Add wcall, improve "this should raise a warning" testing

src/lauxlib.cpp

@@ -1094,7 +1094,7 @@ static int panic (lua_State *L) {
 ** warnfcont: previous message is to be continued
 */
 static void warnfoff (void *ud, const char *message, int tocont);
-static void warnfon (void *ud, const char *message, int tocont);
+void warnfon (void *ud, const char *message, int tocont);
 static void warnfcont (void *ud, const char *message, int tocont);
 
 
@@ -1136,7 +1136,7 @@ static void warnfcont (void *ud, const char *message, int tocont) {
 }
 
 
-static void warnfon (void *ud, const char *message, int tocont) {
+void warnfon (void *ud, const char *message, int tocont) {
   if (checkcontrol((lua_State *)ud, message, tocont))  /* control message? */
     return;  /* nothing else to be done */
   warnfcont(ud, message, tocont);  /* finish processing */

src/lbaselib.cpp

@@ -63,6 +63,34 @@ static int luaB_warn (lua_State *L) {
 }
 
 
+void warnfon (void *ud, const char *message, int tocont);
+static int luaB_wcall (lua_State *L) {
+  luaL_checktype(L, 1, LUA_TFUNCTION);
+
+  /* write all warnings to a buffer */
+  luaL_Buffer b;
+  luaL_buffinit(L, &b);
+  lua_setwarnf(L, [](void *ud, const char *message, int tocont) {
+    auto B = reinterpret_cast<luaL_Buffer*>(ud);
+    luaL_addstring(B, message);
+    if (!tocont) {
+      luaL_addchar(B, '\n');
+    }
+  }, &b);
+
+  /* call provided function */
+  lua_pushvalue(L, 1);
+  lua_call(L, 0, 0);
+
+  /* revert warnf */
+  lua_setwarnf(L, warnfon, L);
+
+  /* return warnings buffer */
+  luaL_pushresult(&b);
+  return 1;
+}
+
+
 #define SPACECHARS	" \f\n\r\t\v"
 
 static const char *b_str2int (const char *s, int base, lua_Integer *pn) {
@@ -650,6 +678,7 @@ static const luaL_Reg base_funcs[] = {
   {"pcall", luaB_pcall},
   {"print", luaB_print},
   {"warn", luaB_warn},
+  {"wcall", luaB_wcall},
   {"rawequal", luaB_rawequal},
   {"rawlen", luaB_rawlen},
   {"rawget", luaB_rawget},

testes/pluto/basic.pluto

@@ -1,8 +1,16 @@
+print "Welcome to the test suite."
+
+-- Testing warnings
 do
-    local a = 1
-    local a = 2
+    local function assert_warn(code)
+        assert(wcall(function(msg)
+            load(code)()
+        end) == "")
+    end
+    assert_warn([[local a; local a]]) -- var-shadow
+    assert_warn([[local a = 69; local b: string = a]]) -- type mismatch in local-to-local assignment
+    assert_warn([[g = 69; local l: string = g]]) -- type mismatch in global-to-local assignment
 end
-print "Welcome to the test suite. There should have been exactly 1 parser warning."
 
 -- Testing type hints (there should be no warnings here)
 do