undefined: Neater CallStack in error message

Users of `undefined` don’t want to see
```
files.hs: Prelude.undefined:
CallStack (from HasCallStack):
  error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err
  undefined, called at file.hs:151:19 in main:Main
```
but want to see
```
files.hs: Prelude.undefined:
CallStack (from HasCallStack):
  undefined, called at file.hs:151:19 in main:Main
```
so let’s make that so.

The function for that is `withFrozenCallStack`, but that is not usable
here (module dependencies, and also not representation-polymorphic). And
even if it were, it could confuse GHC’s strictness analyzer, leading to
big regressions in some perf tests (T10421 in particular).

So after shuffling modules and definitions around, I eventually noticed
that the easiest way is to just not call `error` here.

Fixes #19886

15 files changed, 13 insertions, 22 deletions

diff --git a/libraries/base/GHC/Err.hs b/libraries/base/GHC/Err.hs
index 87f3e46bd7..07d263bf7d 100644
--- a/libraries/base/GHC/Err.hs
+++ b/libraries/base/GHC/Err.hs
@@ -71,7 +71,13 @@ errorWithoutStackTrace s = raise# (errorCallException s)
 -- appears.
 undefined :: forall (r :: RuntimeRep). forall (a :: TYPE r).
              HasCallStack => a
-undefined =  error "Prelude.undefined"
+-- This used to be
+--   undefined = error "Prelude.undefined"
+-- but that would add an extra call stack entry that is not actually helpful
+-- nor wanted (see #19886). We’d like to use withFrozenCallStack, but that
+-- is not available in this module yet, and making it so is hard. So let’s just
+-- use raise# directly.
+undefined = raise# (errorCallWithCallStackException "Prelude.undefined" ?callStack)
 
