Import 'futures-macro' rust crate version 0.3.4

Bug: b/151760391
Test: m crosvm.experimental
Change-Id: I8169563a9a5da3508965ddca4d9d5e12b8bdb340

12 files changed, 893 insertions, 0 deletions

diff --git a/Android.bp b/Android.bp
new file mode 100644
index 0000000..a442b34
--- /dev/null
+++ b/Android.bp
@@ -0,0 +1,23 @@
+// This file is generated by cargo2android.py.
+
+rust_proc_macro {
+    name: "libfutures_macro",
+    crate_name: "futures_macro",
+    srcs: ["src/lib.rs"],
+    edition: "2018",
+    rlibs: [
+        "libproc_macro2",
+        "libquote",
+        "libsyn",
+    ],
+    proc_macros: [
+        "libproc_macro_hack",
+    ],
+}
+
+// dependent_library ["feature_list"]
+//   proc-macro-hack-0.5.11
+//   proc-macro2-1.0.9 "default,proc-macro"
+//   quote-1.0.3 "default,proc-macro"
+//   syn-1.0.16 "clone-impls,default,derive,full,parsing,printing,proc-macro,quote"
+//   unicode-xid-0.2.0 "default"
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..14dfe71
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,39 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies
+#
+# If you believe there's an error in this file please file an
+# issue against the rust-lang/cargo repository. If you're
+# editing this file be aware that the upstream Cargo.toml
+# will likely look very different (and much more reasonable)
+
+[package]
+edition = "2018"
+name = "futures-macro"
+version = "0.3.4"
+authors = ["Taylor Cramer <cramertj@google.com>", "Taiki Endo <te316e89@gmail.com>"]
+description = "The futures-rs procedural macro implementations.\n"
+homepage = "https://rust-lang.github.io/futures-rs"
+documentation = "https://docs.rs/futures-macro/0.3.0"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-lang/futures-rs"
+
+[lib]
+proc-macro = true
+[dependencies.proc-macro-hack]
+version = "0.5.9"
+
+[dependencies.proc-macro2]
+version = "1.0"
+
+[dependencies.quote]
+version = "1.0"
+
+[dependencies.syn]
+version = "1.0"
+features = ["full"]
+
+[features]
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
new file mode 100644
index 0000000..ccc1715
--- /dev/null
+++ b/Cargo.toml.orig
@@ -0,0 +1,23 @@
+[package]
+name = "futures-macro"
+edition = "2018"
+version = "0.3.4"
+authors = ["Taylor Cramer <cramertj@google.com>", "Taiki Endo <te316e89@gmail.com>"]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-lang/futures-rs"
+homepage = "https://rust-lang.github.io/futures-rs"
+documentation = "https://docs.rs/futures-macro/0.3.0"
+description = """
+The futures-rs procedural macro implementations.
+"""
+
+[lib]
+proc-macro = true
+
+[features]
+
+[dependencies]
+proc-macro2 = "1.0"
+proc-macro-hack = "0.5.9"
+quote = "1.0"
+syn = { version = "1.0", features = ["full"] }
diff --git a/LICENSE b/LICENSE
new file mode 120000
index 0000000..6b579aa
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1 @@
+LICENSE-APACHE
\ No newline at end of file
diff --git a/LICENSE-APACHE b/LICENSE-APACHE
new file mode 100644
index 0000000..9eb0b09
--- /dev/null
+++ b/LICENSE-APACHE
@@ -0,0 +1,202 @@
+                              Apache License
+                        Version 2.0, January 2004
+                     http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+1. Definitions.
+
+   "License" shall mean the terms and conditions for use, reproduction,
+   and distribution as defined by Sections 1 through 9 of this document.
+
+   "Licensor" shall mean the copyright owner or entity authorized by
+   the copyright owner that is granting the License.
+
+   "Legal Entity" shall mean the union of the acting entity and all
+   other entities that control, are controlled by, or are under common
+   control with that entity. For the purposes of this definition,
+   "control" means (i) the power, direct or indirect, to cause the
+   direction or management of such entity, whether by contract or
+   otherwise, or (ii) ownership of fifty percent (50%) or more of the
+   outstanding shares, or (iii) beneficial ownership of such entity.
