fix: Fixed argument parsing to allow a flag value with a newline deli…

…mited by =

toys-core/lib/toys/arg_parser.rb

@@ -451,7 +451,7 @@ def check_flag(arg)
       case arg
       when "--"
         @flags_allowed = false
-      when /\A(--\w[?\w-]*)=(.*)\z/
+      when /\A(--\w[?\w-]*)=(.*)\z/m
         handle_valued_flag(::Regexp.last_match(1), ::Regexp.last_match(2))
       when /\A--.+\z/
         handle_plain_flag(arg)

toys-core/test/test_arg_parser.rb

@@ -321,6 +321,22 @@ def assert_errors_include(expected, errors)
         arg_parser.finish
         assert_errors_include('Flag "--aa" is missing a value.', arg_parser.errors)
       end
+
+      it "allows an = value with a newline" do
+        tool.add_flag(:a, ["-a", "--aa=VALUE"])
+        arg_parser.parse(["--aa=hi\nho"])
+        arg_parser.finish
+        assert_data_includes({a: "hi\nho"}, arg_parser.data)
+        assert_empty(arg_parser.errors)
+      end
+
+      it "allows a separate value with a newline" do
+        tool.add_flag(:a, ["-a", "--aa=VALUE"])
+        arg_parser.parse(["--aa", "hi\nho"])
+        arg_parser.finish
+        assert_data_includes({a: "hi\nho"}, arg_parser.data)
+        assert_empty(arg_parser.errors)
+      end
     end
 
     describe "optional value flag" do