fix incorrect path resolution in tidy

Previously, reading the current path from the environment led to failure when invoking
x from outside the source root. This change fixes this issue by reading the second argument,
which always equals to the source root (see https://github.com/rust-lang/rust/blob/a655e648a9f94d74263108366b83e677af56e35d/src/bootstrap/src/core/build_steps/test.rs#L1081).

Signed-off-by: onur-ozkan <[email protected]>

src/tools/tidy/src/ui_tests.rs

@@ -5,6 +5,7 @@ use ignore::Walk;
 use lazy_static::lazy_static;
 use regex::Regex;
 use std::collections::{BTreeSet, HashMap};
+use std::env;
 use std::ffi::OsStr;
 use std::fs;
 use std::io::Write;
@@ -184,7 +185,7 @@ pub fn check(path: &Path, bless: bool, bad: &mut bool) {
 */
 [
 "#;
-        let tidy_src = std::env::current_dir().unwrap().join("src/tools/tidy/src");
+        let tidy_src = PathBuf::from(env::args_os().nth(1).unwrap()).join("src/tools/tidy/src");
         // instead of overwriting the file, recreate it and use an "atomic rename"
         // so we don't bork things on panic or a contributor using Ctrl+C
         let blessed_issues_path = tidy_src.join("issues_blessed.txt");