Ranged number abilities are derived and compiled correctly

Closes #5089

crates/compiler/derive_key/src/decoding.rs

@@ -96,7 +96,9 @@ impl FlatDecodable {
                 // by the backend, and the backend treats opaques like structural aliases.
                 _ => Self::from_var(subs, real_var),
             },
-            Content::RangedNumber(_) => Err(Underivable),
+            Content::RangedNumber(range) => {
+                Self::from_var(subs, range.default_compilation_variable())
+            }
             //
             Content::RecursionVar { .. } => Err(Underivable),
             Content::Error => Err(Underivable),

crates/compiler/derive_key/src/encoding.rs

@@ -131,7 +131,9 @@ impl FlatEncodable {
                 // by the backend, and the backend treats opaques like structural aliases.
                 _ => Self::from_var(subs, real_var),
             },
-            Content::RangedNumber(_) => Err(Underivable),
+            Content::RangedNumber(range) => {
+                Self::from_var(subs, range.default_compilation_variable())
+            }
             //
             Content::RecursionVar { .. } => Err(Underivable),
             Content::Error => Err(Underivable),

crates/compiler/test_gen/src/gen_abilities.rs

@@ -485,6 +485,25 @@ mod encode_immediate {
         )
     }
 
+    #[test]
+    #[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
+    fn ranged_number() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                app "test" imports [Encode, Json] provides [main] to "./platform"
+
+                main =
+                    when Str.fromUtf8 (Encode.toBytes [1, 2, 3] Json.toUtf8) is
+                        Ok s -> s
+                        _ -> "<bad>"
+                "#
+            ),
+            RocStr::from(r"[1,2,3]"),
+            RocStr
+        )
+    }
+
     macro_rules! num_immediate {
         ($($num:expr, $typ:ident)*) => {$(
             #[test]
@@ -960,6 +979,28 @@ mod decode_immediate {
         )
     }
 
+    #[test]
+    #[cfg(any(feature = "gen-llvm"))]
+    fn ranged_number() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                app "test" imports [Json] provides [main] to "./platform"
+
+                main =
+                    input = Str.toUtf8 "[1,2,3]"
+                    expected = [1,2,3]
+
+                    actual = Decode.fromBytes input Json.fromUtf8 |> Result.withDefault []
+
+                    actual == expected
+                "#
+            ),
+            true,
+            bool
+        )
+    }
+
     macro_rules! num_immediate {
         ($($num:expr, $typ:ident)*) => {$(
             #[test]

crates/compiler/types/src/num.rs

@@ -146,6 +146,11 @@ impl NumericRange {
             .expect("if number doesn't fit, should have been a type error"),
         }
     }
+
+    /// Chooses the type variable to compile this ranged number as.
+    pub fn default_compilation_variable(&self) -> Variable {
+        int_lit_width_to_variable(self.default_compilation_width())
+    }
 }
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]