+
+   "You" (or "Your") shall mean an individual or Legal Entity
+   exercising permissions granted by this License.
+
+   "Source" form shall mean the preferred form for making modifications,
+   including but not limited to software source code, documentation
+   source, and configuration files.
+
+   "Object" form shall mean any form resulting from mechanical
+   transformation or translation of a Source form, including but
+   not limited to compiled object code, generated documentation,
+   and conversions to other media types.
+
+   "Work" shall mean the work of authorship, whether in Source or
+   Object form, made available under the License, as indicated by a
+   copyright notice that is included in or attached to the work
+   (an example is provided in the Appendix below).
+
+   "Derivative Works" shall mean any work, whether in Source or Object
+   form, that is based on (or derived from) the Work and for which the
+   editorial revisions, annotations, elaborations, or other modifications
+   represent, as a whole, an original work of authorship. For the purposes
+   of this License, Derivative Works shall not include works that remain
+   separable from, or merely link (or bind by name) to the interfaces of,
+   the Work and Derivative Works thereof.
+
+   "Contribution" shall mean any work of authorship, including
+   the original version of the Work and any modifications or additions
+   to that Work or Derivative Works thereof, that is intentionally
+   submitted to Licensor for inclusion in the Work by the copyright owner
+   or by an individual or Legal Entity authorized to submit on behalf of
+   the copyright owner. For the purposes of this definition, "submitted"
+   means any form of electronic, verbal, or written communication sent
+   to the Licensor or its representatives, including but not limited to
+   communication on electronic mailing lists, source code control systems,
+   and issue tracking systems that are managed by, or on behalf of, the
+   Licensor for the purpose of discussing and improving the Work, but
+   excluding communication that is conspicuously marked or otherwise
+   designated in writing by the copyright owner as "Not a Contribution."
+
+   "Contributor" shall mean Licensor and any individual or Legal Entity
+   on behalf of whom a Contribution has been received by Licensor and
+   subsequently incorporated within the Work.
+
+2. Grant of Copyright License. Subject to the terms and conditions of
+   this License, each Contributor hereby grants to You a perpetual,
+   worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+   copyright license to reproduce, prepare Derivative Works of,
+   publicly display, publicly perform, sublicense, and distribute the
+   Work and such Derivative Works in Source or Object form.
+
+3. Grant of Patent License. Subject to the terms and conditions of
+   this License, each Contributor hereby grants to You a perpetual,
+   worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+   (except as stated in this section) patent license to make, have made,
+   use, offer to sell, sell, import, and otherwise transfer the Work,
+   where such license applies only to those patent claims licensable
+   by such Contributor that are necessarily infringed by their
+   Contribution(s) alone or by combination of their Contribution(s)
+   with the Work to which such Contribution(s) was submitted. If You
+   institute patent litigation against any entity (including a
+   cross-claim or counterclaim in a lawsuit) alleging that the Work
+   or a Contribution incorporated within the Work constitutes direct
+   or contributory patent infringement, then any patent licenses
+   granted to You under this License for that Work shall terminate
+   as of the date such litigation is filed.
+
+4. Redistribution. You may reproduce and distribute copies of the
+   Work or Derivative Works thereof in any medium, with or without
+   modifications, and in Source or Object form, provided that You
+   meet the following conditions:
+
+   (a) You must give any other recipients of the Work or
+       Derivative Works a copy of this License; and
+
+   (b) You must cause any modified files to carry prominent notices
+       stating that You changed the files; and
+
+   (c) You must retain, in the Source form of any Derivative Works
+       that You distribute, all copyright, patent, trademark, and
+       attribution notices from the Source form of the Work,
+       excluding those notices that do not pertain to any part of
+       the Derivative Works; and
+
+   (d) If the Work includes a "NOTICE" text file as part of its
+       distribution, then any Derivative Works that You distribute must
+       include a readable copy of the attribution notices contained
+       within such NOTICE file, excluding those notices that do not
+       pertain to any part of the Derivative Works, in at least one
+       of the following places: within a NOTICE text file distributed
+       as part of the Derivative Works; within the Source form or
+       documentation, if provided along with the Derivative Works; or,
+       within a display generated by the Derivative Works, if and
+       wherever such third-party notices normally appear. The contents
+       of the NOTICE file are for informational purposes only and
+       do not modify the License. You may add Your own attribution
+       notices within Derivative Works that You distribute, alongside
+       or as an addendum to the NOTICE text from the Work, provided
+       that such additional attribution notices cannot be construed
+       as modifying the License.
