1 files changed, 109 insertions, 0 deletions
diff --git a/src/utils/path.rs b/src/utils/path.rs
new file mode 100644
index 00000000..6891e81a
--- /dev/null
+++ b/src/utils/path.rs
@@ -0,0 +1,109 @@
+use std::path::{Component, Path, PathBuf};
+
+use crate::config::Config;
+
+use super::process::calling_process;
+
+// Infer absolute path to `relative_path`.
+pub fn absolute_path(relative_path: &str, config: &Config) -> Option<PathBuf> {
+    match (
+        &config.cwd_of_delta_process,
+        &config.cwd_of_user_shell_process,
+        calling_process().paths_in_input_are_relative_to_cwd() || config.relative_paths,
+    ) {
+        // Note that if we were invoked by git then cwd_of_delta_process == repo_root
+        (Some(cwd_of_delta_process), _, false) => Some(cwd_of_delta_process.join(relative_path)),
+        (_, Some(cwd_of_user_shell_process), true) => {
+            Some(cwd_of_user_shell_process.join(relative_path))
+        }
+        (Some(cwd_of_delta_process), None, true) => {
+            // This might occur when piping from git to delta?
+            Some(cwd_of_delta_process.join(relative_path))
+        }
+        _ => None,
+    }
+    .map(normalize_path)
+}
+
+/// Relativize path if delta config demands that and paths are not already relativized by git.
+pub fn relativize_path_maybe(path: &str, config: &Config) -> Option<PathBuf> {
+    if config.relative_paths && !calling_process().paths_in_input_are_relative_to_cwd() {
+        if let Some(base) = config.cwd_relative_to_repo_root.as_deref() {
+            pathdiff::diff_paths(&path, base)
+        } else {
+            None
+        }
+    } else {
+        None
+    }
+}
+
+/// Return current working directory of the user's shell process. I.e. the directory which they are
+/// in when delta exits. This is the directory relative to which the file paths in delta output are
+/// constructed if they are using either (a) delta's relative-paths option or (b) git's --relative
+/// flag.
+pub fn cwd_of_user_shell_process(
+    cwd_of_delta_process: Option<&PathBuf>,
+    cwd_relative_to_repo_root: Option<&str>,
+) -> Option<PathBuf> {
+    match (cwd_of_delta_process, cwd_relative_to_repo_root) {
+        (Some(cwd), None) => {
+            // We are not a child process of git
+            Some(PathBuf::from(cwd))
+        }
+        (Some(repo_root), Some(cwd_relative_to_repo_root)) => {
+            // We are a child process of git; git spawned us from repo_root and preserved the user's
+            // original cwd in the GIT_PREFIX env var (available as config.cwd_relative_to_repo_root)
+            Some(PathBuf::from(repo_root).join(cwd_relative_to_repo_root))
+        }
+        (None, _) => {
+            // Unexpected
+            None
+        }
+    }
+}
+
+// Copied from
+// https://github.com/rust-lang/cargo/blob/c6745a3d7fcea3a949c3e13e682b8ddcbd213add/crates/cargo-util/src/paths.rs#L73-L106
+// as suggested by matklad: https://www.reddit.com/r/rust/comments/hkkquy/comment/fwtw53s/?utm_source=share&utm_medium=web2x&context=3
+fn normalize_path<P>(path: P) -> PathBuf
+where
+    P: AsRef<Path>,
+{
+    let mut components = path.as_ref().components().peekable();
+    let mut ret = if let Some(c @ Component::Prefix(..)) = components.peek().cloned() {
+        components.next();
+        PathBuf::from(c.as_os_str())
+    } else {
+        PathBuf::new()
+    };
+
+    for component in components {
+        match component {
+            Component::Prefix(..) => unreachable!(),
+            Component::RootDir => {
+                ret.push(component.as_os_str());
+            }
+            Component::CurDir => {}
+            Component::ParentDir => {
+                ret.pop();
+            }
+            Component::Normal(c) => {
+                ret.push(c);
+            }
+        }
+    }
+    ret
+}
+
+#[cfg(test)]
+pub fn fake_delta_cwd_for_tests() -> PathBuf {
+    #[cfg(not(target_os = "windows"))]
+    {
+        PathBuf::from("/fake/delta/cwd")
+    }
+    #[cfg(target_os = "windows")]
+    {
+        PathBuf::from(r"C:\fake\delta\cwd")
+    }
+}