[wasm] Have the WasmError::User member be a String;

cranelift/wasm/Cargo.toml

@@ -27,7 +27,7 @@ target-lexicon = "0.4.0"
 
 [features]
 default = ["std"]
-std = ["cranelift-codegen/std", "cranelift-frontend/std", "wasmparser/std", "failure/std"]
+std = ["cranelift-codegen/std", "cranelift-frontend/std", "wasmparser/std"]
 core = ["hashmap_core", "cranelift-codegen/core", "cranelift-frontend/core", "wasmparser/core"]
 
 [badges]

cranelift/wasm/src/environ/spec.rs

@@ -68,17 +68,9 @@ pub enum WasmError {
     #[fail(display = "Implementation limit exceeded")]
     ImplLimitExceeded,
 
-    /// Any user-defined error. Requires an std build, where failure::Error is defined.
-    #[cfg(feature = "std")]
+    /// Any user-defined error.
     #[fail(display = "User error: {}", _0)]
-    User(failure::Error),
-}
-
-#[cfg(feature = "std")]
-impl From<failure::Error> for WasmError {
-    fn from(err: failure::Error) -> Self {
-        WasmError::User(err)
-    }
+    User(std::string::String),
 }
 
 impl From<BinaryReaderError> for WasmError {