fix: syntax error when return; is not last statement of block (#893)

Fixes #495.

spec/lang/parser/parser_spec.lua

@@ -34,6 +34,26 @@ describe("parser", function()
       assert.same("return", result.ast[1].kind)
    end)
 
+   it("does not accept statements after 'return;' (regression test for #495)", function ()
+      local result = tl.process_string([[
+         return;
+         print("")
+      ]])
+      assert.same(1, #result.syntax_errors)
+      assert.same(result.syntax_errors[1].msg, "return must be the last statement of its block")
+
+      local result = tl.process_string([[
+         local function get_foo(): string
+            if true then
+               return "foo";
+               print("")
+            end
+         end
+      ]])
+      assert.same(1, #result.syntax_errors)
+      assert.same(result.syntax_errors[1].msg, "return must be the last statement of its block")
+   end)
+
    it("accepts semicolons in tables (regression test for #54)", function ()
       local result = tl.process_string([[
          local t = {

tl.tl

@@ -3708,6 +3708,9 @@ local function parse_return(ps: ParseState, i: integer): integer, Node
    i = parse_list(ps, i, node.exps, stop_return_list, "sep", parse_expression)
    if ps.tokens[i].kind == ";" then
       i = i + 1
+      if ps.tokens[i].kind ~= "$EOF$" and not stop_statement_list[ps.tokens[i].kind] then
+         return fail(ps, i, "return must be the last statement of its block")
+      end
    end
    return i, node
 end