+
+   You may add Your own copyright statement to Your modifications and
+   may provide additional or different license terms and conditions
+   for use, reproduction, or distribution of Your modifications, or
+   for any such Derivative Works as a whole, provided Your use,
+   reproduction, and distribution of the Work otherwise complies with
+   the conditions stated in this License.
+
+5. Submission of Contributions. Unless You explicitly state otherwise,
+   any Contribution intentionally submitted for inclusion in the Work
+   by You to the Licensor shall be under the terms and conditions of
+   this License, without any additional terms or conditions.
+   Notwithstanding the above, nothing herein shall supersede or modify
+   the terms of any separate license agreement you may have executed
+   with Licensor regarding such Contributions.
+
+6. Trademarks. This License does not grant permission to use the trade
+   names, trademarks, service marks, or product names of the Licensor,
+   except as required for reasonable and customary use in describing the
+   origin of the Work and reproducing the content of the NOTICE file.
+
+7. Disclaimer of Warranty. Unless required by applicable law or
+   agreed to in writing, Licensor provides the Work (and each
+   Contributor provides its Contributions) on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+   implied, including, without limitation, any warranties or conditions
+   of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+   PARTICULAR PURPOSE. You are solely responsible for determining the
+   appropriateness of using or redistributing the Work and assume any
+   risks associated with Your exercise of permissions under this License.
+
+8. Limitation of Liability. In no event and under no legal theory,
+   whether in tort (including negligence), contract, or otherwise,
+   unless required by applicable law (such as deliberate and grossly
+   negligent acts) or agreed to in writing, shall any Contributor be
+   liable to You for damages, including any direct, indirect, special,
+   incidental, or consequential damages of any character arising as a
+   result of this License or out of the use or inability to use the
+   Work (including but not limited to damages for loss of goodwill,
+   work stoppage, computer failure or malfunction, or any and all
+   other commercial damages or losses), even if such Contributor
+   has been advised of the possibility of such damages.
+
+9. Accepting Warranty or Additional Liability. While redistributing
+   the Work or Derivative Works thereof, You may choose to offer,
+   and charge a fee for, acceptance of support, warranty, indemnity,
+   or other liability obligations and/or rights consistent with this
+   License. However, in accepting such obligations, You may act only
+   on Your own behalf and on Your sole responsibility, not on behalf
+   of any other Contributor, and only if You agree to indemnify,
+   defend, and hold each Contributor harmless for any liability
+   incurred by, or claims asserted against, such Contributor by reason
+   of your accepting any such warranty or additional liability.
+
+END OF TERMS AND CONDITIONS
+
+APPENDIX: How to apply the Apache License to your work.
+
+   To apply the Apache License to your work, attach the following
+   boilerplate notice, with the fields enclosed by brackets "[]"
+   replaced with your own identifying information. (Don't include
+   the brackets!)  The text should be enclosed in the appropriate
+   comment syntax for the file format. We also recommend that a
+   file or class name and description of purpose be included on the
+   same "printed page" as the copyright notice for easier
+   identification within third-party archives.
+
+Copyright (c) 2016 Alex Crichton
+Copyright (c) 2017 The Tokio Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+	http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
diff --git a/LICENSE-MIT b/LICENSE-MIT
new file mode 100644
index 0000000..8ad082e
--- /dev/null
+++ b/LICENSE-MIT
@@ -0,0 +1,26 @@
+Copyright (c) 2016 Alex Crichton
+Copyright (c) 2017 The Tokio Authors
+
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
+limitation the rights to use, copy, modify, merge,
+publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software
+is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/METADATA b/METADATA
new file mode 100644
index 0000000..a29b746
--- /dev/null
+++ b/METADATA
@@ -0,0 +1,17 @@
+name: "futures-macro"
+description:
+    "The futures-rs procedural macro implementations."
