feat: option to prevent cross-filesystem traversal (#363)

Adds support for skipping directories on different filesystems, similar to the `-x`/`--one-file-system` flag found in tools like `du`. This allows users to analyze disk usage within a single filesystem without counting mounted directories.

https://claude.ai/code/session_01LfpnUZrgq93MVZgA3KVqE6

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: 3 people

.devcontainer/devcontainer.json

@@ -1,6 +1,9 @@
 {
   "name": "parallel-disk-usage (Rust only)",
   "image": "mcr.microsoft.com/devcontainers/rust:1",
+  "remoteEnv": {
+    "TEST_SKIP": "cross_device_excludes_mount"
+  },
   "customizations": {
     "vscode": {
       "extensions": [

.devcontainer/full/devcontainer.json

@@ -1,6 +1,9 @@
 {
   "name": "parallel-disk-usage (full)",
   "image": "mcr.microsoft.com/devcontainers/rust:1",
+  "remoteEnv": {
+    "TEST_SKIP": "cross_device_excludes_mount"
+  },
   "features": {
     "ghcr.io/devcontainers/features/node:1": {
       "version": "lts",

.github/workflows/deploy.yaml

@@ -29,6 +29,12 @@ jobs:
           curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs > $installer
           bash $installer --default-toolchain $(cat rust-toolchain) -y
 
+      - name: Install external test dependencies
+        if: runner.os == 'Linux'
+        run: |
+          sudo apt update
+          sudo apt install -y squashfs-tools squashfuse fuse3
+
       - name: Test (dev)
         shell: bash
         env:

.github/workflows/test.yaml

@@ -42,6 +42,12 @@ jobs:
           curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs > $installer
           bash $installer --default-toolchain $(cat rust-toolchain) -y
 
+      - name: Install external test dependencies
+        if: runner.os == 'Linux'
+        run: |
+          sudo apt update
+          sudo apt install -y squashfs-tools squashfuse fuse3
+
       - name: Test (dev)
         shell: bash
         env:

CONTRIBUTING.md

@@ -351,6 +351,16 @@ rustup toolchain install "$(< rust-toolchain)"
 rustup component add --toolchain "$(< rust-toolchain)" rustfmt clippy
 ```
 
+## Optional External Dependencies
+
+Some integration tests require external (non-Cargo) tools that are **not** managed by `Cargo.toml`. These tests panic when the tools are absent; CI installs them to get full coverage.
+
+- `squashfs-tools` (provides `mksquashfs`) — cross-device (`--one-file-system`) FUSE test
+- `squashfuse` (provides `squashfuse`) — cross-device (`--one-file-system`) FUSE test
+- `fuse3` (provides `fusermount3`, `/dev/fuse`) — cross-device (`--one-file-system`) FUSE test
+
+Tests that need these tools will panic with a diagnostic message if they are missing. The panic message includes the specific `TEST_SKIP` variable to skip the test via `./test.sh`.
+
 ## Automated Checks
 
 Before submitting, ensure:

Cargo.lock

@@ -91,3 +91,4 @@ maplit = "1.0.2"
 normalize-path = "0.2.1"
 pretty_assertions = "1.4.1"
 rand = "0.10.0"
+which = "8.0.2"

Cargo.toml

@@ -61,7 +61,6 @@ The benchmark was generated by [a GitHub Workflow](https://github.com/KSXGitHub/
 
 * Ignorant of reflinks (from COW filesystems such as BTRFS and ZFS).
 * Does not follow symbolic links.
-* Does not differentiate filesystems: Mounted folders are counted as normal folders.
 * The runtime is optimized at the expense of binary size.
 
 ## Usage

README.md

@@ -39,6 +39,13 @@ How to display the numbers of bytes.
 
 Detect and subtract the sizes of hardlinks from their parent directory totals.
 
+<a id="option-x" name="option-x"></a><a id="one-file-system" name="one-file-system"></a>
+### `--one-file-system`
+
+* _Aliases:_ `-x`.
+
+Skip directories on different filesystems.
+
 <a id="top-down" name="top-down"></a>
 ### `--top-down`
 

USAGE.md

@@ -23,7 +23,7 @@ _pdu() {
 
     case "${cmd}" in
         pdu)
-            opts="-b -H -q -d -w -m -s -p -h -V --json-input --json-output --bytes-format --detect-links --dedupe-links --deduplicate-hardlinks --top-down --align-right --quantity --depth --max-depth --width --total-width --column-width --min-ratio --no-sort --no-errors --silent-errors --progress --threads --omit-json-shared-details --omit-json-shared-summary --help --version [FILES]..."
+            opts="-b -H -x -q -d -w -m -s -p -h -V --json-input --json-output --bytes-format --detect-links --dedupe-links --deduplicate-hardlinks --one-file-system --top-down --align-right --quantity --depth --max-depth --width --total-width --column-width --min-ratio --no-sort --no-errors --silent-errors --progress --threads --omit-json-shared-details --omit-json-shared-summary --help --version [FILES]..."
             if [[ ${cur} == -* || ${COMP_CWORD} -eq 1 ]] ; then
                 COMPREPLY=( $(compgen -W "${opts}" -- "${cur}") )
                 return 0