provider: improve error message if provider is missing (#9487)

Move `has_eval_provider()` check to `eval_call_provider()` to make sure that
every code path calls it first.

Previously we would, when pynvim was missing, get a nice error message for
`:python3 1`, but not for `:py3file blah`.

Fixes https://github.com/neovim/neovim/issues/9485

2 files changed, 11 insertions, 6 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index d67818aa81..5191328b5d 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -22683,6 +22683,16 @@ static void script_host_eval(char *name, typval_T *argvars, typval_T *rettv)
 
 typval_T eval_call_provider(char *provider, char *method, list_T *arguments)
 {
+  if (!eval_has_provider(provider)) {
+    emsgf("E319: No \"%s\" provider found. Run \":checkhealth provider\"",
+          provider);
+    return (typval_T){
+      .v_type = VAR_NUMBER,
+      .v_lock = VAR_UNLOCKED,
+      .vval.v_number = (varnumber_T)0
+    };
+  }
+
   char func[256];
   int name_len = snprintf(func, sizeof(func), "provider#%s#Call", provider);
 
diff --git a/src/nvim/ex_cmds2.c b/src/nvim/ex_cmds2.c
index 1ffcf67ef7..dd7afa5c77 100644
--- a/src/nvim/ex_cmds2.c
+++ b/src/nvim/ex_cmds2.c
@@ -3908,12 +3908,7 @@ static void script_host_execute(char *name, exarg_T *eap)
     tv_list_append_number(args, (int)eap->line1);
     tv_list_append_number(args, (int)eap->line2);
 
-    if (!eval_has_provider(name)) {
-      emsgf("E319: No \"%s\" provider found. Run \":checkhealth provider\"",
-            name);
-    } else {
-      (void)eval_call_provider(name, "execute", args);
-    }
+    (void)eval_call_provider(name, "execute", args);
   }
 }