Enable Cargo's new build-dir layout in tests+ci (#6879)

* test: Add support for cargo's build-dir v2 layout

* chore: Move CI to use Cargo's v2 layout

Author: ranger-ross

.github/workflows/linux.yml

@@ -38,4 +38,5 @@ jobs:
     - name: Build and Test
       env:
         RUSTFLAGS: -D warnings
+        CARGO_UNSTABLE_BUILD_DIR_NEW_LAYOUT: true
       run: cargo run --manifest-path ci/Cargo.toml build-and-test

.github/workflows/mac.yml

@@ -34,4 +34,5 @@ jobs:
     - name: Build and Test
       env:
         RUSTFLAGS: -D warnings
+        CARGO_UNSTABLE_BUILD_DIR_NEW_LAYOUT: true
       run: cargo run --manifest-path ci/Cargo.toml build-and-test

.github/workflows/windows.yml

@@ -60,4 +60,5 @@ jobs:
     - name: Build and Test
       env:
         RUSTFLAGS: -D warnings
+        CARGO_UNSTABLE_BUILD_DIR_NEW_LAYOUT: true
       run: cargo run --manifest-path ci/Cargo.toml build-and-test

src/test/mod.rs

@@ -1130,8 +1130,23 @@ fn rustfmt() -> PathBuf {
     let mut me = env::current_exe().expect("failed to get current executable");
     // Chop of the test name.
     me.pop();
-    // Chop off `deps`.
-    me.pop();
+
+    // Handle Cargo's old and new filesystem layouts
+    // * v1: `target/<profile>/deps/test-bin-[HASH][EXE]`
+    // * v2: `target/<profile>/build/<pkgname>/[HASH]/out/test-bin-[HASH][EXE]`
+    if me.ends_with("deps") {
+        // Chop off `deps`.
+        me.pop();
+    } else if me.ends_with("out") {
+        // Chop off `out`.
+        me.pop();
+        // Chop off `<hash>`.
+        me.pop();
+        // Chop off `<pkgname>`.
+        me.pop();
+        // Chop off `build`.
+        me.pop();
+    }
 
     me.push("rustfmt");
     assert!(

tests/cargo-fmt/main.rs

@@ -10,8 +10,17 @@ use rustfmt_config_proc_macro::rustfmt_only_ci_test;
 fn cargo_fmt(args: &[&str]) -> (String, String) {
     let mut bin_dir = env::current_exe().unwrap();
     bin_dir.pop(); // chop off test exe name
+
+    // Handle Cargo's old and new filesystem layouts
+    // * v1: `target/<profile>/deps/test-bin-[HASH][EXE]`
+    // * v2: `target/<profile>/build/<pkgname>/[HASH]/out/test-bin-[HASH][EXE]`
     if bin_dir.ends_with("deps") {
         bin_dir.pop();
+    } else if bin_dir.ends_with("out") {
+        bin_dir.pop(); // chop off `out`
+        bin_dir.pop(); // chop off `<hash>`
+        bin_dir.pop(); // chop off `<pkgname>`
+        bin_dir.pop(); // chop off `build`
     }
     let cmd = bin_dir.join(format!("cargo-fmt{}", env::consts::EXE_SUFFIX));