extracts .roc files from folders before formatting

cli/src/format.rs

@@ -25,7 +25,45 @@ use roc_parse::{
 };
 use roc_region::all::{Loc, Region};
 
+fn flatten_folders(files: std::vec::Vec<PathBuf>) -> std::vec::Vec<PathBuf> {
+    files.into_iter().flat_map(|file| {
+        if file.is_dir() {
+            match file.read_dir() {
+                Ok(directory) => directory
+                    .flat_map(|result| match result {
+                        Ok(file) => {
+                            let path = file.path();
+
+                            if path.is_dir() {
+                                flatten_folders(vec![path])
+                            } else if path.ends_with(".roc") {
+                                vec![path]
+                            } else {
+                                vec![]
+                            }
+                        }
+                        Err(error) => internal_error!(
+                            "There was an error while trying to read a file from a folder: {:?}",
+                            error
+                        ),
+                    })
+                    .collect(),
+                Err(error) => {
+                    internal_error!(
+                        "There was an error while trying to read the contents of a directory: {:?}",
+                        error
+                    );
+                }
+            }
+        } else {
+            vec![file]
+        }
+    }).collect()
+}
+
 pub fn format(files: std::vec::Vec<PathBuf>, mode: FormatMode) -> Result<(), String> {
+    let files = flatten_folders(files);
+
     for file in files {
         let arena = Bump::new();