eval: Make setmatches() return -1 in case of some failures

src/nvim/eval.c

@@ -14680,6 +14680,7 @@ static void f_setmatches(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 
     clear_matches(curwin);
     li = l->lv_first;
+    bool match_add_failed = false;
     while (li != NULL) {
       int i = 0;
 
@@ -14728,19 +14729,25 @@ static void f_setmatches(typval_T *argvars, typval_T *rettv, FunPtr fptr)
                                        &conceal_di->di_tv)
                                    : NULL);
       if (i == 0) {
-        match_add(curwin, group,
+        if (match_add(curwin, group,
                       tv_dict_get_string(d, "pattern", false),
-                  priority, id, NULL, conceal);
+                      priority, id, NULL, conceal) != id) {
+          match_add_failed = true;
+        }
       } else {
-        match_add(curwin, group, NULL, priority, id, s, conceal);
+        if (match_add(curwin, group, NULL, priority, id, s, conceal) != id) {
+          match_add_failed = true;
+        }
         tv_list_unref(s);
         s = NULL;
       }
       li = li->li_next;
     }
+    if (!match_add_failed) {
       rettv->vval.v_number = 0;
     }
   }
+}
 
 /*
  * "setpos()" function

test/functional/eval/match_functions_spec.lua

@@ -36,4 +36,11 @@ describe('setmatches()', function()
       conceal='5',
     }}, funcs.getmatches())
   end)
+
+  it('fails with -1 if highlight group is not defined', function()
+    eq(-1, funcs.setmatches({{group=1, pattern=2, id=3, priority=4}}))
+    eq({}, funcs.getmatches())
+    eq(-1, funcs.setmatches({{group=1, pos1={2}, pos2={6}, id=3, priority=4, conceal=5}}))
+    eq({}, funcs.getmatches())
+  end)
 end)

test/functional/legacy/063_match_and_matchadd_spec.lua

@@ -97,11 +97,10 @@ describe('063: Test for ":match", "matchadd()" and related functions', function(
 
     -- Check that "setmatches()" will not add two matches with the same ID. The
     -- expected behaviour (for now) is to add the first match but not the
-    -- second and to return 0 (even though it is a matter of debate whether
-    -- this can be considered successful behaviour).
+    -- second and to return -1.
     execute("let r1 = setmatches([{'group': 'MyGroup1', 'pattern': 'TODO', 'priority': 10, 'id': 1}, {'group': 'MyGroup2', 'pattern': 'FIXME', 'priority': 10, 'id': 1}])")
     feed("<cr>")
-    eq(0, eval("r1"))
+    eq(-1, eval("r1"))
     eq({{group = 'MyGroup1', pattern = 'TODO', priority = 10, id = 1}}, eval('getmatches()'))
 
     -- Check that "setmatches()" returns 0 if successful and otherwise -1.