feat: resolve path function

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 
 ## Unreleased
+- Add `resolve` function, which resolves relative paths to absolute paths based on the current working directory.
 
 ## v2.3.2 - 26 December 2025 
 - Fix bug where unknown errors were not properly converted to the Unknown variant in Erlang ffi.

gleam.toml

@@ -4,7 +4,7 @@ description = "Basic file operations that work on all targets"
 
 licences = ["Apache-2.0"]
 repository = { type = "github", user = "bcpeinhardt", repo = "simplifile" }
-gleam = ">= 1.9.0"
+gleam = ">= 1.11.0"
 # links = [{ title = "Website", href = "https://gleam.run" }]
 
 [javascript.deno]

src/simplifile.gleam

@@ -743,3 +743,29 @@ pub fn current_directory() -> Result(String, FileError) {
 
 @external(erlang, "file", "get_cwd")
 fn erl_do_current_directory() -> Result(List(UtfCodepoint), FileError)
+
+/// Converts a relative path to an absolute path which starts in the current working directory.
+///
+/// Returns an error if the relative path could not be resolved.
+/// 
+/// # Example:
+/// ```gleam
+/// // Resolving a relative path resolves the full absolute path.
+/// // Assume the current working directory is /home/lucy.
+/// assert resolve("./tmp/../gleam") == Ok("/home/lucy/gleam")
+///
+/// // Resolving an absolute path returns that absolute path.
+/// assert resolve("/tmp/gleam") == Ok("/tmp/gleam")
+/// 
+/// // Tried to go two directories back, but was only able to go one back. Path is unresolvable.
+/// assert resolve("/tmp/../..") == Error(Enoent) 
+/// ```
+pub fn resolve(path path: String) -> Result(String, FileError) {
+  do_resolve(path)
+  |> filepath.expand
+  |> result.replace_error(Enoent)
+}
+
+@external(erlang, "filename", "absname")
+@external(javascript, "./simplifile_js.mjs", "resolve")
+fn do_resolve(path: String) -> String

src/simplifile_js.mjs

@@ -398,3 +398,13 @@ function cast_error(error_code) {
       return new $simplifile.Unknown(error_code);
   }
 }
+
+/**
+ * Resolves a relative path to an absolute path based on the current working directory.
+ * 
+ * @param {string} filepath The file path to resolve
+ * @returns {string} The resolved file path
+ */
+export function resolve(filepath) {
+  return path.resolve(filepath);
+} 

test/simplifile_test.gleam

@@ -781,3 +781,23 @@ pub fn unknown_errors_return_unknown_test() {
 @external(erlang, "simplifile_erl", "create_directory")
 @external(javascript, "./simplifile_js.mjs", "createDirectory")
 fn create_directory_with_bad_arg(arg: #(Nil, Nil)) -> Result(Nil, FileError)
+
+pub fn resolve_empty_path_test() {
+  assert simplifile.resolve("") == simplifile.current_directory()
+}
+
+pub fn resolve_relative_path_test() {
+  let assert Ok(actual) = simplifile.resolve("./simplifile_test.gleam")
+  let assert Ok(cwd) = simplifile.current_directory()
+  let expected = cwd <> "/simplifile_test.gleam"
+
+  assert actual == expected
+}
+
+// only works on Unix(-like) systems
+pub fn resolve_absolute_path_test() {
+  let initial = "/bin/hello"
+  let assert Ok(actual) = simplifile.resolve(initial)
+
+  assert initial == actual
+}