Move cabi_realloc to a wit-bindgen-rt crate (#876)

* Move `cabi_realloc` to a `wit-bindgen-rt` crate

This commit extracts out a `wit-bindgen-rt` crate which unconditionally
provides the `cabi_realloc` function. This'll exist for `cargo
component` to add a dependency on and otherwise the `wit-bindgen` crate
isn't actually need at runtime at all.

* Remove realloc feature gate

* Add runtime to publish script

* Remove realloc feature guard in build script

.github/workflows/main.yml

@@ -137,6 +137,12 @@ jobs:
     - run: cargo build --no-default-features --features csharp
     - run: cargo build --no-default-features --features markdown
 
+    # Feature combos of the `wit-bindgen` crate
+    - run: cargo build --target wasm32-wasi -p wit-bindgen --no-default-features
+    - run: cargo build --target wasm32-wasi -p wit-bindgen --no-default-features --features realloc
+    - run: cargo build --target wasm32-wasi -p wit-bindgen --no-default-features --features macros
+    - run: cargo build --target wasm32-wasi -p wit-bindgen --no-default-features --features macros,realloc
+
     # Verity that documentation can be generated for the rust bindings crate.
     - run: cargo doc -p wit-bindgen --no-deps
       env:

ci/publish.rs

@@ -25,6 +25,7 @@ const CRATES_TO_PUBLISH: &[&str] = &[
     "wit-bindgen-teavm-java",
     "wit-bindgen-markdown",
     "wit-bindgen-rust-macro",
+    "wit-bindgen-rt",
     "wit-bindgen",
     "wit-bindgen-cli",
 ];

ci/rebuild-libcabi-realloc.sh

@@ -43,7 +43,7 @@ version=$(grep '^version =' ./Cargo.toml | sed 's/.*"\(.*\)"/\1/' | sed 's/\./_/
 
 sym=cabi_realloc_wit_bindgen_$version
 
-cat >./crates/guest-rust/src/cabi_realloc.rs <<-EOF
+cat >./crates/guest-rust/rt/src/cabi_realloc.rs <<-EOF
 // This file is generated by $0
 
 #[no_mangle]
@@ -53,11 +53,11 @@ pub unsafe extern "C" fn $sym(
     align: usize,
     new_len: usize,
 ) -> *mut u8 {
-    crate::rt::cabi_realloc(old_ptr, old_len, align, new_len)
+    crate::cabi_realloc(old_ptr, old_len, align, new_len)
 }
 EOF
 
-cat >./crates/guest-rust/src/cabi_realloc.c <<-EOF
+cat >./crates/guest-rust/rt/src/cabi_realloc.c <<-EOF
 // This file is generated by $0
 
 #include <stdint.h>
@@ -70,16 +70,16 @@ void *cabi_realloc(void *ptr, size_t old_size, size_t align, size_t new_size) {
 }
 EOF
 
-rm -f crates/guest-rust/src/cabi_realloc.o
-$WASI_SDK_PATH/bin/clang crates/guest-rust/src/cabi_realloc.c \
-  -O -c -o crates/guest-rust/src/cabi_realloc.o
+rm -f crates/guest-rust/rt/src/cabi_realloc.o
+$WASI_SDK_PATH/bin/clang crates/guest-rust/rt/src/cabi_realloc.c \
+  -O -c -o crates/guest-rust/rt/src/cabi_realloc.o
 
 # 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/src/cabi_realloc.o \
-  -o ./crates/guest-rust/src/cabi_realloc.o
+wasm-tools strip -d producers ./crates/guest-rust/rt/src/cabi_realloc.o \
+  -o ./crates/guest-rust/rt/src/cabi_realloc.o
 
-rm -f crates/guest-rust/src/libwit_bindgen_cabi_realloc.a
-$WASI_SDK_PATH/bin/llvm-ar crus crates/guest-rust/src/libwit_bindgen_cabi_realloc.a \
-  crates/guest-rust/src/cabi_realloc.o
+rm -f crates/guest-rust/rt/src/libwit_bindgen_cabi_realloc.a
+$WASI_SDK_PATH/bin/llvm-ar crus crates/guest-rust/rt/src/libwit_bindgen_cabi_realloc.a \
+  crates/guest-rust/rt/src/cabi_realloc.o

crates/guest-rust/Cargo.toml

@@ -12,10 +12,11 @@ Used when compiling Rust programs to the component model.
 """
 
