Fixes #30: Remove JSON file descriptor parsing.

This didn't seem to be really used, and didn't match any rustc feature.

Cargo.toml

@@ -15,13 +15,6 @@ edition = "2018"
 failure = { version = "0.1.3", default-features = false, features = ["derive"] }
 failure_derive = { version = "0.1.3", default-features = false }
 
-[build-dependencies]
-serde_json = { version = "1.0", optional = true }
-
-[features]
-default = ["enable-serde"]
-enable-serde = ["serde_json"]
-
 [badges]
 maintenance = { status = "passively-maintained" }
 travis-ci = { repository = "CraneStation/target-lexicon" }

build.rs

@@ -11,9 +11,6 @@ use std::str::FromStr;
 
 extern crate alloc;
 
-#[cfg(feature = "enable-serde")]
-extern crate serde_json;
-
 // Include triple.rs and targets.rs so we can parse the TARGET environment variable.
 mod triple {
     include!("src/triple.rs");
@@ -38,97 +35,11 @@ mod parse_error {
 
 use self::triple::Triple;
 
-#[cfg(feature = "enable-serde")]
-fn triple_from_target(target: &str) -> Triple {
-    use self::triple::{Endianness, PointerWidth};
-    use serde_json::Value;
-    use std::ffi::OsString;
-    use std::fs;
-    use std::path::Path;
-
-    /// Assuming `target` is a path to a custom target json config file, open it
-    /// and build a `Triple` using its contents.
-    fn read_target_from_file(path: &Path) -> Triple {
-        let json = fs::read_to_string(path).expect("error reading target file");
-
-        let v: Value = serde_json::from_str(&json).expect("error parsing target file as json");
-        let target = v["llvm-target"]
-            .as_str()
-            .expect("error parsing \"llvm-target\" as a string");
-        let triple = Triple::from_str(target).expect("error parsing host target");
-
-        // Check that the JSON describes a known target configuration.
-        //
-        // Unfortunately, none of Rust's "arch", "os", "env", nor "vendor"
-        // fields directly correspond to triple fields, so we can't easily
-        // check them.
-        if let Some(endian) = v["target-endian"].as_str() {
-            assert_eq!(
-                endian,
-                match triple.endianness().unwrap() {
-                    Endianness::Little => "little",
-                    Endianness::Big => "big",
-                },
-                "\"target-endian\" field disagrees with the target triple"
-            );
-        }
-        if let Some(pointer_width) = v["target-pointer-width"].as_str() {
-            assert_eq!(
-                pointer_width,
-                match triple.pointer_width().unwrap() {
-                    PointerWidth::U16 => "16",
-                    PointerWidth::U32 => "32",
-                    PointerWidth::U64 => "64",
-                },
-                "\"target-pointer-width\" field disagrees with the target triple"
-            );
-        }
-
-        triple
-    }
-
-    /// Assuming `target` is a target identifier, search for an appropriate custom
-    /// target json config file in the way that rustc does, and then call
-    /// `read_target_from_file` on that.
-    fn read_target_from_file_in_path(target: &str) -> Triple {
-        let mut target_filename = target.to_owned();
-        target_filename.push_str(".json");
-        let target_basename = PathBuf::from(target_filename);
-        let target_path = env::var_os("RUST_TARGET_PATH").unwrap_or_else(|| OsString::new());
-        for dir in env::split_paths(&target_path) {
-            let p = dir.join(&target_basename);
-            if p.is_file() {
-                return read_target_from_file(&p);
-            }
-        }
-        panic!("can't find custom target {}", target);
-    }
-
-    // The following intends to match the logic in rustc.
-    if target.ends_with(".json") {
-        read_target_from_file(Path::new(&target))
-    } else {
-        Triple::from_str(&target).unwrap_or_else(|_| read_target_from_file_in_path(&target))
-    }
-}
-
-#[cfg(not(feature = "enable-serde"))]
-fn triple_from_target(target: &str) -> Triple {
-    Triple::from_str(&target).expect(&format!(
-        "Invalid target name: '{}'. Use the
-                enable-serde feature to fallback on JSON Rust targets descriptors.",
-        target
-    ))
-}
-
 fn main() {
     let out_dir =
         PathBuf::from(env::var("OUT_DIR").expect("The OUT_DIR environment variable must be set"));
-
     let target = env::var("TARGET").expect("The TARGET environment variable must be set");
-
-    let triple = triple_from_target(&target);
-
+    let triple = Triple::from_str(&target).expect(&format!("Invalid target name: '{}'", target));
     let out = File::create(out_dir.join("host.rs")).expect("error creating host.rs");
     write_host_rs(out, triple).expect("error writing host.rs");
 }