Add support for (absolut) target JSON paths

src/main.rs

@@ -151,12 +151,7 @@ fn run() -> Result<ExitStatus> {
         };
 
         let cmode = if let Some(triple) = args.target() {
-            if Path::new(triple).is_file() {
-                bail!(
-                    "Xargo doesn't support files as an argument to --target. \
-                     Use `--target foo` instead of `--target foo.json`."
-                )
-            } else if triple == meta.host {
+            if triple == meta.host {
                 Some(CompilationMode::Native(meta.host.clone()))
             } else {
                 Target::new(triple, &cd, verbose)?.map(CompilationMode::Cross)

src/rustc.rs

@@ -121,6 +121,19 @@ impl Target {
         if rustc::targets(verbose)?.iter().any(|t| t == &triple) {
             Ok(Some(Target::Builtin { triple: triple }))
         } else {
+            if Path::new(&triple).exists() {
+                let path = match Path::new(&triple).canonicalize() {
+                    Ok(path) => path,
+                    Err(_) => bail!("target path {:?} is invalid", triple),
+                };
+                let file_stem = match path.file_stem().and_then(|stem| stem.to_str()) {
+                    Some(stem) => stem.into(),
+                    None => {
+                        bail!("target file name {:?} is empty or contains invalid unicode", path)
+                    }
+                };
+                return Ok(Some(Target::Custom { json: path, triple: file_stem }))
+            }
             let mut json = cd.path().join(&triple);
             json.set_extension("json");