base: use Show for ErrorCall in uncaughtExceptionHandler

The default top-level exception handler now uses the `Show` instance for
`ErrorCall` when printing exceptions, so it will actually print the out-of-band
data (e.g. `CallStack`s) in compiled binaries, instead of just printing the
error message.

This also updates the hpc submodule to fix the test output.

Reviewed By: austin, thomie

Differential Revision: https://phabricator.haskell.org/D1217

6 files changed, 14 insertions, 3 deletions

diff --git a/libraries/base/GHC/Conc/Sync.hs b/libraries/base/GHC/Conc/Sync.hs
index 48a3b2a4c6..c417226da9 100644
--- a/libraries/base/GHC/Conc/Sync.hs
+++ b/libraries/base/GHC/Conc/Sync.hs
@@ -875,9 +875,7 @@ uncaughtExceptionHandler = unsafePerformIO (newIORef defaultHandler)
          (hFlush stdout) `catchAny` (\ _ -> return ())
          let msg = case cast ex of
                Just Deadlock -> "no threads to run:  infinite loop or deadlock?"
-               _ -> case cast ex of
-                    Just (ErrorCall s) -> s
-                    _                  -> showsPrec 0 se ""
+               _                  -> showsPrec 0 se ""
          withCString "%s" $ \cfmt ->
           withCString msg $ \cmsg ->
             errorBelch cfmt cmsg
diff --git a/libraries/base/tests/all.T b/libraries/base/tests/all.T
index 96cb551a26..f53ad0cb80 100644
--- a/libraries/base/tests/all.T
+++ b/libraries/base/tests/all.T
@@ -162,6 +162,10 @@ test('topHandler03',
       ignore_output,
       signal_exit_code(15)
      ], compile_and_run, [''])
+test('topHandler04',
+     [when(opsys('mingw32'), skip),
+      exit_code(1)
+     ], compile_and_run, [''])
 
 
 test('T8766',
diff --git a/libraries/base/tests/readFloat.stderr b/libraries/base/tests/readFloat.stderr
index 929906187e..99049a35b7 100644
--- a/libraries/base/tests/readFloat.stderr
+++ b/libraries/base/tests/readFloat.stderr
@@ -1 +1,3 @@
 readFloat: Prelude.read: no parse
+CallStack:
+  error, called at libraries/base/Text/Read.hs:90:17 in base:Text.Read
diff --git a/libraries/base/tests/topHandler04.hs b/libraries/base/tests/topHandler04.hs
new file mode 100644
index 0000000000..ae669a07b4
--- /dev/null
+++ b/libraries/base/tests/topHandler04.hs
@@ -0,0 +1,5 @@
+import Control.Exception
+
+-- test that the out-of-band data in an ErrorCall exception is printed
+
+main = throw (ErrorCallWithLocation "error" "out-of-band")
diff --git a/libraries/base/tests/topHandler04.stderr b/libraries/base/tests/topHandler04.stderr
new file mode 100644
index 0000000000..e9bba9e480
--- /dev/null
+++ b/libraries/base/tests/topHandler04.stderr
@@ -0,0 +1,2 @@
+topHandler04: error
+out-of-band
diff --git a/libraries/hpc b/libraries/hpc
-Subproject 315b78ac8fe7b42912d2146783b0366f6b0e950
+Subproject 886429bf84097bbc16cdb6602b60ba1b9156cf6