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, 2 insertions, 2 deletions

diff --git a/src/nvim/api/vimscript.c b/src/nvim/api/vimscript.c
index a28bfd2ab9..f6d0e39327 100644
--- a/src/nvim/api/vimscript.c
+++ b/src/nvim/api/vimscript.c
@@ -137,7 +137,7 @@ Object nvim_eval(String expr, Error *err)
     if (!recursive) {
       force_abort = false;
       suppress_errthrow = false;
-      current_exception = NULL;
+      did_throw = false;
       // `did_emsg` is set by emsg(), which cancels execution.
       did_emsg = false;
     }
@@ -196,7 +196,7 @@ static Object _call_function(String fn, Array args, dict_T *self, Error *err)
     if (!recursive) {
       force_abort = false;
       suppress_errthrow = false;
-      current_exception = NULL;
+      did_throw = false;
       // `did_emsg` is set by emsg(), which cancels execution.
       did_emsg = false;
     }