Factor out the extern crate alloc into the guest-rust crate.

Author: sunfishcode

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

@@ -167,6 +167,10 @@ impl Generator for RustWasm {
             ));
         }
 
+        self.src.push_str("#[allow(unused_imports)]");
+        self.src
+            .push_str("use wit_bindgen_guest_rust::{alloc, vec::Vec, string::String};");
+
         self.sizes.fill(iface);
     }
 
@@ -510,9 +514,7 @@ impl Generator for RustWasm {
         } = f;
 
         if needs_cleanup_list {
-            self.src.push_str("extern crate alloc;\n");
-            self.src
-                .push_str("let mut cleanup_list = alloc::vec::Vec::new();\n");
+            self.src.push_str("let mut cleanup_list = Vec::new();\n");
         }
         self.src.push_str(&String::from(src));
 
@@ -760,15 +762,14 @@ impl FunctionBindgen<'_> {
     fn emit_cleanup(&mut self) {
         for (ptr, layout) in mem::take(&mut self.cleanup) {
             self.push_str(&format!(
-                "if {layout}.size() != 0 {{\nextern crate alloc;\nalloc::alloc::dealloc({ptr}, {layout});\n}}\n"
+                "if {layout}.size() != 0 {{\nalloc::dealloc({ptr}, {layout});\n}}\n"
             ));
         }
         if self.needs_cleanup_list {
             self.push_str(
                 "for (ptr, layout) in cleanup_list {\n
                     if layout.size() != 0 {\n
-                        extern crate alloc;\n
-                        alloc::alloc::dealloc(ptr, layout);\n
+                        alloc::dealloc(ptr, layout);\n
                     }\n
                 }\n",
             );
@@ -1346,9 +1347,8 @@ impl Bindgen for FunctionBindgen<'_> {
                 let tmp = self.tmp();
                 let len = format!("len{}", tmp);
                 self.push_str(&format!("let {} = {} as usize;\n", len, operands[1]));
-                self.push_str("extern crate alloc;\n");
                 let result = format!(
-                    "alloc::vec::Vec::from_raw_parts({} as *mut _, {1}, {1})",
+                    "Vec::from_raw_parts({} as *mut _, {1}, {1})",
                     operands[0], len
                 );
                 results.push(result);
@@ -1378,21 +1378,14 @@ impl Bindgen for FunctionBindgen<'_> {
                 let tmp = self.tmp();
                 let len = format!("len{}", tmp);
                 self.push_str(&format!("let {} = {} as usize;\n", len, operands[1]));
-                self.push_str("extern crate alloc;\n");
                 let result = format!(
-                    "alloc::vec::Vec::from_raw_parts({} as *mut _, {1}, {1})",
+                    "Vec::from_raw_parts({} as *mut _, {1}, {1})",
                     operands[0], len
                 );
                 if unchecked {
-                    results.push(format!(
-                        "alloc::string::String::from_utf8_unchecked({})",
-                        result
-                    ));
+                    results.push(format!("String::from_utf8_unchecked({})", result));
                 } else {
-                    results.push(format!(
-                        "alloc::string::String::from_utf8({}).unwrap()",
-                        result
-                    ));
+                    results.push(format!("String::from_utf8({}).unwrap()", result));
                 }
             }
 
@@ -1411,13 +1404,13 @@ impl Bindgen for FunctionBindgen<'_> {
                 let size = self.gen.sizes.size(element);
                 let align = self.gen.sizes.align(element);
                 self.push_str(&format!(
-                    "let {layout} = core::alloc::Layout::from_size_align_unchecked({vec}.len() * {size}, {align});\n",
+                    "let {layout} = alloc::Layout::from_size_align_unchecked({vec}.len() * {size}, {align});\n",
                 ));
                 self.push_str(&format!(
-                    "let {result} = if {layout}.size() != 0\n{{\nextern crate alloc;\nlet ptr = alloc::alloc::alloc({layout});\n",
+                    "let {result} = if {layout}.size() != 0\n{{\nlet ptr = alloc::alloc({layout});\n",
                 ));
                 self.push_str(&format!(
-                    "if ptr.is_null()\n{{\nextern crate alloc;\nalloc::alloc::handle_alloc_error({layout});\n}}\nptr\n}}",
+                    "if ptr.is_null()\n{{\nalloc::handle_alloc_error({layout});\n}}\nptr\n}}",
                 ));
                 self.push_str(&format!("else {{\ncore::ptr::null_mut()\n}};\n",));
                 self.push_str(&format!("for (i, e) in {vec}.into_iter().enumerate() {{\n",));
@@ -1453,9 +1446,8 @@ impl Bindgen for FunctionBindgen<'_> {
                     "let {len} = {operand1};\n",
                     operand1 = operands[1]
                 ));
-                self.push_str("extern crate alloc;\n");
                 self.push_str(&format!(
-                    "let mut {result} = alloc::vec::Vec::with_capacity({len} as usize);\n",
+                    "let mut {result} = Vec::with_capacity({len} as usize);\n",
                 ));
 
                 self.push_str("for i in 0..");

crates/gen-rust-lib/src/lib.rs

@@ -213,9 +213,7 @@ pub trait RustGenerator {
                 TypeMode::AllBorrowed(lt) | TypeMode::LeafBorrowed(lt) => {
                     self.print_borrowed_str(lt)
                 }
-                TypeMode::Owned | TypeMode::HandlesBorrowed(_) => {
-                    self.push_str("alloc::string::String")
-                }
+                TypeMode::Owned | TypeMode::HandlesBorrowed(_) => self.push_str("String"),
             },
         }
     }
@@ -337,13 +335,13 @@ pub trait RustGenerator {
                 if iface.all_bits_valid(ty) {
                     self.print_borrowed_slice(iface, false, ty, lt);
                 } else {
-                    self.push_str("alloc::vec::Vec<");
+                    self.push_str("Vec<");
                     self.print_ty(iface, ty, mode);
                     self.push_str(">");
                 }
             }
             TypeMode::HandlesBorrowed(_) | TypeMode::Owned => {
-                self.push_str("alloc::vec::Vec<");
+                self.push_str("Vec<");
                 self.print_ty(iface, ty, mode);
                 self.push_str(">");
             }

crates/guest-rust/src/lib.rs

@@ -1,12 +1,12 @@
 #![no_std]
 
-extern crate alloc;
+extern crate alloc as liballoc;
 
-use alloc::boxed::Box;
 use core::fmt;
 use core::marker;
 use core::mem;
 use core::ops::Deref;
+use liballoc::boxed::Box;
 
 #[cfg(feature = "macros")]
 pub use wit_bindgen_guest_rust_macro::{export, import};
@@ -15,6 +15,9 @@ pub use wit_bindgen_guest_rust_macro::{export, import};
 #[doc(hidden)]
 pub use bitflags;
 
+// Re-export things from liballoc for convenient use.
+pub use liballoc::{alloc, string, vec};
+
 /// A type for handles to resources that appear in exported functions.
 ///
 /// This type is used as `Handle<T>` for argument types and return values of
@@ -128,7 +131,7 @@ pub unsafe trait LocalHandle: HandleType {
 
 #[doc(hidden)]
 pub mod rt {
-    use ::alloc::alloc::{self, Layout};
+    use super::alloc::{self, Layout};
 
     #[no_mangle]
     unsafe extern "C" fn cabi_realloc(