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Tracking ticket: #20115
MR: !10336
This converts uses of `mkTcRnUnknownMessage` to newly added constructors
of `TcRnMessage`.
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This brings the `IrredPred` case in sync with the treatment of `ClassPred`s as
described in `Note [Valid 'deriving' predicate]` in `GHC.Tc.Validity`. Namely,
we should reject `IrredPred`s that are inferred from `deriving` clauses whose
arguments contain other type constructors, as described in `(VD2) Reject exotic
constraints` of that Note. This has the nice property that `deriving` clauses
whose inferred instance context mention `TypeError` will now emit the type
error in the resulting error message, which better matches existing intuitions
about how `TypeError` should work.
While I was in town, I noticed that much of `Note [Valid 'deriving' predicate]`
was duplicated in a separate `Note [Exotic derived instance contexts]` in
`GHC.Tc.Deriv.Infer`. I decided to fold the latter Note into the former so that
there is a single authority on describing the conditions under which an
inferred `deriving` constraint can be considered valid.
This changes the behavior of `deriving` in a way that existing code might
break, so I have made a mention of this in the GHC User's Guide. It seems very,
very unlikely that much code is relying on this strange behavior, however, and
even if there is, there is a clear, backwards-compatible migration path using
`StandaloneDeriving`.
Fixes #22696.
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This patch moves the field-based logic for disambiguating record updates
to the renamer. The type-directed logic, scheduled for removal, remains
in the typechecker.
To do this properly (and fix the myriad of bugs surrounding the treatment
of duplicate record fields), we took the following main steps:
1. Create GREInfo, a renamer-level equivalent to TyThing which stores
information pertinent to the renamer.
This allows us to uniformly treat imported and local Names in the
renamer, as described in Note [GREInfo].
2. Remove GreName. Instead of a GlobalRdrElt storing GreNames, which
distinguished between normal names and field names, we now store
simple Names in GlobalRdrElt, along with the new GREInfo information
which allows us to recover the FieldLabel for record fields.
3. Add namespacing for record fields, within the OccNames themselves.
This allows us to remove the mangling of duplicate field selectors.
This change ensures we don't print mangled names to the user in
error messages, and allows us to handle duplicate record fields
in Template Haskell.
4. Move record disambiguation to the renamer, and operate on the
level of data constructors instead, to handle #21443.
The error message text for ambiguous record updates has also been
changed to reflect that type-directed disambiguation is on the way
out.
(3) means that OccEnv is now a bit more complex: we first key on the
textual name, which gives an inner map keyed on NameSpace:
OccEnv a ~ FastStringEnv (UniqFM NameSpace a)
Note that this change, along with (2), both increase the memory residency
of GlobalRdrEnv = OccEnv [GlobalRdrElt], which causes a few tests to
regress somewhat in compile-time allocation.
Even though (3) simplified a lot of code (in particular the treatment of
field selectors within Template Haskell and in error messages), it came
with one important wrinkle: in the situation of
-- M.hs-boot
module M where { data A; foo :: A -> Int }
-- M.hs
module M where { data A = MkA { foo :: Int } }
we have that M.hs-boot exports a variable foo, which is supposed to match
with the record field foo that M exports. To solve this issue, we add a
new impedance-matching binding to M
foo{var} = foo{fld}
This mimics the logic that existed already for impedance-binding DFunIds,
but getting it right was a bit tricky.
See Note [Record field impedance matching] in GHC.Tc.Module.
We also needed to be careful to avoid introducing space leaks in GHCi.
So we dehydrate the GlobalRdrEnv before storing it anywhere, e.g. in
ModIface. This means stubbing out all the GREInfo fields, with the
function forceGlobalRdrEnv.
When we read it back in, we rehydrate with rehydrateGlobalRdrEnv.
This robustly avoids any space leaks caused by retaining old type
environments.
Fixes #13352 #14848 #17381 #17551 #19664 #21443 #21444 #21720 #21898 #21946 #21959 #22125 #22160 #23010 #23062 #23063
Updates haddock submodule
-------------------------
Metric Increase:
MultiComponentModules
MultiLayerModules
MultiLayerModulesDefsGhci
MultiLayerModulesNoCode
T13701
T14697
hard_hole_fits
-------------------------
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I've turned almost all occurrences of TcRnUnknownMessage in GHC.Rename.Module
module into a proper TcRnMessage.
