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/isa/mod.rs

@@ -65,8 +65,8 @@ use crate::settings::SetResult;
 use crate::timing;
 use alloc::boxed::Box;
 use core::fmt;
-use failure_derive::Fail;
 use target_lexicon::{triple, Architecture, PointerWidth, Triple};
+use thiserror::Error;
 
 #[cfg(feature = "riscv")]
 mod riscv;
@@ -124,14 +124,14 @@ pub fn lookup_by_name(name: &str) -> Result<Builder, LookupError> {
 }
 
 /// Describes reason for target lookup failure
-#[derive(Fail, PartialEq, Eq, Copy, Clone, Debug)]
+#[derive(Error, PartialEq, Eq, Copy, Clone, Debug)]
 pub enum LookupError {
     /// Support for this target was disabled in the current build.
-    #[fail(display = "Support for this target is disabled")]
+    #[error("Support for this target is disabled")]
     SupportDisabled,
 
     /// Support for this target has not yet been implemented.
-    #[fail(display = "Support for this target has not been implemented yet")]
+    #[error("Support for this target has not been implemented yet")]
     Unsupported,
 }
 

cranelift/codegen/src/result.rs

@@ -1,19 +1,19 @@
 //! Result and error types representing the outcome of compiling a function.
 
 use crate::verifier::VerifierErrors;
-use failure_derive::Fail;
+use thiserror::Error;
 
 /// A compilation error.
 ///
 /// When Cranelift fails to compile a function, it will return one of these error codes.
-#[derive(Fail, Debug, PartialEq, Eq)]
+#[derive(Error, Debug, PartialEq, Eq)]
 pub enum CodegenError {
     /// A list of IR verifier errors.
     ///
     /// This always represents a bug, either in the code that generated IR for Cranelift, or a bug
     /// in Cranelift itself.
-    #[fail(display = "Verifier errors:\n{}", _0)]
-    Verifier(#[cause] VerifierErrors),
+    #[error("Verifier errors")]
+    Verifier(#[from] VerifierErrors),
 
     /// An implementation limit was exceeded.
     ///
@@ -21,22 +21,16 @@ pub enum CodegenError {
     /// limits][limits] that cause compilation to fail when they are exceeded.
     ///
     /// [limits]: https://cranelift.readthedocs.io/en/latest/ir.html#implementation-limits
-    #[fail(display = "Implementation limit exceeded")]
+    #[error("Implementation limit exceeded")]
     ImplLimitExceeded,
 
     /// The code size for the function is too large.
     ///
     /// Different target ISAs may impose a limit on the size of a compiled function. If that limit
     /// is exceeded, compilation fails.
-    #[fail(display = "Code for function is too large")]
+    #[error("Code for function is too large")]
     CodeTooLarge,
 }
 
 /// A convenient alias for a `Result` that uses `CodegenError` as the error type.
 pub type CodegenResult<T> = Result<T, CodegenError>;
-
-impl From<VerifierErrors> for CodegenError {
-    fn from(e: VerifierErrors) -> Self {
-        Self::Verifier(e)
-    }
-}

cranelift/codegen/src/settings.rs

@@ -26,7 +26,7 @@ use alloc::boxed::Box;
 use alloc::string::{String, ToString};
 use core::fmt;
 use core::str;
-use failure_derive::Fail;
+use thiserror::Error;
 
 /// A string-based configurator for settings groups.
 ///
@@ -165,18 +165,18 @@ impl Configurable for Builder {
 }
 
 /// An error produced when changing a setting.
-#[derive(Fail, Debug, PartialEq, Eq)]
+#[derive(Error, Debug, PartialEq, Eq)]
 pub enum SetError {
     /// No setting by this name exists.
-    #[fail(display = "No existing setting named '{}'", _0)]
+    #[error("No existing setting named '{0}'")]
     BadName(String),
 
     /// Type mismatch for setting (e.g., setting an enum setting as a bool).
-    #[fail(display = "Trying to set a setting with the wrong type")]
+    #[error("Trying to set a setting with the wrong type")]
     BadType,
 
     /// This is not a valid value for this setting.
-    #[fail(display = "Unexpected value for a setting, expected {}", _0)]
+    #[error("Unexpected value for a setting, expected {0}")]
     BadValue(String),
 }
 

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 {