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Test Plan: Validate, ensure the `f7` program of `IPLocation` doesn't
crash.
Reviewers: gridaphobe, austin, hvr
Reviewed By: gridaphobe
Subscribers: rwbarton, thomie
GHC Trac Issues: #14028
Differential Revision: https://phabricator.haskell.org/D3795
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We originally wanted CallStacks to be opt-in, but dealing with let
binders complicated things, forcing us to infer CallStacks. It turns
out that the inference is actually unnecessary though, we can let the
wanted CallStacks bubble up to the outer context by refusing to
quantify over them. Eventually they'll be solved from a given CallStack
or defaulted to the empty CallStack if they reach the top.
So this patch prevents GHC from quantifying over CallStacks, getting us
back to the original plan. There's a small ugliness to do with
PartialTypeSignatures, if the partial theta contains a CallStack
constraint, we *do* want to quantify over the CallStack; the user asked
us to!
Note that this means that
foo :: _ => CallStack
foo = getCallStack callStack
will be an *empty* CallStack, since we won't infer a CallStack for the
hole in the theta. I think this is the right move though, since we want
CallStacks to be opt-in. One can always write
foo :: (HasCallStack, _) => CallStack
foo = getCallStack callStack
to get the CallStack and still have GHC infer the rest of the theta.
Test Plan: ./validate
Reviewers: goldfire, simonpj, austin, hvr, bgamari
Reviewed By: simonpj, bgamari
Subscribers: bitemyapp, thomie
Projects: #ghc
Differential Revision: https://phabricator.haskell.org/D1912
GHC Trac Issues: #11573
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Summary:
Ties up loose ends from D1894.
GHC 7.10.2 and 7.10.3 featured a `Show` instance for `CallStack`, but since it
was derived, it broke encapsulation. This adds a `Show` instance which displays
the `CallStack` as if it were a `[(String, SrcLoc)]`.
To ensure that the output of `Show` is technically a valid Haskell term, we
also add a corresponding `IsList CallStack` instance.
Reviewers: gridaphobe, austin, hvr, bgamari
Reviewed By: gridaphobe, bgamari
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D1903
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The implicit parameter isn't actually very relevant to the CallStack
machinery, so we hide the implementation details behind a constraint
alias
```
type HasCallStack = (?callStack :: CallStack)
```
This has a few benefits:
1. No need to enable `ImplicitParams` in user code.
2. No need to remember the `?callStack` naming convention.
3. Gives us the option to change the implementation details in the
future with less user-land breakage.
The revised `CallStack` API is exported from `GHC.Stack` and makes no
mention of the implicit parameter.
Test Plan: ./validate
Reviewers: simonpj, austin, hvr, bgamari
Reviewed By: simonpj, bgamari
Subscribers: thomie
Projects: #ghc
Differential Revision: https://phabricator.haskell.org/D1818
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This introduces "freezing," an operation which prevents further
locations from being appended to a CallStack. Library authors may want
to prevent CallStacks from exposing implementation details, as a matter
of hygiene. For example, in
```
head [] = error "head: empty list"
ghci> head []
*** Exception: head: empty list
CallStack (from implicit params):
error, called at ...
```
including the call-site of `error` in `head` is not strictly necessary
as the error message already specifies clearly where the error came
from.
So we add a function `freezeCallStack` that wraps an existing CallStack,
preventing further call-sites from being pushed onto it. In other words,
```
pushCallStack callSite (freezeCallStack callStack) = freezeCallStack callStack
```
Now we can define `head` to not produce a CallStack at all
```
head [] =
let ?callStack = freezeCallStack emptyCallStack
in error "head: empty list"
ghci> head []
*** Exception: head: empty list
CallStack (from implicit params):
error, called at ...
```
---
1. We add the `freezeCallStack` and `emptyCallStack` and update the
definition of `CallStack` to support this functionality.
2. We add `errorWithoutStackTrace`, a variant of `error` that does not
produce a stack trace, using this feature. I think this is a sensible
wrapper function to provide in case users want it.