Instead, these TcRnMessage messages were introduced:
TcRnIllegalInstanceHeadDecl
TcRnUnexpectedStandaloneDerivingDecl
TcRnUnusedVariableInRuleDecl
TcRnUnexpectedStandaloneKindSig
TcRnIllegalRuleLhs
TcRnBadAssocRhs
TcRnDuplicateRoleAnnot
TcRnDuplicateKindSig
TcRnIllegalDerivStrategy
TcRnIllegalMultipleDerivClauses
TcRnNoDerivStratSpecified
TcRnStupidThetaInGadt
TcRnBadImplicitSplice
TcRnShadowedTyVarNameInFamResult
TcRnIncorrectTyVarOnLhsOfInjCond
TcRnUnknownTyVarsOnRhsOfInjCond
Was introduced one helper type:
RuleLhsErrReason
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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.
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See https://github.com/haskell/core-libraries-committee/issues/91 for
discussion.
This change relates Bifunctor with Functor by requiring second = fmap.
Moreover this change is a step towards unblocking the major version bump
of bifunctors and profunctors to major version 6. This paves the way to
move the Profunctor class into base. For that Functor first similarly
becomes a superclass of Profunctor in the new major version 6.
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The following `TcRnDiagnostic` messages have been introduced:
TcRnWarnUnsatisfiedMinimalDefinition
TcRnMisplacedInstSig
TcRnBadBootFamInstDeclErr
TcRnIllegalFamilyInstance
TcRnAssocInClassErr
TcRnBadFamInstDecl
TcRnNotOpenFamily
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Ticket #22379 revealed that skolemiseQuantifiedTyVar was
dropping the passed-in skol_info on the floor when it encountered
a SkolemTv. Bad! Several TyCons thereby share a single SkolemInfo
on their binders, which lead to bogus error reports.
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Necessary for newer cross-compiling backends (JS, Wasm) that don't
support TH yet.
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Previously, derived instances of `Functor` (as well as the related classes
`Foldable`, `Traversable`, and `Generic1`) would determine which constraints to
infer by checking for fields that contain the last type variable. The problem
was that this last type variable was taken from `tyConTyVars`. For GADTs, the
type variables in each data constructor are _not_ the same type variables as
in `tyConTyVars`, leading to #22167.
This fixes the issue by instead checking for the last type variable using
`dataConUnivTyVars`. (This is very similar in spirit to the fix for #21185,
which also replaced an errant use of `tyConTyVars` with type variables from
each data constructor.)
Fixes #22167.
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The testsuite output now contains diagnostic codes, so many tests need
to be updated at once.
We decided it was best to keep the diagnostic codes in the testsuite
output, so that contributors don't inadvertently make changes to the
diagnostic codes.
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This patch improves the uniformity of error message formatting by
printing constraints in quotes, as we do for types.
Fix #21167
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This adds a test for #21871, which was fixed by the No Skolem Info
rework (MR !7105).
Fixes #21871
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This commit fixes #20312
It deprecates "TypeInType" extension
according to the following proposal:
https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0083-no-type-in-type.rst
It has been already implemented.
The migration strategy:
1. Disable TypeInType
2. Enable both DataKinds and PolyKinds extensions
Metric Decrease:
T16875
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This commit redefines the structure of Splices in the AST.
We get rid of `HsSplice` which used to represent typed and untyped
splices, quasi quotes, and the result of splicing either an expression,
a type or a pattern.
Instead we have `HsUntypedSplice` which models an untyped splice or a
quasi quoter, which works in practice just like untyped splices.
The `HsExpr` constructor `HsSpliceE` which used to be constructed with
an `HsSplice` is split into `HsTypedSplice` and `HsUntypedSplice`. The
former is directly constructed with an `HsExpr` and the latter now takes
an `HsUntypedSplice`.
Both `HsType` and `Pat` constructors `HsSpliceTy` and `SplicePat` now
take an `HsUntypedSplice` instead of a `HsSplice` (remember only
/untyped splices/ can be spliced as types or patterns).
The result of splicing an expression, type, or pattern is now
comfortably stored in the extension fields `XSpliceTy`, `XSplicePat`,
`XUntypedSplice` as, respectively, `HsUntypedSpliceResult (HsType
GhcRn)`, `HsUntypedSpliceResult (Pat GhcRn)`, and `HsUntypedSpliceResult
(HsExpr GhcRn)`
Overall the TTG extension points are now better used to
make invalid states unrepresentable and model the progression between
stages better.
See Note [Lifecycle of an untyped splice, and PendingRnSplice]
and Note [Lifecycle of an typed splice, and PendingTcSplice] for more
details.
Updates haddock submodule
Fixes #21263
-------------------------
Metric Decrease:
hard_hole_fits
-------------------------
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The free-var test (now documented as (VD3)) was too narrow,
affecting only class predicates. #21302 demonstrated that
this wasn't enough!
Fixes #21302.
Co-authored-by: Ryan Scott <ryan.gl.scott@gmail.com>
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Users are supposed to import GHC.Exts rather than GHC.Prim.
Part of #18749.
