Optimization of tilde expansion (#9709)

* Use next and avoid a redundant prefix strip

* Avoid allocations

Especially when `expand_tilde` is claled on a path
that doesn't contain a tilde.

* Add a test

* Use Into<Cow<…>>

* Put the expand_tilde test at the end of the file

* Remove unused importsw

4 files changed, 57 insertions, 22 deletions

diff --git a/helix-loader/src/lib.rs b/helix-loader/src/lib.rs
index f8fac670..93488e45 100644
--- a/helix-loader/src/lib.rs
+++ b/helix-loader/src/lib.rs
@@ -53,7 +53,7 @@ fn prioritize_runtime_dirs() -> Vec<PathBuf> {
     rt_dirs.push(conf_rt_dir);
 
     if let Ok(dir) = std::env::var("HELIX_RUNTIME") {
-        let dir = path::expand_tilde(dir);
+        let dir = path::expand_tilde(Path::new(&dir));
         rt_dirs.push(path::normalize(dir));
     }
 
diff --git a/helix-stdx/src/path.rs b/helix-stdx/src/path.rs
index 5746657c..1dc4d0b2 100644
--- a/helix-stdx/src/path.rs
+++ b/helix-stdx/src/path.rs
@@ -1,6 +1,9 @@
 pub use etcetera::home_dir;
 
-use std::path::{Component, Path, PathBuf};
+use std::{
+    borrow::Cow,
+    path::{Component, Path, PathBuf},
+};
 
 use crate::env::current_working_dir;
 
@@ -19,19 +22,22 @@ pub fn fold_home_dir(path: &Path) -> PathBuf {
 /// Expands tilde `~` into users home directory if available, otherwise returns the path
 /// unchanged. The tilde will only be expanded when present as the first component of the path
 /// and only slash follows it.
-pub fn expand_tilde(path: impl AsRef<Path>) -> PathBuf {
-    let path = path.as_ref();
-    let mut components = path.components().peekable();
-    if let Some(Component::Normal(c)) = components.peek() {
-        if c == &"~" {
-            if let Ok(home) = home_dir() {
-                // it's ok to unwrap, the path starts with `~`
-                return home.join(path.strip_prefix("~").unwrap());
+pub fn expand_tilde<'a, P>(path: P) -> Cow<'a, Path>
+where
+    P: Into<Cow<'a, Path>>,
+{
+    let path = path.into();
+    let mut components = path.components();
+    if let Some(Component::Normal(c)) = components.next() {
+        if c == "~" {
+            if let Ok(mut buf) = home_dir() {
+                buf.push(components);
+                return Cow::Owned(buf);
             }
         }
     }
 
-    path.to_path_buf()
+    path
 }
 
 /// Normalize a path without resolving symlinks.
@@ -109,9 +115,9 @@ pub fn normalize(path: impl AsRef<Path>) -> PathBuf {
 /// This function is used instead of [`std::fs::canonicalize`] because we don't want to verify
 /// here if the path exists, just normalize it's components.
 pub fn canonicalize(path: impl AsRef<Path>) -> PathBuf {
-    let path = expand_tilde(path);
+    let path = expand_tilde(path.as_ref());
     let path = if path.is_relative() {
-        current_working_dir().join(path)
+        Cow::Owned(current_working_dir().join(path))
     } else {
         path
     };
@@ -183,3 +189,32 @@ pub fn get_truncated_path(path: impl AsRef<Path>) -> PathBuf {
     ret.push(file);
     ret
 }
+
+#[cfg(test)]
+mod tests {
+    use std::{
+        ffi::OsStr,
+        path::{Component, Path},
+    };
+
+    use crate::path;
+
+    #[test]
+    fn expand_tilde() {
+        for path in ["~", "~/foo"] {
+            let expanded = path::expand_tilde(Path::new(path));
+
+            let tilde = Component::Normal(OsStr::new("~"));
+
+            let mut component_count = 0;
+            for component in expanded.components() {
+                // No tilde left.
+                assert_ne!(component, tilde);
+                component_count += 1;
+            }
+
+            // The path was at least expanded to something.
+            assert_ne!(component_count, 0);
+        }
+    }
+}
diff --git a/helix-term/src/commands/typed.rs b/helix-term/src/commands/typed.rs
index b7ceeba5..3d7ea3fc 100644
--- a/helix-term/src/commands/typed.rs
+++ b/helix-term/src/commands/typed.rs
@@ -110,14 +110,14 @@ fn open(cx: &mut compositor::Context, args: &[Cow<str>], event: PromptEvent) ->
     ensure!(!args.is_empty(), "wrong argument count");
     for arg in args {
         let (path, pos) = args::parse_file(arg);
-        let path = helix_stdx::path::expand_tilde(&path);
+        let path = helix_stdx::path::expand_tilde(path);
         // If the path is a directory, open a file picker on that directory and update the status
         // message
         if let Ok(true) = std::fs::canonicalize(&path).map(|p| p.is_dir()) {
             let callback = async move {
                 let call: job::Callback = job::Callback::EditorCompositor(Box::new(
                     move |editor: &mut Editor, compositor: &mut Compositor| {
-                        let picker = ui::file_picker(path, &editor.config());
+                        let picker = ui::file_picker(path.into_owned(), &editor.config());
                         compositor.push(Box::new(overlaid(picker)));
                     },
                 ));
@@ -1078,11 +1078,11 @@ fn change_current_directory(
         return Ok(());
     }
 
-    let dir = helix_stdx::path::expand_tilde(
-        args.first()
-            .context("target directory not provided")?
-            .as_ref(),
-    );
+    let dir = args
+        .first()
+        .context("target directory not provided")?
+        .as_ref();
+    let dir = helix_stdx::path::expand_tilde(Path::new(dir));
 
     helix_stdx::env::set_current_working_dir(dir)?;
 
diff --git a/helix-term/src/ui/mod.rs b/helix-term/src/ui/mod.rs
index d27e8355..0873116c 100644
--- a/helix-term/src/ui/mod.rs
+++ b/helix-term/src/ui/mod.rs
@@ -428,9 +428,9 @@ pub mod completers {
                 path
             } else {
                 match path.parent() {
-                    Some(path) if !path.as_os_str().is_empty() => path.to_path_buf(),
+                    Some(path) if !path.as_os_str().is_empty() => Cow::Borrowed(path),
                     // Path::new("h")'s parent is Some("")...
-                    _ => helix_stdx::env::current_working_dir(),
+                    _ => Cow::Owned(helix_stdx::env::current_working_dir()),
                 }
             };