fprintCCS_stderr (+RTS -xc) should be able to traverse into stacks that evaluated a given stack even if the latter does not come from a CAF

Tested in GHC 8.2.2, 8.4.3 and 8.6.1:

Test-good.hs

import GHC.Base

data X = X Int deriving (Eq, Show)

main :: IO ()
main = (returnIO undefined) `bindIO` (const (print $ X (error "XXX")))

Test-bad.hs

import GHC.Base

data X = X Int deriving (Eq, Show)

main :: IO ()
main = (returnIO undefined) `bindIO` (\_ -> (print $ X (error "XXX")))

build.sh

#!/bin/sh
set -e
p="${1:-stg}"
for i in good bad; do
  rm -rf ghc*_* Test-$i Test-$i.dump-* Test-$i.hi Test-$i.o
  ghc "-ddump-$p" -dsuppress-module-prefixes -dsuppress-uniques \
    -keep-tmp-files -dumpdir . -ddump-to-file \
    -fno-cse -prof -fprof-auto -fprof-auto-calls -fprof-cafs \
    -dinitial-unique=0 -dunique-increment=1 \
    Test-$i.hs
  ./Test-$i +RTS -xc || true
done
colordiff -ruw Test-*.dump-"$p" | less -R

Running sh build.sh gives the following output:

[1 of 1] Compiling Main             ( Test-good.hs, Test-good.o )
Linking Test-good ...
*** Exception (reporting due to +RTS -xc): (THUNK_2_0), stack trace: 
  Main.main,
  called from Main.main,
  called from Main.main,
  called from Main.main,
  called from Main.main,
  called from Main.CAF:main
  --> evaluated by: Main.main,
  called from Main.main,
  called from Main.main,
  called from Main.CAF:main
  --> evaluated by: Main.main,
  called from Main.main,
  called from Main.main
Test-good: XXX
CallStack (from HasCallStack):
  error, called at Test-good.hs:6:57 in main:Main
CallStack (from -prof):
  Main.main (Test-good.hs:6:57-67)
  Main.main (Test-good.hs:6:54-68)
  Main.main (Test-good.hs:6:46-68)
  Main.main (Test-good.hs:6:39-69)
  Main.main (Test-good.hs:6:8-70)
  Main.CAF:main (Test-good.hs:6:1-4)
[1 of 1] Compiling Main             ( Test-bad.hs, Test-bad.o )
Linking Test-bad ...
*** Exception (reporting due to +RTS -xc): (THUNK_2_0), stack trace: 
  Main.main,
  called from Main.main,
  called from Main.main,
  called from Main.main
Test-bad: XXX
CallStack (from HasCallStack):
  error, called at Test-bad.hs:6:57 in main:Main
CallStack (from -prof):
  Main.main (Test-bad.hs:6:57-67)
  Main.main (Test-bad.hs:6:54-68)
  Main.main (Test-bad.hs:6:46-68)
  Main.main (Test-bad.hs:6:8-70)

As you can see, in Test-bad.hs all the entries below "evaluated by" are missing.

I am not familiar with STG output, but running the script also shows you a diff of the STG dump. It seems innocent enough. Running sh build.sh cmm shows many more differences.

Trac metadata

Trac field	Value
Version	8.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

evaluated by: Main.main,\r\n called from Main.main,\r\n called from Main.main,\r\n called from Main.CAF:main\r\n --> evaluated by: Main.main,\r\n called from Main.main,\r\n called from Main.main\r\nTest-good: XXX\r\nCallStack (from HasCallStack):\r\n error, called at Test-good.hs:6:57 in main:Main\r\nCallStack (from -prof):\r\n Main.main (Test-good.hs:6:57-67)\r\n Main.main (Test-good.hs:6:54-68)\r\n Main.main (Test-good.hs:6:46-68)\r\n Main.main (Test-good.hs:6:39-69)\r\n Main.main (Test-good.hs:6:8-70)\r\n Main.CAF:main (Test-good.hs:6:1-4)\r\n[1 of 1] Compiling Main ( Test-bad.hs, Test-bad.o )\r\nLinking Test-bad ...\r\n*** Exception (reporting due to +RTS -xc): (THUNK_2_0), stack trace: \r\n Main.main,\r\n called from Main.main,\r\n called from Main.main,\r\n called from Main.main\r\nTest-bad: XXX\r\nCallStack (from HasCallStack):\r\n error, called at Test-bad.hs:6:57 in main:Main\r\nCallStack (from -prof):\r\n Main.main (Test-bad.hs:6:57-67)\r\n Main.main (Test-bad.hs:6:54-68)\r\n Main.main (Test-bad.hs:6:46-68)\r\n Main.main (Test-bad.hs:6:8-70)\r\n}}}\r\n\r\nAs you can see, in Test-bad.hs all the entries below \"evaluated by\" are missing.\r\n\r\nI am not familiar with STG output, but running the script also shows you a diff of the STG dump. It seems innocent enough. Running `sh build.sh cmm` shows many more differences.\r\n","type_of_failure":"OtherFailure","blocking":[]} -->