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As explained in `Note [Gathering and simplifying constraints for DeriveAnyClass]`
in `GHC.Tc.Deriv.Infer`, `DeriveAnyClass` infers instance contexts by emitting
implication constraints. Previously, these implication constraints were
constructed by hand. This is a terribly trick thing to get right, as it
involves a delicate interplay of skolemisation, metavariable instantiation, and
`TcLevel` bumping. Despite much effort, we discovered in #20719 that the
implementation was subtly incorrect, leading to valid programs being rejected.
While we could scrutinize the code that manually constructs implication
constraints and repair it, there is a better, less error-prone way to do
things. After all, the heart of `DeriveAnyClass` is generating code which
fills in each class method with defaults, e.g., `foo = $gdm_foo`. Typechecking
this sort of code is tantamount to calling `tcSubTypeSigma`, as we much ensure
that the type of `$gdm_foo` is a subtype of (i.e., more polymorphic than) the
type of `foo`. As an added bonus, `tcSubTypeSigma` is a battle-tested function
that handles skolemisation, metvariable instantiation, `TcLevel` bumping, and
all other means of tricky bookkeeping correctly.
With this insight, the solution to the problems uncovered in #20719 is simple:
use `tcSubTypeSigma` to check if `$gdm_foo`'s type is a subtype of `foo`'s
type. As a side effect, `tcSubTypeSigma` will emit exactly the implication
constraint that we were attempting to construct by hand previously. Moreover,
it does so correctly, fixing #20719 as a consequence.
This patch implements the solution thusly:
* The `PredSpec` data type (previously named `PredOrigin`) is now split into
`SimplePredSpec`, which directly stores a `PredType`, and `SubTypePredSpec`,
which stores the actual and expected types in a subtype check.
`SubTypePredSpec` is only used for `DeriveAnyClass`; all other deriving
strategies use `SimplePredSpec`.
* Because `tcSubTypeSigma` manages the finer details of type variable
instantiation and constraint solving under the hood, there is no longer any
need to delicately split apart the method type signatures in
`inferConstraintsAnyclass`. This greatly simplifies the implementation of
`inferConstraintsAnyclass` and obviates the need to store skolems,
metavariables, or given constraints in a `ThetaSpec` (previously named
`ThetaOrigin`). As a bonus, this means that `ThetaSpec` now simply becomes a
synonym for a list of `PredSpec`s, which is conceptually much simpler than it
was before.
* In `simplifyDeriv`, each `SubTypePredSpec` results in a call to
`tcSubTypeSigma`. This is only performed for its side effect of emitting
an implication constraint, which is fed to the rest of the constraint solving
machinery in `simplifyDeriv`. I have updated
`Note [Gathering and simplifying constraints for DeriveAnyClass]` to explain
this in more detail.
To make the changes in `simplifyDeriv` more manageable, I also performed some
auxiliary refactoring:
* Previously, every iteration of `simplifyDeriv` was skolemising the type
variables at the start, simplifying, and then performing a reverse
substitution at the end to un-skolemise the type variables. This is not
necessary, however, since we can just as well skolemise once at the
beginning of the `deriving` pipeline and zonk the `TcTyVar`s after
`simplifyDeriv` is finished. This patch does just that, having been made
possible by prior work in !7613. I have updated `Note [Overlap and deriving]`
in `GHC.Tc.Deriv.Infer` to explain this, and I have also left comments on
the relevant data structures (e.g., `DerivEnv` and `DerivSpec`) to explain
when things might be `TcTyVar`s or `TyVar`s.
* All of the aforementioned cleanup allowed me to remove an ad hoc
deriving-related in `checkImplicationInvariants`, as all of the skolems in
a `tcSubTypeSigma`–produced implication constraint should now be `TcTyVar`
at the time the implication is created.
* Since `simplifyDeriv` now needs a `SkolemInfo` and `UserTypeCtxt`, I have
added `ds_skol_info` and `ds_user_ctxt` fields to `DerivSpec` to store these.
Similarly, I have also added a `denv_skol_info` field to `DerivEnv`, which
ultimately gets used to initialize the `ds_skol_info` in a `DerivSpec`.
Fixes #20719.
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This patch improves code generation for derived Eq instances.
The idea is to use 'dataToTag' to evaluate both arguments.
This allows to 'short-circuit' when tags do not match.
Unfortunately, inner evals are still present when we branch
on tags. This is due to the way 'dataToTag#' primop
evaluates its argument in the code generator. #21207 was
created to explore further optimizations.
Metric Decrease:
LargeRecord
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* Users can define their own (~) type operator
* Haddock can display documentation for the built-in (~)
* New transitional warnings implemented:
-Wtype-equality-out-of-scope
-Wtype-equality-requires-operators
Updates the haddock submodule.
