fix(exceptions): restore `did_throw` (#20000)

`!did_throw` doesn't exactly imply `!current_exception`, as `did_throw = false`
is sometimes used to defer exception handling for later (without forgetting the
exception). E.g: uncaught exception handling in `do_cmdline()` may be deferred
to a different call (e.g: when `try_level > 0`).

In #7881, `current_exception = NULL` in `do_cmdline()` is used as an analogue of
`did_throw = false`, but also causes the pending exception to be lost, which
also leaks as `discard_exception()` wasn't used.

It may be possible to fix this by saving/restoring `current_exception`, but
handling all of `did_throw`'s edge cases seems messier. Maybe not worth
diverging over.

This fix also uncovers a `man_spec.lua` bug on Windows: exceptions are thrown
due to Windows missing `man`, but they're lost; skip these tests if `man` isn't
executable.

1 files changed, 6 insertions, 2 deletions

diff --git a/src/nvim/api/private/helpers.c b/src/nvim/api/private/helpers.c
index e35c58bf1b..ebcf6cca6d 100644
--- a/src/nvim/api/private/helpers.c
+++ b/src/nvim/api/private/helpers.c
@@ -58,6 +58,7 @@ void try_enter(TryState *const tstate)
     .private_msg_list = NULL,
     .trylevel = trylevel,
     .got_int = got_int,
+    .did_throw = did_throw,
     .need_rethrow = need_rethrow,
     .did_emsg = did_emsg,
   };
@@ -65,6 +66,7 @@ void try_enter(TryState *const tstate)
   current_exception = NULL;
   trylevel = 1;
   got_int = false;
+  did_throw = false;
   need_rethrow = false;
   did_emsg = false;
 }
@@ -85,6 +87,7 @@ bool try_leave(const TryState *const tstate, Error *const err)
   assert(trylevel == 0);
   assert(!need_rethrow);
   assert(!got_int);
+  assert(!did_throw);
   assert(!did_emsg);
   assert(msg_list == &tstate->private_msg_list);
   assert(*msg_list == NULL);
@@ -93,6 +96,7 @@ bool try_leave(const TryState *const tstate, Error *const err)
   current_exception = tstate->current_exception;
   trylevel = tstate->trylevel;
   got_int = tstate->got_int;
+  did_throw = tstate->did_throw;
   need_rethrow = tstate->need_rethrow;
   did_emsg = tstate->did_emsg;
   return ret;
@@ -127,7 +131,7 @@ bool try_end(Error *err)
   force_abort = false;
 
   if (got_int) {
-    if (current_exception) {
+    if (did_throw) {
       // If we got an interrupt, discard the current exception
       discard_current_exception();
     }
@@ -146,7 +150,7 @@ bool try_end(Error *err)
     if (should_free) {
       xfree(msg);
     }
-  } else if (current_exception) {
+  } else if (did_throw) {
     api_set_error(err, kErrorTypeException, "%s", current_exception->value);
     discard_current_exception();
   }