syntax: make \p{cf} work

It turns out that 'cf' is also an abbreviation for the 'Case_Folding'
property. Even though we don't actually support a 'Case_Folding'
property, a quirk of our code caused 'cf' to fail since it was treated
as a normal boolean property instead of a general category. We fix it be
special casing it.

Note that '\p{gc=cf}' worked and continues to work.

If we ever do add the 'Case_Folding' property, we'll not be able to
support its abbreviation since it is now taken by 'Format'.

Fixes #719

CHANGELOG.md

@@ -1,3 +1,13 @@
+1.4.1 (2020-10-13)
+==================
+This is a small bug fix release that makes `\p{cf}` work. Previously, it would
+report "property not found" even though `cf` is a valid abbreviation for the
+`Format` general category.
+
+* [BUG #719](https://github.com/rust-lang/regex/issues/719):
+  Fixes bug that prevented `\p{cf}` from working.
+
+
 1.4.0 (2020-10-11)
 ==================
 This releases has a few minor documentation fixes as well as some very minor

regex-syntax/src/unicode.rs

@@ -237,8 +237,16 @@ impl<'a> ClassQuery<'a> {
     fn canonical_binary(&self, name: &str) -> Result<CanonicalClassQuery> {
         let norm = symbolic_name_normalize(name);
 
-        if let Some(canon) = canonical_prop(&norm)? {
-            return Ok(CanonicalClassQuery::Binary(canon));
+        // This is a special case where 'cf' refers to the 'Format' general
+        // category, but where the 'cf' abbreviation is also an abbreviation
+        // for the 'Case_Folding' property. But we want to treat it as
+        // a general category. (Currently, we don't even support the
+        // 'Case_Folding' property. But if we do in the future, users will be
+        // required to spell it out.)
+        if norm != "cf" {
+            if let Some(canon) = canonical_prop(&norm)? {
+                return Ok(CanonicalClassQuery::Binary(canon));
+            }
         }
         if let Some(canon) = canonical_gencat(&norm)? {
             return Ok(CanonicalClassQuery::GeneralCategory(canon));

tests/unicode.rs

@@ -74,6 +74,9 @@ mat!(
     Some((0, 3))
 );
 mat!(uni_class_gencat_format, r"\p{Format}", "\u{E007F}", Some((0, 4)));
+// See: https://github.com/rust-lang/regex/issues/719
+mat!(uni_class_gencat_format_abbrev1, r"\p{cf}", "\u{E007F}", Some((0, 4)));
+mat!(uni_class_gencat_format_abbrev2, r"\p{gc=cf}", "\u{E007F}", Some((0, 4)));
 mat!(
     uni_class_gencat_initial_punctuation,
     r"\p{Initial_Punctuation}",