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When instances overlap, we now include additional information
about why we weren't able to select an instance: perhaps
one instance overlapped another but was not strictly more specific,
so we aren't able to directly choose it.
Fixes #20542
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Trac #14394 showed that it's possible to get redundant
constraints in the inferred provided constraints of a pattern
synonym. This patch removes the redundancy with mkMinimalBySCs.
To do this I had to generalise the type of mkMinimalBySCs slightly.
And, to reduce confusing reversal, I made it stable: it now returns
its result in the same order as its input. That led to a raft of
error message wibbles, mostly for the better.
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Summary:
Add prettyprinter tests, which take a file, parse it, pretty print it,
re-parse the pretty printed version and then compare the original and
new ASTs (ignoring locations)
Updates haddock submodule to match the AST changes.
There are three issues outstanding
1. Extra parens around a context are not reproduced. This will require an
AST change and will be done in a separate patch.
2. Currently if an `HsTickPragma` is found, this is not pretty-printed,
to prevent noise in the output.
I am not sure what the desired behaviour in this case is, so have left
it as before. Test Ppr047 is marked as expected fail for this.
3. Apart from in a context, the ParsedSource AST keeps all the parens from
the original source. Something is happening in the renamer to remove the
parens around visible type application, causing T12530 to fail, as the
dumped splice decl is after the renamer.
This needs to be fixed by keeping the parens, but I do not know where they
are being removed. I have amended the test to pass, by removing the parens
in the expected output.
Test Plan: ./validate
Reviewers: goldfire, mpickering, simonpj, bgamari, austin
Reviewed By: simonpj, bgamari
Subscribers: simonpj, goldfire, thomie, mpickering
Differential Revision: https://phabricator.haskell.org/D2752
GHC Trac Issues: #3384
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This patch does a raft of useful tidy-ups in the type checker.
I've been meaning to do this for some time, and finally made
time to do it en route to ICFP.
1. Modify TcType.ExpType to make a distinct data type,
InferResult for the Infer case, and consequential
refactoring.
2. Define a new function TcUnify.fillInferResult, to fill in
an InferResult. It uses TcMType.promoteTcType to promote
the type to the level of the InferResult.
See TcMType Note [Promoting a type]
This refactoring is in preparation for an improvement
to typechecking pattern bindings, coming next.
I flirted with an elaborate scheme to give better
higher rank inference, but it was just too complicated.
See TcMType Note [Promotion and higher rank types]
3. Add to InferResult a new field ir_inst :: Bool to say
whether or not the type used to fill in the
InferResult should be deeply instantiated. See
TcUnify Note [Deep instantiation of InferResult].
4. Add a TcLevel to SkolemTvs. This will be useful generally
- it's a fast way to see if the type
variable escapes when floating (not used yet)
- it provides a good consistency check when updating a
unification variable (TcMType.writeMetaTyVarRef, the
level_check_ok check)
I originally had another reason (related to the flirting
in (2), but I left it in because it seems like a step in
the right direction.
5. Reduce and simplify the plethora of uExpType,
tcSubType and related functions in TcUnify. It was
such an opaque mess and it's still not great, but it's
better.
6. Simplify the uo_expected field of TypeEqOrigin. Richard
had generatlised it to a ExpType, but it was almost always
a Check type. Now it's back to being a plain TcType which
is much, much easier.
7. Improve error messages by refraining from skolemisation when
it's clear that there's an error: see
TcUnify Note [Don't skolemise unnecessarily]
8. Type.isPiTy and isForAllTy seem to be missing a coreView check,
so I added it
9. Kill off tcs_used_tcvs. Its purpose is to track the
givens used by wanted constraints. For dictionaries etc
we do that via the free vars of the /bindings/ in the
implication constraint ic_binds. But for coercions we
just do update-in-place in the type, rather than
generating a binding. So we need something analogous to
bindings, to track what coercions we have added.
That was the purpose of tcs_used_tcvs. But it only
worked for a /single/ iteration, whereas we may have
multiple iterations of solving an implication. Look
at (the old) 'setImplicationStatus'. If the constraint
is unsolved, it just drops the used_tvs on the floor.