+
+third_party {
+  url {
+    type: HOMEPAGE
+    value: "https://crates.io/crates/futures-macro"
+  }
+  url {
+    type: GIT
+    value: "https://github.com/rust-lang/futures-rs"
+  }
+  version: "0.3.4"
+  last_upgrade_date { year: 2020 month: 3 day: 17 }
+  license_type: NOTICE
+}
diff --git a/MODULE_LICENSE_APACHE2 b/MODULE_LICENSE_APACHE2
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/MODULE_LICENSE_APACHE2
diff --git a/NOTICE b/NOTICE
new file mode 120000
index 0000000..7a694c9
--- /dev/null
+++ b/NOTICE
@@ -0,0 +1 @@
+LICENSE
\ No newline at end of file
diff --git a/src/join.rs b/src/join.rs
new file mode 100644
index 0000000..2a7b11c
--- /dev/null
+++ b/src/join.rs
@@ -0,0 +1,170 @@
+//! The futures-rs `join! macro implementation.
+
+use proc_macro::TokenStream;
+use proc_macro2::{Span, TokenStream as TokenStream2};
+use quote::{format_ident, quote};
+use syn::parse::{Parse, ParseStream};
+use syn::{parenthesized, parse_quote, Expr, Ident, Token};
+
+mod kw {
+    syn::custom_keyword!(futures_crate_path);
+}
+
+#[derive(Default)]
+struct Join {
+    futures_crate_path: Option<syn::Path>,
+    fut_exprs: Vec<Expr>,
+}
+
+impl Parse for Join {
+    fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
+        let mut join = Join::default();
+
+        // When `futures_crate_path(::path::to::futures::lib)` is provided,
+        // it sets the path through which futures library functions will be
+        // accessed.
+        if input.peek(kw::futures_crate_path) {
+            input.parse::<kw::futures_crate_path>()?;
+            let content;
+            parenthesized!(content in input);
+            join.futures_crate_path = Some(content.parse()?);
+        }
+
+        while !input.is_empty() {
+            join.fut_exprs.push(input.parse::<Expr>()?);
+
+            if !input.is_empty() {
+                input.parse::<Token![,]>()?;
+            }
+        }
+
+        Ok(join)
+    }
+}
+
+fn bind_futures(
+    futures_crate: &syn::Path,
+    fut_exprs: Vec<Expr>,
+    span: Span,
+) -> (Vec<TokenStream2>, Vec<Ident>) {
+    let mut future_let_bindings = Vec::with_capacity(fut_exprs.len());
+    let future_names: Vec<_> = fut_exprs
+        .into_iter()
+        .enumerate()
+        .map(|(i, expr)| {
+            let name = format_ident!("_fut{}", i, span = span);
+            future_let_bindings.push(quote! {
+                // Move future into a local so that it is pinned in one place and
+                // is no longer accessible by the end user.
+                let mut #name = #futures_crate::future::maybe_done(#expr);
+            });
+            name
+        })
+        .collect();
+
+    (future_let_bindings, future_names)
+}
+
+/// The `join!` macro.
+pub(crate) fn join(input: TokenStream) -> TokenStream {
+    let parsed = syn::parse_macro_input!(input as Join);
+
+    let futures_crate = parsed
+        .futures_crate_path
+        .unwrap_or_else(|| parse_quote!(::futures_util));
+
+    // should be def_site, but that's unstable
+    let span = Span::call_site();
+
+    let (future_let_bindings, future_names) = bind_futures(&futures_crate, parsed.fut_exprs, span);
+
+    let poll_futures = future_names.iter().map(|fut| {
+        quote! {
+            __all_done &= #futures_crate::core_reexport::future::Future::poll(
+                unsafe { #futures_crate::core_reexport::pin::Pin::new_unchecked(&mut #fut) }, __cx).is_ready();
+        }
+    });
+    let take_outputs = future_names.iter().map(|fut| {
+        quote! {
+            unsafe { #futures_crate::core_reexport::pin::Pin::new_unchecked(&mut #fut) }.take_output().unwrap(),
+        }
+    });
+
+    TokenStream::from(quote! { {
+        #( #future_let_bindings )*
+
+        #futures_crate::future::poll_fn(move |__cx: &mut #futures_crate::task::Context<'_>| {
+            let mut __all_done = true;
+            #( #poll_futures )*
+            if __all_done {
+                #futures_crate::core_reexport::task::Poll::Ready((
+                    #( #take_outputs )*
+                ))
+            } else {
+                #futures_crate::core_reexport::task::Poll::Pending
+            }
+        }).await
+    } })
+}
+
+/// The `try_join!` macro.
