init

.gitignore

@@ -0,0 +1,2 @@
+/target
+

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+    "rust-analyzer.checkOnSave": false
+}

Cargo.lock

@@ -0,0 +1,105 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "futures-core"
+version = "0.3.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "05f29059c0c2090612e8d742178b0580d2dc940c837851ad723096f87af6663e"
+
+[[package]]
+name = "futures-macro"
+version = "0.3.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "162ee34ebcb7c64a8abebc059ce0fee27c2262618d7b60ed8faf72fef13c3650"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "futures-task"
+version = "0.3.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f90f7dce0722e95104fcb095585910c0977252f286e354b5e3bd38902cd99988"
+
+[[package]]
+name = "futures-util"
+version = "0.3.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9fa08315bb612088cc391249efdc3bc77536f16c91f6cf495e6fbe85b20a4a81"
+dependencies = [
+ "futures-core",
+ "futures-macro",
+ "futures-task",
+ "pin-project-lite",
+ "pin-utils",
+ "slab",
+]
+
+[[package]]
+name = "pin-project-lite"
+version = "0.2.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3b3cff922bd51709b605d9ead9aa71031d81447142d828eb4a6eba76fe619f9b"
+
+[[package]]
+name = "pin-utils"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8b870d8c151b6f2fb93e84a13146138f05d02ed11c7e7c54f8826aaaf7c9f184"
+
+[[package]]
+name = "proc-macro-thing"
+version = "0.1.0"
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.101"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "89ae43fd86e4158d6db51ad8e2b80f313af9cc74f5c0e03ccb87de09998732de"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.41"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ce25767e7b499d1b604768e7cde645d14cc8584231ea6b295e9c9eb22c02e1d1"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "reproduction"
+version = "0.1.0"
+dependencies = [
+ "futures-util",
+ "proc-macro-thing",
+]
+
+[[package]]
+name = "slab"
+version = "0.4.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a2ae44ef20feb57a68b23d846850f861394c2e02dc425a50098ae8c90267589"
+
+[[package]]
+name = "syn"
+version = "2.0.106"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ede7c438028d4436d71104916910f5bb611972c5cfd7f89b8300a8186e6fada6"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f63a545481291138910575129486daeaf8ac54aee4387fe7906919f7830c7d9d"

Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "reproduction"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+futures-util = "0.3.31"
+proc-macro-thing = { path = "proc-macro-thing" }

proc-macro-thing/.gitignore

@@ -0,0 +1 @@
+/target

proc-macro-thing/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "proc-macro-thing"
+version = "0.1.0"
+edition = "2024"
+
+[lib]
+proc-macro = true

proc-macro-thing/src/lib.rs

@@ -0,0 +1,6 @@
+use proc_macro::TokenStream;
+
+#[proc_macro_derive(MyMacro, attributes(helper))]
+pub fn hello(_: TokenStream) -> TokenStream {
+    "".parse().unwrap()
+} 

repro.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+
+cargo clean -p reproduction
+
+node toggle.js
+
+cargo build
+
+node toggle.js
+
+cargo build

src/main.rs

@@ -0,0 +1,62 @@
+use futures_util::future::{Map, MapOk};
+use std::pin::Pin;
+
+struct MapOk2<Fut, F>(Fut, F);
+impl<Fut, F> Future for MapOk2<Fut, F>
+where
+    Map<Fut, F>: Future,
+{
+    type Output = <Map<Fut, F> as Future>::Output;
+    fn poll(
+        self: Pin<&mut Self>,
+        cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Self::Output> {
+        loop {}
+    }
+}
+
+pub struct MaybeDone<Fut: Future>(Fut);
+
+pub fn take_output<Fut: Future>(x: Pin<&mut MaybeDone<Fut>>) -> Fut::Output {
+    loop {}
+}
+
+struct AndThen<Fut1, F>(Fut1, F);
+impl<Fut1, F> Future for AndThen<Fut1, F>
+where
+    MapOk<Fut1, F>: Future,
+{
+    type Output = ();
+    fn poll(
+        self: Pin<&mut Self>,
+        cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Self::Output> {
+        loop {}
+    }
+}
+
+fn and_then<This, F>(s: This, f: F) -> AndThen<This, F> {
+    loop {}
+}
+
+pub async fn bar_baz() {
+    let bazz = and_then(async { Ok::<(), ()>(()) }, async |_| Ok::<(), ()>(()));
+    let barr = async { Bazz {} };
+
+    let mut _fut0 = MaybeDone(bazz);
+    let mut _fut0 = unsafe { std::pin::Pin::new_unchecked(&mut _fut0) };
+    let mut _fut1 = MaybeDone(barr);
+    let mut _fut1 = unsafe { std::pin::Pin::new_unchecked(&mut _fut1) };
+    std::future::poll_fn(move |__cx: &mut std::task::Context<'_>| {
+        std::task::Poll::Ready((take_output(_fut0.as_mut()), take_output(_fut1.as_mut())))
+    });
+}
+
+// 1
+    // 2
+
+#[derive(proc_macro_thing::MyMacro)]
+#[helper]
+pub struct Bazz {}
+
+fn main() {}

toggle.js

@@ -0,0 +1,13 @@
+const fs = require("fs");
+
+const c = fs.readFileSync("src/main.rs", "utf-8").split("\n");
+
+const one = c.findIndex(l => l.includes("// 1"));
+
+if (c[one + 1].includes("// 2")) {
+    c.splice(one + 1, 1);
+} else {
+    c.splice(one + 1, 0, "    // 2")
+}
+
+fs.writeFileSync("src/main.rs", c.join("\n"));