os: add os.walk_with_context/3 and a test for it

vlib/os/os.v

@@ -473,9 +473,13 @@ fn impl_walk_ext(path string, ext string, mut out []string) {
 	}
 }
 
-// walk recursively traverses the given directory `path`.
-// When a file is encountred it will call the callback function with current file as argument.
+// walk traverses the given directory `path`.
+// When a file is encountred it will call the
+// callback function `f` with current file as argument.
 pub fn walk(path string, f fn (string)) {
+	if path.len == 0 {
+		return
+	}
 	if !is_dir(path) {
 		return
 	}
@@ -495,13 +499,39 @@ pub fn walk(path string, f fn (string)) {
 	return
 }
 
+// FnWalkContextCB is used to define the callback functions, passed to os.walk_context
+pub type FnWalkContextCB = fn (voidptr, string)
+
+// walk_with_context traverses the given directory `path`.
+// For each encountred file, it will call your `fcb` callback,
+// passing it the arbitrary `context` in its first parameter,
+// and the path to the file in its second parameter.
+pub fn walk_with_context(path string, context voidptr, fcb FnWalkContextCB) {
+	if path.len == 0 {
+		return
+	}
+	if !is_dir(path) {
+		return
+	}
+	mut files := ls(path) or { return }
+	mut local_path_separator := path_separator
+	if path.ends_with(path_separator) {
+		local_path_separator = ''
+	}
+	for file in files {
+		p := path + local_path_separator + file
+		if is_dir(p) && !is_link(p) {
+			walk_with_context(p, context, fcb)
+		} else {
+			fcb(context, p)
+		}
+	}
+	return
+}
+
 // log will print "os.log: "+`s` ...
 pub fn log(s string) {
-	//$if macos {
-	// Use NSLog() on macos
-	//} $else {
 	println('os.log: ' + s)
-	//}
 }
 
 // mkdir_all will create a valid full path of all directories given in `path`.

vlib/os/os_test.v

@@ -193,13 +193,12 @@ fn test_ls() {
 	}
 	if x := os.ls('.') {
 		assert x.len > 0
-		dump(x)
 	} else {
 		assert false
 	}
 }
 
-fn test_walk_ext() ? {
+fn create_tree() ? {
 	os.mkdir_all('myfolder/f1/f2/f3') ?
 	os.mkdir_all('myfolder/a1/a2/a3') ?
 	create_file('myfolder/f1/f2/f3/a.txt') ?
@@ -213,6 +212,17 @@ fn test_walk_ext() ? {
 	create_file('myfolder/a1/a2/a3/z.txt') ?
 	create_file('myfolder/a1/1.txt') ?
 	create_file('myfolder/xyz.ini') ?
+}
+
+fn remove_tree() {
+	os.rmdir_all('myfolder') or {}
+}
+
+fn test_walk_ext() ? {
+	create_tree() ?
+	defer {
+		remove_tree()
+	}
 	all := os.walk_ext('.', '')
 	assert all.len > 10
 	mut top := os.walk_ext('myfolder', '.txt')
@@ -237,7 +247,19 @@ fn test_walk_ext() ? {
 	mut mds := os.walk_ext('myfolder', '.md')
 	mds.sort()
 	assert mds == ['myfolder/another.md', 'myfolder/f1/f2/f3/d.md']
-	os.rmdir_all('myfolder') ?
+}
+
+fn test_walk_with_context() ? {
+	create_tree() ?
+	defer {
+		remove_tree()
+	}
+	mut res := []string{}
+	os.walk_with_context('myfolder', &res, fn (mut res []string, fpath string) {
+		res << fpath
+	})
+	assert 'myfolder/f1/f2/f3/b.txt' in res
+	assert 'myfolder/another.md' in res
 }
 
 fn test_create_and_delete_folder() {