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As noted in #21071 we were missing adding this edge so there were
situations where the .hs file would get compiled before the .hs-boot
file which leads to issues with -j.
I fixed this properly by adding the edge in downsweep so the definition
of nodeDependencies can be simplified to avoid adding this dummy edge
in.
There are plenty of tests which seem to have these redundant boot files
anyway so no new test. #21094 tracks the more general issue of
identifying redundant hs-boot and SOURCE imports.
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Co-authored by: Sam Derbyshire
Previously, GHC had three flavours of constraint:
Wanted, Given, and Derived. This removes Derived constraints.
Though serving a number of purposes, the most important role
of Derived constraints was to enable better error messages.
This job has been taken over by the new RewriterSets, as explained
in Note [Wanteds rewrite wanteds] in GHC.Tc.Types.Constraint.
Other knock-on effects:
- Various new Notes as I learned about under-described bits of GHC
- A reshuffling around the AST for implicit-parameter bindings,
with better integration with TTG.
- Various improvements around fundeps. These were caused by the
fact that, previously, fundep constraints were all Derived,
and Derived constraints would get dropped. Thus, an unsolved
Derived didn't stop compilation. Without Derived, this is no
longer possible, and so we have to be considerably more careful
around fundeps.
- A nice little refactoring in GHC.Tc.Errors to center the work
on a new datatype called ErrorItem. Constraints are converted
into ErrorItems at the start of processing, and this allows for
a little preprocessing before the main classification.
- This commit also cleans up the behavior in generalisation around
functional dependencies. Now, if a variable is determined by
functional dependencies, it will not be quantified. This change
is user facing, but it should trim down GHC's strange behavior
around fundeps.
- Previously, reportWanteds did quite a bit of work, even on an empty
WantedConstraints. This commit adds a fast path.
- Now, GHC will unconditionally re-simplify constraints during
quantification. See Note [Unconditionally resimplify constraints when
quantifying], in GHC.Tc.Solver.
Close #18398.
Close #18406.
Solve the fundep-related non-confluence in #18851.
Close #19131.
Close #19137.
Close #20922.
Close #20668.
Close #19665.
-------------------------
Metric Decrease:
LargeRecord
T9872b
T9872b_defer
T9872d
TcPlugin_RewritePerf
-------------------------
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`check_special_inst_head` includes logic that disallows hand-written
instances for built-in classes such as Typeable, KnownNat
and KnownSymbol.
However, it also allowed standalone deriving declarations. This was
because we do want to allow standalone deriving instances with
Typeable as they are harmless, but we certainly don't want to allow
instances for e.g. KnownNat.
This patch ensures that we don't allow derived instances for
KnownNat, KnownSymbol (and also KnownChar, which was previously
omitted entirely).
Fixes #21087
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Note [Tidying multiple names at once] indicates that if multiple
variables have the same name then we shouldn't prioritise one of them
and instead rename them all to a1, a2, a3... etc
This patch implements that change, some error message changes as
expected.
Closes #20932
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The main purpose of this patch is to attach a SkolemInfo directly to
each SkolemTv. This fixes the large number of bugs which have
accumulated over the years where we failed to report errors due to
having "no skolem info" for particular type variables. Now the origin of
each type varible is stored on the type variable we can always report
accurately where it cames from.
Fixes #20969 #20732 #20680 #19482 #20232 #19752 #10946
#19760 #20063 #13499 #14040
The main changes of this patch are:
* SkolemTv now contains a SkolemInfo field which tells us how the
SkolemTv was created. Used when reporting errors.
* Enforce invariants relating the SkolemInfoAnon and level of an implication (ic_info, ic_tclvl)
to the SkolemInfo and level of the type variables in ic_skols.
* All ic_skols are TcTyVars -- Check is currently disabled
* All ic_skols are SkolemTv
* The tv_lvl of the ic_skols agrees with the ic_tclvl
* The ic_info agrees with the SkolInfo of the implication.
These invariants are checked by a debug compiler by
checkImplicationInvariants.
* Completely refactor kcCheckDeclHeader_sig which kept
doing my head in. Plus, it wasn't right because it wasn't skolemising
the binders as it decomposed the kind signature.
The new story is described in Note [kcCheckDeclHeader_sig]. The code
is considerably shorter than before (roughly 240 lines turns into 150
lines).
It still has the same awkward complexity around computing arity as
before, but that is a language design issue.
See Note [Arity inference in kcCheckDeclHeader_sig]
* I added new type synonyms MonoTcTyCon and PolyTcTyCon, and used
them to be clear which TcTyCons have "finished" kinds etc, and
which are monomorphic. See Note [TcTyCon, MonoTcTyCon, and PolyTcTyCon]
* I renamed etaExpandAlgTyCon to splitTyConKind, becuase that's a
better name, and it is very useful in kcCheckDeclHeader_sig, where
eta-expansion isn't an issue.