+pub(crate) fn try_join(input: TokenStream) -> TokenStream {
+    let parsed = syn::parse_macro_input!(input as Join);
+
+    let futures_crate = parsed
+        .futures_crate_path
+        .unwrap_or_else(|| parse_quote!(::futures_util));
+
+    // should be def_site, but that's unstable
+    let span = Span::call_site();
+
+    let (future_let_bindings, future_names) = bind_futures(&futures_crate, parsed.fut_exprs, span);
+
+    let poll_futures = future_names.iter().map(|fut| {
+        quote! {
+            if #futures_crate::core_reexport::future::Future::poll(
+                unsafe { #futures_crate::core_reexport::pin::Pin::new_unchecked(&mut #fut) }, __cx).is_pending()
+            {
+                __all_done = false;
+            } else if unsafe { #futures_crate::core_reexport::pin::Pin::new_unchecked(&mut #fut) }.output_mut().unwrap().is_err() {
+                // `.err().unwrap()` rather than `.unwrap_err()` so that we don't introduce
+                // a `T: Debug` bound.
+                // Also, for an error type of ! any code after `err().unwrap()` is unreachable.
+                #[allow(unreachable_code)]
+                return #futures_crate::core_reexport::task::Poll::Ready(
+                    #futures_crate::core_reexport::result::Result::Err(
+                        unsafe { #futures_crate::core_reexport::pin::Pin::new_unchecked(&mut #fut) }.take_output().unwrap().err().unwrap()
+                    )
+                );
+            }
+        }
+    });
+    let take_outputs = future_names.iter().map(|fut| {
+        quote! {
+            // `.ok().unwrap()` rather than `.unwrap()` so that we don't introduce
+            // an `E: Debug` bound.
+            // Also, for an ok type of ! any code after `ok().unwrap()` is unreachable.
+            #[allow(unreachable_code)]
+            unsafe { #futures_crate::core_reexport::pin::Pin::new_unchecked(&mut #fut) }.take_output().unwrap().ok().unwrap(),
+        }
+    });
+
+    TokenStream::from(quote! { {
+        #( #future_let_bindings )*
+
+        #[allow(clippy::diverging_sub_expression)]
+        #futures_crate::future::poll_fn(move |__cx: &mut #futures_crate::task::Context<'_>| {
+            let mut __all_done = true;
+            #( #poll_futures )*
+            if __all_done {
+                #futures_crate::core_reexport::task::Poll::Ready(
+                    #futures_crate::core_reexport::result::Result::Ok((
+                        #( #take_outputs )*
+                    ))
+                )
+            } else {
+                #futures_crate::core_reexport::task::Poll::Pending
+            }
+        }).await
+    } })
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..932ec2e
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,46 @@
+//! The futures-rs procedural macro implementations.
+
+#![recursion_limit = "128"]
+#![warn(rust_2018_idioms, unreachable_pub)]
+// It cannot be included in the published code because this lints have false positives in the minimum required version.
+#![cfg_attr(test, warn(single_use_lifetimes))]
+#![warn(clippy::all)]
+
+#![doc(test(attr(deny(warnings), allow(dead_code, unused_assignments, unused_variables))))]
+
+#![doc(html_root_url = "https://docs.rs/futures-join-macro/0.3.0")]
+
+// Since https://github.com/rust-lang/cargo/pull/7700 `proc_macro` is part of the prelude for
+// proc-macro crates, but to support older compilers we still need this explicit `extern crate`.
