Remove dependency on proc-macro-hack

Author: taiki-e

futures-macro/Cargo.toml

@@ -15,11 +15,7 @@ proc-macro = true
 
 [features]
 
-[build-dependencies]
-autocfg = "1"
-
 [dependencies]
 proc-macro2 = "1.0"
-proc-macro-hack = "0.5.19"
 quote = "1.0"
 syn = { version = "1.0.56", features = ["full"] }

futures-macro/build.rs

@@ -22,43 +22,38 @@ mod select;
 mod stream_select;
 
 /// The `join!` macro.
-#[cfg_attr(fn_like_proc_macro, proc_macro)]
-#[cfg_attr(not(fn_like_proc_macro), proc_macro_hack::proc_macro_hack)]
+#[proc_macro]
 pub fn join_internal(input: TokenStream) -> TokenStream {
     crate::join::join(input)
 }
 
 /// The `try_join!` macro.
-#[cfg_attr(fn_like_proc_macro, proc_macro)]
-#[cfg_attr(not(fn_like_proc_macro), proc_macro_hack::proc_macro_hack)]
+#[proc_macro]
 pub fn try_join_internal(input: TokenStream) -> TokenStream {
     crate::join::try_join(input)
 }
 
 /// The `select!` macro.
-#[cfg_attr(fn_like_proc_macro, proc_macro)]
-#[cfg_attr(not(fn_like_proc_macro), proc_macro_hack::proc_macro_hack)]
+#[proc_macro]
 pub fn select_internal(input: TokenStream) -> TokenStream {
     crate::select::select(input)
 }
 
 /// The `select_biased!` macro.
-#[cfg_attr(fn_like_proc_macro, proc_macro)]
-#[cfg_attr(not(fn_like_proc_macro), proc_macro_hack::proc_macro_hack)]
+#[proc_macro]
 pub fn select_biased_internal(input: TokenStream) -> TokenStream {
     crate::select::select_biased(input)
 }
 
-// TODO: Change this to doc comment once rustdoc bug fixed.
+// TODO: Change this to doc comment once rustdoc bug fixed: https://github.com/rust-lang/futures-rs/pull/2435
 // The `test` attribute.
 #[proc_macro_attribute]
 pub fn test_internal(input: TokenStream, item: TokenStream) -> TokenStream {
     crate::executor::test(input, item)
 }
 
 /// The `stream_select!` macro.
-#[cfg_attr(fn_like_proc_macro, proc_macro)]
-#[cfg_attr(not(fn_like_proc_macro), proc_macro_hack::proc_macro_hack)]
+#[proc_macro]
 pub fn stream_select_internal(input: TokenStream) -> TokenStream {
     crate::stream_select::stream_select(input.into())
         .unwrap_or_else(syn::Error::into_compile_error)

futures-macro/src/lib.rs

@@ -15,7 +15,7 @@ default = ["std", "async-await", "async-await-macro"]
 std = ["alloc", "futures-core/std", "futures-task/std", "slab"]
 alloc = ["futures-core/alloc", "futures-task/alloc"]
 async-await = []
-async-await-macro = ["async-await", "futures-macro", "proc-macro-hack", "proc-macro-nested"]
+async-await-macro = ["async-await", "futures-macro"]
 compat = ["std", "futures_01"]
 io-compat = ["io", "compat", "tokio-io"]
 sink = ["futures-sink"]
@@ -34,18 +34,13 @@ write-all-vectored = ["io"]
 # TODO: remove in the next major version.
 cfg-target-has-atomic = []
 
-[build-dependencies]
-autocfg = "1"
-
 [dependencies]
 futures-core = { path = "../futures-core", version = "0.3.17", default-features = false }
 futures-task = { path = "../futures-task", version = "0.3.17", default-features = false }
 futures-channel = { path = "../futures-channel", version = "0.3.17", default-features = false, features = ["std"], optional = true }
 futures-io = { path = "../futures-io", version = "0.3.17", default-features = false, features = ["std"], optional = true }
 futures-sink = { path = "../futures-sink", version = "0.3.17", default-features = false, optional = true }
 futures-macro = { path = "../futures-macro", version = "=0.3.17", default-features = false, optional = true }
-proc-macro-hack = { version = "0.5.19", optional = true }
-proc-macro-nested = { version = "0.1.2", optional = true }
 slab = { version = "0.4.2", optional = true }
 memchr = { version = "2.2", optional = true }
 futures_01 = { version = "0.1.25", optional = true, package = "futures" }

futures-util/Cargo.toml

@@ -1,6 +1,5 @@
 #![warn(rust_2018_idioms, single_use_lifetimes)]
 
