From 90bd0f0589ef54a79ed00dc8be6dfa2088914421 Mon Sep 17 00:00:00 2001
From: Arsenii Lyashenko <arsenylyashenko.3@gmail.com>
Date: Sat, 7 Dec 2024 04:09:45 +0300
Subject: [PATCH] Add `no_std` support to `wasm-encoder` (#1938)

* Add `no_std` support to `wasm-encoder`

* Manual fmt

* Implement `Error` only with `std` enabled

* Fix error implementation

* Update MSRV comment
---
 Cargo.toml                                    |  9 ++++---
 crates/wasm-encoder/Cargo.toml                |  5 +++-
 crates/wasm-encoder/build.rs                  | 27 +++++++++++++++++++
 crates/wasm-encoder/src/component.rs          |  1 +
 crates/wasm-encoder/src/component/aliases.rs  |  1 +
 crates/wasm-encoder/src/component/builder.rs  |  3 ++-
 .../wasm-encoder/src/component/canonicals.rs  |  1 +
 .../wasm-encoder/src/component/components.rs  |  1 +
 crates/wasm-encoder/src/component/exports.rs  |  1 +
 crates/wasm-encoder/src/component/imports.rs  |  1 +
 .../wasm-encoder/src/component/instances.rs   |  1 +
 crates/wasm-encoder/src/component/modules.rs  |  1 +
 crates/wasm-encoder/src/component/names.rs    |  3 ++-
 crates/wasm-encoder/src/component/start.rs    |  1 +
 crates/wasm-encoder/src/component/types.rs    |  1 +
 crates/wasm-encoder/src/core.rs               |  1 +
 crates/wasm-encoder/src/core/branch_hints.rs  |  3 ++-
 crates/wasm-encoder/src/core/code.rs          |  4 ++-
 crates/wasm-encoder/src/core/custom.rs        |  5 ++--
 crates/wasm-encoder/src/core/data.rs          |  1 +
 crates/wasm-encoder/src/core/dump.rs          |  6 +++--
 crates/wasm-encoder/src/core/elements.rs      |  3 ++-
 crates/wasm-encoder/src/core/exports.rs       |  1 +
 crates/wasm-encoder/src/core/functions.rs     |  1 +
 crates/wasm-encoder/src/core/globals.rs       |  1 +
 crates/wasm-encoder/src/core/imports.rs       |  1 +
 crates/wasm-encoder/src/core/linking.rs       |  5 ++--
 crates/wasm-encoder/src/core/memories.rs      |  1 +
 crates/wasm-encoder/src/core/names.rs         |  5 ++--
 crates/wasm-encoder/src/core/producers.rs     |  4 +--
 crates/wasm-encoder/src/core/start.rs         |  1 +
 crates/wasm-encoder/src/core/tables.rs        |  1 +
 crates/wasm-encoder/src/core/tags.rs          |  1 +
 crates/wasm-encoder/src/core/types.rs         |  2 ++
 crates/wasm-encoder/src/lib.rs                |  8 ++++++
 crates/wasm-encoder/src/raw.rs                |  1 +
 crates/wasm-encoder/src/reencode.rs           | 21 ++++++++++-----
 crates/wasm-encoder/src/reencode/component.rs |  3 +++
 38 files changed, 110 insertions(+), 27 deletions(-)
 create mode 100644 crates/wasm-encoder/build.rs

diff --git a/Cargo.toml b/Cargo.toml
index 8f1e1e93bc..40fcf796bf 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -64,8 +64,9 @@ version = "0.221.2"
 # Current policy for wasm-tools is the same as Wasmtime which is that this
 # number can be no larger than the current stable release of Rust minus 2.
 #
-# NB: if this number increases to 1.81-or-later delete the
-# `crates/wasmparser/build.rs` script as it's no longer necessary.
+# NB: if this number increases to 1.81-or-later delete
+# `crates/wasmparser/build.rs` and `crates/wasm-encoder/build.rs` scripts
+# as they are no longer necessary.
 rust-version = "1.76.0"
 
