Add docstring

google-apis-common/src/field_mask.rs

@@ -35,6 +35,8 @@ fn snakecase(source: &str) -> String {
 pub struct FieldMask(Vec<String>);
 
 impl FieldMask {
+    /// Create a new `FieldMask` from a list of paths. These are converted to snake
+    /// case if they aren't already.
     pub fn new<S: AsRef<str>>(values: &[S]) -> Self {
         return Self(values.iter().map(|s| snakecase(s.as_ref())).collect());
     }