* Kill off the nasty `ClassScopedTvEnv` entirely.
Co-authored-by: Simon Peyton Jones <simon.peytonjones@gmail.com>
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Previously, `DeriveGeneric` would look up the fixity of a data constructor
using `getFixityEnv`, but this is subtly incorrect for data constructors
defined in external modules. This sort of situation can happen with
`StandaloneDeriving`, as noticed in #20994. In fact, the same bug has occurred
in the past in #9830, and while that bug was fixed for `deriving Read` and
`deriving Show`, the fix was never extended to `DeriveGeneric` due to an
oversight. This patch corrects that oversight.
Fixes #20994.
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Multiple home units allows you to load different packages which may depend on
each other into one GHC session. This will allow both GHCi and HLS to support
multi component projects more naturally.
Public Interface
~~~~~~~~~~~~~~~~
In order to specify multiple units, the -unit @⟨filename⟩ flag
is given multiple times with a response file containing the arguments for each unit.
The response file contains a newline separated list of arguments.
```
ghc -unit @unitLibCore -unit @unitLib
```
where the `unitLibCore` response file contains the normal arguments that cabal would pass to `--make` mode.
```
-this-unit-id lib-core-0.1.0.0
-i
-isrc
LibCore.Utils
LibCore.Types
```
The response file for lib, can specify a dependency on lib-core, so then modules in lib can use modules from lib-core.
```
-this-unit-id lib-0.1.0.0
-package-id lib-core-0.1.0.0
-i
-isrc
Lib.Parse
Lib.Render
```
Then when the compiler starts in --make mode it will compile both units lib and lib-core.
There is also very basic support for multiple home units in GHCi, at the
moment you can start a GHCi session with multiple units but only the
:reload is supported. Most commands in GHCi assume a single home unit,
and so it is additional work to work out how to modify the interface to
support multiple loaded home units.
Options used when working with Multiple Home Units
There are a few extra flags which have been introduced specifically for
working with multiple home units. The flags allow a home unit to pretend
it’s more like an installed package, for example, specifying the package
name, module visibility and reexported modules.
-working-dir ⟨dir⟩
It is common to assume that a package is compiled in the directory
where its cabal file resides. Thus, all paths used in the compiler
are assumed to be relative to this directory. When there are
multiple home units the compiler is often not operating in the
standard directory and instead where the cabal.project file is
located. In this case the -working-dir option can be passed which
specifies the path from the current directory to the directory the
unit assumes to be it’s root, normally the directory which contains
the cabal file.
When the flag is passed, any relative paths used by the compiler are
offset by the working directory. Notably this includes -i and
-I⟨dir⟩ flags.
-this-package-name ⟨name⟩
This flag papers over the awkward interaction of the PackageImports
and multiple home units. When using PackageImports you can specify
the name of the package in an import to disambiguate between modules
which appear in multiple packages with the same name.
This flag allows a home unit to be given a package name so that you
can also disambiguate between multiple home units which provide
modules with the same name.
-hidden-module ⟨module name⟩
This flag can be supplied multiple times in order to specify which
modules in a home unit should not be visible outside of the unit it
belongs to.
The main use of this flag is to be able to recreate the difference
between an exposed and hidden module for installed packages.
-reexported-module ⟨module name⟩
This flag can be supplied multiple times in order to specify which
modules are not defined in a unit but should be reexported. The
effect is that other units will see this module as if it was defined
in this unit.
The use of this flag is to be able to replicate the reexported
modules feature of packages with multiple home units.
Offsetting Paths in Template Haskell splices
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When using Template Haskell to embed files into your program,
traditionally the paths have been interpreted relative to the directory
where the .cabal file resides. This causes problems for multiple home
units as we are compiling many different libraries at once which have
.cabal files in different directories.
For this purpose we have introduced a way to query the value of the
-working-dir flag to the Template Haskell API. By using this function we
can implement a makeRelativeToProject function which offsets a path
which is relative to the original project root by the value of
-working-dir.
```
import Language.Haskell.TH.Syntax ( makeRelativeToProject )
foo = $(makeRelativeToProject "./relative/path" >>= embedFile)
```
> If you write a relative path in a Template Haskell splice you should use the makeRelativeToProject function so that your library works correctly with multiple home units.
A similar function already exists in the file-embed library. The
function in template-haskell implements this function in a more robust
manner by honouring the -working-dir flag rather than searching the file
system.
Closure Property for Home Units
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For tools or libraries using the API there is one very important closure
property which must be adhered to:
> Any dependency which is not a home unit must not (transitively) depend
on a home unit.