+#[allow(unused_extern_crates)]
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+use proc_macro_hack::proc_macro_hack;
+
+mod join;
+mod select;
+
+/// The `join!` macro.
+#[proc_macro_hack]
+pub fn join(input: TokenStream) -> TokenStream {
+    crate::join::join(input)
+}
+
+/// The `try_join!` macro.
+#[proc_macro_hack]
+pub fn try_join(input: TokenStream) -> TokenStream {
+    crate::join::try_join(input)
+}
+
+/// The `select!` macro.
+#[proc_macro_hack]
+pub fn select(input: TokenStream) -> TokenStream {
+    crate::select::select(input)
+}
+
+/// The `select_biased!` macro.
+#[proc_macro_hack]
+pub fn select_biased(input: TokenStream) -> TokenStream {
+    crate::select::select_biased(input)
+}
diff --git a/src/select.rs b/src/select.rs
new file mode 100644
index 0000000..f7f688b
--- /dev/null
+++ b/src/select.rs
@@ -0,0 +1,345 @@
+//! The futures-rs `select! macro implementation.
+
+use proc_macro::TokenStream;
+use proc_macro2::Span;
+use quote::{format_ident, quote};
+use syn::{parenthesized, parse_quote, Expr, Ident, Pat, Token};
+use syn::parse::{Parse, ParseStream};
+
+mod kw {
+    syn::custom_keyword!(complete);
+    syn::custom_keyword!(futures_crate_path);
+}
+
+struct Select {
+    futures_crate_path: Option<syn::Path>,
+    // span of `complete`, then expression after `=> ...`
+    complete: Option<Expr>,
+    default: Option<Expr>,
+    normal_fut_exprs: Vec<Expr>,
+    normal_fut_handlers: Vec<(Pat, Expr)>,
+}
+
+#[allow(clippy::large_enum_variant)]
+enum CaseKind {
+    Complete,
+    Default,
+    Normal(Pat, Expr),
+}
+
+impl Parse for Select {
+    fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
+        let mut select = Select {
+            futures_crate_path: None,
+            complete: None,
+            default: None,
+            normal_fut_exprs: vec![],
+            normal_fut_handlers: vec![],
+        };
+
+        // When `futures_crate_path(::path::to::futures::lib)` is provided,
+        // it sets the path through which futures library functions will be
+        // accessed.
+        if input.peek(kw::futures_crate_path) {
+            input.parse::<kw::futures_crate_path>()?;
+            let content;
+            parenthesized!(content in input);
+            select.futures_crate_path = Some(content.parse()?);
+        }
+
+        while !input.is_empty() {
+            let case_kind = if input.peek(kw::complete) {
+                // `complete`
+                if select.complete.is_some() {
+                    return Err(input.error("multiple `complete` cases found, only one allowed"));
+                }
+                input.parse::<kw::complete>()?;
+                CaseKind::Complete
+            } else if input.peek(Token![default]) {
+                // `default`
+                if select.default.is_some() {
+                    return Err(input.error("multiple `default` cases found, only one allowed"));
+                }
+                input.parse::<Ident>()?;
+                CaseKind::Default
+            } else {
+                // `<pat> = <expr>`
+                let pat = input.parse()?;
+                input.parse::<Token![=]>()?;
+                let expr = input.parse()?;
+                CaseKind::Normal(pat, expr)
+            };
+
+            // `=> <expr>`
+            input.parse::<Token![=>]>()?;
+            let expr = input.parse::<Expr>()?;
+
+            // Commas after the expression are only optional if it's a `Block`
+            // or it is the last branch in the `match`.
+            let is_block = match expr { Expr::Block(_) => true, _ => false };
+            if is_block || input.is_empty() {
+                input.parse::<Option<Token![,]>>()?;
+            } else {
+                input.parse::<Token![,]>()?;
+            }
+
+            match case_kind {
+                CaseKind::Complete => select.complete = Some(expr),
+                CaseKind::Default => select.default = Some(expr),
+                CaseKind::Normal(pat, fut_expr) => {
+                    select.normal_fut_exprs.push(fut_expr);
+                    select.normal_fut_handlers.push((pat, expr));
+                },
+            }
+        }
+
+        Ok(select)
+    }
+}
+
+// Enum over all the cases in which the `select!` waiting has completed and the result
+// can be processed.
