fileset: fall back to bare pattern/string if no operator-like character found

While I like strict parsing, it's not uncommon that we have to deal with file
names containing spaces, and doubly-quoted strings such as '"Foo Bar"' look
ugly. So, this patch adds an exception that accepts top-level bare strings.
This parsing rule is specific to command arguments, and won't be enabled when
loading fileset aliases.

cli/src/cli_util.rs

@@ -748,7 +748,7 @@ impl WorkspaceCommandHelper {
         let ctx = self.fileset_parse_context();
         let expressions: Vec<_> = file_args
             .iter()
-            .map(|arg| fileset::parse(arg, &ctx))
+            .map(|arg| fileset::parse_maybe_bare(arg, &ctx))
             .try_collect()?;
         Ok(FilesetExpression::union_all(expressions))
     }

cli/src/commands/debug.rs

@@ -151,7 +151,7 @@ fn cmd_debug_fileset(
     let workspace_command = command.workspace_helper(ui)?;
     let ctx = workspace_command.fileset_parse_context();
 
-    let expression = fileset::parse(&args.path, &ctx)?;
+    let expression = fileset::parse_maybe_bare(&args.path, &ctx)?;
     writeln!(ui.stdout(), "-- Parsed:")?;
     writeln!(ui.stdout(), "{expression:#?}")?;
     writeln!(ui.stdout())?;