 [workspace.dependencies]
@@ -100,12 +101,12 @@ gimli = "0.30.0"
 id-arena = "2"
 
 wasm-compose = { version = "0.221.2", path = "crates/wasm-compose" }
-wasm-encoder = { version = "0.221.2", path = "crates/wasm-encoder", default-features = false }
+wasm-encoder = { version = "0.221.2", path = "crates/wasm-encoder", default-features = false, features = ["std"] }
 wasm-metadata = { version = "0.221.2", path = "crates/wasm-metadata" }
 wasm-mutate = { version = "0.221.2", path = "crates/wasm-mutate" }
 wasm-shrink = { version = "0.221.2", path = "crates/wasm-shrink" }
 wasm-smith = { version = "0.221.2", path = "crates/wasm-smith" }
-wasmparser = { version = "0.221.2", path = "crates/wasmparser", default-features = false, features = ['std','simd'] }
+wasmparser = { version = "0.221.2", path = "crates/wasmparser", default-features = false, features = ['std', 'simd'] }
 wasmprinter = { version = "0.221.2", path = "crates/wasmprinter", default-features = false }
 wast = { version = "221.0.2", path = "crates/wast", default-features = false }
 wat = { version = "1.221.2", path = "crates/wat", default-features = false }
diff --git a/crates/wasm-encoder/Cargo.toml b/crates/wasm-encoder/Cargo.toml
index eea73ba858..9332255e09 100644
--- a/crates/wasm-encoder/Cargo.toml
+++ b/crates/wasm-encoder/Cargo.toml
@@ -33,7 +33,10 @@ wasmparser = { path = "../wasmparser" }
 wasmprinter = { workspace = true }
 
 [features]
-default = ['component-model']
+default = ['std', 'component-model']
+
+# A feature which enables implementations of `std::error::Error` as appropriate.
+std = []
 
 # On-by-default: conditional support for emitting components in addition to
 # core modules.
diff --git a/crates/wasm-encoder/build.rs b/crates/wasm-encoder/build.rs
new file mode 100644
index 0000000000..305853b591
--- /dev/null
+++ b/crates/wasm-encoder/build.rs
@@ -0,0 +1,27 @@
+use std::process::Command;
+use std::str;
+
+fn main() {
+    // Temporary check to see if the rustc version >= 1.81 in which case the
+    // `Error` trait is always available. This is temporary because in the
+    // future the MSRV of this crate will be beyond 1.81 in which case this
+    // build script can be deleted.
+    let minor = rustc_minor_version().unwrap_or(0);
+    if minor >= 81 {
+        println!("cargo:rustc-cfg=core_error");
+    }
+    if minor >= 80 {
+        println!("cargo:rustc-check-cfg=cfg(core_error)");
+    }
+}
+
+fn rustc_minor_version() -> Option<u32> {
+    let rustc = std::env::var("RUSTC").unwrap();
+    let output = Command::new(rustc).arg("--version").output().ok()?;
+    let version = str::from_utf8(&output.stdout).ok()?;
+    let mut pieces = version.split('.');
+    if pieces.next() != Some("rustc 1") {
+        return None;
+    }
+    pieces.next()?.parse().ok()
+}
diff --git a/crates/wasm-encoder/src/component.rs b/crates/wasm-encoder/src/component.rs
index e3f36a88a2..03e441bdaa 100644
--- a/crates/wasm-encoder/src/component.rs
+++ b/crates/wasm-encoder/src/component.rs
@@ -23,6 +23,7 @@ pub use self::start::*;
 pub use self::types::*;
 
 use crate::{CustomSection, Encode, ProducersSection, RawCustomSection};
+use alloc::vec::Vec;
 
 // Core sorts extended by the component model
 const CORE_TYPE_SORT: u8 = 0x10;
diff --git a/crates/wasm-encoder/src/component/aliases.rs b/crates/wasm-encoder/src/component/aliases.rs
index 1e317fb0e2..07a93d0737 100644
--- a/crates/wasm-encoder/src/component/aliases.rs
+++ b/crates/wasm-encoder/src/component/aliases.rs
@@ -2,6 +2,7 @@ use super::{COMPONENT_SORT, CORE_MODULE_SORT, CORE_SORT, CORE_TYPE_SORT, TYPE_SO
 use crate::{
     encode_section, ComponentExportKind, ComponentSection, ComponentSectionId, Encode, ExportKind,
 };
+use alloc::vec::Vec;
 
