From 277dfde5354112e4ed7aa5e730fd2b4e47aaaed5 Mon Sep 17 00:00:00 2001
From: Nicolas Boichat <nicolas@boichat.ch>
Date: Sun, 22 Mar 2026 17:28:25 +0800
Subject: [PATCH] Add CACHEDIR.TAG to .embuild/espressif directories

On Linux, this is the standard way to prevent cache directories
from being included in backups, and mirrors what cargo does (look
at `target` directory).

cargo does quite a bit more though, including preventing backup
on MacOS and indexing on Windows, we might want to pull in more
of the code (sadly we can't directly pull these functions from
cargo-util).
---
 CHANGELOG.md  |  4 ++++
 src/espidf.rs |  1 +
 src/fs.rs     | 24 ++++++++++++++++++++++++
 src/pio.rs    |  1 +
 4 files changed, 30 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index cb9892f..41bc881 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [main] - TBD
+- Add CACHEDIR.TAG to idf and pio temporary directories, to prevent Linux backups
+  from picking them up (see TODO, no support is added for MacOS/Windows).
+
 ## [0.33.1] - 2025-07-27
 - Fix a bug where the cmake utilities refused to work with CMake 4 due to a broken version check
 
diff --git a/src/espidf.rs b/src/espidf.rs
index a4d4444..5b2ba1f 100644
--- a/src/espidf.rs
+++ b/src/espidf.rs
@@ -658,6 +658,7 @@ impl Installer {
                 install_dir.display()
             )
         })?;
+        crate::fs::exclude_from_backups(&install_dir);
 
         let (esp_idf_dir, managed_repo) = match self.esp_idf_origin {
             EspIdfOrigin::Managed(managed) => (
diff --git a/src/fs.rs b/src/fs.rs
index 6952764..4e89acb 100644
--- a/src/fs.rs
+++ b/src/fs.rs
@@ -6,6 +6,30 @@ use std::path::Path;
 
 use anyhow::Result;
 
+/// Marks the directory as excluded from archives/backups by writing a `CACHEDIR.TAG` file.
+///
+/// This prevents derived/temporary files from bloating backups. Errors are ignored since
+/// this is an optional best-effort feature.
+///
+/// See the [Cache Directory Tagging Specification](https://bford.info/cachedir/).
+///
+/// TODO: This only replicates _part_ of what cargo_util::paths::exclude_from_backups_and_indexing does:
+/// https://doc.rust-lang.org/beta/nightly-rustc/cargo_util/paths/fn.exclude_from_backups_and_indexing.html
+/// we should consider lifting more of the code to prevent backup on MacOS, and indexing on Windows.
+pub fn exclude_from_backups(path: &Path) {
+    let file = path.join("CACHEDIR.TAG");
+    if !file.exists() {
+        let _ = std::fs::write(
+            file,
+            "Signature: 8a477f597d28d172789f06886806bc55
+# This file is a cache directory tag created by embuild.
+# For information about cache directory tags see https://bford.info/cachedir/
+",
+        );
+        // We ignore errors here as it's an optional feature.
+    }
+}
+
 /// Copy `src_file` to `dest_file_or_dir` if `src_file` is different or the destination
 /// file doesn't exist.
 ///
diff --git a/src/pio.rs b/src/pio.rs
index cf12ed0..476ea1e 100644
--- a/src/pio.rs
+++ b/src/pio.rs
@@ -243,6 +243,7 @@ impl Pio {
             if !pio_dir.exists() {
                 fs::create_dir_all(pio_dir)?;
             }
+            crate::fs::exclude_from_backups(pio_dir);
 
             pio_installer.pio(pio_dir);
         }