feat(stdlib): add os.walk, makedirs(exist_ok), getpid, getppid and os.path improvements (#287)

* feat(stdlib): add os.walk, makedirs(exist_ok), getpid, getppid and os.path improvements

Add missing but commonly-needed functions to the Os module:

- os.makedirs(path, exist_ok) overload using keyword arg emission so
  callers can write os.makedirs(dir, true) without specifying mode
- os.walk / os.walk(topdown) for directory tree traversal
- os.getpid() and os.getppid() to query current/parent process IDs
- os.path.isabs to test if a path is absolute
- os.path.islink to test if a path is a symbolic link
- os.path.realpath to resolve symlinks and canonicalize a path
- os.path.getsize to get the size of a file in bytes

Also adds 7 new tests to TestOs.fs covering all new members.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix(stdlib): address review feedback on Os bindings

- Change os.path.getsize return type from int to int64 to handle files >= 2 GiB
- Reorder getpid/getppid next to getenv; move walk near rmdir for grouping
- Improve walk test to assert dirpath="." and that subdirs+files match listdir
- Add getppid test
- Add walk(topdown=false) test using a controlled temp dir
- Use unique /tmp paths and clean up after makedirs/walk tests
- Revert CHANGELOG.md addition (AGENTS.md forbids modifying CHANGELOG)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Dag Brattli <dag@brattli.net>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 4 people

src/stdlib/Os.fs

@@ -30,6 +30,12 @@ type IExports =
     /// Return the value of the environment variable key or default if not set
     /// See https://docs.python.org/3/library/os.html#os.getenv
     abstract getenv: key: string * ``default``: string -> string
+    /// Return the current process id.
+    /// See https://docs.python.org/3/library/os.html#os.getpid
+    abstract getpid: unit -> int
+    /// Return the parent process id.
+    /// See https://docs.python.org/3/library/os.html#os.getppid
+    abstract getppid: unit -> int
     /// Send signal sig to the process pid
     /// See https://docs.python.org/3/library/os.html#os.kill
     abstract kill: pid: int * ``sig``: int -> unit
@@ -42,8 +48,14 @@ type IExports =
     /// Recursive directory creation function
     /// See https://docs.python.org/3/library/os.html#os.makedirs
     abstract makedirs: path: string -> unit
-    /// Recursive directory creation with optional mode and exist_ok flag
+    /// Recursive directory creation, creating parent directories as needed.
+    /// Raises FileExistsError if the directory already exists and exist_ok is false.
     /// See https://docs.python.org/3/library/os.html#os.makedirs
+    [<Emit("$0.makedirs($1, exist_ok=$2)")>]
+    abstract makedirs: path: string * exist_ok: bool -> unit
+    /// Recursive directory creation with explicit mode and exist_ok flag.
+    /// See https://docs.python.org/3/library/os.html#os.makedirs
+    [<Emit("$0.makedirs($1, $2, $3)")>]
     abstract makedirs: path: string * mode: int * exist_ok: bool -> unit
     /// Set the environment variable named key to the string value
     /// See https://docs.python.org/3/library/os.html#os.putenv
@@ -60,6 +72,15 @@ type IExports =
     /// Remove (delete) the directory path
     /// See https://docs.python.org/3/library/os.html#os.rmdir
     abstract rmdir: path: string -> unit
+    /// Walk a directory tree, yielding (dirpath, dirnames, filenames) for each directory.
+    /// When topdown is true (the default) the caller can modify the dirnames list in-place
+    /// to prune the search or impose a specific visiting order.
+    /// See https://docs.python.org/3/library/os.html#os.walk
+    abstract walk: top: string -> seq<string * ResizeArray<string> * ResizeArray<string>>
+    /// Walk a directory tree top-down or bottom-up (topdown=false).
+    /// See https://docs.python.org/3/library/os.html#os.walk
+    [<Emit("$0.walk($1, topdown=$2)")>]
+    abstract walk: top: string * topdown: bool -> seq<string * ResizeArray<string> * ResizeArray<string>>
     /// Test whether a path exists
     /// See https://docs.python.org/3/library/os.path.html#os.path.exists
     abstract path: PathModule
@@ -96,6 +117,18 @@ and [<Erase>] PathModule =
     /// Split the pathname path into a pair (root, ext)
     /// See https://docs.python.org/3/library/os.path.html#os.path.splitext
     abstract splitext: path: string -> string * string
+    /// Return True if path is an absolute pathname
+    /// See https://docs.python.org/3/library/os.path.html#os.path.isabs
+    abstract isabs: path: string -> bool
+    /// Return True if path refers to a symbolic link
+    /// See https://docs.python.org/3/library/os.path.html#os.path.islink
+    abstract islink: path: string -> bool
+    /// Return the canonical path of the specified filename, resolving symlinks
+    /// See https://docs.python.org/3/library/os.path.html#os.path.realpath
+    abstract realpath: path: string -> string
+    /// Return the size, in bytes, of path
+    /// See https://docs.python.org/3/library/os.path.html#os.path.getsize
+    abstract getsize: path: string -> int64
 