-use autocfg::AutoCfg;
 use std::env;
 
 include!("no_atomic_cas.rs");
@@ -39,23 +38,5 @@ fn main() {
         println!("cargo:rustc-cfg=futures_no_atomic_cas");
     }
 
-    let cfg = match AutoCfg::new() {
-        Ok(cfg) => cfg,
-        Err(e) => {
-            println!(
-                "cargo:warning={}: unable to determine rustc version: {}",
-                env!("CARGO_PKG_NAME"),
-                e
-            );
-            return;
-        }
-    };
-
-    // Function like procedural macros in expressions patterns statements stabilized in Rust 1.45:
-    // https://blog.rust-lang.org/2020/07/16/Rust-1.45.0.html#stabilizing-function-like-procedural-macros-in-expressions-patterns-and-statements
-    if cfg.probe_rustc_version(1, 45) {
-        println!("cargo:rustc-cfg=fn_like_proc_macro");
-    }
-
     println!("cargo:rerun-if-changed=no_atomic_cas.rs");
 }

futures-util/build.rs

@@ -81,12 +81,10 @@ macro_rules! document_join_macro {
 
 #[allow(unreachable_pub)]
 #[doc(hidden)]
-#[cfg_attr(not(fn_like_proc_macro), proc_macro_hack::proc_macro_hack(support_nested))]
 pub use futures_macro::join_internal;
 
 #[allow(unreachable_pub)]
 #[doc(hidden)]
-#[cfg_attr(not(fn_like_proc_macro), proc_macro_hack::proc_macro_hack(support_nested))]
 pub use futures_macro::try_join_internal;
 
 document_join_macro! {

futures-util/src/async_await/join_mod.rs

@@ -29,9 +29,6 @@ macro_rules! document_select_macro {
         /// It is also gated behind the `async-await` feature of this library, which is
         /// activated by default.
         ///
-        /// Note that `select!` relies on `proc-macro-hack`, and may require to set the
-        /// compiler's recursion limit very high, e.g. `#![recursion_limit="1024"]`.
-        ///
         /// # Examples
         ///
         /// ```
@@ -309,12 +306,10 @@ macro_rules! document_select_macro {
 #[cfg(feature = "std")]
 #[allow(unreachable_pub)]
 #[doc(hidden)]
-#[cfg_attr(not(fn_like_proc_macro), proc_macro_hack::proc_macro_hack(support_nested))]
 pub use futures_macro::select_internal;
 
 #[allow(unreachable_pub)]
 #[doc(hidden)]
-#[cfg_attr(not(fn_like_proc_macro), proc_macro_hack::proc_macro_hack(support_nested))]
 pub use futures_macro::select_biased_internal;
 
 document_select_macro! {

futures-util/src/async_await/select_mod.rs

@@ -3,7 +3,6 @@
 #[cfg(feature = "std")]
 #[allow(unreachable_pub)]
 #[doc(hidden)]
-#[cfg_attr(not(fn_like_proc_macro), proc_macro_hack::proc_macro_hack(support_nested))]
 pub use futures_macro::stream_select_internal;
 
 /// Combines several streams, all producing the same `Item` type, into one stream.
@@ -13,10 +12,6 @@ pub use futures_macro::stream_select_internal;
 ///
 /// If multiple streams are ready, one will be pseudo randomly selected at runtime.
 ///
-/// This macro is gated behind the `async-await` feature of this library, which is activated by default.
-/// Note that `stream_select!` relies on `proc-macro-hack`, and may require to set the compiler's recursion
-/// limit very high, e.g. `#![recursion_limit="1024"]`.
-///
 /// # Examples
 ///
 /// ```