If it becomes solved next time round, we'll pick up
coercions used in that round, but ignore ones used in
the first round.
There was an outright bug. Result = (potentialy) bogus
unused-constraint errors. Constructing a case where this
actually happens seems quite trick so I did not do so.
Solution: expand EvBindsVar to include the (free vars of
the) coercions, so that the coercions are tracked in
essentially the same way as the bindings.
This turned out to be much simpler. Less code, more
correct.
10. Make the ic_binds field in an implication have type
ic_binds :: EvBindsVar
instead of (as previously)
ic_binds :: Maybe EvBindsVar
This is notably simpler, and faster to use -- less
testing of the Maybe. But in the occaional situation
where we don't have anywhere to put the bindings, the
belt-and-braces error check is lost. So I put it back
as an ASSERT in 'setImplicationStatus' (see the use of
'termEvidenceAllowed')
All these changes led to quite bit of error message wibbling
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Before this patch, following the TypeInType innovations,
each TyCon had two lists:
- tyConBinders :: [TyBinder]
- tyConTyVars :: [TyVar]
They were in 1-1 correspondence and contained
overlapping information. More broadly, there were many
places where we had to pass around this pair of lists,
instead of a single list.
This commit tidies all that up, by having just one list of
binders in a TyCon:
- tyConBinders :: [TyConBinder]
The new data types look like this:
Var.hs:
data TyVarBndr tyvar vis = TvBndr tyvar vis
data VisibilityFlag = Visible | Specified | Invisible
type TyVarBinder = TyVarBndr TyVar VisibilityFlag
TyCon.hs:
type TyConBinder = TyVarBndr TyVar TyConBndrVis
data TyConBndrVis
= NamedTCB VisibilityFlag
| AnonTCB
TyCoRep.hs:
data TyBinder
= Named TyVarBinder
| Anon Type
Note that Var.TyVarBdr has moved from TyCoRep and has been
made polymorphic in the tyvar and visiblity fields:
type TyVarBinder = TyVarBndr TyVar VisibilityFlag
-- Used in ForAllTy
type TyConBinder = TyVarBndr TyVar TyConBndrVis
-- Used in TyCon
type IfaceForAllBndr = TyVarBndr IfaceTvBndr VisibilityFlag
type IfaceTyConBinder = TyVarBndr IfaceTvBndr TyConBndrVis
-- Ditto, in interface files
There are a zillion knock-on changes, but everything
arises from these types. It was a bit fiddly to get the
module loops to work out right!
Some smaller points
~~~~~~~~~~~~~~~~~~~
* Nice new functions
TysPrim.mkTemplateKiTyVars
TysPrim.mkTemplateTyConBinders
which help you make the tyvar binders for dependently-typed
TyCons. See comments with their definition.
* The change showed up a bug in TcGenGenerics.tc_mkRepTy, where the code
was making an assumption about the order of the kind variables in the
kind of GHC.Generics.(:.:). I fixed this; see TcGenGenerics.mkComp.
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Summary:
foldUFM introduces unnecessary non-determinism that actually
leads to different generated code as explained in
Note [TrieMap determinism].
As we're switching from UniqFM to UniqDFM here you might be
concerned about performance. There's nothing that ./validate
detects. nofib reports no change in Compile Allocations, but
Compile Time got better on some tests and worse on some,
yielding this summary:
-1 s.d. ----- -3.8%
+1 s.d. ----- +5.4%
Average ----- +0.7%
This is not a fair comparison as the order of Uniques
changes what GHC is actually doing. One benefit from making
this deterministic is also that it will make the
performance results more stable.
Full nofib results: P108
Test Plan: ./validate, nofib
Reviewers: goldfire, simonpj, simonmar, austin, bgamari
Reviewed By: simonpj
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D2169
GHC Trac Issues: #4012
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The idea here is described in [wiki:Typechecker]. Briefly,
this refactor keeps solid track of "synthesis" mode vs
"checking" in GHC's bidirectional type-checking algorithm.
When in synthesis mode, the expected type is just an IORef
to write to.
