Fix core.get_content_info docs and harden implementation (#15925)

doc/menu_lua_api.md

@@ -331,7 +331,7 @@ Package - content which is downloadable from the content db, may or may not be i
       ```lua
       {
           name             = "technical_id",
-          type             = "mod" or "modpack" or "game" or "txp",
+          type             = "mod" or "modpack" or "game" or "txp" or "unknown",
           title            = "Human readable title",
           description      = "description",
           author           = "author",

src/script/lua_api/l_mainmenu.cpp

@@ -30,8 +30,12 @@
 #include "common/c_converter.h"
 #include "gui/guiOpenURL.h"
 #include "gettext.h"
+#include "log.h"
 #include "util/string.h"
 
+#include <cassert>
+#include <iostream>
+
 /******************************************************************************/
 std::string ModApiMainMenu::getTextData(lua_State *L, const std::string &name)
 {
@@ -355,6 +359,14 @@ int ModApiMainMenu::l_get_content_info(lua_State *L)
 	spec.path = path;
 	parseContentInfo(spec);
 
+	if (spec.type == "unknown") {
+		// In <=5.11.0 the API call was erroneously not documented as
+		// being able to return type "unknown".
+		// TODO inspect call sites and make sure this is handled, then we can
+		// likely remove the warning.
+		warningstream << "Requested content info has type \"unknown\"" << std::endl;
+	}
+
 	lua_newtable(L);
 
 	lua_pushstring(L, spec.name.c_str());
@@ -369,11 +381,6 @@ int ModApiMainMenu::l_get_content_info(lua_State *L)
 	lua_pushstring(L, spec.author.c_str());
 	lua_setfield(L, -2, "author");
 
-	if (!spec.title.empty()) {
-		lua_pushstring(L, spec.title.c_str());
-		lua_setfield(L, -2, "title");
-	}
-
 	lua_pushinteger(L, spec.release);
 	lua_setfield(L, -2, "release");
 
@@ -389,8 +396,12 @@ int ModApiMainMenu::l_get_content_info(lua_State *L)
 	if (spec.type == "mod") {
 		ModSpec spec;
 		spec.path = path;
-		// TODO return nothing on failure (needs callers to handle it)
-		static_cast<void>(parseModContents(spec));
+		// Since the content was already determined to be a mod,
+		// the parsing is guaranteed to succeed unless the init.lua
+		// file happens to be deleted between the content parse and
+		// the mod parse.
+		[[maybe_unused]] bool success = parseModContents(spec);
+		assert(success);
 
 		// Dependencies
 		lua_newtable(L);