Add error messages

src/error.rs

@@ -1,3 +1,5 @@
+use std::{error::Error, fmt::Display};
+
 /// Enumerates the possible error values that can be generated by this crate
 #[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]
 #[non_exhaustive]
@@ -12,3 +14,38 @@ pub enum VSCError {
         staged_files: Vec<String>,
     },
 }
+
+impl Display for VSCError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            VSCError::NoVCS => write!(f, "no VCS found but this not allowed"),
+            VSCError::NotAllowedFilesFound {
+                dirty_files,
+                staged_files,
+            } => {
+                let mut files_list = String::new();
+                for file in dirty_files {
+                    files_list.push_str("  * ");
+                    files_list.push_str(file);
+                    files_list.push_str(" (dirty)\n");
+                }
+                for file in staged_files {
+                    files_list.push_str("  * ");
+                    files_list.push_str(file);
+                    files_list.push_str(" (staged)\n");
+                }
+
+                write!(
+                    f,
+                    "disallowed files found:\n\
+                     \n\
+                     {}\n\
+                     ",
+                    files_list
+                )
+            }
+        }
+    }
+}
+
+impl Error for VSCError {}