 /// Represents the kinds of outer aliasable items in a component.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
diff --git a/crates/wasm-encoder/src/component/builder.rs b/crates/wasm-encoder/src/component/builder.rs
index d587ae99f5..c5d2deebf4 100644
--- a/crates/wasm-encoder/src/component/builder.rs
+++ b/crates/wasm-encoder/src/component/builder.rs
@@ -1,6 +1,7 @@
 use crate::component::*;
 use crate::{ExportKind, Module, RawSection, ValType};
-use std::mem;
+use alloc::vec::Vec;
+use core::mem;
 
 /// Convenience type to build a component incrementally and automatically keep
 /// track of index spaces.
diff --git a/crates/wasm-encoder/src/component/canonicals.rs b/crates/wasm-encoder/src/component/canonicals.rs
index 8bb4ad2c89..3407d5dd89 100644
--- a/crates/wasm-encoder/src/component/canonicals.rs
+++ b/crates/wasm-encoder/src/component/canonicals.rs
@@ -1,4 +1,5 @@
 use crate::{encode_section, ComponentSection, ComponentSectionId, Encode};
+use alloc::vec::Vec;
 
 /// Represents options for canonical function definitions.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
diff --git a/crates/wasm-encoder/src/component/components.rs b/crates/wasm-encoder/src/component/components.rs
index c08645e3b9..ad072a3a83 100644
--- a/crates/wasm-encoder/src/component/components.rs
+++ b/crates/wasm-encoder/src/component/components.rs
@@ -1,4 +1,5 @@
 use crate::{Component, ComponentSection, ComponentSectionId, Encode};
+use alloc::vec::Vec;
 
 /// An encoder for the component section of WebAssembly components.
 ///
diff --git a/crates/wasm-encoder/src/component/exports.rs b/crates/wasm-encoder/src/component/exports.rs
index 4d988e574b..314f9b31ed 100644
--- a/crates/wasm-encoder/src/component/exports.rs
+++ b/crates/wasm-encoder/src/component/exports.rs
@@ -3,6 +3,7 @@ use super::{
     VALUE_SORT,
 };
 use crate::{encode_section, ComponentSection, ComponentSectionId, ComponentTypeRef, Encode};
+use alloc::vec::Vec;
 
 /// Represents the kind of an export from a WebAssembly component.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
diff --git a/crates/wasm-encoder/src/component/imports.rs b/crates/wasm-encoder/src/component/imports.rs
index b818a17814..9bd6716895 100644
--- a/crates/wasm-encoder/src/component/imports.rs
+++ b/crates/wasm-encoder/src/component/imports.rs
@@ -2,6 +2,7 @@ use crate::{
     encode_section, ComponentExportKind, ComponentSection, ComponentSectionId, ComponentValType,
     Encode,
 };
+use alloc::vec::Vec;
 
 /// Represents the possible type bounds for type references.
 #[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
diff --git a/crates/wasm-encoder/src/component/instances.rs b/crates/wasm-encoder/src/component/instances.rs
index fd3fc3c3af..c7f26987bf 100644
--- a/crates/wasm-encoder/src/component/instances.rs
+++ b/crates/wasm-encoder/src/component/instances.rs
@@ -2,6 +2,7 @@ use super::CORE_INSTANCE_SORT;
 use crate::{
     encode_section, ComponentExportKind, ComponentSection, ComponentSectionId, Encode, ExportKind,
 };
+use alloc::vec::Vec;
 
 /// Represents an argument to a module instantiation.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
diff --git a/crates/wasm-encoder/src/component/modules.rs b/crates/wasm-encoder/src/component/modules.rs
index 437cd353af..ee43e486f7 100644
--- a/crates/wasm-encoder/src/component/modules.rs
+++ b/crates/wasm-encoder/src/component/modules.rs
@@ -1,4 +1,5 @@
 use crate::{ComponentSection, ComponentSectionId, Encode, Module};
+use alloc::vec::Vec;
 
 /// An encoder for the module section of WebAssembly components.
 ///
diff --git a/crates/wasm-encoder/src/component/names.rs b/crates/wasm-encoder/src/component/names.rs
index f09b2152b1..bd2df42c01 100644
--- a/crates/wasm-encoder/src/component/names.rs
+++ b/crates/wasm-encoder/src/component/names.rs
@@ -1,4 +1,5 @@
-use std::borrow::Cow;
+use alloc::borrow::Cow;
+use alloc::vec::Vec;
 
 use super::*;
 use crate::{encoding_size, ExportKind, NameMap, SectionId};
diff --git a/crates/wasm-encoder/src/component/start.rs b/crates/wasm-encoder/src/component/start.rs
index d4b60e1dfc..7a68de9ea0 100644
--- a/crates/wasm-encoder/src/component/start.rs
+++ b/crates/wasm-encoder/src/component/start.rs
@@ -1,4 +1,5 @@
 use crate::{ComponentSection, ComponentSectionId, Encode};
+use alloc::vec::Vec;
 