+//
+// `enum __PrivResult<_1, _2, ...> { _1(_1), _2(_2), ..., Complete }`
+fn declare_result_enum(
+    result_ident: Ident,
+    variants: usize,
+    complete: bool,
+    span: Span
+) -> (Vec<Ident>, syn::ItemEnum) {
+    // "_0", "_1", "_2"
+    let variant_names: Vec<Ident> =
+        (0..variants)
+            .map(|num| format_ident!("_{}", num, span = span))
+            .collect();
+
+    let type_parameters = &variant_names;
+    let variants = &variant_names;
+
+    let complete_variant = if complete {
+        Some(quote!(Complete))
+    } else {
+        None
+    };
+
+    let enum_item = parse_quote! {
+        enum #result_ident<#(#type_parameters,)*> {
+            #(
+                #variants(#type_parameters),
+            )*
+            #complete_variant
+        }
+    };
+
+    (variant_names, enum_item)
+}
+
+/// The `select!` macro.
+pub(crate) fn select(input: TokenStream) -> TokenStream {
+    select_inner(input, true)
+}
+
+/// The `select_biased!` macro.
+pub(crate) fn select_biased(input: TokenStream) -> TokenStream {
+    select_inner(input, false)
+}
+
+fn select_inner(input: TokenStream, random: bool) -> TokenStream {
+    let parsed = syn::parse_macro_input!(input as Select);
+
+    let futures_crate: syn::Path = parsed.futures_crate_path.unwrap_or_else(|| parse_quote!(::futures_util));
+
+    // should be def_site, but that's unstable
+    let span = Span::call_site();
+
+    let enum_ident = Ident::new("__PrivResult", span);
+
+    let (variant_names, enum_item) = declare_result_enum(
+        enum_ident.clone(),
+        parsed.normal_fut_exprs.len(),
+        parsed.complete.is_some(),
+        span,
+    );
+
+    // bind non-`Ident` future exprs w/ `let`
+    let mut future_let_bindings = Vec::with_capacity(parsed.normal_fut_exprs.len());
+    let bound_future_names: Vec<_> = parsed.normal_fut_exprs.into_iter()
+        .zip(variant_names.iter())
+        .map(|(expr, variant_name)| {
+            match expr {
+                syn::Expr::Path(path) => {
+                    // Don't bind futures that are already a path.
+                    // This prevents creating redundant stack space
+                    // for them.
+                    // Passing Futures by path requires those Futures to implement Unpin.
+                    // We check for this condition here in order to be able to
+                    // safely use Pin::new_unchecked(&mut #path) later on.
+                    future_let_bindings.push(quote! {
+                        #futures_crate::async_await::assert_fused_future(&#path);
+                        #futures_crate::async_await::assert_unpin(&#path);
+                    });
+                    path
+                },
+                _ => {
+                    // Bind and pin the resulting Future on the stack. This is
+                    // necessary to support direct select! calls on !Unpin
+                    // Futures. The Future is not explicitly pinned here with
+                    // a Pin call, but assumed as pinned. The actual Pin is
+                    // created inside the poll() function below to defer the
+                    // creation of the temporary pointer, which would otherwise
+                    // increase the size of the generated Future.
+                    // Safety: This is safe since the lifetime of the Future
+                    // is totally constraint to the lifetime of the select!
+                    // expression, and the Future can't get moved inside it
+                    // (it is shadowed).
+                    future_let_bindings.push(quote! {
+                        let mut #variant_name = #expr;
+                    });
+                    parse_quote! { #variant_name }
+                }
+            }
+        })
+        .collect();
+
+    // For each future, make an `&mut dyn FnMut(&mut Context<'_>) -> Option<Poll<__PrivResult<...>>`
+    // to use for polling that individual future. These will then be put in an array.
+    let poll_functions = bound_future_names.iter().zip(variant_names.iter())
+        .map(|(bound_future_name, variant_name)| {
+            // Below we lazily create the Pin on the Future below.
