[GHC] #15832: returnIO/bindIO destroys runtime explicit stack information in some cases
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Fri Nov 2 03:18:10 UTC 2018
#15832: returnIO/bindIO destroys runtime explicit stack information in some cases
-------------------------------------+-------------------------------------
Reporter: infinity0 | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 8.6.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
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Comment (by infinity0):
Here is an even more realistic example, which hopefully convinces you that
this is a Very Important bug (at least with stack-trace printing), and
closer to my real-world code:
Good code:
{{{#!hs
data X = X Int | XX deriving (Eq, Show)
mkX = X
doInnocentThings a = case a of
X i -> putStr ""
XX -> putStr "XX"
doBadThing a = case a of
X i -> print i
XX -> print "XX"
main :: IO ()
main = do
return undefined
let a = mkX (error "XXX")
doInnocentThings a
doBadThing a
}}}
Good stack trace:
{{{
*** Exception (reporting due to +RTS -xc): (THUNK_2_0), stack trace:
Main.main.a,
called from Main.main.a,
called from Main.CAF:sat_s2O2
--> evaluated by: Main.doBadThing,
called from Main.main,
called from Main.CAF:sat_s2O2
--> evaluated by: Main.doBadThing,
called from Main.main
Test-good: XXX
CallStack (from HasCallStack):
error, called at Test-good.hs:16:16 in main:Main
CallStack (from -prof):
Main.main.a (Test-good.hs:16:16-26)
Main.main.a (Test-good.hs:16:11-27)
Main.CAF:sat_s2O2 (<no location info>)
}}}
Here the stack trace mentions "doBadThing", it is obvious which piece of
code is at fault. Now:
Bad code:
(change `return undefined` to `_ <- return undefined` in the good code)
Bad stack trace:
{{{
*** Exception (reporting due to +RTS -xc): (THUNK_2_0), stack trace:
Main.main.a,
called from Main.main.a
Test-bad: XXX
CallStack (from HasCallStack):
error, called at Test-bad.hs:16:16 in main:Main
CallStack (from -prof):
Main.main.a (Test-bad.hs:16:16-26)
Main.main.a (Test-bad.hs:16:11-27)
}}}
There is no "evaluated by" entry, the only thing I see is the `let a =`
statement being mentioned, which is perfectly fine logic-wise. There is no
way to debug this, except by guessing based on knowledge of the whole
codebase.
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15832#comment:6>
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