For example, if you have three packages p, q and r, then if p depends on
q which depends on r then it is illegal to load both p and r as home
units but not q, because q is a dependency of the home unit p which
depends on another home unit r.
If you are using GHC by the command line then this property is checked,
but if you are using the API then you need to check this property
yourself. If you get it wrong you will probably get some very confusing
errors about overlapping instances.
Limitations of Multiple Home Units
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There are a few limitations of the initial implementation which will be smoothed out on user demand.
* Package thinning/renaming syntax is not supported
* More complicated reexports/renaming are not yet supported.
* It’s more common to run into existing linker bugs when loading a
large number of packages in a session (for example #20674, #20689)
* Backpack is not yet supported when using multiple home units.
* Dependency chasing can be quite slow with a large number of
modules and packages.
* Loading wired-in packages as home units is currently not supported
(this only really affects GHC developers attempting to load
template-haskell).
* Barely any normal GHCi features are supported, it would be good to
support enough for ghcid to work correctly.
Despite these limitations, the implementation works already for nearly
all packages. It has been testing on large dependency closures,
including the whole of head.hackage which is a total of 4784 modules
from 452 packages.
Internal Changes
~~~~~~~~~~~~~~~~
* The biggest change is that the HomePackageTable is replaced with the
HomeUnitGraph. The HomeUnitGraph is a map from UnitId to HomeUnitEnv,
which contains information specific to each home unit.
* The HomeUnitEnv contains:
- A unit state, each home unit can have different package db flags
- A set of dynflags, each home unit can have different flags
- A HomePackageTable
* LinkNode: A new node type is added to the ModuleGraph, this is used to
place the linking step into the build plan so linking can proceed in
parralel with other packages being built.
* New invariant: Dependencies of a ModuleGraphNode can be completely
determined by looking at the value of the node. In order to achieve
this, downsweep now performs a more complete job of downsweeping and
then the dependenices are recorded forever in the node rather than
being computed again from the ModSummary.
* Some transitive module calculations are rewritten to use the
ModuleGraph which is more efficient.
* There is always an active home unit, which simplifies modifying a lot
of the existing API code which is unit agnostic (for example, in the
driver).
The road may be bumpy for a little while after this change but the
basics are well-tested.
One small metric increase, which we accept and also submodule update to
haddock which removes ExtendedModSummary.
Closes #10827
-------------------------
Metric Increase:
MultiLayerModules
-------------------------
Co-authored-by: Fendor <power.walross@gmail.com>
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The reqlib modifer was supposed to indicate that a test needed a certain
library in order to work. If the library happened to be installed then
the test would run as normal.
However, CI has never run these tests as the packages have not been
installed and we don't want out tests to depend on things which might
get externally broken by updating the compiler.
The new strategy is to run these tests in head.hackage, where the tests
have been cabalised as well as possible. Some tests couldn't be
transferred into the normal style testsuite but it's better than never
running any of the reqlib tests. https://gitlab.haskell.org/ghc/head.hackage/-/merge_requests/169
A few submodules also had reqlib tests and have been updated to remove
it.
Closes #16264 #20032 #17764 #16561
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It isn't much more complicated to be more precise when deriving Lift so
we now generate
```
data Foo = Foo Int Bool
instance Lift Foo where
lift (Foo a b) = [| Foo $(lift a) $(lift b) |]
liftTyped (Foo a b) = [|| Foo $$(lift a) $$(lift b) |]
```
This fixes #20688 which complained about using implicit lifting in the
derived code.
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Previously, the `deriving` machinery was very loosey-goosey about how it used
the types of data constructor fields when generating code. It would usually
just consult `dataConOrigArgTys`, which returns the _uninstantiated_ field
types of each data constructor. Usually, you can get away with this, but
issues #20375 and #20387 revealed circumstances where this approach fails.
Instead, when generated code for a stock-derived instance
`C (T arg_1 ... arg_n)`, one must take care to instantiate the field types of
each data constructor with `arg_1 ... arg_n`. The particulars of how this is
accomplished is described in the new
`Note [Instantiating field types in stock deriving]` in
`GHC.Tc.Deriv.Generate`. Some highlights:
* `DerivInstTys` now has a new `dit_dc_inst_arg_env :: DataConEnv [Type]`
field that caches the instantiated field types of each data constructor.
Whenever we need to consult the field types somewhere in `GHC.Tc.Deriv.*`
we avoid using `dataConOrigArgTys` and instead look it up in
`dit_dc_inst_arg_env`.