 
 /// Miscellaneous operating system interfaces

test/TestOs.fs

@@ -58,3 +58,72 @@ let ``test os.listdir works`` () =
     let entries = os.listdir "."
     // Current directory should have at least some entries
     entries.Length > 0 |> equal true
+
+[<Fact>]
+let ``test os.path.isabs works`` () =
+    os.path.isabs "/absolute/path" |> equal true
+    os.path.isabs "relative/path" |> equal false
+    os.path.isabs "." |> equal false
+
+[<Fact>]
+let ``test os.path.realpath works`` () =
+    let real = os.path.realpath "."
+    real.StartsWith("/") |> equal true
+    // realpath should not contain symlink components; at minimum equal to abspath for "."
+    real.Length > 0 |> equal true
+
+[<Fact>]
+let ``test os.path.islink works`` () =
+    // "." is never a symlink
+    os.path.islink "." |> equal false
+
+[<Fact>]
+let ``test os.path.getsize works`` () =
+    // The test directory itself has a positive size
+    os.path.getsize "." > 0L |> equal true
+
+[<Fact>]
+let ``test os.getpid works`` () =
+    let pid = os.getpid ()
+    pid > 0 |> equal true
+
+[<Fact>]
+let ``test os.getppid works`` () =
+    let ppid = os.getppid ()
+    ppid > 0 |> equal true
+
+[<Fact>]
+let ``test os.makedirs with exist_ok works`` () =
+    let dir = sprintf "/tmp/fable_test_makedirs_%d" (os.getpid ())
+    os.makedirs (dir, true)
+    os.path.isdir dir |> equal true
+    // Second call must not raise when exist_ok=true
+    os.makedirs (dir, true)
+    os.path.isdir dir |> equal true
+    os.rmdir dir
+
+[<Fact>]
+let ``test os.walk yields entries`` () =
+    let entries = os.walk "." |> Seq.truncate 1 |> Seq.toList
+    entries.Length |> equal 1
+    let dirpath, subdirs, files = entries.[0]
+    dirpath |> equal "."
+    // The first walk entry's dirnames + filenames should equal listdir of the root
+    let walkAll = Seq.append subdirs files |> Seq.sort |> Seq.toList
+    let listdirAll = os.listdir "." |> Array.sort |> Array.toList
+    walkAll |> equal listdirAll
+
+[<Fact>]
+let ``test os.walk with topdown=false works`` () =
+    let root = sprintf "/tmp/fable_test_walk_%d" (os.getpid ())
+    let nested = os.path.join (root, "nested")
+    os.makedirs (nested, true)
+    let entries = os.walk (root, false) |> Seq.toList
+    // Bottom-up: deepest dir is yielded first, root is yielded last
+    entries.Length |> equal 2
+    let firstDir, _, _ = entries.[0]
+    let lastDir, _, _ = List.last entries
+    firstDir |> equal nested
+    lastDir |> equal root
+    os.rmdir nested
+    os.rmdir root