fileset: relax identifier rule to accept more path-like strings

Since fileset is primarily used in CLI, it's better to avoid inner quoting if
possible. For example, ".." would have to be quoted in the original grammar
derived from the revset.

This patch also adds a stricter version of an identifier rule. If we add a
symbol alias, it will follow the "strict_identifier" rule.

lib/src/fileset.pest

@@ -14,10 +14,17 @@
 
 whitespace = _{ " " | "\t" | "\r" | "\n" | "\x0c" }
 
-// TODO: adjust identifier rule for file names
-identifier_part = @{ (ASCII_ALPHANUMERIC | "_" | "/")+ }
+// XID_CONTINUE: https://www.unicode.org/reports/tr31/#Default_Identifier_Syntax
+// +, -, ., @, _: commonly used in file name including "." and ".."
+// /: path separator
+// \: path separator (Windows)
+// TODO: accept glob characters as identifier?
 identifier = @{
-  identifier_part ~ (("." | "-" | "+") ~ identifier_part)*
+  (XID_CONTINUE | "+" | "-" | "." | "@" | "_" | "/" | "\\")+
+}
+strict_identifier_part = @{ (ASCII_ALPHANUMERIC | "_")+ }
+strict_identifier = @{
+  strict_identifier_part ~ ("-" ~ strict_identifier_part)*
 }
 
 string_escape = @{ "\\" ~ ("t" | "r" | "n" | "0" | "\"" | "\\") }
@@ -42,7 +49,7 @@ function_arguments = {
 }
 
 // TODO: change rhs to string_literal to require quoting? #2101
-string_pattern = { identifier ~ pattern_kind_op ~ (identifier | string_literal) }
+string_pattern = { strict_identifier ~ pattern_kind_op ~ (identifier | string_literal) }
 
 primary = {
   "(" ~ whitespace* ~ expression ~ whitespace* ~ ")"

lib/src/fileset.rs

@@ -396,8 +396,7 @@ mod tests {
             cwd: Path::new("/ws/cur"),
             workspace_root: Path::new("/ws"),
         };
-        // TODO: adjust identifier rule and test the expression parser instead
-        let parse = |input| FilePattern::parse(&ctx, input).map(FilesetExpression::pattern);
+        let parse = |text| parse(text, &ctx);
 
         // cwd-relative patterns
         assert_eq!(

lib/src/fileset_parser.rs

@@ -40,8 +40,9 @@ impl Rule {
         match self {
             Rule::EOI => None,
             Rule::whitespace => None,
-            Rule::identifier_part => None,
             Rule::identifier => None,
+            Rule::strict_identifier_part => None,
+            Rule::strict_identifier => None,
             Rule::string_escape => None,
             Rule::string_content_char => None,
             Rule::string_content => None,
@@ -237,7 +238,7 @@ fn parse_primary_node(pair: Pair<Rule>) -> FilesetParseResult<ExpressionNode> {
         }
         Rule::string_pattern => {
             let (lhs, op, rhs) = first.into_inner().collect_tuple().unwrap();
-            assert_eq!(lhs.as_rule(), Rule::identifier);
+            assert_eq!(lhs.as_rule(), Rule::strict_identifier);
             assert_eq!(op.as_rule(), Rule::pattern_kind_op);
             let kind = lhs.as_str();
             let value = match rhs.as_rule() {
@@ -399,6 +400,18 @@ mod tests {
             parse_into_kind("dir/foo-bar_0.baz"),
             Ok(ExpressionKind::Identifier("dir/foo-bar_0.baz"))
         );
+        assert_eq!(
+            parse_into_kind("cli-reference@.md.snap"),
+            Ok(ExpressionKind::Identifier("cli-reference@.md.snap"))
+        );
+        assert_eq!(
+            parse_into_kind("柔術.jj"),
+            Ok(ExpressionKind::Identifier("柔術.jj"))
+        );
+        assert_eq!(
+            parse_into_kind(r#"Windows\Path"#),
+            Ok(ExpressionKind::Identifier(r#"Windows\Path"#))
+        );
     }
 
     #[test]