Tiny steps towards understanding rev-parsing better (#427)

They parse it backwards, which we most certainly won't do though.

git-revision/src/spec.rs

@@ -18,10 +18,12 @@ impl Default for Kind {
 
 pub mod parse {
     #![allow(missing_docs)]
-    use bstr::BStr;
+    use bstr::{BStr, BString};
 
     #[derive(Debug, thiserror::Error)]
     pub enum Error {
+        #[error("A portion of the input could not be parsed: {:?}", .input)]
+        UnconsumedInput { input: BString },
         #[error("The delegate didn't indicate success - check delegate for more information")]
         Delegate,
     }
@@ -77,12 +79,11 @@ pub mod parse {
             }
             input = revision(input, delegate)?;
 
-            assert!(
-                input.is_empty(),
-                "BUG: we must parse all of our input or fail gracefully: {:?}",
-                input
-            );
-            Ok(())
+            if input.is_empty() {
+                Ok(())
+            } else {
+                Err(Error::UnconsumedInput { input: input.into() })
+            }
         }
 
         fn try_range(input: &BStr) -> Option<(&[u8], spec::Kind)> {

git-revision/tests/spec/parse.rs

@@ -90,7 +90,7 @@ fn all_characters_are_taken_verbatim_which_includes_whitespace() {
 }
 
 mod revision {
-    use crate::spec::parse::parse;
+    use crate::spec::parse::{parse, try_parse_opts};
 
     #[test]
     fn at_by_iteself_is_shortcut_for_head() {
@@ -99,6 +99,13 @@ mod revision {
         assert_eq!(rec.resolve_ref_input.unwrap(), "HEAD");
     }
 
+    #[test]
+    #[ignore]
+    fn lonely_at_after_ref_is_invalid() {
+        let _err = try_parse_opts("HEAD@", Default::default()).unwrap_err();
+        // TODO: assertion
+    }
+
     #[test]
     fn refname_head() {
         let rec = parse("HEAD");
@@ -113,6 +120,14 @@ mod revision {
         assert!(rec.kind.is_none());
         assert_eq!(rec.resolve_ref_input.unwrap(), "HEADfake");
     }
+
+    #[test]
+    #[ignore]
+    fn full_head_ref_name() {
+        let rec = parse("refs/heads/main");
+        assert!(rec.kind.is_none());
+        assert_eq!(rec.resolve_ref_input.unwrap(), "refs/heads/main");
+    }
 }
 
 mod range {