* Because `DerivInstTys` now stores the instantiated field types of each
constructor, some of the details of the `GHC.Tc.Deriv.Generics.mkBindsRep`
function were able to be simplified. In particular, we no longer need to
apply a substitution to instantiate the field types in a `Rep(1)` instance,
as that is already done for us by `DerivInstTys`. We still need a
substitution to implement the "wrinkle" section of
`Note [Generating a correctly typed Rep instance]`, but the code is
nevertheless much simpler than before.
* The `tyConInstArgTys` function has been removed in favor of the new
`GHC.Core.DataCon.dataConInstUnivs` function, which is really the proper tool
for the job. `dataConInstUnivs` is much like `tyConInstArgTys` except that it
takes a data constructor, not a type constructor, as an argument, and it adds
extra universal type variables from that data constructor at the end of the
returned list if need be. `dataConInstUnivs` takes care to instantiate the
kinds of the universal type variables at the end, thereby avoiding a bug in
`tyConInstArgTys` discovered in
https://gitlab.haskell.org/ghc/ghc/-/issues/20387#note_377037.
Fixes #20375. Fixes #20387.
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Previously, derived instances that use `deriving` clauses would infer
`DatatypeContexts` by using `tyConStupidTheta`. But this sometimes causes
redundant constraints to be included in the derived instance contexts, as the
constraints that appear in the `tyConStupidTheta` may not actually appear in
the types of the data constructors (i.e., the `dataConStupidTheta`s). For
instance, in `data Show a => T a = MkT deriving Eq`, the type of `MkT` does
not require `Show`, so the derived `Eq` instance should not require `Show`
either. This patch makes it so with some small tweaks to
`inferConstraintsStock`.
Fixes #20501.
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(#20496)
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PHASE 1: we never rewrite Concrete# evidence.
This patch migrates all the representation polymorphism checks to
the typechecker, using a new constraint form
Concrete# :: forall k. k -> TupleRep '[]
Whenever a type `ty` must be representation-polymorphic
(e.g. it is the type of an argument to a function), we emit a new
`Concrete# ty` Wanted constraint. If this constraint goes
unsolved, we report a representation-polymorphism error to the user.
The 'FRROrigin' datatype keeps track of the context of the
representation-polymorphism check, for more informative error messages.
This paves the way for further improvements, such as
allowing type families in RuntimeReps and improving the soundness
of typed Template Haskell. This is left as future work (PHASE 2).
fixes #17907 #20277 #20330 #20423 #20426
updates haddock submodule
-------------------------
Metric Decrease:
T5642
-------------------------
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This (big) commit finishes porting the GHC.Tc.Deriv module to support
the new diagnostic infrastructure (#18516) by getting rid of the legacy
calls to `TcRnUnknownMessage`. This work ended up being quite pervasive
and touched not only the Tc.Deriv module but also the Tc.Deriv.Utils and
Tc.Deriv.Generics module, which needed to be adapted to use the new
infrastructure. This also required generalising `Validity`.
More specifically, this is a breakdown of the work done:
* Add and use the TcRnUselessTypeable data constructor
* Add and use TcRnDerivingDefaults data constructor
* Add and use the TcRnNonUnaryTypeclassConstraint data constructor
* Add and use TcRnPartialTypeSignatures
* Add T13324_compile2 test to test another part of the
TcRnPartialTypeSignatures diagnostic
* Add and use TcRnCannotDeriveInstance data constructor, which introduces a
new data constructor to TcRnMessage called TcRnCannotDeriveInstance, which
is further sub-divided to carry a `DeriveInstanceErrReason` which explains
the reason why we couldn't derive a typeclass instance.
* Add DerivErrSafeHaskellGenericInst data constructor to DeriveInstanceErrReason
* Add DerivErrDerivingViaWrongKind and DerivErrNoEtaReduce
* Introduce the SuggestExtensionInOrderTo Hint, which adds (and use) a new
constructor to the hint type `LanguageExtensionHint` called `SuggestExtensionInOrderTo`,
which can be used to give a bit more "firm" recommendations when it's
obvious what the required extension is, like in the case for the
`DerivingStrategies`, which automatically follows from having enabled
both `DeriveAnyClass` and `GeneralizedNewtypeDeriving`.
* Wildcard-free pattern matching in mk_eqn_stock, which removes `_` in
favour of pattern matching explicitly on `CanDeriveAnyClass` and
`NonDerivableClass`, because that determine whether or not we can
suggest to the user `DeriveAnyClass` or not.
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This flag is used to remove the output of core stats per binding in Core
dumps.
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This fixes a long standard bug where the module prefix was omitted
from the data type name supplied by Data.Typeable instances.
Instead of reusing the Outputable instance for TyCon, we now take
matters into our own hands and explicitly print the module followed by
the type constructor name.
Fixes #20371
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- Add 19 new messages. Update test outputs accordingly.
