Add function to canonicalize paths (#1859)

README.md

@@ -1381,7 +1381,10 @@ The process ID is: 420
 ##### Fallible
 
 - `absolute_path(path)` - Absolute path to relative `path` in the working
-  directory. `absolute_path("./bar.txt")` in directory `/foo` is `/foo/bar.txt`.
+  directory. `absolute_path("./bar.txt")` in directory `/foo` is
+  `/foo/bar.txt`.
+- `canonicalize(path)` - Canonicalize `path` by resolving symlinks and removing
+  `.`, `..`, and extra `/`s where possible.
 - `extension(path)` - Extension of `path`. `extension("/foo/bar.txt")` is
   `txt`.
 - `file_name(path)` - File name of `path` with any leading directory components

src/function.rs

@@ -21,6 +21,7 @@ pub(crate) fn get(name: &str) -> Option<Function> {
   let function = match name {
     "absolute_path" => Unary(absolute_path),
     "arch" => Nullary(arch),
+    "canonicalize" => Unary(canonicalize),
     "cache_directory" => Nullary(|_| dir("cache", dirs::cache_dir)),
     "capitalize" => Unary(capitalize),
     "clean" => Unary(clean),
@@ -106,6 +107,18 @@ fn arch(_context: &FunctionContext) -> Result<String, String> {
   Ok(target::arch().to_owned())
 }
 
+fn canonicalize(_context: &FunctionContext, path: &str) -> Result<String, String> {
+  let canonical =
+    std::fs::canonicalize(path).map_err(|err| format!("I/O error canonicalizing path: {err}"))?;
+
+  canonical.to_str().map(str::to_string).ok_or_else(|| {
+    format!(
+      "Canonical path is not valid unicode: {}",
+      canonical.display(),
+    )
+  })
+}
+
 fn capitalize(_context: &FunctionContext, s: &str) -> Result<String, String> {
   let mut capitalized = String::new();
   for (i, c) in s.chars().enumerate() {

tests/functions.rs

@@ -662,3 +662,14 @@ fn just_pid() {
 
   assert_eq!(stdout.parse::<u32>().unwrap(), pid);
 }
+
+#[cfg(unix)]
+#[test]
+fn canonicalize() {
+  Test::new()
+    .args(["--evaluate", "x"])
+    .justfile("x := canonicalize('foo')")
+    .symlink("justfile", "foo")
+    .stdout_regex(".*/justfile")
+    .run();
+}

tests/test.rs

@@ -113,6 +113,17 @@ impl Test {
     self.tempdir.path().join("justfile")
   }
 
+  #[cfg(unix)]
+  #[track_caller]
+  pub(crate) fn symlink(self, original: &str, link: &str) -> Self {
+    std::os::unix::fs::symlink(
+      self.tempdir.path().join(original),
+      self.tempdir.path().join(link),
+    )
+    .unwrap();
+    self
+  }
+
   pub(crate) fn no_justfile(mut self) -> Self {
     self.justfile = None;
     self