fix: Parse revisions with @ in their name (#802).

Previously these would cause a parse error due to confusing `@` with
the short form of `HEAD`.

Merge branch 'fix-rev-parse-with-at'

Author: Byron

gix-revision/src/spec/parse/function.rs

@@ -344,8 +344,19 @@ where
     {
         let mut cursor = input;
         let mut ofs = 0;
-        while let Some((pos, b)) = cursor.iter().enumerate().find(|(_, b)| {
-            if b"@~^:.".contains(b) {
+        const SEPARATORS: &[u8] = b"~^:.";
+        while let Some((pos, b)) = cursor.iter().enumerate().find(|(pos, b)| {
+            if **b == b'@' {
+                if cursor.len() == 1 {
+                    return true;
+                }
+                let next = cursor.get(pos + 1);
+                let next_next = cursor.get(pos + 2);
+                if *pos != 0 && (next, next_next) == (Some(&b'.'), Some(&b'.')) {
+                    return false;
+                }
+                next == Some(&b'{') || next.map_or(false, |b| SEPARATORS.contains(b))
+            } else if SEPARATORS.contains(b) {
                 true
             } else {
                 if let Some(num) = consecutive_hex_chars.as_mut() {

gix-revision/tests/spec/parse/anchor/refnames.rs

@@ -1,5 +1,3 @@
-use gix_revision::spec;
-
 use crate::spec::parse::{parse, try_parse};
 
 #[test]
@@ -10,15 +8,37 @@ fn at_by_itself_is_shortcut_for_head() {
 }
 
 #[test]
-fn multiple_ats_are_invalid_but_may_cause_callbacks() {
-    let err = try_parse("@@").unwrap_err();
-    assert!(matches!(err, spec::parse::Error::AtNeedsCurlyBrackets {input} if input == "@"));
+fn at_is_allowed() {
+    for name in ["a@b", "@branch", "branch@", "@@", "@inner@"] {
+        let rec = parse(name);
+        assert!(rec.kind.is_none());
+        assert_eq!(rec.get_ref(0), name);
+        assert_eq!(rec.find_ref[1], None);
+    }
+}
+
+#[test]
+fn at_in_ranges_is_allowed() {
+    let input = "@@@..";
+    let rec = parse(input);
+    assert_eq!(rec.kind, Some(gix_revision::spec::Kind::RangeBetween));
+    assert_eq!(rec.get_ref(0), "@@@");
+    assert_eq!(rec.get_ref(1), "HEAD");
+
+    let input = "@@...@@";
+    let rec = parse(input);
+    assert_eq!(rec.kind, Some(gix_revision::spec::Kind::ReachableToMergeBase));
+    assert_eq!(rec.get_ref(0), "@@");
+    assert_eq!(rec.get_ref(1), "@@");
 }
 
 #[test]
-fn lonely_at_after_ref_is_invalid() {
-    let err = try_parse("HEAD@").unwrap_err();
-    assert!(matches!(err, spec::parse::Error::AtNeedsCurlyBrackets {input} if input == "@"));
+fn strange_revspecs_do_not_panic() {
+    let err = try_parse(".@.").unwrap_err();
+    assert!(matches!(
+        err,
+        gix_revision::spec::parse::Error::AtNeedsCurlyBrackets { input } if input == "@."
+    ));
 }
 
 #[test]