- Pretty print suggest-extensions hints: remove space before
interspersed commas.
- Refactor Rank's MonoType constructors. Each MonoType constructor
should represent a specific case. With the Doc suggestion belonging
to the TcRnMessage diagnostics instead.
- Move Rank from Validity to its own `GHC.Tc.Types.Rank` module.
- Remove the outdated `check_irred_pred` check.
- Remove the outdated duplication check in `check_valid_theta`, which
was subsumed by `redundant-constraints`.
- Add missing test cases for quantified-constraints/T16474 & th/T12387a.
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Fixes #19616.
This commit changes the `GHC.Driver.Errors.handleFlagWarnings` function
to rely on the newly introduced `DiagnosticReason`. This allows us to
correctly pretty-print the flags which triggered some warnings and in
turn remove the cruft around this function (like the extra filtering
and the `shouldPrintWarning` function.
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Other than that:
* Fix T16167,json,json2,T7478,T10637 tests to reflect the introduction of
the `MessageClass` type
* Remove `makeIntoWarning`
* Remove `warningsToMessages`
* Refactor GHC.Tc.Errors
1. Refactors GHC.Tc.Errors so that we use `DiagnosticReason` for "choices"
(defer types errors, holes, etc);
2. We get rid of `reportWarning` and `reportError` in favour of a general
`reportDiagnostic`.
* Introduce `DiagnosticReason`, `Severity` is an enum: This big commit makes
`Severity` a simple enumeration, and introduces the concept of `DiagnosticReason`,
which classifies the /reason/ why we are emitting a particular diagnostic.
It also adds a monomorphic `DiagnosticMessage` type which is used for
generic messages.
* The `Severity` is computed (for now) from the reason, statically.
Later improvement will add a `diagReasonSeverity` function to compute
the `Severity` taking `DynFlags` into account.
* Rename `logWarnings` into `logDiagnostics`
* Add note and expand description of the `mkHoleError` function
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Metric Increase:
T10370
parsing001
Updates haddock submodule
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This implements the BoxedRep proposal, refactoring the `RuntimeRep`
hierarchy from:
```haskell
data RuntimeRep = LiftedPtrRep | UnliftedPtrRep | ...
```
to
```haskell
data RuntimeRep = BoxedRep Levity | ...
data Levity = Lifted | Unlifted
```
Updates binary, haddock submodules.
Closes #17526.
Metric Increase:
T12545
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This commit also consolidates documentation in the user
manual around UndecidableSuperClasses, UndecidableInstances,
and FlexibleContexts.
Close #19186.
Close #19187.
Test case: typecheck/should_compile/T19186,
typecheck/should_fail/T19187{,a}
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Use `mkConstrTag` to explicitly pass the constructor tag instead of
using `mkConstr` which queries the tag at runtime by querying the index
of the constructor name (a string) in the list of constructor names.
Perf improvement:
T16577(normal) ghc/alloc 11325573876.0 9249786992.0 -18.3% GOOD
Thanks to @sgraf812 for suggesting an additional list fusion fix during
reviews.
Metric Decrease:
T16577
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Instead of producing auxiliary con2tag bindings we now rely on
dataToTag#, eliminating a fair bit of generated code.
Co-Authored-By: Ben Gamari <ben@well-typed.com>
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Issue #18914 revealed that `GeneralizedNewtypeDeriving` would generate code
that mentions unbound type variables, which is dangerously fragile. The
problem (and fix) is described in the new `Wrinkle: Use HsOuterExplicit`
in `Note [GND and QuantifiedConstraints]`. The gist of it: make sure to
put the top-level `forall`s in `deriving`-generated instance signatures in an
`HsOuterExplicit` to ensure that they scope over the bodies of methods
correctly. A side effect of this process is that it will expand any type
synonyms in the instance signature, which will surface any `forall`s that
are hidden underneath type synonyms (such as in the test case for #18914).
While I was in town, I also performed some maintenance on `NewHsTypeX`, which
powers `GeneralizedNewtypeDeriving`:
* I renamed `NewHsTypeX` to `HsCoreTy`, which more accurately describes its
intended purpose (#15706). I also made `HsCoreTy` a type synonym instead of
a newtype, as making it a distinct data type wasn't buying us much.
* To make sure that mistakes similar to #18914 do not occur later, I added an
additional validity check when renaming `HsCoreTy`s that complains if an
`HsCoreTy`s contains an out-of-scope type variable. See the new
`Note [Renaming HsCoreTys]` in `GHC.Rename.HsType` for the details.
Fixes #15706. Fixes #18914. Bumps the `haddock` submodule.
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This was inadvertently merged.
This reverts commit 6c2eb2232b39ff4720fda0a4a009fb6afbc9dcea.
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