fix(excmd): nlua_call_excmd require() failure is a "lua_error"

Although `nlua_call_excmd` is semantically for implementing Ex-commands,
the `require()` should never fail, so that's a "Lua error".

But if the call itself fails (the later `semsg` call), that's an "Ex
cmd" error.

2 files changed, 6 insertions, 4 deletions

diff --git a/src/nvim/ex_eval.c b/src/nvim/ex_eval.c
index cedb58b4d0..ebbb940422 100644
--- a/src/nvim/ex_eval.c
+++ b/src/nvim/ex_eval.c
@@ -378,7 +378,9 @@ bool do_intthrow(cstack_T *cstack)
   return true;
 }
 
-/// Get an exception message that is to be stored in current_exception->value.
+/// Gets an exception message that is to be stored in current_exception->value.
+///
+/// For error exceptions (ET_ERROR), formats the message as "Vim(cmdname):Exx: …".
 char *get_exception_string(void *value, except_type_T type, char *cmdname, bool *should_free)
 {
   char *ret;
diff --git a/src/nvim/lua/executor.c b/src/nvim/lua/executor.c
index d770cdbb5e..1771a01565 100644
--- a/src/nvim/lua/executor.c
+++ b/src/nvim/lua/executor.c
@@ -1785,8 +1785,7 @@ bool nlua_call_excmd(const char *module, const char *func, exarg_T *eap, const c
   lua_getglobal(lstate, "require");
   lua_pushstring(lstate, module);
   if (lua_pcall(lstate, 1, 1, 0) != 0) {
-    semsg("E5108: %s", lua_tostring(lstate, -1));
-    lua_pop(lstate, 1);
+    nlua_error(lstate, "E5108: %s");
     return false;
   }
   lua_getfield(lstate, -1, func);
@@ -1802,7 +1801,8 @@ bool nlua_call_excmd(const char *module, const char *func, exarg_T *eap, const c
   }
 
   if (nlua_pcall(lstate, nargs, 0)) {
-    semsg("E5108: %s", lua_tostring(lstate, -1));
+    // Not "E5108" because this is a logical/application error, not a "Lua error".
+    emsg(lua_tostring(lstate, -1));
     lua_pop(lstate, 1);
     return false;
   }