 /// An encoder for the start section of WebAssembly components.
 ///
diff --git a/crates/wasm-encoder/src/component/types.rs b/crates/wasm-encoder/src/component/types.rs
index 39853d5f7b..ccb45447c4 100644
--- a/crates/wasm-encoder/src/component/types.rs
+++ b/crates/wasm-encoder/src/component/types.rs
@@ -3,6 +3,7 @@ use crate::{
     encode_section, Alias, ComponentExportKind, ComponentOuterAliasKind, ComponentSection,
     ComponentSectionId, ComponentTypeRef, CoreTypeEncoder, Encode, EntityType, ValType,
 };
+use alloc::vec::Vec;
 
 /// Represents the type of a core module.
 #[derive(Debug, Clone, Default)]
diff --git a/crates/wasm-encoder/src/core.rs b/crates/wasm-encoder/src/core.rs
index f671a05925..48ce15e7b8 100644
--- a/crates/wasm-encoder/src/core.rs
+++ b/crates/wasm-encoder/src/core.rs
@@ -37,6 +37,7 @@ pub use tags::*;
 pub use types::*;
 
 use crate::Encode;
+use alloc::vec::Vec;
 
 pub(crate) const CORE_FUNCTION_SORT: u8 = 0x00;
 pub(crate) const CORE_TABLE_SORT: u8 = 0x01;
diff --git a/crates/wasm-encoder/src/core/branch_hints.rs b/crates/wasm-encoder/src/core/branch_hints.rs
index 0f325377ef..96231b11e9 100644
--- a/crates/wasm-encoder/src/core/branch_hints.rs
+++ b/crates/wasm-encoder/src/core/branch_hints.rs
@@ -1,5 +1,6 @@
 use crate::{CustomSection, Encode, Section, SectionId};
-use std::borrow::Cow;
+use alloc::borrow::Cow;
+use alloc::vec::Vec;
 
 /// Helper structure to encode the `metadata.code.branch_hint` custom section.
 ///
diff --git a/crates/wasm-encoder/src/core/code.rs b/crates/wasm-encoder/src/core/code.rs
index c2bcdafd6a..0b544fe914 100644
--- a/crates/wasm-encoder/src/core/code.rs
+++ b/crates/wasm-encoder/src/core/code.rs
@@ -1,5 +1,7 @@
 use crate::{encode_section, Encode, HeapType, RefType, Section, SectionId, ValType};
-use std::borrow::Cow;
+use alloc::borrow::Cow;
+use alloc::vec;
+use alloc::vec::Vec;
 
 /// An encoder for the code section.
 ///
diff --git a/crates/wasm-encoder/src/core/custom.rs b/crates/wasm-encoder/src/core/custom.rs
index 1fbeb10223..552011550a 100644
--- a/crates/wasm-encoder/src/core/custom.rs
+++ b/crates/wasm-encoder/src/core/custom.rs
@@ -1,6 +1,6 @@
-use std::borrow::Cow;
-
 use crate::{encoding_size, Encode, Section, SectionId};
+use alloc::borrow::Cow;
+use alloc::vec::Vec;
 
 /// A custom section holding arbitrary data.
 #[derive(Clone, Debug, PartialEq)]
@@ -47,6 +47,7 @@ impl Section for RawCustomSection<'_> {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use alloc::vec;
 
     #[test]
     fn test_custom_section() {
diff --git a/crates/wasm-encoder/src/core/data.rs b/crates/wasm-encoder/src/core/data.rs
index 6f408befe5..9d7ac752a3 100644
--- a/crates/wasm-encoder/src/core/data.rs
+++ b/crates/wasm-encoder/src/core/data.rs
@@ -1,4 +1,5 @@
 use crate::{encode_section, encoding_size, ConstExpr, Encode, Section, SectionId};
+use alloc::vec::Vec;
 