 [dependencies]
-wit-bindgen-rust-macro = { path = "../rust-macro", optional = true, version = "0.20.0" }
+wit-bindgen-rust-macro = { path = "./macro", optional = true, version = "0.20.0" }
+wit-bindgen-rt = { path = "./rt", optional = true, version = "0.20.0" }
 bitflags = { workspace = true }
 
 [features]
 default = ["macros", "realloc"]
-macros = ["wit-bindgen-rust-macro"]
-realloc = []
+macros = ["dep:wit-bindgen-rust-macro"]
+realloc = ["dep:wit-bindgen-rt"]

crates/guest-rust/rt/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "wit-bindgen-rt"
+version.workspace = true
+edition.workspace = true
+repository = 'https://github.com/bytecodealliance/wit-bindgen'
+license = "Apache-2.0 WITH LLVM-exception"
+homepage = 'https://github.com/bytecodealliance/wit-bindgen'
+description = """
+Runtime support for the `wit-bindgen` crate
+"""

crates/guest-rust/build.rs → crates/guest-rust/rt/build.rs

@@ -1,8 +1,4 @@
 fn main() {
-    if !cfg!(feature = "realloc") {
-        return;
-    }
-
     let target_arch = std::env::var("CARGO_CFG_TARGET_ARCH").unwrap_or(String::new());
     let target_family = std::env::var("CARGO_CFG_TARGET_FAMILY").unwrap_or(String::new());
 

crates/guest-rust/src/cabi_realloc.rs → crates/guest-rust/rt/src/cabi_realloc.rs

@@ -7,5 +7,5 @@ pub unsafe extern "C" fn cabi_realloc_wit_bindgen_0_20_0(
     align: usize,
     new_len: usize,
 ) -> *mut u8 {
-    crate::rt::cabi_realloc(old_ptr, old_len, align, new_len)
+    crate::cabi_realloc(old_ptr, old_len, align, new_len)
 }

crates/guest-rust/rt/src/lib.rs

@@ -0,0 +1,79 @@
+extern crate alloc;
+
+/// For more information about this see `./ci/rebuild-libcabi-realloc.sh`.
+mod cabi_realloc;
+
+/// This function is called from generated bindings and will be deleted by
+/// the linker. The purpose of this function is to force a reference to the
+/// symbol `cabi_realloc` to make its way through to the final linker
+/// command line. That way `wasm-ld` will pick it up, see it needs to be
+/// exported, and then export it.
+///
+/// For more information about this see `./ci/rebuild-libcabi-realloc.sh`.
+pub fn maybe_link_cabi_realloc() {
+    #[cfg(target_family = "wasm")]
+    {
+        extern "C" {
+            fn cabi_realloc(
+                old_ptr: *mut u8,
+                old_len: usize,
+                align: usize,
+                new_len: usize,
+            ) -> *mut u8;
+        }
+        // Force the `cabi_realloc` symbol to be referenced from here. This
+        // is done with a `#[used]` Rust `static` to ensure that this
+        // reference makes it all the way to the linker before it's
+        // considered for garbage collection. When the linker sees it it'll
+        // remove this `static` here (due to it not actually being needed)
+        // but the linker will have at that point seen the `cabi_realloc`
+        // symbol and it should get exported.
+        #[used]
+        static _NAME_DOES_NOT_MATTER: unsafe extern "C" fn(
+            *mut u8,
+            usize,
+            usize,
+            usize,
+        ) -> *mut u8 = cabi_realloc;
+    }
+}
+
+/// NB: this function is called by a generated function in the
+/// `cabi_realloc` module above. It's otherwise never explicitly called.
+///
+/// For more information about this see `./ci/rebuild-libcabi-realloc.sh`.
+pub unsafe fn cabi_realloc(
+    old_ptr: *mut u8,
+    old_len: usize,
+    align: usize,
+    new_len: usize,
+) -> *mut u8 {
+    use self::alloc::alloc::{self, Layout};
+
+    let layout;
+    let ptr = if old_len == 0 {
+        if new_len == 0 {
+            return align as *mut u8;
+        }
+        layout = Layout::from_size_align_unchecked(new_len, align);
+        alloc::alloc(layout)
+    } else {
+        debug_assert_ne!(new_len, 0, "non-zero old_len requires non-zero new_len!");
+        layout = Layout::from_size_align_unchecked(old_len, align);
+        alloc::realloc(old_ptr, layout, new_len)
+    };
+    if ptr.is_null() {
+        // Print a nice message in debug mode, but in release mode don't
+        // pull in so many dependencies related to printing so just emit an
+        // `unreachable` instruction.
+        if cfg!(debug_assertions) {
+            alloc::handle_alloc_error(layout);
+        } else {
+            #[cfg(target_arch = "wasm32")]
+            core::arch::wasm32::unreachable();
+            #[cfg(not(target_arch = "wasm32"))]
+            unreachable!();
+        }
+    }
+    return ptr;
+}

