a TERRIBLE error message when you
have an out of scope variable applied in a visible type application:
(outOfScope @Int True)
This very simple patch improves matters.
See TcExpr Note [VTA for out-of-scope functions]
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Test case: indexed-types/should_fail/T13571
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Previously, we had an elaborate mechanism for selecting the warnings to
generate in the presence of different `COMPLETE` matching groups that,
albeit finely-tuned, produced wrong results from an end user's
perspective in some cases (#13363).
The underlying issue is that at the point where the `ConVar` case has to
commit to a particular `COMPLETE` group, there's not enough information
to do so and the status quo was to just enumerate all possible complete
sets nondeterministically. The `getResult` function would then pick the
outcome according to metrics defined in accordance to the user's guide.
But crucially, it lacked knowledge about the order in which affected
clauses appear, leading to the surprising behavior in #13363.
In !1010 we taught the term oracle to reason about literal values a
variable can certainly not take on. This MR extends that idea to
`ConLike`s and thereby fixes #13363: Instead of committing to a
particular `COMPLETE` group in the `ConVar` case, we now split off the
matching constructor incrementally and record the newly covered case as
a refutable shape in the oracle. Whenever the set of refutable shapes
covers any `COMPLETE` set, the oracle recognises vacuosity of the
uncovered set.
This patch goes a step further: Since at this point the information
in value abstractions is merely a cut down representation of what the
oracle knows, value abstractions degenerate to a single `Id`, the
semantics of which is determined by the oracle state `Delta`.
Value vectors become lists of `[Id]` given meaning to by a single
`Delta`, value set abstractions (of which the uncovered set is an
instance) correspond to a union of `Delta`s which instantiate the
same `[Id]` (akin to models of formula).
Fixes #11528 #13021, #13363, #13965, #14059, #14253, #14851, #15753, #17096, #17149
-------------------------
Metric Decrease:
ManyAlternatives
T11195
-------------------------
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There was an outright bug in TcInteract.solveOneFromTheOther
which meant that we did not always pick the innermost
implicit parameter binding, causing #17104.
The fix is easy, just a rearrangement of conditional tests
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Fixes #16833
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Add StgToCmm module hierarchy. Platform modules that are used in several
other places (NCG, LLVM codegen, Cmm transformations) are put into
GHC.Platform.
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The tightens up the kinds a bit. I use type synnonyms to avoid adding
promotion ticks everywhere.
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Add another small test step
Use the same identifier name in different
scopes and see, if ':uses' handles that.
Add another test step
to check wether local bindings with the
same identifier name might get confused
Add easier to understand test output
Fix annotated lines from file correctly
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The `mkOneConFull` function of the pattern match checker used to try to
guess the type arguments of the data type's type constructor by looking
at the ambient type of the match. This doesn't work well for Pattern
Synonyms, where the result type isn't even necessarily a TyCon
application, and it shows in #11336 and #17112.
Also the effort seems futile; why try to try hard when the type checker
has already done the hard lifting? After this patch, we instead supply
the type constructors arguments as an argument to the function and
lean on the type-annotated AST.
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`TcTyClsDecls.tcFamDecl1` was using `NotInjective` when creating data
family type constructors, which is just plain wrong. This tweaks it
to use `Injective` instead.
Fixes #17067.
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Fixes #16509.
See Note [Not-necessarily-lifted join points] in ByteCodeGen,
which tells the full story.
This commit also adds some comments and cleans some code
in the byte-code generator, as I was exploring around trying
to understand it.
(This commit removes an old test -- this is really a GHCi problem,
not a pattern-synonym problem.)
test case: ghci/scripts/T16509
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The later caused issues on windows by being translated into
"\\dev\\null" and python then trying to open this non-existant file.
So we now use os.devnull inside python and convert it to "/dev/null"
when calling out to the shell, which is bound to run in a unix like
environment.
This fixes an issue a test producing unexpected stderr output failed
with a framework failure instead of showing a diff of the output.
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files
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Supply branch incomps when building an IfaceClosedSynFamilyTyCon
`pprTyThing` now has access to incomps. This also causes them to be
written out to .hi files, but that doesn't pose an issue other than a
more faithful bijection between `tyThingToIfaceDecl` and `tcIfaceDecl`.