 /// An encoder for the data section.
 ///
diff --git a/crates/wasm-encoder/src/core/dump.rs b/crates/wasm-encoder/src/core/dump.rs
index f9c01d9e1e..5eec139f39 100644
--- a/crates/wasm-encoder/src/core/dump.rs
+++ b/crates/wasm-encoder/src/core/dump.rs
@@ -1,6 +1,8 @@
-use std::borrow::Cow;
-
 use crate::{CustomSection, Encode, Section};
+use alloc::borrow::Cow;
+use alloc::string::String;
+use alloc::vec;
+use alloc::vec::Vec;
 
 /// The "core" custom section for coredumps, as described in the
 /// [tool-conventions
diff --git a/crates/wasm-encoder/src/core/elements.rs b/crates/wasm-encoder/src/core/elements.rs
index e44022e7fd..b3a3b5139d 100644
--- a/crates/wasm-encoder/src/core/elements.rs
+++ b/crates/wasm-encoder/src/core/elements.rs
@@ -1,5 +1,6 @@
 use crate::{encode_section, ConstExpr, Encode, RefType, Section, SectionId};
-use std::borrow::Cow;
+use alloc::borrow::Cow;
+use alloc::vec::Vec;
 
 /// An encoder for the element section.
 ///
diff --git a/crates/wasm-encoder/src/core/exports.rs b/crates/wasm-encoder/src/core/exports.rs
index 7d78220e28..a9422952a1 100644
--- a/crates/wasm-encoder/src/core/exports.rs
+++ b/crates/wasm-encoder/src/core/exports.rs
@@ -2,6 +2,7 @@ use super::{
     CORE_FUNCTION_SORT, CORE_GLOBAL_SORT, CORE_MEMORY_SORT, CORE_TABLE_SORT, CORE_TAG_SORT,
 };
 use crate::{encode_section, Encode, Section, SectionId};
+use alloc::vec::Vec;
 
 /// Represents the kind of an export from a WebAssembly module.
 #[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
diff --git a/crates/wasm-encoder/src/core/functions.rs b/crates/wasm-encoder/src/core/functions.rs
index e21d8c10a7..063b48953e 100644
--- a/crates/wasm-encoder/src/core/functions.rs
+++ b/crates/wasm-encoder/src/core/functions.rs
@@ -1,4 +1,5 @@
 use crate::{encode_section, Encode, Section, SectionId};
+use alloc::vec::Vec;
 
 /// An encoder for the function section of WebAssembly modules.
 ///
diff --git a/crates/wasm-encoder/src/core/globals.rs b/crates/wasm-encoder/src/core/globals.rs
index dcd96ac33f..ae1ba8789c 100644
--- a/crates/wasm-encoder/src/core/globals.rs
+++ b/crates/wasm-encoder/src/core/globals.rs
@@ -1,4 +1,5 @@
 use crate::{encode_section, ConstExpr, Encode, Section, SectionId, ValType};
+use alloc::vec::Vec;
 
 /// An encoder for the global section.
 ///
diff --git a/crates/wasm-encoder/src/core/imports.rs b/crates/wasm-encoder/src/core/imports.rs
index b3a0879da1..7db71ba4d0 100644
--- a/crates/wasm-encoder/src/core/imports.rs
+++ b/crates/wasm-encoder/src/core/imports.rs
@@ -2,6 +2,7 @@ use crate::{
     encode_section, Encode, GlobalType, MemoryType, Section, SectionId, TableType, TagType,
     CORE_FUNCTION_SORT, CORE_GLOBAL_SORT, CORE_MEMORY_SORT, CORE_TABLE_SORT, CORE_TAG_SORT,
 };
+use alloc::vec::Vec;
 
 /// The type of an entity.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
diff --git a/crates/wasm-encoder/src/core/linking.rs b/crates/wasm-encoder/src/core/linking.rs
index 9a2995721f..e75034c929 100644
--- a/crates/wasm-encoder/src/core/linking.rs
+++ b/crates/wasm-encoder/src/core/linking.rs
@@ -1,6 +1,7 @@
-use std::borrow::Cow;
-
 use crate::{encode_section, CustomSection, Encode, Section, SectionId};
+use alloc::borrow::Cow;
+use alloc::vec;
+use alloc::vec::Vec;
 
 const VERSION: u32 = 2;
 
diff --git a/crates/wasm-encoder/src/core/memories.rs b/crates/wasm-encoder/src/core/memories.rs
index d0c9087fff..40395306d0 100644
--- a/crates/wasm-encoder/src/core/memories.rs
+++ b/crates/wasm-encoder/src/core/memories.rs
@@ -1,4 +1,5 @@
 use crate::{encode_section, Encode, Section, SectionId};
+use alloc::vec::Vec;
 