crates/guest-rust/src/lib.rs

@@ -845,94 +845,20 @@ pub use wit_bindgen_rust_macro::generate;
 #[doc(hidden)]
 pub use bitflags;
 
-/// For more information about this see `./ci/rebuild-libcabi-realloc.sh`.
-#[cfg(feature = "realloc")]
-mod cabi_realloc;
-
 mod pre_wit_bindgen_0_20_0;
 
 #[cfg(docsrs)]
 pub mod examples;
 
 #[doc(hidden)]
 pub mod rt {
-    /// This function is called from generated bindings and will be deleted by
-    /// the linker. The purpose of this function is to force a reference to the
-    /// symbol `cabi_realloc` to make its way through to the final linker
-    /// command line. That way `wasm-ld` will pick it up, see it needs to be
-    /// exported, and then export it.
-    ///
-    /// For more information about this see `./ci/rebuild-libcabi-realloc.sh`.
     pub fn maybe_link_cabi_realloc() {
-        #[cfg(target_family = "wasm")]
-        {
-            #[cfg(feature = "realloc")]
-            extern "C" {
-                fn cabi_realloc(
-                    old_ptr: *mut u8,
-                    old_len: usize,
-                    align: usize,
-                    new_len: usize,
-                ) -> *mut u8;
-            }
-            // Force the `cabi_realloc` symbol to be referenced from here. This
-            // is done with a `#[used]` Rust `static` to ensure that this
-            // reference makes it all the way to the linker before it's
-            // considered for garbage collection. When the linker sees it it'll
-            // remove this `static` here (due to it not actually being needed)
-            // but the linker will have at that point seen the `cabi_realloc`
-            // symbol and it should get exported.
-            #[cfg(feature = "realloc")]
-            #[used]
-            static _NAME_DOES_NOT_MATTER: unsafe extern "C" fn(
-                *mut u8,
-                usize,
-                usize,
-                usize,
-            ) -> *mut u8 = cabi_realloc;
-        }
+        #[cfg(feature = "realloc")]
+        wit_bindgen_rt::maybe_link_cabi_realloc();
     }
 
-    /// NB: this function is called by a generated function in the
-    /// `cabi_realloc` module above. It's otherwise never explicitly called.
-    ///
-    /// For more information about this see `./ci/rebuild-libcabi-realloc.sh`.
     #[cfg(feature = "realloc")]
-    pub unsafe fn cabi_realloc(
-        old_ptr: *mut u8,
-        old_len: usize,
-        align: usize,
-        new_len: usize,
-    ) -> *mut u8 {
-        use alloc::Layout;
-
-        let layout;
-        let ptr = if old_len == 0 {
-            if new_len == 0 {
-                return align as *mut u8;
-            }
-            layout = Layout::from_size_align_unchecked(new_len, align);
-            alloc::alloc(layout)
-        } else {
-            debug_assert_ne!(new_len, 0, "non-zero old_len requires non-zero new_len!");
-            layout = Layout::from_size_align_unchecked(old_len, align);
-            alloc::realloc(old_ptr, layout, new_len)
-        };
-        if ptr.is_null() {
-            // Print a nice message in debug mode, but in release mode don't
-            // pull in so many dependencies related to printing so just emit an
-            // `unreachable` instruction.
-            if cfg!(debug_assertions) {
-                alloc::handle_alloc_error(layout);
-            } else {
-                #[cfg(target_arch = "wasm32")]
-                core::arch::wasm32::unreachable();
-                #[cfg(not(target_arch = "wasm32"))]
-                unreachable!();
-            }
-        }
-        return ptr;
-    }
+    pub use wit_bindgen_rt::cabi_realloc;
 
     pub use crate::pre_wit_bindgen_0_20_0::*;
 }