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authorEric Seidel <gridaphobe@gmail.com>2015-12-23 10:10:04 +0100
committerBen Gamari <ben@smart-cactus.org>2015-12-23 11:30:42 +0100
commit380b25ea4754c2aea683538ffdb179f8946219a0 (patch)
tree722784415e0f1b29a46fc115baff56f3495c0c9b /testsuite/.gitignore
parent78248702b0b8189d73f08c89d86f5cb7a3c6ae8c (diff)
downloadhaskell-380b25ea4754c2aea683538ffdb179f8946219a0.tar.gz
Allow CallStacks to be frozen
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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@@ -1613,3 +1613,4 @@ mk/ghcconfig*_test___spaces_ghc*.exe.mk
/timeout/calibrate.out
/timeout/dist/
/timeout/install-inplace/
+/tests/typecheck/should_run/T11049