 /// An encoder for the memory section.
 ///
diff --git a/crates/wasm-encoder/src/core/names.rs b/crates/wasm-encoder/src/core/names.rs
index 37f390d2e4..b3b96c8189 100644
--- a/crates/wasm-encoder/src/core/names.rs
+++ b/crates/wasm-encoder/src/core/names.rs
@@ -1,6 +1,7 @@
-use std::borrow::Cow;
-
 use crate::{encoding_size, CustomSection, Encode, Section, SectionId};
+use alloc::borrow::Cow;
+use alloc::vec;
+use alloc::vec::Vec;
 
 /// An encoder for the custom `name` section.
 ///
diff --git a/crates/wasm-encoder/src/core/producers.rs b/crates/wasm-encoder/src/core/producers.rs
index 00b3853f9c..38e7f0dab0 100644
--- a/crates/wasm-encoder/src/core/producers.rs
+++ b/crates/wasm-encoder/src/core/producers.rs
@@ -1,6 +1,6 @@
-use std::borrow::Cow;
-
 use crate::{CustomSection, Encode, Section, SectionId};
+use alloc::borrow::Cow;
+use alloc::vec::Vec;
 
 /// An encoder for the [producers custom
 /// section](https://github.com/WebAssembly/tool-conventions/blob/main/ProducersSection.md).
diff --git a/crates/wasm-encoder/src/core/start.rs b/crates/wasm-encoder/src/core/start.rs
index 8f12c0d0ef..22294a1952 100644
--- a/crates/wasm-encoder/src/core/start.rs
+++ b/crates/wasm-encoder/src/core/start.rs
@@ -1,4 +1,5 @@
 use crate::{encoding_size, Encode, Section, SectionId};
+use alloc::vec::Vec;
 
 /// An encoder for the start section of WebAssembly modules.
 ///
diff --git a/crates/wasm-encoder/src/core/tables.rs b/crates/wasm-encoder/src/core/tables.rs
index 3bb2d58e3a..6df54bc145 100644
--- a/crates/wasm-encoder/src/core/tables.rs
+++ b/crates/wasm-encoder/src/core/tables.rs
@@ -1,4 +1,5 @@
 use crate::{encode_section, ConstExpr, Encode, RefType, Section, SectionId, ValType};
+use alloc::vec::Vec;
 
 /// An encoder for the table section.
 ///
diff --git a/crates/wasm-encoder/src/core/tags.rs b/crates/wasm-encoder/src/core/tags.rs
index 413055f2af..008d40ebc2 100644
--- a/crates/wasm-encoder/src/core/tags.rs
+++ b/crates/wasm-encoder/src/core/tags.rs
@@ -1,4 +1,5 @@
 use crate::{encode_section, Encode, Section, SectionId};
+use alloc::vec::Vec;
 
 /// An encoder for the tag section.
 ///
diff --git a/crates/wasm-encoder/src/core/types.rs b/crates/wasm-encoder/src/core/types.rs
index 5dda818f37..e9611849d5 100644
--- a/crates/wasm-encoder/src/core/types.rs
+++ b/crates/wasm-encoder/src/core/types.rs
@@ -1,4 +1,6 @@
 use crate::{encode_section, Encode, Section, SectionId};
+use alloc::boxed::Box;
+use alloc::vec::Vec;
 
 /// Represents a subtype of possible other types in a WebAssembly module.
 #[derive(Debug, Clone)]
diff --git a/crates/wasm-encoder/src/lib.rs b/crates/wasm-encoder/src/lib.rs
index 5b436b3f8b..395e5cff55 100644
--- a/crates/wasm-encoder/src/lib.rs
+++ b/crates/wasm-encoder/src/lib.rs
@@ -69,8 +69,14 @@
 //! ```
 
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![no_std]
 #![deny(missing_docs, missing_debug_implementations)]
 