+            // This is done in order to avoid allocating memory in the generator
+            // for the Pin variable.
+            // Safety: This is safe because one of the following condition applies:
+            // 1. The Future is passed by the caller by name, and we assert that
+            //    it implements Unpin.
+            // 2. The Future is created in scope of the select! function and will
+            //    not be moved for the duration of it. It is thereby stack-pinned
+            quote! {
+                let mut #variant_name = |__cx: &mut #futures_crate::task::Context<'_>| {
+                    let mut #bound_future_name = unsafe {
+                        ::core::pin::Pin::new_unchecked(&mut #bound_future_name)
+                    };
+                    if #futures_crate::future::FusedFuture::is_terminated(&#bound_future_name) {
+                        None
+                    } else {
+                        Some(#futures_crate::future::FutureExt::poll_unpin(
+                            &mut #bound_future_name,
+                            __cx,
+                        ).map(#enum_ident::#variant_name))
+                    }
+                };
+                let #variant_name: &mut dyn FnMut(
+                    &mut #futures_crate::task::Context<'_>
+                ) -> Option<#futures_crate::task::Poll<_>> = &mut #variant_name;
+            }
+        });
+
+    let none_polled = if parsed.complete.is_some() {
+        quote! {
+            #futures_crate::task::Poll::Ready(#enum_ident::Complete)
+        }
+    } else {
+        quote! {
+            panic!("all futures in select! were completed,\
+                    but no `complete =>` handler was provided")
+        }
+    };
+
+    let branches = parsed.normal_fut_handlers.into_iter()
+        .zip(variant_names.iter())
+        .map(|((pat, expr), variant_name)| {
+            quote! {
+                #enum_ident::#variant_name(#pat) => { #expr },
+            }
+        });
+    let branches = quote! { #( #branches )* };
+
+    let complete_branch = parsed.complete.map(|complete_expr| {
+        quote! {
+            #enum_ident::Complete => { #complete_expr },
+        }
+    });
+
+    let branches = quote! {
+        #branches
+        #complete_branch
+    };
+
+    let await_select_fut = if parsed.default.is_some() {
+        // For select! with default this returns the Poll result
+        quote! {
+            __poll_fn(&mut #futures_crate::task::Context::from_waker(
+                #futures_crate::task::noop_waker_ref()
+            ))
+        }
+    } else {
+        quote! {
+            #futures_crate::future::poll_fn(__poll_fn).await
+        }
+    };
+
+    let execute_result_expr = if let Some(default_expr) = &parsed.default {
+        // For select! with default __select_result is a Poll, otherwise not
+        quote! {
+            match __select_result {
+                #futures_crate::task::Poll::Ready(result) => match result {
+                    #branches
+                },
+                _ => #default_expr
+            }
+        }
+    } else {
+        quote! {
+            match __select_result {
+                #branches
+            }
+        }
+    };
+
+    let shuffle = if random {
+        quote! {
+            #futures_crate::async_await::shuffle(&mut __select_arr);
+        }
+    } else {
+        quote!()
+    };
+
+    TokenStream::from(quote! { {
+        #enum_item
+
+        let __select_result = {
+            #( #future_let_bindings )*
+
+            let mut __poll_fn = |__cx: &mut #futures_crate::task::Context<'_>| {
+                let mut __any_polled = false;
+
+                #( #poll_functions )*
+
+                let mut __select_arr = [#( #variant_names ),*];
+                #shuffle
+                for poller in &mut __select_arr {
+                    let poller: &mut &mut dyn FnMut(
+                        &mut #futures_crate::task::Context<'_>
+                    ) -> Option<#futures_crate::task::Poll<_>> = poller;
+                    match poller(__cx) {
+                        Some(x @ #futures_crate::task::Poll::Ready(_)) =>
+                            return x,
+                        Some(#futures_crate::task::Poll::Pending) => {
+                            __any_polled = true;
+                        }
+                        None => {}
+                    }
+                }
+
+                if !__any_polled {
+                    #none_polled
+                } else {
+                    #futures_crate::task::Poll::Pending
+                }
+            };
+
+            #await_select_fut
+        };
+
+        #execute_result_expr
+    } })
+}