Implement length macro in luaify

crates/luaify/src/generate.rs

@@ -796,6 +796,7 @@ fn generate_receiver(f: &mut Formatter, recv: &Receiver) -> Result<()> {
 fn generate_macro(f: &mut Formatter, mac: &Macro, cx: Context) -> Result<()> {
     match format!("{}", mac.path.require_ident()?).as_str() {
         "concat" => generate_macro_concat(f, mac, cx),
+        "len" => generate_macro_len(f, mac, cx),
         "variadic" => generate_macro_variadic(f, mac, cx),
         "embed" => generate_macro_embed(f, mac, cx),
         "raw" => generate_macro_raw(f, mac, cx),
@@ -815,6 +816,13 @@ fn generate_macro_concat(f: &mut Formatter, mac: &Macro, cx: Context) -> Result<
     Ok(())
 }
 
+fn generate_macro_len(f: &mut Formatter, mac: &Macro, cx: Context) -> Result<()> {
+    syn_assert!(cx.is_value(), mac, "len! must be in expression position");
+    cx.is_ret().then(|| f.write("return"));
+    f.write("#");
+    generate_expr(f, &mac.parse_body()?, Context::expr(false))
+}
+
 fn generate_macro_variadic(f: &mut Formatter, mac: &Macro, cx: Context) -> Result<()> {
     syn_assert!(
         cx.is_multi_expr(),

crates/luaify/tests/test.rs

@@ -391,3 +391,14 @@ fn variadic() {
         r#"function(a,...)local a,b=a,b,c,...;return func(a,b,c,d,...);end"#
     );
 }
+
+#[test]
+fn length() {
+    assert_eq!(luaify!(len!(a)), r#"#a"#);
+    assert_eq!(
+        luaify!({
+            let (a, b, c) = (len!(a), len!(b), len!(c));
+        }),
+        r#"local a,b,c=#a,#b,#c;"#
+    );
+}