*: Make sure that !did_throw implies !current_exception

Fixes #7876

src/nvim/api/private/helpers.c

@@ -47,6 +47,9 @@ typedef struct {
 /// @param[out]  tstate  Location where try state should be saved.
 void try_enter(TryState *const tstate)
 {
+  // TODO(ZyX-I): Check whether try_enter()/try_leave() may use
+  //              enter_cleanup()/leave_cleanup(). Or
+  //              save_dbg_stuff()/restore_dbg_stuff().
   *tstate = (TryState) {
     .current_exception = current_exception,
     .msg_list = (const struct msglist *const *)msg_list,

src/nvim/ex_docmd.c

@@ -403,13 +403,12 @@ int do_cmdline(char_u *cmdline, LineGetter fgetline,
   /*
    * "did_throw" will be set to TRUE when an exception is being thrown.
    */
-  did_throw = FALSE;
-  /*
-   * "did_emsg" will be set to TRUE when emsg() is used, in which case we
-   * cancel the whole command line, and any if/endif or loop.
-   * If force_abort is set, we cancel everything.
-   */
-  did_emsg = FALSE;
+  did_throw = false;
+  current_exception = NULL;
+  // "did_emsg" will be set to TRUE when emsg() is used, in which case we
+  // cancel the whole command line, and any if/endif or loop.
+  // If force_abort is set, we cancel everything.
+  did_emsg = false;
 
   /*
    * KeyTyped is only set when calling vgetc().  Reset it here when not
@@ -715,10 +714,11 @@ int do_cmdline(char_u *cmdline, LineGetter fgetline,
      */
     if (cstack.cs_lflags & CSL_HAD_FINA) {
       cstack.cs_lflags &= ~CSL_HAD_FINA;
-      report_make_pending(cstack.cs_pending[cstack.cs_idx]
-          & (CSTP_ERROR | CSTP_INTERRUPT | CSTP_THROW),
-          did_throw ? (void *)current_exception : NULL);
-      did_emsg = got_int = did_throw = FALSE;
+      report_make_pending((cstack.cs_pending[cstack.cs_idx]
+                           & (CSTP_ERROR | CSTP_INTERRUPT | CSTP_THROW)),
+                          (did_throw ? (void *)current_exception : NULL));
+      did_emsg = got_int = did_throw = false;
+      current_exception = NULL;
       cstack.cs_flags[cstack.cs_idx] |= CSF_ACTIVE | CSF_FINALLY;
     }
 
@@ -1782,13 +1782,14 @@ static char_u * do_one_cmd(char_u **cmdlinep,
     ));
 
 
-  /* forced commands */
+  // Forced commands.
   if (*p == '!' && ea.cmdidx != CMD_substitute
       && ea.cmdidx != CMD_smagic && ea.cmdidx != CMD_snomagic) {
-    ++p;
-    ea.forceit = TRUE;
-  } else
-    ea.forceit = FALSE;
+    p++;
+    ea.forceit = true;
+  } else {
+    ea.forceit = false;
+  }
 
   /*
    * 6. Parse arguments.

src/nvim/ex_eval.c

@@ -1426,6 +1426,10 @@ void ex_catch(exarg_T *eap)
       if (cstack->cs_exception[cstack->cs_idx] != current_exception) {
         internal_error("ex_catch()");
       }
+      // Discarding current_exceptions happens based on what is stored in
+      // cstack->cs_exception, *all* calls to discard_current_exception() are
+      // (and must be) guarded by did_throw which was already unset above.
+      current_exception = NULL;
     } else {
       /*
        * If there is a preceding catch clause and it caught the exception,
@@ -1785,7 +1789,8 @@ void enter_cleanup(cleanup_T *csp)
         cause_abort = FALSE;
       }
     }
-    did_emsg = got_int = did_throw = need_rethrow = FALSE;
+    did_emsg = got_int = did_throw = need_rethrow = false;
+    current_exception = NULL;
 
     /* Report if required by the 'verbose' option or when debugging.  */
     report_make_pending(pending, csp->exception);

src/nvim/globals.h

@@ -325,7 +325,8 @@ EXTERN except_T *current_exception;
  * did_throw: An exception is being thrown.  Reset when the exception is caught
  * or as long as it is pending in a finally clause.
  */
-EXTERN int did_throw INIT(= FALSE);
+// FIXME: Replace did_throw checks with current_exception checks.
+EXTERN int did_throw INIT(= false);
 
 /*
  * need_rethrow: set to TRUE when a throw that cannot be handled in do_cmdline()

test/functional/ui/cmdline_highlight_spec.lua

@@ -737,6 +737,22 @@ describe('Command-line coloring', function()
     feed('<CR><CR>')
     eq('', meths.get_var('out'))
   end)
+  it('does not crash when callback has caught not-a-editor-command exception',
+  function()
+    source([[
+      function CaughtExc(cmdline) abort
+        try
+          gibberish
+        catch
+          " Do nothing
+        endtry
+        return []
+      endfunction
+    ]])
+    set_color_cb('CaughtExc')
+    start_prompt('1')
+    eq(1, meths.eval('1'))
+  end)
 end)
 describe('Ex commands coloring support', function()
   it('works', function()