fix(compiler) Implement thiserror::Error if std is present.

`thiserror` doesn't work in `no_std` mode, see dtolnay/thiserror#64.

lib/compiler/src/error.rs

@@ -1,48 +1,57 @@
 use crate::lib::std::string::String;
+#[cfg(feature = "std")]
 use thiserror::Error;
 
 // Compilation Errors
+//
+// If `std` feature is enable, we can't use `thiserror` until
+// https://github.com/dtolnay/thiserror/pull/64 is merged.
 
 /// The WebAssembly.CompileError object indicates an error during
 /// WebAssembly decoding or validation.
 ///
 /// This is based on the [Wasm Compile Error][compile-error] API.
 ///
 /// [compiler-error]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/CompileError
-#[derive(Error, Debug)]
+#[derive(Debug)]
+#[cfg_attr(feature = "std", derive(Error))]
 pub enum CompileError {
     /// A Wasm translation error occured.
-    #[error("WebAssembly translation error: {0}")]
-    Wasm(#[from] WasmError),
+    #[cfg_attr(feature = "std", error("WebAssembly translation error: {0}"))]
+    Wasm(#[cfg_attr(feature = "std", from)] WasmError),
 
     /// A compilation error occured.
-    #[error("Compilation error: {0}")]
+    #[cfg_attr(feature = "std", error("Compilation error: {0}"))]
     Codegen(String),
 
     /// The module did not pass validation.
-    #[error("Validation error: {0}")]
+    #[cfg_attr(feature = "std", error("Validation error: {0}"))]
     Validate(String),
 
     /// The compiler doesn't support a Wasm feature
-    #[error("Feature {0} is not yet supported")]
+    #[cfg_attr(feature = "std", error("Feature {0} is not yet supported"))]
     UnsupportedFeature(String),
 
     /// Insufficient resources available for execution.
-    #[error("Insufficient resources: {0}")]
+    #[cfg_attr(feature = "std", error("Insufficient resources: {0}"))]
     Resource(String),
 }
 
 /// A WebAssembly translation error.
 ///
 /// When a WebAssembly function can't be translated, one of these error codes will be returned
 /// to describe the failure.
-#[derive(Error, Debug)]
+#[derive(Debug)]
+#[cfg_attr(feature = "std", derive(Error))]
 pub enum WasmError {
     /// The input WebAssembly code is invalid.
     ///
     /// This error code is used by a WebAssembly translator when it encounters invalid WebAssembly
     /// code. This should never happen for validated WebAssembly code.
-    #[error("Invalid input WebAssembly code at offset {offset}: {message}")]
+    #[cfg_attr(
+        feature = "std",
+        error("Invalid input WebAssembly code at offset {offset}: {message}")
+    )]
     InvalidWebAssembly {
         /// A string describing the validation error.
         message: String,
@@ -53,17 +62,27 @@ pub enum WasmError {
     /// A feature used by the WebAssembly code is not supported by the embedding environment.
     ///
     /// Embedding environments may have their own limitations and feature restrictions.
-    #[error("Unsupported feature: {0}")]
+    #[cfg_attr(feature = "std", error("Unsupported feature: {0}"))]
     Unsupported(String),
 
     /// An implementation limit was exceeded.
-    #[error("Implementation limit exceeded")]
+    #[cfg_attr(feature = "std", error("Implementation limit exceeded"))]
     ImplLimitExceeded,
 
     /// A generic error.
-    #[error("{0}")]
+    #[cfg_attr(feature = "std", error("{0}"))]
     Generic(String),
 }
 
+/// The error that can happen while parsing a `str`
+/// to retrieve a [`CpuFeature`].
+#[derive(Debug)]
+#[cfg_attr(feature = "std", derive(Error))]
+pub enum ParseCpuFeatureError {
+    /// The provided string feature doesn't exist
+    #[cfg_attr(feature = "std", error("CpuFeature {0} not recognized"))]
+    Missing(String),
+}
+
 /// A convenient alias for a `Result` that uses `WasmError` as the error type.
 pub type WasmResult<T> = Result<T, WasmError>;

lib/compiler/src/target.rs

@@ -1,12 +1,12 @@
 //! Target configuration
+use crate::error::ParseCpuFeatureError;
 use enumset::{EnumSet, EnumSetType};
 use std::str::FromStr;
 use std::string::ToString;
 pub use target_lexicon::{
     Architecture, BinaryFormat, CallingConvention, Endianness, OperatingSystem, PointerWidth,
     Triple,
 };
-use thiserror::Error;
 
 #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
 use raw_cpuid::CpuId;
@@ -112,15 +112,6 @@ impl CpuFeature {
     }
 }
 
-/// The error that can happen while parsing a `str`
-/// to retrieve a [`CpuFeature`].
-#[derive(Error, Debug)]
-pub enum ParseCpuFeatureError {
-    /// The provided string feature doesn't exist
-    #[error("CpuFeature {0} not recognized")]
-    Missing(String),
-}
-
 // This options should map exactly the GCC options indicated
 // here by architectures:
 //