emit error for unused header values

Author: ratmice

lrlex/src/main.rs

@@ -2,6 +2,7 @@ use getopts::Options;
 use std::{
     env,
     error::Error,
+    fmt,
     fs::File,
     io::{stderr, stdin, Read, Write},
     path::Path,
@@ -17,6 +18,22 @@ use lrpar::{
 
 const ERROR: &str = "[Error]";
 
+/// A string which uses `Display` for it's `Debug` impl.
+struct ErrorString(String);
+impl fmt::Display for ErrorString {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let ErrorString(s) = self;
+        write!(f, "{}", s)
+    }
+}
+impl fmt::Debug for ErrorString {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let ErrorString(s) = self;
+        write!(f, "{}", s)
+    }
+}
+impl Error for ErrorString {}
+
 fn usage(prog: &str, msg: &str) {
     let path = Path::new(prog);
     let leaf = match path.file_name() {
@@ -109,9 +126,18 @@ fn main() -> Result<(), Box<dyn Error>> {
             lexerdef
         }
         _ => {
-            return Err("Unrecognized lexer kind")?;
+            return Err(ErrorString("Unrecognized lexer kind".to_string()))?;
         }
     };
+    {
+        let unused_header_values = header.unused();
+        if !unused_header_values.is_empty() {
+            return Err(ErrorString(format!(
+                "Unused header values: {}",
+                unused_header_values.join(", ")
+            )))?;
+        }
+    }
     let input = &read_file(&matches.free[1]);
     for r in lexerdef.lexer(input).iter() {
         match r {