fix(package): exclude target dir from backups with CACHEDIR.TAG

Create CACHEDIR.TAG files in build directories during `cargo package`
to exclude them from system backups. This ensures that temporary
packaging artifacts in target/package are not unnecessarily included
by backup tools like Time Machine on macOS.

The fix calls `create_dir_all_excluded_from_backups_atomic` when
creating the build directory and target directory for packaging,
which automatically creates the CACHEDIR.TAG file.

Update existing tests to verify that CACHEDIR.TAG files are now
created in the expected locations.

Fixes #16238

Author: SepehrGanji

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

@@ -7825,10 +7825,10 @@ fn package_dir_not_excluded_from_backups() {
 "#]])
         .run();
 
-    // Verify CACHEDIR.TAG does NOT exist in target (documenting the buggy behavior)
+    // 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 not exist yet (this is the bug)"
+        cachedir_tag.exists(),
+        "CACHEDIR.TAG should exist in target directory to exclude it from backups"
     );
 }