revset: add a function for escaping a symbol

When we have e.g. a bookmark name or a remote name and we want to
produce a revset from it, we may need to quote and escape it. This
patch implements a function for that.

Perhaps we'll want to more generally be able to format a whole
`RevsetExpression` later.

lib/src/dsl_util.rs

@@ -429,6 +429,24 @@ impl<R: RuleType> StringLiteralParser<R> {
     }
 }
 
+/// Escape special characters in the input
+pub fn escape_string(unescaped: &str) -> String {
+    let mut escaped = String::with_capacity(unescaped.len());
+    for c in unescaped.chars() {
+        match c {
+            '"' => escaped.push_str(r#"\""#),
+            '\\' => escaped.push_str(r#"\\"#),
+            '\t' => escaped.push_str(r#"\t"#),
+            '\r' => escaped.push_str(r#"\r"#),
+            '\n' => escaped.push_str(r#"\n"#),
+            '\0' => escaped.push_str(r#"\0"#),
+            '\x1b' => escaped.push_str(r#"\e"#),
+            c => escaped.push(c),
+        }
+    }
+    escaped
+}
+
 /// Helper to parse function call.
 #[derive(Debug)]
 pub struct FunctionCallParser<R> {

lib/src/revset.rs

@@ -2686,6 +2686,15 @@ pub struct RevsetWorkspaceContext<'a> {
     pub workspace_id: &'a WorkspaceId,
 }
 
+/// Formats a string as symbol by quoting and escaping it if necessary
+pub fn format_symbol(literal: &str) -> String {
+    if revset_parser::is_identifier(literal) {
+        literal.to_string()
+    } else {
+        format!(r#""{}""#, dsl_util::escape_string(literal))
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use std::path::PathBuf;
@@ -4327,4 +4336,29 @@ mod tests {
         }
         "###);
     }
+
+    #[test]
+    fn test_escape_string_literal() {
+        // Valid identifiers don't need quoting
+        assert_eq!(format_symbol("foo"), "foo");
+        assert_eq!(format_symbol("foo.bar"), "foo.bar");
+
+        // Invalid identifiers need quoting
+        assert_eq!(format_symbol("foo@bar"), r#""foo@bar""#);
+        assert_eq!(format_symbol("foo bar"), r#""foo bar""#);
+        assert_eq!(format_symbol("(foo)"), r#""(foo)""#);
+        assert_eq!(format_symbol("all:foo"), r#""all:foo""#);
+
+        // Some characters also need escaping
+        assert_eq!(format_symbol(r#"foo"bar"#), r#""foo\"bar""#);
+        assert_eq!(format_symbol(r#"foo\bar"#), r#""foo\\bar""#);
+        assert_eq!(format_symbol(r#"foo\"bar"#), r#""foo\\\"bar""#);
+        assert_eq!(format_symbol("foo\nbar"), r#""foo\nbar""#);
+
+        // Some characters don't technically need escaping, but we escape them for
+        // clarity
+        assert_eq!(format_symbol(r#"foo"bar"#), r#""foo\"bar""#);
+        assert_eq!(format_symbol(r#"foo\bar"#), r#""foo\\bar""#);
+        assert_eq!(format_symbol(r#"foo\"bar"#), r#""foo\\\"bar""#);
+    }
 }

lib/src/revset_parser.rs

@@ -681,6 +681,14 @@ fn parse_as_string_literal(pair: Pair<Rule>) -> String {
     }
 }
 
+/// Checks if the text is a valid identifier
+pub fn is_identifier(text: &str) -> bool {
+    match RevsetParser::parse(Rule::identifier, text) {
+        Ok(mut pairs) => pairs.next().unwrap().as_span().end() == text.len(),
+        Err(_) => false,
+    }
+}
+
 pub type RevsetAliasesMap = AliasesMap<RevsetAliasParser, String>;
 
 #[derive(Clone, Debug, Default)]