Refactor the wit-bindgen crate for being suitable again to include with the Rust standard library (#1369)

* Remove old wit-bindgen compat module

This has long since become unnecessary, so delete it.

* Merge `wit-bindgen-rt` back into `wit-bindgen`

This was originally done a long time ago at this point to split out the
"abi stable bits" from `wit-bindgen` for the purpose of `cargo
component` where one version of the macro was used in the binary itself
and a different version might be linked at runtime. Over time though
this has proven effectively intractable and isn't really serving much
purpose any more. This commit instead merges everything into the
`wit-bindgen` crate. This should make it easier to integrate elsewhere
and additionally integrate into Rust's standard library.

* Get `wit-bindgen` working without `bitflags` dep.

Generate a bare-bones `bitflags!` macro.

* Update rebuild script

* Fix CI issues

* More CI fixes

Author: alexcrichton

.github/workflows/main.yml

@@ -152,13 +152,13 @@ jobs:
     - run: cargo test
     - run: cargo test -p wit-bindgen-core
     - run: cargo test -p wit-bindgen
+    - run: cargo test -p wit-bindgen --all-features
     - run: cargo test -p wit-bindgen-rust
     - run: cargo test --workspace --exclude 'wit-bindgen*'
-    - run: cargo test -p wit-bindgen-rt --all-features
     - run: rustup update nightly --no-self-update
     - run: rustup component add miri --toolchain nightly
     - run: rustup component add rust-src --toolchain nightly
-    - run: cargo +nightly miri test -p wit-bindgen-rt --all-features
+    - run: cargo +nightly miri test -p wit-bindgen --all-features
 
   check:
     name: Check

Cargo.lock

@@ -43,10 +43,10 @@ version=$(./ci/print-current-version.sh | sed 's/\./_/g')
 
 realloc=cabi_realloc_wit_bindgen_$version
 
-rm -f crates/guest-rust/rt/src/wit_bindgen_*.{rs,o,c}
-rm -f crates/guest-rust/rt/src/libwit_bindgen_cabi.a
+rm -f crates/guest-rust/src/rt/wit_bindgen_*.{rs,o,c}
+rm -f crates/guest-rust/src/rt/libwit_bindgen_cabi.a
 
-cat >./crates/guest-rust/rt/src/wit_bindgen_cabi_realloc.rs <<-EOF
+cat >./crates/guest-rust/src/rt/wit_bindgen_cabi_realloc.rs <<-EOF
 // This file is generated by $0
 
 #[unsafe(no_mangle)]
@@ -56,11 +56,11 @@ pub unsafe extern "C" fn $realloc(
     align: usize,
     new_len: usize,
 ) -> *mut u8 {
-    crate::cabi_realloc(old_ptr, old_len, align, new_len)
+    crate::rt::cabi_realloc(old_ptr, old_len, align, new_len)
 }
 EOF
 
-cat >./crates/guest-rust/rt/src/wit_bindgen_cabi_realloc.c <<-EOF
+cat >./crates/guest-rust/src/rt/wit_bindgen_cabi_realloc.c <<-EOF
 // This file is generated by $0
 
 #include <stdint.h>
@@ -73,7 +73,7 @@ void *cabi_realloc(void *ptr, size_t old_size, size_t align, size_t new_size) {
 }
 EOF
 
-cat >./crates/guest-rust/rt/src/wit_bindgen_cabi_wasip3.c <<-EOF
+cat >./crates/guest-rust/src/rt/wit_bindgen_cabi_wasip3.c <<-EOF
 // This file is generated by $0
 
 #include <stdlib.h>
@@ -90,18 +90,18 @@ EOF
 
 build() {
   file=$1
-  $WASI_SDK_PATH/bin/clang crates/guest-rust/rt/src/$1.c \
-    -O -c -o crates/guest-rust/rt/src/$1.o -mcpu=mvp
+  $WASI_SDK_PATH/bin/clang crates/guest-rust/src/rt/$1.c \
+    -O -c -o crates/guest-rust/src/rt/$1.o -mcpu=mvp
   # Remove the `producers` section. This appears to differ whether the host for
   # clang is either macOS or Linux. Not needed here anyway, so discard it to help
   # either host produce the same object.
-  wasm-tools strip -d producers ./crates/guest-rust/rt/src/$1.o \
-    -o ./crates/guest-rust/rt/src/$1.o
+  wasm-tools strip -d producers ./crates/guest-rust/src/rt/$1.o \
+    -o ./crates/guest-rust/src/rt/$1.o
 }
 
 build wit_bindgen_cabi_realloc
 build wit_bindgen_cabi_wasip3
 
-$WASI_SDK_PATH/bin/llvm-ar crus crates/guest-rust/rt/src/libwit_bindgen_cabi.a \
-  crates/guest-rust/rt/src/wit_bindgen_cabi_realloc.o \
-  crates/guest-rust/rt/src/wit_bindgen_cabi_wasip3.o
+$WASI_SDK_PATH/bin/llvm-ar crus crates/guest-rust/src/rt/libwit_bindgen_cabi.a \
+  crates/guest-rust/src/rt/wit_bindgen_cabi_realloc.o \
+  crates/guest-rust/src/rt/wit_bindgen_cabi_wasip3.o

ci/rebuild-libwit-bindgen-cabi.sh

@@ -17,10 +17,21 @@ all-features = true
 
 [dependencies]
 wit-bindgen-rust-macro = { path = "./macro", optional = true, version = "0.44.0" }
-wit-bindgen-rt = { path = "./rt", version = "0.44.0", features = ["bitflags"] }
+bitflags = { workspace = true, optional = true }
+futures = { version = "0.3.30", optional = true }
+once_cell = { version = "1.19.0", optional = true }
+
+# When built as part of libstd
+core = { version = "1.0", optional = true, package = "rustc-std-workspace-core" }
+alloc = { version = "1.0", optional = true, package = "rustc-std-workspace-alloc" }
 
 [features]
-default = ["macros", "realloc", "async"]
+default = ["macros", "realloc", "async", "std", "bitflags"]
 macros = ["dep:wit-bindgen-rust-macro"]
 realloc = []
-async = ["macros", "wit-bindgen-rt/async", "wit-bindgen-rust-macro/async"]
+std = []
+async = ["macros", "dep:futures", "dep:once_cell", "wit-bindgen-rust-macro/async"]
+bitflags = ["dep:bitflags"]
+
+# Unstable feature to support being a libstd dependency
+rustc-dep-of-std = ["dep:core", "dep:alloc"]

crates/guest-rust/Cargo.toml

@@ -16,6 +16,7 @@ fn main() {
 
     let mut src = env::current_dir().unwrap();
     src.push("src");
+    src.push("rt");
     src.push("libwit_bindgen_cabi.a");
 
     let dst_name = format!(