os/os2: recursive directory walker, expose errors in read_directory, file clone

Adds a directory walker, a method of exposing and retrieving errors from
the existing read directory iterator, allows reusing of the existing
read directory iterator, and adds a file clone procedure

core/os/os2/dir_wasi.odin

@@ -1,6 +1,8 @@
 #+private
 package os2
 
+import "base:runtime"
+import "core:slice"
 import "base:intrinsics"
 import "core:sys/wasm/wasi"
 
@@ -8,7 +10,6 @@ Read_Directory_Iterator_Impl :: struct {
 	fullpath: [dynamic]byte,
 	buf:      []byte,
 	off:      int,
-	idx:      int,
 }
 
 @(require_results)
@@ -17,8 +18,8 @@ _read_directory_iterator :: proc(it: ^Read_Directory_Iterator) -> (fi: File_Info
 
 	buf := it.impl.buf[it.impl.off:]
 
-	index = it.impl.idx
-	it.impl.idx += 1
+	index = it.index
+	it.index += 1
 
 	for {
 		if len(buf) < size_of(wasi.dirent_t) {
@@ -28,10 +29,7 @@ _read_directory_iterator :: proc(it: ^Read_Directory_Iterator) -> (fi: File_Info
 		entry := intrinsics.unaligned_load((^wasi.dirent_t)(raw_data(buf)))
 		buf    = buf[size_of(wasi.dirent_t):]
 
-		if len(buf) < int(entry.d_namlen) {
-			// shouldn't be possible.
-			return
-		}
+		assert(len(buf) < int(entry.d_namlen))
 
 		name := string(buf[:entry.d_namlen])
 		buf = buf[entry.d_namlen:]
@@ -43,7 +41,8 @@ _read_directory_iterator :: proc(it: ^Read_Directory_Iterator) -> (fi: File_Info
 
 		n := len(fimpl.name)+1
 		if alloc_err := non_zero_resize(&it.impl.fullpath, n+len(name)); alloc_err != nil {
-			// Can't really tell caller we had an error, sad.
+			read_directory_iterator_set_error(it, name, alloc_err)
+			ok = true
 			return
 		}
 		copy(it.impl.fullpath[n:], name)
@@ -55,6 +54,7 @@ _read_directory_iterator :: proc(it: ^Read_Directory_Iterator) -> (fi: File_Info
 				ino      = entry.d_ino,
 				filetype = entry.d_type,
 			}
+			read_directory_iterator_set_error(it, string(it.impl.fullpath[:]), _get_platform_error(err))
 		}
 
 		fi = internal_stat(stat, string(it.impl.fullpath[:]))
@@ -63,27 +63,35 @@ _read_directory_iterator :: proc(it: ^Read_Directory_Iterator) -> (fi: File_Info
 	}
 }
 
-@(require_results)
-_read_directory_iterator_create :: proc(f: ^File) -> (iter: Read_Directory_Iterator, err: Error) {
+_read_directory_iterator_init :: proc(it: ^Read_Directory_Iterator, f: ^File) {
+	// NOTE: Allow calling `init` to target a new directory with the same iterator.
+	it.impl.off = 0
+
 	if f == nil || f.impl == nil {
-		err = .Invalid_File
+		read_directory_iterator_set_error(it, "", .Invalid_File)
 		return
 	}
 
 	impl := (^File_Impl)(f.impl)
-	iter.f = f
 
 	buf: [dynamic]byte
+	// NOTE: Allow calling `init` to target a new directory with the same iterator.
+	if it.impl.buf != nil {
+		buf = slice.into_dynamic(it.impl.buf)
+	}
 	buf.allocator = file_allocator()
-	defer if err != nil { delete(buf) }
 
-	// NOTE: this is very grug.
+	defer if it.err.err != nil { delete(buf) }
+
 	for {
-		non_zero_resize(&buf, 512 if len(buf) == 0 else len(buf)*2) or_return
+		if err := non_zero_resize(&buf, 512 if len(buf) == 0 else len(buf)*2); err != nil {
+			read_directory_iterator_set_error(it, name(f), err)
+			return
+		}
 
-		n, _err := wasi.fd_readdir(__fd(f), buf[:], 0)
-		if _err != nil {
-			err = _get_platform_error(_err)
+		n, err := wasi.fd_readdir(__fd(f), buf[:], 0)
+		if err != nil {
+			read_directory_iterator_set_error(it, name(f), _get_platform_error(err))
 			return
 		}
 
@@ -94,11 +102,18 @@ _read_directory_iterator_create :: proc(f: ^File) -> (iter: Read_Directory_Itera
 
 		assert(n == len(buf))
 	}
-	iter.impl.buf = buf[:]
+	it.impl.buf = buf[:]
 
-	iter.impl.fullpath = make([dynamic]byte, 0, len(impl.name)+128, file_allocator()) or_return
-	append(&iter.impl.fullpath, impl.name)
-	append(&iter.impl.fullpath, "/")
+	// NOTE: Allow calling `init` to target a new directory with the same iterator.
+	it.impl.fullpath.allocator = file_allocator()
+	clear(&it.impl.fullpath)
+	if err := reserve(&it.impl.fullpath, len(impl.name)+128); err != nil {
+		read_directory_iterator_set_error(it, name(f), err)
+		return
+	}
+
+	append(&it.impl.fullpath, impl.name)
+	append(&it.impl.fullpath, "/")
 
 	return
 }
@@ -106,5 +121,4 @@ _read_directory_iterator_create :: proc(f: ^File) -> (iter: Read_Directory_Itera
 _read_directory_iterator_destroy :: proc(it: ^Read_Directory_Iterator) {
 	delete(it.impl.buf, file_allocator())
 	delete(it.impl.fullpath)
-	it^ = {}
 }