Prefer enum Endian in rustc_target::Target

compiler/rustc_target/src/abi/mod.rs

@@ -4,11 +4,14 @@ pub use Primitive::*;
 use crate::spec::Target;
 
 use std::convert::{TryFrom, TryInto};
+use std::fmt;
 use std::num::NonZeroUsize;
 use std::ops::{Add, AddAssign, Deref, Mul, Range, RangeInclusive, Sub};
+use std::str::FromStr;
 
 use rustc_index::vec::{Idx, IndexVec};
 use rustc_macros::HashStable_Generic;
+use rustc_serialize::json::{Json, ToJson};
 use rustc_span::Span;
 
 pub mod call;
@@ -152,22 +155,19 @@ impl TargetDataLayout {
         }
 
         // Perform consistency checks against the Target information.
-        let endian_str = match dl.endian {
-            Endian::Little => "little",
-            Endian::Big => "big",
-        };
-        if endian_str != target.endian {
+        if dl.endian != target.endian {
             return Err(format!(
                 "inconsistent target specification: \"data-layout\" claims \
-                                architecture is {}-endian, while \"target-endian\" is `{}`",
-                endian_str, target.endian
+                 architecture is {}-endian, while \"target-endian\" is `{}`",
+                dl.endian.as_str(),
+                target.endian.as_str(),
             ));
         }
 
         if dl.pointer_size.bits() != target.pointer_width.into() {
             return Err(format!(
                 "inconsistent target specification: \"data-layout\" claims \
-                                pointers are {}-bit, while \"target-pointer-width\" is `{}`",
+                 pointers are {}-bit, while \"target-pointer-width\" is `{}`",
                 dl.pointer_size.bits(),
                 target.pointer_width
             ));
@@ -234,6 +234,39 @@ pub enum Endian {
     Big,
 }
 
+impl Endian {
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            Self::Little => "little",
+            Self::Big => "big",
+        }
+    }
+}
+
+impl fmt::Debug for Endian {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(self.as_str())
+    }
+}
+
+impl FromStr for Endian {
+    type Err = String;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "little" => Ok(Self::Little),
+            "big" => Ok(Self::Big),
+            _ => Err(format!(r#"unknown endian: "{}""#, s)),
+        }
+    }
+}
+
+impl ToJson for Endian {
+    fn to_json(&self) -> Json {
+        self.as_str().to_json()
+    }
+}
+
 /// Size of a type in bytes.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Encodable, Decodable)]
 #[derive(HashStable_Generic)]

compiler/rustc_target/src/spec/mod.rs

@@ -34,6 +34,7 @@
 //! the target's settings, though `target-feature` and `link-args` will *add*
 //! to the list specified by the target, rather than replace.
 
+use crate::abi::Endian;
 use crate::spec::abi::{lookup as lookup_abi, Abi};
 use crate::spec::crt_objects::{CrtObjects, CrtObjectsFallback};
 use rustc_serialize::json::{Json, ToJson};
@@ -705,8 +706,8 @@ pub struct TargetOptions {
     /// Whether the target is built-in or loaded from a custom target specification.
     pub is_builtin: bool,
 
-    /// String to use as the `target_endian` `cfg` variable. Defaults to "little".
-    pub endian: String,
+    /// Used as the `target_endian` `cfg` variable. Defaults to little endian.
+    pub endian: Endian,
     /// Width of c_int type. Defaults to "32".
     pub c_int_width: String,
     /// OS name to use for conditional compilation (`target_os`). Defaults to "none".
@@ -1010,7 +1011,7 @@ impl Default for TargetOptions {
     fn default() -> TargetOptions {
         TargetOptions {
             is_builtin: false,
-            endian: "little".to_string(),
+            endian: Endian::Little,
             c_int_width: "32".to_string(),
             os: "none".to_string(),
             env: String::new(),
@@ -1439,8 +1440,10 @@ impl Target {
             } );
         }
 
+        if let Some(s) = obj.find("target-endian").and_then(Json::as_string) {
+            base.endian = s.parse()?;
+        }
         key!(is_builtin, bool);
-        key!(endian = "target-endian");
         key!(c_int_width = "target-c-int-width");
         key!(os);
         key!(env);