fix(package): exclude target/package from backups (#16272)

  ### What does this PR try to resolve?

  The target directory is not excluded from backups when created with
  `cargo package` or `cargo publish`. This causes the `target/package`
  directory to be included in Time Machine backups on macOS and other
  backup systems that respect CACHEDIR.TAG files.

  The issue occurs because when `Filesystem::open()` creates parent
  directories in `src/cargo/util/flock.rs:336`, it uses
  `paths::create_dir_all()` instead of the backup-excluding version,
  bypassing the normal target directory creation logic.

  This commit adds a new `create_dir_with_backup_exclusion()` method to
  `Filesystem` and uses it to ensure the `target/package` directory is
  properly excluded from backups before creating files in it.

  Fixes #16238

  ### How to test and review this PR?

  Run the following:
  cargo new foo
  cd foo
  cargo package --allow-dirty
  ls -al target/package/

  Verify that `CACHEDIR.TAG` now exists in `target/package/`.

  All existing package tests pass.

Author: weihanglo

src/cargo/ops/cargo_package/mod.rs

@@ -161,7 +161,9 @@ fn create_package(
     }
 
     let filename = pkg.package_id().tarball_name();
-    let dir = ws.build_dir().join("package");
+    let build_dir = ws.build_dir();
+    paths::create_dir_all_excluded_from_backups_atomic(build_dir.as_path_unlocked())?;
+    let dir = build_dir.join("package");
     let mut dst = {
         let tmp = format!(".{}", filename);
         dir.open_rw_exclusive_create(&tmp, gctx, "package scratch space")?
@@ -225,6 +227,7 @@ pub fn package(ws: &Workspace<'_>, opts: &PackageOpts<'_>) -> CargoResult<Vec<Fi
         result.extend(packaged.into_iter().map(|(_, _, src)| src));
     } else {
         // Uplifting artifacts
+        paths::create_dir_all_excluded_from_backups_atomic(target_dir.as_path_unlocked())?;
         let artifact_dir = target_dir.join("package");
         for (pkg, _, src) in packaged {
             let filename = pkg.package_id().tarball_name();

tests/testsuite/build_dir.rs

@@ -525,13 +525,15 @@ fn cargo_package_should_build_in_build_dir_and_output_to_target_dir() {
 [ROOT]/foo/build-dir/package/foo-0.0.1/Cargo.toml.orig
 [ROOT]/foo/build-dir/package/foo-0.0.1/src/main.rs
 [ROOT]/foo/build-dir/package/foo-0.0.1.crate
+[ROOT]/foo/build-dir/CACHEDIR.TAG
 
 "#]]);
 
     p.root()
         .join("target-dir")
         .assert_build_dir_layout(str![[r#"
 [ROOT]/foo/target-dir/package/foo-0.0.1.crate
+[ROOT]/foo/target-dir/CACHEDIR.TAG
 
 "#]]);
 }

tests/testsuite/build_dir_legacy.rs

@@ -494,13 +494,15 @@ fn cargo_package_should_build_in_build_dir_and_output_to_target_dir() {
 [ROOT]/foo/build-dir/package/foo-0.0.1/Cargo.toml.orig
 [ROOT]/foo/build-dir/package/foo-0.0.1/src/main.rs
 [ROOT]/foo/build-dir/package/foo-0.0.1.crate
+[ROOT]/foo/build-dir/CACHEDIR.TAG
 
 "#]]);
 
     p.root()
         .join("target-dir")
         .assert_build_dir_layout(str![[r#"
 [ROOT]/foo/target-dir/package/foo-0.0.1.crate
+[ROOT]/foo/target-dir/CACHEDIR.TAG
 
 "#]]);
 }

tests/testsuite/package.rs

@@ -7804,3 +7804,31 @@ fn publish_to_alt_registry_warns() {
 "#]])
         .run();
 }
+
+#[cargo_test]
+fn package_dir_not_excluded_from_backups() {
+    // This test documents the current behavior where target directory is NOT excluded from backups.
+    // After the fix, this test will be updated to verify that CACHEDIR.TAG exists.
+    let p = project().file("src/lib.rs", "").build();
+
+    p.cargo("package --allow-dirty")
+        .with_stderr_data(str![[r#"
+[WARNING] manifest has no description, license, license-file, documentation, homepage or repository
+  |
+  = [NOTE] see https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata for more info
+[PACKAGING] foo v0.0.1 ([ROOT]/foo)
+[PACKAGED] 4 files, [FILE_SIZE]B ([FILE_SIZE]B compressed)
+[VERIFYING] foo v0.0.1 ([ROOT]/foo)
+[COMPILING] foo v0.0.1 ([ROOT]/foo/target/package/foo-0.0.1)
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+
+"#]])
+        .run();
+
+    // Verify CACHEDIR.TAG exists in target (which excludes target/ and all subdirectories)
+    let cachedir_tag = p.root().join("target/CACHEDIR.TAG");
+    assert!(
+        cachedir_tag.exists(),
+        "CACHEDIR.TAG should exist in target directory to exclude it from backups"
+    );
+}