diff options
Diffstat (limited to 'libraries/base/GHC/Err.hs')
| -rw-r--r-- | libraries/base/GHC/Err.hs | 31 |
1 files changed, 29 insertions, 2 deletions
diff --git a/libraries/base/GHC/Err.hs b/libraries/base/GHC/Err.hs index 6c40cba570..af6d119ff1 100644 --- a/libraries/base/GHC/Err.hs +++ b/libraries/base/GHC/Err.hs @@ -21,7 +21,7 @@ -- ----------------------------------------------------------------------------- -module GHC.Err( absentErr, error, undefined ) where +module GHC.Err( absentErr, error, errorWithoutStackTrace, undefined ) where import GHC.CString () import GHC.Types (Char) import GHC.Stack.Types @@ -35,6 +35,33 @@ import {-# SOURCE #-} GHC.Exception( errorCallWithCallStackException ) error :: (?callStack :: CallStack) => [Char] -> a error s = raise# (errorCallWithCallStackException s ?callStack) +-- | A variant of 'error' that does not produce a stack trace. +-- +-- @since 4.9.0.0 +errorWithoutStackTrace :: [Char] -> a +errorWithoutStackTrace s + = let ?callStack = freezeCallStack ?callStack + in error s +{-# NOINLINE errorWithoutStackTrace #-} + +-- Note [Errors in base] +-- ~~~~~~~~~~~~~~~~~~~~~ +-- As of base-4.9.0.0, `error` produces a stack trace alongside the +-- error message using the Implicit CallStack machinery. This provides +-- a partial stack trace, containing the call-site of each function +-- with a (?callStack :: CallStack) implicit parameter constraint. +-- +-- In base, however, the only functions that have such constraints are +-- error and undefined, so the stack traces from partial functions in +-- base will never contain a call-site in user code. Instead we'll +-- usually just get the actual call to error. Base functions already +-- have a good habit of providing detailed error messages, including the +-- name of the offending partial function, so the partial stack-trace +-- does not provide any extra information, just noise. Thus, we export +-- the callstack-aware error, but within base we use the +-- errorWithoutStackTrace variant for more hygienic erorr messages. + + -- | A special case of 'error'. -- It is expected that compilers will recognize this and insert error -- messages which are more appropriate to the context in which 'undefined' @@ -45,4 +72,4 @@ undefined = error "Prelude.undefined" -- | Used for compiler-generated error message; -- encoding saves bytes of string junk. absentErr :: a -absentErr = error "Oops! The program has entered an `absent' argument!\n" +absentErr = errorWithoutStackTrace "Oops! The program has entered an `absent' argument!\n" |