Prevent testsuite from loading config out of sandbox.

src/bin/cargo/commands/install.rs

@@ -78,6 +78,7 @@ pub fn exec(config: &mut Config, args: &ArgMatches<'_>) -> CliResult {
     if let Some(path) = args.value_of_path("path", config) {
         config.reload_rooted_at(path)?;
     } else {
+        // TODO: Consider calling set_search_stop_path(home).
         config.reload_rooted_at(config.home().clone().into_path_unlocked())?;
     }
 

src/cargo/core/workspace.rs

@@ -461,7 +461,7 @@ impl<'cfg> Workspace<'cfg> {
             }
         }
 
-        for path in paths::ancestors(manifest_path).skip(2) {
+        for path in paths::ancestors(manifest_path, None).skip(2) {
             if path.ends_with("target/package") {
                 break;
             }

src/cargo/ops/cargo_new.rs

@@ -872,7 +872,7 @@ fn find_tests_git_config(path: &Path) -> Option<GitConfig> {
     // Don't escape the test sandbox when looking for a git repository.
     // NOTE: libgit2 has support to define the path ceiling in
     // git_repository_discover, but the git2 bindings do not expose that.
-    for path in paths::ancestors(path) {
+    for path in paths::ancestors(path, None) {
         if let Ok(repo) = GitRepository::open(path) {
             return Some(repo.config().expect("test repo should have valid config"));
         }

src/cargo/util/config/mod.rs

@@ -132,6 +132,8 @@ pub struct Config {
     cli_config: Option<Vec<String>>,
     /// The current working directory of cargo
     cwd: PathBuf,
+    /// Directory where config file searching should stop (inclusive).
+    search_stop_path: Option<PathBuf>,
     /// The location of the cargo executable (path to current process)
     cargo_exe: LazyCell<PathBuf>,
     /// The location of the rustdoc executable
@@ -218,6 +220,7 @@ impl Config {
             home_path: Filesystem::new(homedir),
             shell: RefCell::new(shell),
             cwd,
+            search_stop_path: None,
             values: LazyCell::new(),
             cli_config: None,
             cargo_exe: LazyCell::new(),
@@ -422,6 +425,14 @@ impl Config {
         }
     }
 
+    /// Sets the path where ancestor config file searching will stop. The
+    /// given path is included, but its ancestors are not.
+    pub fn set_search_stop_path<P: Into<PathBuf>>(&mut self, path: P) {
+        let path = path.into();
+        debug_assert!(self.cwd.starts_with(&path));
+        self.search_stop_path = Some(path);
+    }
+
     /// Reloads on-disk configuration values, starting at the given path and
     /// walking up its ancestors.
     pub fn reload_rooted_at<P: AsRef<Path>>(&mut self, path: P) -> CargoResult<()> {
@@ -1028,7 +1039,7 @@ impl Config {
     {
         let mut stash: HashSet<PathBuf> = HashSet::new();
 
-        for current in paths::ancestors(pwd) {
+        for current in paths::ancestors(pwd, self.search_stop_path.as_deref()) {
             if let Some(path) = self.get_file_path(&current.join(".cargo"), "config", true)? {
                 walk(&path)?;
                 stash.insert(path);

src/cargo/util/important_paths.rs

@@ -5,7 +5,7 @@ use std::path::{Path, PathBuf};
 /// Finds the root `Cargo.toml`.
 pub fn find_root_manifest_for_wd(cwd: &Path) -> CargoResult<PathBuf> {
     let file = "Cargo.toml";
-    for current in paths::ancestors(cwd) {
+    for current in paths::ancestors(cwd, None) {
         let manifest = current.join(file);
         if manifest.exists() {
             return Ok(manifest);

src/cargo/util/paths.rs

@@ -306,8 +306,8 @@ pub fn bytes2path(bytes: &[u8]) -> CargoResult<PathBuf> {
     }
 }
 
-pub fn ancestors(path: &Path) -> PathAncestors<'_> {
-    PathAncestors::new(path)
+pub fn ancestors<'a>(path: &'a Path, stop_root_at: Option<&Path>) -> PathAncestors<'a> {
+    PathAncestors::new(path, stop_root_at)
 }
 
 pub struct PathAncestors<'a> {
@@ -316,11 +316,15 @@ pub struct PathAncestors<'a> {
 }
 
 impl<'a> PathAncestors<'a> {
-    fn new(path: &Path) -> PathAncestors<'_> {
+    fn new(path: &'a Path, stop_root_at: Option<&Path>) -> PathAncestors<'a> {
+        let stop_at = env::var("__CARGO_TEST_ROOT")
+            .ok()
+            .map(PathBuf::from)
+            .or_else(|| stop_root_at.map(|p| p.to_path_buf()));
         PathAncestors {
             current: Some(path),
             //HACK: avoid reading `~/.cargo/config` when testing Cargo itself.
-            stop_at: env::var("__CARGO_TEST_ROOT").ok().map(PathBuf::from),
+            stop_at,
         }
     }
 }

tests/testsuite/config.rs

@@ -77,6 +77,7 @@ impl ConfigBuilder {
         let homedir = paths::home();
         let mut config = Config::new(shell, cwd, homedir);
         config.set_env(self.env.clone());
+        config.set_search_stop_path(paths::root());
         config.configure(
             0,
             false,