The machinery for displaying axiom incomps was already present but not
in use. Since this is now a thing that pops up in ghci's :info the
format was modified to look like a haskell comment.
Documentation and a test for the new feature included.
Test Plan: T15546
Reviewers: simonpj, bgamari, goldfire
Reviewed By: simonpj
Subscribers: rwbarton, carter
GHC Trac Issues: #15546
Differential Revision: https://phabricator.haskell.org/D5097
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Breaks fragile tests into two groups, allowing us to easily preserve
stdout/stderr of failing fragile tests.
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Previously, we detected dodgy type family instances binders by
expanding type synonyms (via `exactTyCoVarsOfType`) and looking for
type variables on the RHS that weren't mentioned on the (expanded)
LHS. But this doesn't account for type families (like the example
in #17008), so we instead use `injectiveVarsOfType` to only count
LHS type variables that are in injective positions. That way, the `a`
in `type instance F (x :: T a) = a` will not count if `T` is a type
synonym _or_ a type family.
Along the way, I moved `exactTyCoVarsOfType` to `TyCoFVs` to live
alongside its sibling functions that also compute free variables.
Fixes #17008.
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GHC had an ad hoc validity check in place to rule out pattern
variables bound by type synonyms, such as in the following example:
```hs
type ItemColID a b = Int -- Discards a,b
get :: ItemColID a b -> ItemColID a b
get (x :: ItemColID a b) = x :: ItemColID a b
```
This hack is wholly unnecessary nowadays, since OutsideIn(X) is more
than capable of instantiating `a` and `b` to `Any`. In light of this,
let's rip out this validity check.
Fixes #17007.
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1. Slightly increased the waiting time for the tested effect to be more
profound.
2. Introduced measuring of the actual time spent waiting and adjusing
CPU time by it to compensate for threadDelay waiting time
inconsistencies.
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The `mkEtaWW` case for newtypes forgot to apply the substitution to
the newtype coercion, resulting in the Core Lint errors observed
in #16979. Easily fixed.
Fixes #16979.
Co-authored-by: Ryan Scott <ryan.gl.scott@gmail.com>
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separate file and add -ddump-cmm-verbose-by-proc to keep old behaviour (#16930)
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GHC used to reject programs of this form:
```
newtype Age = MkAge Int
deriving Eq via Const Int a
```
That's because an earlier implementation of `DerivingVia` would
generate the following instance:
```
instance Eq Age where
(==) = coerce @(Const Int a -> Const Int a -> Bool)
@(Age -> Age -> Bool)
(==)
```
Note that the `a` in `Const Int a` is not bound anywhere, which
causes all sorts of issues. I figured that no one would ever want to
write code like this anyway, so I simply banned "floating" `via` type
variables like `a`, checking for their presence in the aptly named
`reportFloatingViaTvs` function.
`reportFloatingViaTvs` ended up being implemented in a subtly
incorrect way, as #15831 demonstrates. Following counsel with the
sage of gold fire, I decided to abandon `reportFloatingViaTvs`
entirely and opt for a different approach that would _accept_
the instance above. This is because GHC now generates this instance
instead:
```
instance forall a. Eq Age where
(==) = coerce @(Const Int a -> Const Int a -> Bool)
@(Age -> Age -> Bool)
(==)
```
Notice that we now explicitly quantify the `a` in
`instance forall a. Eq Age`, so everything is peachy scoping-wise.
See `Note [Floating `via` type variables]` in `TcDeriv` for the full
scoop.
A pleasant benefit of this refactoring is that it made it much easier
to catch the problem observed in #16181, so this patch fixes that
issue too.
Fixes #15831. Fixes #16181.
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To display the free variables for a single breakpoint, GHCi pulls out the
information from the fields `modBreaks_breakInfo` and `modBreaks_vars`
of the `ModBreaks` data structure. For a specific breakpoint this gives 2
lists of types 'Id` (`Var`) and `OccName`. They are used to create the Id's
for the free variables and must be kept in sync:
If we remove an element from the Names list, then we also must remove the
corresponding element from the OccNames list.
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Kqueue/kevent implementation used to ignore events to be unsubscribed
from when events to be subscribed to were provided. This resulted in a
lost notification subscription, when GHC runtime didn't listen for any
events, yet the kernel considered otherwise and kept waking up the IO
manager thread.
This commit fixes this issue by always adding and removing all of the
provided subscriptions.
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