Show breakpoint locations of breakpoints which were ignored during :force (#2950)

GHCi is split up into 2 major parts: The user-interface (UI)
and the byte-code interpreter. With `-fexternal-interpreter`
they even run in different processes. Communication between
the UI and the Interpreter (called `iserv`) is done using
messages over a pipe. This is called `Remote GHCI` and
explained in the Note [Remote GHCi] in `compiler/ghci/GHCi.hs`.

To process a `:force` command the UI sends a `Seq` message
to the `iserv` process. Then `iserv` does the effective
evaluation of the value. When during this process a breakpoint
is hit, the `iserv` process has no additional information to
enhance the `Ignoring breakpoint` output with the breakpoint
location.

To be able to print additional breakpoint information,
there are 2 possible implementation choices:
1. Store the needed information in the `iserv` process.
2. Print the `Ignoring breakpoint` from the UI process.

For option 1 we need to store the breakpoint info redundantely
in 2 places and this is bad. Therfore option 2 was implemented
in this MR:
- The user enters a `force` command
- The UI sends  a `Seq` message to the `iserv` process.
- If processing of the `Seq` message hits a breakpoint,
  the `iserv` process returns control to the UI process.
- The UI looks up the source location of the breakpoint,
  and prints the enhanced `Ignoring breakpoint` output.
- The UI sends a `ResumeSeq` message to the `iserv` process,
  to continue forcing.

1 files changed, 0 insertions, 8 deletions

diff --git a/compiler/GHC/Runtime/Eval.hs b/compiler/GHC/Runtime/Eval.hs
index 7b5962e6bf..51acffec11 100644
--- a/compiler/GHC/Runtime/Eval.hs
+++ b/compiler/GHC/Runtime/Eval.hs
@@ -142,14 +142,6 @@ getHistorySpan hsc_env History{..} =
     Just hmi -> modBreaks_locs (getModBreaks hmi) ! breakInfo_number
     _ -> panic "getHistorySpan"
 
-getModBreaks :: HomeModInfo -> ModBreaks
-getModBreaks hmi
-  | Just linkable <- hm_linkable hmi,
-    [BCOs cbc _] <- linkableUnlinked linkable
-  = fromMaybe emptyModBreaks (bc_breaks cbc)
-  | otherwise
-  = emptyModBreaks -- probably object code
-
 {- | Finds the enclosing top level function name -}
 -- ToDo: a better way to do this would be to keep hold of the decl_path computed
 -- by the coverage pass, which gives the list of lexically-enclosing bindings