3. We replace uses of `error` in base with `errorWithoutStackTrace`. The
rationale is that base does not export any functions that use CallStacks
(except for `error` and `undefined`) so there's no way for the stack
traces (from Implicit CallStacks) to include user-defined functions.
They'll only contain the call to `error` itself. As base already has a
good habit of providing useful error messages that name the triggering
function, the stack trace really just adds noise to the error. (I don't
have a strong opinion on whether we should include this third commit,
but the change was very mechanical so I thought I'd include it anyway in
case there's interest)
4. Updates tests in `array` and `stm` submodules
Test Plan: ./validate, new test is T11049
Reviewers: simonpj, nomeata, goldfire, austin, hvr, bgamari
Reviewed By: simonpj
Subscribers: thomie
Projects: #ghc
Differential Revision: https://phabricator.haskell.org/D1628
GHC Trac Issues: #11049
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Summary:
Breakpoints become SCCs, so we have detailed call-stack info for
interpreted code. Currently this only works when GHC is compiled with
-prof, but D1562 (Remote GHCi) removes this constraint so that in the
future call stacks will be available without building your own GHCi.
How can you get a stack trace?
* programmatically: GHC.Stack.currentCallStack
* I've added an experimental :where command that shows the stack when
stopped at a breakpoint
* `error` attaches a call stack automatically, although since calls to
`error` are often lifted out to the top level, this is less useful
than it might be (ImplicitParams still works though).
* Later we might attach call stacks to all exceptions
Other related changes in this diff:
* I reduced the number of places that get ticks attached for
breakpoints. In particular there was a breakpoint around the whole
declaration, which was often redundant because it bound no variables.
This reduces clutter in the stack traces and speeds up compilation.
* I tidied up some RealSrcSpan stuff in InteractiveUI, and made a few
other small cleanups
Test Plan: validate
Reviewers: ezyang, bgamari, austin, hvr
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D1595
GHC Trac Issues: #11047
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We can't just solve CallStack constraints indiscriminately when they
occur in the RHS of a let-binder. The top-level given CallStack (if
any) will not be in scope, so I've re-worked the CallStack solver as
follows:
1. CallStacks are treated like regular IPs unless one of the following
two rules apply.
2. In a function call, we push the call-site onto a NEW wanted
CallStack, which GHC will solve as a regular IP (either directly from a
given, or by quantifying over it in a local let).
3. If, after the constraint solver is done, any wanted CallStacks
remain, we default them to the empty CallStack. This rule exists mainly
to clean up after rule 2 in a top-level binder with no given CallStack.
In rule (2) we have to be careful to emit the new wanted with an
IPOccOrigin instead of an OccurrenceOf origin, so rule (2) doesn't fire
again. This is a bit shady but I've updated the Note to explain the
trick.
Test Plan: validate
Reviewers: simonpj, austin, bgamari, hvr
Reviewed By: simonpj, bgamari
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D1422
GHC Trac Issues: #10845
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This was added in 8988be8561ce0857f3befd6ab3b6c29060685c0a, probably due
to an incorrect merge resolution. The build system has been building
`Stack.hs`.
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Summary:
The idea here is that this gives a more detailed stack trace in two
cases:
1. With `-prof` and `-fprof-auto`
2. In GHCi (see #11047)
Example, with an error inserted in nofib/shootout/binary-trees:
```
$ ./Main 3
Main: z
CallStack (from ImplicitParams):
error, called at Main.hs:67:29 in main:Main
CallStack (from -prof):
Main.check' (Main.hs:(67,1)-(68,82))
Main.check (Main.hs:63:1-21)
Main.stretch (Main.hs:32:35-57)
Main.main.c (Main.hs:32:9-57)
Main.main (Main.hs:(27,1)-(43,42))
Main.CAF (<entire-module>)
```
This doesn't quite obsolete +RTS -xc, which also attempts to display
more information in the case when the error is in a CAF, but I'm
exploring other solutions to that.
Includes submodule updates.
Test Plan: validate
Reviewers: simonpj, ezyang, gridaphobe, bgamari, hvr, austin
Reviewed By: bgamari
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D1426
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