fix List[Int].join crash; support joining int lists

cranelift/runtime-abi/runtime_functions.txt

@@ -54,6 +54,7 @@ pith_list_push|pith_list_push|I64,I64,I64|
 pith_list_push_value|pith_list_push_value|I64,I64|
 pith_list_set_value|pith_list_set_value|I64,I64,I64|
 list_join|pith_list_join|I64,I64|I64
+list_join_int|pith_list_join_int|I64,I64|I64
 pith_list_get_value|pith_list_get_value|I64,I64|I64
 pith_list_get_value_unchecked|pith_list_get_value_unchecked|I64,I64|I64
 pith_list_len|pith_list_len|I64|I64

cranelift/runtime/src/collections/list.rs

@@ -410,6 +410,37 @@ pub unsafe extern "C" fn pith_list_join(list: PithList, sep: *const i8) -> *mut
     out
 }
 
+/// Join a list of Int elements with a separator, formatting each as decimal.
+/// Unlike `pith_list_join`, the elements are values rather than string pointers.
+/// Returns a newly allocated C string.
+#[no_mangle]
+pub unsafe extern "C" fn pith_list_join_int(list: PithList, sep: *const i8) -> *mut i8 {
+    let Some(impl_ref) = list_ref(list) else {
+        return std::ptr::null_mut();
+    };
+
+    let sep_str = if sep.is_null() {
+        ""
+    } else {
+        let len = crate::string::pith_cstring_len(sep) as usize;
+        std::str::from_utf8(std::slice::from_raw_parts(sep as *const u8, len)).unwrap_or("")
+    };
+
+    let mut out = String::new();
+    let mut i = 0usize;
+    while i < impl_ref.len() {
+        if let Some(raw) = impl_ref.get_value(i) {
+            if i > 0 {
+                out.push_str(sep_str);
+            }
+            out.push_str(&raw.to_string());
+        }
+        i += 1;
+    }
+
+    crate::pith_copy_bytes_to_cstring(out.as_bytes())
+}
+
 /// Pop element from end of list
 ///
 /// Returns true if successful, false if list is empty

self-host/checker.pith

@@ -3001,6 +3001,10 @@ fn check_list_method_call(method: String, info: TypeInfo, args: List[Int], scope
         return tid_bool
     if method == "join":
         expect_one_typed_argument(method, args, tid_string, scope_id)
+        # join formats elements into a string; only String and Int elements are
+        # supported. other element types would otherwise crash at runtime.
+        if elem != tid_string and is_integer_type(elem) == false:
+            report_error("E219", "join requires a list of String or Int elements, got List[" + get_type_name(elem) + "]; map elements to String first")
         return tid_string
     if method == "index_of":
         expect_one_typed_argument(method, args, elem, scope_id)

self-host/ir_emitter_core.pith

@@ -3288,6 +3288,9 @@ fn ir_emit_method_call(idx: Int) -> Int:
     if self_hosted_list_r >= 0:
         return self_hosted_list_r
     mut emit_name := ir_method_emit_name(mname, obj_type)
+    if emit_name == "list_join" and ir_list_element_kind(node.children[0]) == "int":
+        # list_join assumes string elements; Int lists need decimal formatting
+        emit_name = "list_join_int"
     if ir_is_bool_returning_method(emit_name):
         ir_var_types.insert("__last_call", "bool")
 

self-host/ir_metadata.pith

@@ -9,7 +9,7 @@ LIST_RETURNING_FUNCS := "args,range,repeat_val,zeros,sort,sort_desc,reversed,tak
 LIST_STRING_RETURNING_FUNCS := "sort_strings,zip,enumerate,toml_keys"
 BOOL_RETURNING_METHODS := "contains,starts_with,ends_with,is_empty,string_contains,string_is_empty,contains_key,map_contains_key,map_contains_ikey,map_is_empty,set_contains,set_contains_int,set_is_empty,send,try_send,close,is_closed,is_done"
 VOID_METHODS := "reverse,clear,push,remove,insert,add,list_remove,list_clear,list_reverse,map_insert,map_insert_ikey,map_remove,map_remove_ikey,map_clear,set_add,set_add_int,set_remove,set_remove_int,set_clear,detach,lock,unlock,done,wait,acquire,release"
-STRING_RETURNING_METHODS := "trim,substring,to_upper,to_lower,reverse,replace,repeat,pad_left,pad_right,char_at,join,list_join,read_file,env,chr"
+STRING_RETURNING_METHODS := "trim,substring,to_upper,to_lower,reverse,replace,repeat,pad_left,pad_right,char_at,join,list_join,list_join_int,read_file,env,chr"
 
 fn ir_csv_contains(csv: String, name: String) -> Bool:
     if name.len() == 0:

tests/cases/test_list_join_int.pith

@@ -0,0 +1,20 @@
+# joining Int lists formats each element as decimal; String lists unchanged
+
+fn main():
+    nums := [1, 2, 3, 4, 5]
+    print(nums.join(","))
+    print(nums.join(" -> "))
+
+    empty: List[Int] := []
+    print("empty:[" + empty.join(",") + "]")
+
+    print([42].join(","))
+
+    # negative numbers
+    print([0 - 1, 0, 2].join(","))
+
+    # combines with map
+    print(nums.map(fn(x: Int) => x * 2).join("|"))
+
+    # String lists still join as before
+    print(["a", "b", "c"].join("-"))

tests/expected/test_list_join_int.txt

@@ -0,0 +1,7 @@
+1,2,3,4,5
+1 -> 2 -> 3 -> 4 -> 5
+empty:[]
+42
+-1,0,2
+2|4|6|8|10
+a-b-c

tests/invalid/expected/invalid_join_non_string.codes

@@ -0,0 +1 @@
+E219

tests/invalid/invalid_join_non_string.pith

@@ -0,0 +1,3 @@
+fn main():
+    xs := [1.0, 2.0, 3.0]
+    print(xs.join(","))