fix(parser): Allow multiple_occurrecnes with positional args

This unblocks
- Defining repeated tuples in positional arguments
- Potentially using this in #1772

Fixes #2784

src/build/arg/debug_asserts.rs

@@ -35,15 +35,6 @@ pub(crate) fn assert_arg(arg: &Arg) {
         );
     }
 
-    // Positionals should not have multiple_occurrences
-    if arg.is_positional() {
-        assert!(
-            !arg.is_set(ArgSettings::MultipleOccurrences),
-            "Argument '{}' is a positional argument and can't be set as multiple occurrences",
-            arg.name
-        );
-    }
-
     if arg.is_set(ArgSettings::Required) {
         assert!(
             arg.default_vals.is_empty(),

tests/multiple_values.rs

@@ -1319,3 +1319,64 @@ fn number_of_values_preferred_over_value_names() {
         ["val1", "val2", "val3", "val4"]
     );
 }
+
+#[test]
+fn values_per_occurrence_named() {
+    let mut a = App::new("test").arg(
+        Arg::new("pos")
+            .long("pos")
+            .number_of_values(2)
+            .multiple_occurrences(true),
+    );
+
+    let m = a.try_get_matches_from_mut(vec!["myprog", "--pos", "val1", "val2"]);
+    let m = match m {
+        Ok(m) => m,
+        Err(err) => panic!("{}", err),
+    };
+    assert_eq!(
+        m.values_of("pos").unwrap().collect::<Vec<_>>(),
+        ["val1", "val2"]
+    );
+
+    let m = a.try_get_matches_from_mut(vec![
+        "myprog", "--pos", "val1", "val2", "--pos", "val3", "val4",
+    ]);
+    let m = match m {
+        Ok(m) => m,
+        Err(err) => panic!("{}", err),
+    };
+    assert_eq!(
+        m.values_of("pos").unwrap().collect::<Vec<_>>(),
+        ["val1", "val2", "val3", "val4"]
+    );
+}
+
+#[test]
+fn values_per_occurrence_positional() {
+    let mut a = App::new("test").arg(
+        Arg::new("pos")
+            .number_of_values(2)
+            .multiple_occurrences(true),
+    );
+
+    let m = a.try_get_matches_from_mut(vec!["myprog", "val1", "val2"]);
+    let m = match m {
+        Ok(m) => m,
+        Err(err) => panic!("{}", err),
+    };
+    assert_eq!(
+        m.values_of("pos").unwrap().collect::<Vec<_>>(),
+        ["val1", "val2"]
+    );
+
+    let m = a.try_get_matches_from_mut(vec!["myprog", "val1", "val2", "val3", "val4"]);
+    let m = match m {
+        Ok(m) => m,
+        Err(err) => panic!("{}", err),
+    };
+    assert_eq!(
+        m.values_of("pos").unwrap().collect::<Vec<_>>(),
+        ["val1", "val2", "val3", "val4"]
+    );
+}

tests/positionals.rs

@@ -296,14 +296,3 @@ fn positional_arg_with_short() {
         .arg(Arg::new("arg").index(1).short('a'))
         .try_get_matches();
 }
-
-#[cfg(debug_assertions)]
-#[test]
-#[should_panic = "Argument 'arg' is a positional argument and can't be set as multiple occurrences"]
-fn positional_arg_with_multiple_occurrences() {
-    use clap::{App, Arg};
-
-    let _ = App::new("test")
-        .arg(Arg::new("arg").multiple_occurrences(true))
-        .try_get_matches();
-}