Add actual error messages for the error messages

The annoying part is trying to format!() an OsStr.

src/options/misfire.rs

@@ -92,7 +92,7 @@ impl fmt::Display for Misfire {
 
         match *self {
             BadArgument(ref a, ref b, ref c) => write!(f, "Option {} has no value {:?} (Choices: {})", a, b, c),
-            InvalidOptions(ref e)            => write!(f, "{:?}", e),
+            InvalidOptions(ref e)            => write!(f, "{}", e),
             Help(ref text)                   => write!(f, "{}", text),
             Version(ref version)             => write!(f, "{}", version),
             Conflict(ref a, ref b)           => write!(f, "Option {} conflicts with option {}.", a, b),
@@ -106,3 +106,16 @@ impl fmt::Display for Misfire {
         }
     }
 }
+
+impl fmt::Display for ParseError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        use self::ParseError::*;
+
+        match *self {
+            NeedsValue { ref flag }              => write!(f, "Flag {} needs a value", flag),
+            ForbiddenValue { ref flag }          => write!(f, "Flag {} cannot take a value", flag),
+            UnknownShortArgument { ref attempt } => write!(f, "Unknown argument -{}", *attempt as char),
+            UnknownArgument { ref attempt }      => write!(f, "Unknown argument --{}", attempt.to_string_lossy()),
+        }
+    }
+}

src/options/parser.rs

@@ -60,6 +60,14 @@ impl Flag {
     }
 }
 
+impl fmt::Display for Flag {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        match *self {
+            Flag::Short(short) => write!(f, "-{}", short as char),
+            Flag::Long(long)   => write!(f, "--{}", long),
+        }
+    }
+}
 
 /// Whether redundant arguments should be considered a problem.
 #[derive(PartialEq, Debug, Copy, Clone)]

xtests/error_long

@@ -0,0 +1 @@
+Unknown argument --ternary

xtests/error_overvalued

@@ -0,0 +1 @@
+Flag --long cannot take a value

xtests/error_short

@@ -0,0 +1 @@
+Unknown argument -4

xtests/error_value

@@ -0,0 +1 @@
+Flag --time needs a value

xtests/run.sh

@@ -178,7 +178,11 @@ $exa $testcases/hiddens -l -aa 2>&1 | diff -q - $results/hiddens_laa  || exit 1
 
 
 # Errors
-$exa --binary 2>&1 | diff -q - $results/errors_useless  || exit 1
+$exa --binary     2>&1 | diff -q - $results/error_useless    || exit 1
+$exa --ternary    2>&1 | diff -q - $results/error_long       || exit 1
+$exa -4           2>&1 | diff -q - $results/error_short      || exit 1
+$exa --time       2>&1 | diff -q - $results/error_value      || exit 1
+$exa --long=time  2>&1 | diff -q - $results/error_overvalued || exit 1
 
 
 # And finally...