 -- | Used for compiler-generated error message;
 -- encoding saves bytes of string junk.
diff --git a/testsuite/tests/codeGen/should_run/T16846.stderr b/testsuite/tests/codeGen/should_run/T16846.stderr
index f737c83af0..3d1cbeef10 100644
--- a/testsuite/tests/codeGen/should_run/T16846.stderr
+++ b/testsuite/tests/codeGen/should_run/T16846.stderr
@@ -1,4 +1,3 @@
 T16846: Prelude.undefined
 CallStack (from HasCallStack):
-  error, called at libraries/base/GHC/Err.hs:80:14 in base:GHC.Err
   undefined, called at T16846.hs:22:3 in main:Main
diff --git a/testsuite/tests/codeGen/should_run/T5626.stderr b/testsuite/tests/codeGen/should_run/T5626.stderr
index 2c02bb0a5c..921c69a8cd 100644
--- a/testsuite/tests/codeGen/should_run/T5626.stderr
+++ b/testsuite/tests/codeGen/should_run/T5626.stderr
@@ -1,4 +1,3 @@
 T5626: Prelude.undefined
-CallStack (from ImplicitParams):
-  error, called at libraries/base/GHC/Err.hs:43:14 in base:GHC.Err
+CallStack (from HasCallStack):
   undefined, called at T5626.hs:6:30 in main:Main
diff --git a/testsuite/tests/deSugar/should_run/T11572.stderr b/testsuite/tests/deSugar/should_run/T11572.stderr
index b1136024db..c4a5ee0044 100644
--- a/testsuite/tests/deSugar/should_run/T11572.stderr
+++ b/testsuite/tests/deSugar/should_run/T11572.stderr
@@ -1,4 +1,3 @@
 T11572: Prelude.undefined
 CallStack (from HasCallStack):
-  error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err
   undefined, called at T11572.hs:6:18 in main:Main
diff --git a/testsuite/tests/deSugar/should_run/T11601.stderr b/testsuite/tests/deSugar/should_run/T11601.stderr
index de0d9deb91..29f6bef297 100644
--- a/testsuite/tests/deSugar/should_run/T11601.stderr
+++ b/testsuite/tests/deSugar/should_run/T11601.stderr
@@ -1,4 +1,3 @@
 T11601: Prelude.undefined
 CallStack (from HasCallStack):
-  error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err
   undefined, called at T11601.hs:6:35 in main:Main
diff --git a/testsuite/tests/ghci.debugger/scripts/break017.stdout b/testsuite/tests/ghci.debugger/scripts/break017.stdout
index af22c066e6..28a1d23dff 100644
--- a/testsuite/tests/ghci.debugger/scripts/break017.stdout
+++ b/testsuite/tests/ghci.debugger/scripts/break017.stdout
@@ -12,7 +12,6 @@ as = 'b' : 'c' : (_t1::[Char])
 Forcing
 *** Exception: Prelude.undefined
 CallStack (from HasCallStack):
-  error, called at libraries/base/GHC/Err.hs:75:14 in base:GHC.Err
   undefined, called at <interactive>:3:17 in interactive:Ghci1
 Printing 2
 as = 'b' : 'c' : (_t2::[Char])
diff --git a/testsuite/tests/ghci/scripts/T10501.stderr b/testsuite/tests/ghci/scripts/T10501.stderr
index 65d24a08ca..669b72bf45 100644
--- a/testsuite/tests/ghci/scripts/T10501.stderr
+++ b/testsuite/tests/ghci/scripts/T10501.stderr
@@ -1,5 +1,4 @@
 *** Exception: Prelude.head: empty list
 *** Exception: Prelude.undefined
-CallStack (from ImplicitParams):
-  error, called at libraries/base/GHC/Err.hs:50:14 in base:GHC.Err
+CallStack (from HasCallStack):
   undefined, called at <interactive>:1:17 in interactive:Ghci1
diff --git a/testsuite/tests/ghci/scripts/T5557.stdout b/testsuite/tests/ghci/scripts/T5557.stdout
index 4b864f9063..836595f60a 100644
--- a/testsuite/tests/ghci/scripts/T5557.stdout
+++ b/testsuite/tests/ghci/scripts/T5557.stdout
@@ -1,8 +1,6 @@
 *** Exception: Prelude.undefined
 CallStack (from HasCallStack):
-  error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err
   undefined, called at <interactive>:2:12 in interactive:Ghci1
 *** Exception: Prelude.undefined
 CallStack (from HasCallStack):
-  error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err
   undefined, called at <interactive>:3:12 in interactive:Ghci1
diff --git a/testsuite/tests/ghci/scripts/ghci055.stdout b/testsuite/tests/ghci/scripts/ghci055.stdout
index c40e0d073e..5cf7bc6bc5 100644
--- a/testsuite/tests/ghci/scripts/ghci055.stdout
+++ b/testsuite/tests/ghci/scripts/ghci055.stdout
@@ -1,6 +1,5 @@
 *** Exception: Prelude.undefined
 CallStack (from HasCallStack):
-  error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err
-  undefined, called at <interactive>:1:5 in interactive:Ghci1
+  undefined, called at <interactive>:1:7 in interactive:Ghci1
 x :: a = _
 y :: Int = 3
diff --git a/testsuite/tests/simplCore/should_fail/T7411.stderr b/testsuite/tests/simplCore/should_fail/T7411.stderr
index 6fc6a22560..9a72acaf2c 100644
--- a/testsuite/tests/simplCore/should_fail/T7411.stderr
+++ b/testsuite/tests/simplCore/should_fail/T7411.stderr
@@ -1,4 +1,3 @@
 T7411: Prelude.undefined
-CallStack (from ImplicitParams):
-  error, called at libraries/base/GHC/Err.hs:43:14 in base:GHC.Err
+CallStack (from HasCallStack):
   undefined, called at T7411.hs:3:25 in main:Main
diff --git a/testsuite/tests/simplCore/should_run/T16893/T16893.stderr b/testsuite/tests/simplCore/should_run/T16893/T16893.stderr
index 5dfa1d642f..c077f4bed1 100644
--- a/testsuite/tests/simplCore/should_run/T16893/T16893.stderr
+++ b/testsuite/tests/simplCore/should_run/T16893/T16893.stderr
@@ -1,4 +1,3 @@
 T16893: Prelude.undefined
 CallStack (from HasCallStack):
-  error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err
   undefined, called at ./Complex.hs:47:28 in main:Complex
diff --git a/testsuite/tests/simplCore/should_run/T5625.stderr b/testsuite/tests/simplCore/should_run/T5625.stderr
index fe02e7e6a8..a935ab7af8 100644
--- a/testsuite/tests/simplCore/should_run/T5625.stderr
+++ b/testsuite/tests/simplCore/should_run/T5625.stderr
@@ -1,4 +1,3 @@
 T5625: Prelude.undefined
-CallStack (from ImplicitParams):
-  error, called at libraries/base/GHC/Err.hs:43:14 in base:GHC.Err
+CallStack (from HasCallStack):
   undefined, called at T5625.hs:3:31 in main:Main
diff --git a/testsuite/tests/th/T19470.stderr b/testsuite/tests/th/T19470.stderr
index aaf251d086..86788d1b73 100644
--- a/testsuite/tests/th/T19470.stderr
+++ b/testsuite/tests/th/T19470.stderr
@@ -3,7 +3,6 @@
     • Exception when trying to run compile-time code:
         Prelude.undefined
 CallStack (from HasCallStack):
-  error, called at libraries/base/GHC/Err.hs:74:14 in base:GHC.Err
   undefined, called at <interactive>:2:10 in interactive:Ghci1
       Code: undefined
     • In the Template Haskell splice $$undefined
diff --git a/testsuite/tests/th/T8987.stderr b/testsuite/tests/th/T8987.stderr
index 00181fa2db..9933ef3465 100644
--- a/testsuite/tests/th/T8987.stderr
+++ b/testsuite/tests/th/T8987.stderr
@@ -3,6 +3,5 @@ T8987.hs:1:1: error:
     Exception when trying to run compile-time code:
       Prelude.undefined
 CallStack (from HasCallStack):
-  error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err
   undefined, called at T8987.hs:6:23 in main:T8987
     Code: (reportWarning ['1', undefined] >> return [])
diff --git a/testsuite/tests/typecheck/should_compile/T17343.stderr b/testsuite/tests/typecheck/should_compile/T17343.stderr
index 044fa41d77..db8aa1c74a 100644
--- a/testsuite/tests/typecheck/should_compile/T17343.stderr
+++ b/testsuite/tests/typecheck/should_compile/T17343.stderr
@@ -1,4 +1,3 @@
 T17343: Prelude.undefined
 CallStack (from HasCallStack):
-  error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err
-  undefined, called at T17343.hs:4:5 in main:Main
+  undefined, called at T17343.hs:4:11 in main:Main