Fix eagerly trimming dash in parse_long_flag

src/parse/parser.rs

@@ -1007,7 +1007,7 @@ impl<'help, 'app> Parser<'help, 'app> {
         self.cur_idx.set(self.cur_idx.get() + 1);
 
         debug!("Parser::parse_long_arg: Does it contain '='...");
-        let long_arg = full_arg.trim_start_matches(b'-');
+        let long_arg = full_arg.trim_start_n_matches(2, b'-');
         let (arg, val) = if full_arg.contains_byte(b'=') {
             let (p0, p1) = long_arg.split_at_byte(b'=');
             debug!("Yes '{:?}'", p1);
@@ -1473,6 +1473,7 @@ impl<'help, 'app> Parser<'help, 'app> {
 
 // Error, Help, and Version Methods
 impl<'help, 'app> Parser<'help, 'app> {
+    /// Is only used for the long flag(which is the only one needs fuzzy searching)
     fn did_you_mean_error(
         &mut self,
         arg: &str,

tests/flags.rs

@@ -146,3 +146,24 @@ fn issue_1284_argument_in_flag_style() {
         true
     ));
 }
+
+#[test]
+fn issue_2308_multiple_dashes() {
+    static MULTIPLE_DASHES: &str =
+        "error: Found argument '-----' which wasn't expected, or isn't valid in this context
+
+	If you tried to supply `-----` as a value rather than a flag, use `-- -----`
+
+USAGE:
+    test <arg>
+
+For more information try --help";
+    let app = App::new("test").arg(Arg::new("arg").takes_value(true).required(true));
+
+    assert!(utils::compare_output(
+        app,
+        "test -----",
+        MULTIPLE_DASHES,
+        true
+    ));
+}