In addition, this patch does a significant reworking of
RebindableSyntax, allowing much more freedom in the types
of the rebindable operators. For example, we can now have
`negate :: Int -> Bool` and
`(>>=) :: m a -> (forall x. a x -> m b) -> m b`. The magic
is in tcSyntaxOp.
This addresses tickets #11397, #11452, and #11458.
Tests:
typecheck/should_compile/{RebindHR,RebindNegate,T11397,T11458}
th/T11452
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Commit 547c597112954353cef7157cb0a389bc4f6303eb modifies the
pretty-printer to render names from a set of core packages (`base`,
`ghc-prim`, `template-haskell`) as unqualified. The idea here was that
many of these names typically are not in scope but are well-known by the
user and therefore qualification merely introduces noise.
This, however, is a very large hammer and potentially breaks any
consumer who relies on parsing GHC output (hence #11208). This commit
partially reverts this change, now only printing `Constraint` (which
appears quite often in errors) as unqualified.
Fixes #11208.
Updates tests in `array` submodule.
Test Plan: validate
Reviewers: hvr, thomie, austin
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D1619
GHC Trac Issues: #11208
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Example error message:
MonadFailErrors.hs:16:5: error:
Could not deduce (MonadFail m)
arising from a do statement
with the failable pattern ‘Just x’
Depends on D1248
Reviewers: austin, bgamari
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D1489
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This implements phase 1 of the MonadFail proposal (MFP, #10751).
- MonadFail warnings are all issued as desired, tunable with two new flags
- GHC was *not* made warning-free with `-fwarn-missing-monadfail-warnings`
(but it's disabled by default right now)
Credits/thanks to
- Franz Thoma, whose help was crucial to implementing this
- My employer TNG Technology Consulting GmbH for partially funding us
for this work
Reviewers: goldfire, austin, #core_libraries_committee, hvr, bgamari, fmthoma
Reviewed By: hvr, bgamari, fmthoma
Subscribers: thomie
Projects: #ghc
Differential Revision: https://phabricator.haskell.org/D1248
GHC Trac Issues: #10751
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Improved error messages are only printed when the old message would be
"No instance for...", since they're not as helpful for "Could not deduce..."
No special test case as error messages are tested by other tests already.
Signed-off-by: David Kraeutmann <kane@kane.cx>
Reviewed By: austin, goldfire
Differential Revision: https://phabricator.haskell.org/D1182
GHC Trac Issues: #10733
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Summary: See Note [Displaying potential instances].
Reviewers: austin
Subscribers: KaneTW, thomie
Differential Revision: https://phabricator.haskell.org/D1176
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GHC can't yest build a TypeRep for a type involving kind variables.
(We await kinds = types for that.) But the error message was terrible,
as fixing #10524 reminded me.
This improves it a lot.
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In particular
In the type signature for:
f :: Int -> Int
I added the colon
Also reword the "maybe you haven't applied a function to enough arguments?"
suggestion to make grammatical sense.
These tiny changes affect a lot of error messages.
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Test Plan: Compiled ghc fine. Opened ghci and fed it invalid code. It gave the improved error messages in response.
Reviewers: austin
Subscribers: thomie, simonpj, spacekitteh, rwbarton, simonmar, carter
Differential Revision: https://phabricator.haskell.org/D201
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This matches GCC's choice of Unicode quotation marks (i.e. U+2018 and U+2019)
and therefore looks more familiar on the console. This addresses #2507.
Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
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Almost all are re-orderings of relevant-binding output
Relevant bindings include
+ m :: Map (a, b) elt (bound at T3169.hs:12:17)
+ b :: b (bound at T3169.hs:12:13)
lookup :: (a, b) -> Map (a, b) elt -> Maybe elt
(bound at T3169.hs:12:3)
- b :: b (bound at T3169.hs:12:13)
- m :: Map (a, b) elt (bound at T3169.hs:12:17)
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Notably
* Showing relevant bindings
* Not suggesting add instance (Num T); see Trac #7222
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...in response to Trac #5858
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major TcErrors refactoring
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