oof: add error variant MissingValueToFlag

oof/src/error.rs

@@ -3,7 +3,7 @@ use std::{error, ffi::OsString, fmt};
 use crate::Flag;
 
 #[derive(Debug)]
-pub enum OofError{
+pub enum OofError<'t> {
     FlagValueConflict {
         flag: Flag,
         previous_value: OsString,
@@ -13,16 +13,17 @@ pub enum OofError{
     InvalidUnicode(OsString),
     /// User supplied an unrecognized short flag
     UnknownShortFlag(char),
-    MisplacedShortArgFlagError(char)
+    MisplacedShortArgFlagError(char),
+    MissingValueToFlag(&'t Flag)
 }
 
-impl error::Error for OofError {
+impl<'t> error::Error for OofError<'t> {
     fn source(&self) -> Option<&(dyn error::Error + 'static)> {
         None
     }
 }
 
-impl fmt::Display for OofError {
+impl<'t> fmt::Display for OofError<'t> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         // TODO: implement proper debug messages
         match self {
@@ -38,6 +39,7 @@ impl fmt::Display for OofError {
             OofError::InvalidUnicode(flag) => write!(f, "{:?} is not valid Unicode.", flag),
             OofError::UnknownShortFlag(ch) => write!(f, "Unknown argument '-{}'", ch),
             OofError::MisplacedShortArgFlagError(ch) => write!(f, "Invalid placement of `-{}`.\nOnly the last letter in a sequence of short flags can take values.", ch),
+            OofError::MissingValueToFlag(flag) => write!(f, "Flag {} takes value but none was supplied.", flag)
         }
     }
 }

oof/src/lib.rs

@@ -147,12 +147,9 @@ pub fn filter_flags(
                     }
 
                     // pop the next one
-                    let flag_argument = iter.next().unwrap_or_else(|| {
-                        panic!(
-                            "USer errror: argument flag `argument_flag` came at last, but it \
-                             requires an argument"
-                        )
-                    });
+                    let flag_argument = iter.next().ok_or_else(|| {
+                        OofError::MissingValueToFlag(flag_info)
+                    })?;
 
                     // Otherwise, insert it.
                     result_flags.argument_flags.insert(flag_name, flag_argument);

src/error.rs

@@ -116,7 +116,7 @@ impl From<walkdir::Error> for Error {
     }
 }
 
-impl From<oof::OofError> for Error {
+impl<'t> From<oof::OofError<'t>> for Error {
     fn from(_err: oof::OofError) -> Self {
         todo!("We need to implement this properly");
     }