+extern crate alloc;
+#[cfg(feature = "std")]
+#[macro_use]
+extern crate std;
+
 #[cfg(feature = "component-model")]
 mod component;
 mod core;
@@ -83,6 +89,8 @@ pub use self::component::*;
 pub use self::core::*;
 pub use self::raw::*;
 
+use alloc::vec::Vec;
+
 /// Implemented by types that can be encoded into a byte sink.
 pub trait Encode {
     /// Encode the type into the given byte sink.
diff --git a/crates/wasm-encoder/src/raw.rs b/crates/wasm-encoder/src/raw.rs
index e7b4a5b5b8..ae761d4eb9 100644
--- a/crates/wasm-encoder/src/raw.rs
+++ b/crates/wasm-encoder/src/raw.rs
@@ -1,4 +1,5 @@
 use crate::{Encode, Section};
+use alloc::vec::Vec;
 
 /// A section made up of uninterpreted, raw bytes.
 ///
diff --git a/crates/wasm-encoder/src/reencode.rs b/crates/wasm-encoder/src/reencode.rs
index b85c406166..1d64d8f7be 100644
--- a/crates/wasm-encoder/src/reencode.rs
+++ b/crates/wasm-encoder/src/reencode.rs
@@ -3,8 +3,13 @@
 //! The [`RoundtripReencoder`] allows encoding identical wasm to the parsed
 //! input.
 
+#[cfg(all(not(feature = "std"), core_error))]
+use core::error::Error as StdError;
+#[cfg(feature = "std")]
+use std::error::Error as StdError;
+
 use crate::CoreTypeEncoder;
-use std::convert::Infallible;
+use core::convert::Infallible;
 
 #[cfg(feature = "component-model")]
 mod component;
@@ -546,8 +551,8 @@ impl<E> From<wasmparser::BinaryReaderError> for Error<E> {
     }
 }
 
-impl<E: std::fmt::Display> std::fmt::Display for Error<E> {
-    fn fmt(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl<E: core::fmt::Display> core::fmt::Display for Error<E> {
+    fn fmt(&self, fmt: &mut core::fmt::Formatter) -> core::fmt::Result {
         match self {
             Self::ParseError(_e) => {
                 write!(fmt, "There was an error when parsing")
@@ -574,8 +579,9 @@ impl<E: std::fmt::Display> std::fmt::Display for Error<E> {
     }
 }
 
-impl<E: 'static + std::error::Error> std::error::Error for Error<E> {
-    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+#[cfg(any(feature = "std", core_error))]
+impl<E: 'static + StdError> StdError for Error<E> {
+    fn source(&self) -> Option<&(dyn StdError + 'static)> {
         match self {
             Self::ParseError(e) => Some(e),
             Self::UserError(e) => Some(e),
@@ -602,7 +608,8 @@ impl Reencode for RoundtripReencoder {
 pub mod utils {
     use super::{Error, Reencode};
     use crate::{CoreTypeEncoder, Encode};
-    use std::ops::Range;
+    use alloc::vec::Vec;
+    use core::ops::Range;
 
     pub fn parse_core_module<T: ?Sized + Reencode>(
         reencoder: &mut T,
@@ -616,7 +623,7 @@ pub mod utils {
             last_section: &mut Option<crate::SectionId>,
             next_section: Option<crate::SectionId>,
         ) -> Result<(), Error<T::Error>> {
-            let after = std::mem::replace(last_section, next_section);
+            let after = core::mem::replace(last_section, next_section);
             let before = next_section;
             reencoder.intersperse_section_hook(module, after, before)
         }
diff --git a/crates/wasm-encoder/src/reencode/component.rs b/crates/wasm-encoder/src/reencode/component.rs
index d1c4d369e9..f8135e6822 100644
--- a/crates/wasm-encoder/src/reencode/component.rs
+++ b/crates/wasm-encoder/src/reencode/component.rs
@@ -1,4 +1,5 @@
 use crate::reencode::{Error, Reencode, RoundtripReencoder};
+use alloc::boxed::Box;
 
 #[allow(missing_docs)] // FIXME
 pub trait ReencodeComponent: Reencode {
@@ -386,6 +387,8 @@ pub mod component_utils {
     use super::super::utils::name_map;
     use super::ReencodeComponent;
     use crate::reencode::Error;
+    use alloc::boxed::Box;
+    use alloc::vec::Vec;
 
     pub fn parse_component<T: ?Sized + ReencodeComponent>(
         reencoder: &mut T,