test(package): demonstrate target dir not excluded from backups

Add a test that documents the current behavior where `cargo package`
creates the target/package directory without excluding it from backups.
The CACHEDIR.TAG file does not currently exist in the target directory,
causing backup tools to include these temporary build artifacts.

This test currently passes by asserting the buggy behavior (CACHEDIR.TAG
does not exist). The next commit will fix the issue and update the test
to verify correct behavior.

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

@@ -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"
+    );
+}