Fix for issue 470

src/main.rs

@@ -325,6 +325,9 @@ fn flatten_options(values: &[String]) -> Vec<String> {
         .collect()
 }
 
+/// Folds `.` and `..` away lexically. Only meaningful on an absolute path:
+/// applied to a relative one, `.` and a leading `..` have nothing to resolve
+/// against and simply vanish, so callers go through [`parse_normalized_path`].
 fn normalize_path(path: PathBuf) -> PathBuf {
     path.components()
         .fold(PathBuf::new(), |mut normalized, component| {
@@ -339,8 +342,21 @@ fn normalize_path(path: PathBuf) -> PathBuf {
         })
 }
 
+/// Resolves a path argument against the process working directory, then
+/// normalizes it.
+///
+/// Making the path absolute *first* is what keeps a relative argument
+/// meaningful. Normalizing `.` on its own drops its only component and leaves
+/// the empty path, which then fails every `Command::current_dir` with a
+/// `chdir("")` ENOENT that names the Bazel binary rather than the workspace;
+/// normalizing `../sibling` on its own pops nothing and silently yields
+/// `sibling`. Anchoring to the working directory gives both the directory the
+/// user meant, matching the Kotlin CLI. See
+/// <https://github.com/Tinder/bazel-diff/issues/470>.
 fn parse_normalized_path(value: &str) -> Result<PathBuf, String> {
-    Ok(normalize_path(PathBuf::from(value)))
+    let absolute = std::path::absolute(value)
+        .map_err(|error| format!("failed to resolve path {value:?}: {error}"))?;
+    Ok(normalize_path(absolute))
 }
 
 fn read_lines(path: Option<&Path>) -> Result<BTreeSet<PathBuf>> {
@@ -859,6 +875,107 @@ mod tests {
         );
     }
 
+    /// Regression test for <https://github.com/Tinder/bazel-diff/issues/470>.
+    ///
+    /// `--workspacePath` and `--cacheDir` are anchored to the process working
+    /// directory before they are normalized. Without that, a path built only
+    /// out of `.`/`..` components collapsed to the empty path, and a leading
+    /// `..` was silently dropped.
+    #[test]
+    fn relative_path_arguments_resolve_against_the_working_directory() {
+        let working_directory = std::env::current_dir().unwrap();
+        for value in [".", "./", "./nested/..", "nested/.."] {
+            assert_eq!(
+                parse_normalized_path(value).unwrap(),
+                working_directory,
+                "--workspacePath {value} should be the working directory"
+            );
+        }
+        assert_eq!(
+            parse_normalized_path("nested").unwrap(),
+            working_directory.join("nested")
+        );
+        assert_eq!(
+            parse_normalized_path("./nested/inner/..").unwrap(),
+            working_directory.join("nested")
+        );
+
+        // A leading `..` has a parent to pop now that the path is absolute.
+        assert_eq!(
+            parse_normalized_path("../sibling").unwrap(),
+            working_directory.parent().unwrap().join("sibling")
+        );
+
+        // Absolute arguments keep the normalization they always had.
+        let absolute = working_directory.join("nested/inner/..");
+        assert_eq!(
+            parse_normalized_path(absolute.to_str().unwrap()).unwrap(),
+            working_directory.join("nested")
+        );
+
+        // The empty path never named a directory; it is now rejected instead of
+        // being passed to `chdir`.
+        assert!(parse_normalized_path("").is_err());
+    }
+
+    /// Regression test for <https://github.com/Tinder/bazel-diff/issues/470>:
+    /// the symptom users hit.
+    ///
+    /// [`BazelOptions::command`] does `command.current_dir(&self.workspace)`.
+    /// When `-w .` normalized to the empty path the child's `chdir("")` failed,
+    /// and `std::process::Command` surfaced that as a spawn failure -- so the
+    /// error named the *Bazel binary*, which exists and is executable, instead
+    /// of the workspace:
+    ///
+    /// ```text
+    /// [Error] failed to execute /path/to/bazel: No such file or directory (os error 2)
+    /// ```
+    #[cfg(unix)]
+    #[test]
+    fn relative_workspace_path_spawns_bazel_in_the_working_directory() {
+        use std::os::unix::fs::PermissionsExt;
+        use std::process::Command;
+
+        let directory = tempfile::tempdir().unwrap();
+        let stub_bazel = directory.path().join("bazel");
+        fs::write(&stub_bazel, "#!/bin/sh\npwd -P\n").unwrap();
+        fs::set_permissions(&stub_bazel, fs::Permissions::from_mode(0o755)).unwrap();
+
+        let cli = parse(&[
+            "bazel-diff",
+            "generate-hashes",
+            "-w",
+            ".",
+            "-b",
+            stub_bazel.to_str().unwrap(),
+            "hashes.json",
+        ]);
+        let Commands::GenerateHashes(args) = cli.command else {
+            panic!("expected generate-hashes");
+        };
+        let options = bazel_options(&args.hashing, false).unwrap();
+
+        // Mirrors BazelOptions::command().
+        let output = Command::new(&options.bazel)
+            .current_dir(&options.workspace)
+            .arg("version")
+            .output()
+            .unwrap_or_else(|error| {
+                panic!(
+                    "`-w .` gave workspace {:?}, so spawning {} failed: {error}",
+                    options.workspace,
+                    options.bazel.display()
+                )
+            });
+
+        assert!(output.status.success());
+        assert_eq!(
+            PathBuf::from(String::from_utf8_lossy(&output.stdout).trim()),
+            std::env::current_dir().unwrap(),
+            "the child should run in the working directory `.` named"
+        );
+    }
+
     #[test]
     fn reads_and_trims_seed_and_repository_files() {
         let directory = tempfile::tempdir().unwrap();