Migrate from failure to thiserror

The failure crate invents its own traits that don't use
std::error::Error (because failure predates certain features added to
Error); this prevents using ? on an error from failure in a function
using Error. The thiserror crate integrates with the standard Error
trait instead.

cranelift/codegen/src/verifier/mod.rs

@@ -77,7 +77,7 @@ use alloc::string::String;
 use alloc::vec::Vec;
 use core::cmp::Ordering;
 use core::fmt::{self, Display, Formatter, Write};
-use failure_derive::Fail;
+use thiserror::Error;
 
 pub use self::cssa::verify_cssa;
 pub use self::liveness::verify_liveness;
@@ -127,7 +127,8 @@ mod liveness;
 mod locations;
 
 /// A verifier error.
-#[derive(Fail, Debug, PartialEq, Eq)]
+#[derive(Error, Debug, PartialEq, Eq)]
+#[error("{location}: {message}")]
 pub struct VerifierError {
     /// The entity causing the verifier error.
     pub location: AnyEntity,
@@ -135,12 +136,6 @@ pub struct VerifierError {
     pub message: String,
 }
 
-impl Display for VerifierError {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        write!(f, "{}: {}", self.location, self.message)
-    }
-}
-
 /// Result of a step in the verification process.
 ///
 /// Functions that return `VerifierStepResult<()>` should also take a
@@ -160,7 +155,7 @@ pub type VerifierStepResult<T> = Result<T, ()>;
 pub type VerifierResult<T> = Result<T, VerifierErrors>;
 
 /// List of verifier errors.
-#[derive(Fail, Debug, Default, PartialEq, Eq)]
+#[derive(Error, Debug, Default, PartialEq, Eq)]
 pub struct VerifierErrors(pub Vec<VerifierError>);
 
 impl VerifierErrors {