docs/filesets.md

@@ -12,6 +12,15 @@ consists of file patterns, operators, and functions.
 ui.allow-filesets = true
 ```
 
+Many `jj` commands accept fileset expressions as positional arguments. File
+names passed to these commands must be quoted if they contain whitespace or meta
+characters. However, as a special case, quotes can be omitted if the expression
+has no operators nor function calls. For example:
+
+* `jj diff 'Foo Bar'` (shell quotes are required, but inner quotes are optional)
+* `jj diff '~"Foo Bar"'` (both shell and inner quotes are required)
+* `jj diff '"Foo(1)"'` (both shell and inner quotes are required)
+
 ## File patterns
 
 The following patterns are supported:

lib/src/fileset.pest

@@ -27,6 +27,14 @@ strict_identifier = @{
   strict_identifier_part ~ ("-" ~ strict_identifier_part)*
 }
 
+// TODO: accept glob characters?
+// TODO: accept more ASCII meta characters such as "#" and ","?
+bare_string = @{
+  ( ASCII_ALPHANUMERIC
+  | " " | "+" | "-" | "." | "@" | "_" | "/" | "\\"
+  | '\u{80}'..'\u{10ffff}' )+
+}
+
 string_escape = @{ "\\" ~ ("t" | "r" | "n" | "0" | "\"" | "\\") }
 string_content_char = @{ !("\"" | "\\") ~ ANY }
 string_content = @{ string_content_char+ }
@@ -50,6 +58,7 @@ function_arguments = {
 
 // TODO: change rhs to string_literal to require quoting? #2101
 string_pattern = { strict_identifier ~ pattern_kind_op ~ (identifier | string_literal) }
+bare_string_pattern = { strict_identifier ~ pattern_kind_op ~ bare_string }
 
 primary = {
   "(" ~ whitespace* ~ expression ~ whitespace* ~ ")"
@@ -65,3 +74,8 @@ expression = {
 }
 
 program = _{ SOI ~ whitespace* ~ expression ~ whitespace* ~ EOI }
+program_or_bare_string = _{
+  SOI ~ ( whitespace* ~ expression ~ whitespace* ~ EOI
+        | bare_string_pattern ~ EOI
+        | bare_string ~ EOI )
+}

lib/src/fileset.rs

@@ -462,9 +462,15 @@ fn resolve_expression(
     }
 }
 
-/// Parses text into `FilesetExpression`.
-pub fn parse(text: &str, ctx: &FilesetParseContext) -> FilesetParseResult<FilesetExpression> {
-    let node = fileset_parser::parse_program(text)?;
+/// Parses text into `FilesetExpression` with bare string fallback.
+///
+/// If the text can't be parsed as a fileset expression, and if it doesn't
+/// contain any operator-like characters, it will be parsed as a file path.
+pub fn parse_maybe_bare(
+    text: &str,
+    ctx: &FilesetParseContext,
+) -> FilesetParseResult<FilesetExpression> {
+    let node = fileset_parser::parse_program_or_bare_string(text)?;
     // TODO: add basic tree substitution pass to eliminate redundant expressions
     resolve_expression(ctx, &node)
 }
@@ -483,7 +489,7 @@ mod tests {
             cwd: Path::new("/ws/cur"),
             workspace_root: Path::new("/ws"),
         };
-        let parse = |text| parse(text, &ctx);
+        let parse = |text| parse_maybe_bare(text, &ctx);
 
         // cwd-relative patterns
         assert_eq!(
@@ -535,7 +541,7 @@ mod tests {
             cwd: Path::new("/ws/cur*"),
             workspace_root: Path::new("/ws"),
         };
-        let parse = |text| parse(text, &ctx);
+        let parse = |text| parse_maybe_bare(text, &ctx);
         let glob_expr = |dir: &str, pattern: &str| {
             FilesetExpression::pattern(FilePattern::FileGlob {
                 dir: repo_path_buf(dir),
@@ -618,7 +624,7 @@ mod tests {
             cwd: Path::new("/ws/cur"),
             workspace_root: Path::new("/ws"),
         };
-        let parse = |text| parse(text, &ctx);
+        let parse = |text| parse_maybe_bare(text, &ctx);
 
         assert_eq!(parse("all()").unwrap(), FilesetExpression::all());
         assert_eq!(parse("none()").unwrap(), FilesetExpression::none());
@@ -644,7 +650,7 @@ mod tests {
             cwd: Path::new("/ws/cur"),
             workspace_root: Path::new("/ws"),
         };
-        let parse = |text| parse(text, &ctx);
+        let parse = |text| parse_maybe_bare(text, &ctx);
 
         insta::assert_debug_snapshot!(parse("~x").unwrap(), @r###"
         Difference(

lib/src/fileset_parser.rs

@@ -43,6 +43,7 @@ impl Rule {
             Rule::identifier => None,
             Rule::strict_identifier_part => None,
             Rule::strict_identifier => None,
+            Rule::bare_string => None,
             Rule::string_escape => None,
             Rule::string_content_char => None,
             Rule::string_content => None,
@@ -58,9 +59,11 @@ impl Rule {
             Rule::function_name => None,
             Rule::function_arguments => None,
             Rule::string_pattern => None,
+            Rule::bare_string_pattern => None,
             Rule::primary => None,
             Rule::expression => None,
             Rule::program => None,
+            Rule::program_or_bare_string => None,
         }
     }
 }
@@ -296,12 +299,39 @@ fn parse_expression_node(pair: Pair<Rule>) -> FilesetParseResult<ExpressionNode>
 }
 
 /// Parses text into expression tree. No name resolution is made at this stage.
+#[cfg(test)] // TODO: alias will be parsed with no bare_string fallback
 pub fn parse_program(text: &str) -> FilesetParseResult<ExpressionNode> {
     let mut pairs = FilesetParser::parse(Rule::program, text)?;
     let first = pairs.next().unwrap();
     parse_expression_node(first)
 }
 
+/// Parses text into expression tree with bare string fallback. No name
+/// resolution is made at this stage.
+///
+/// If the text can't be parsed as a fileset expression, and if it doesn't
+/// contain any operator-like characters, it will be parsed as a file path.
+pub fn parse_program_or_bare_string(text: &str) -> FilesetParseResult<ExpressionNode> {
+    let mut pairs = FilesetParser::parse(Rule::program_or_bare_string, text)?;
+    let first = pairs.next().unwrap();
+    let span = first.as_span();
+    let expr = match first.as_rule() {
+        Rule::expression => return parse_expression_node(first),
+        Rule::bare_string_pattern => {
+            let (lhs, op, rhs) = first.into_inner().collect_tuple().unwrap();
+            assert_eq!(lhs.as_rule(), Rule::strict_identifier);
+            assert_eq!(op.as_rule(), Rule::pattern_kind_op);
+            assert_eq!(rhs.as_rule(), Rule::bare_string);
+            let kind = lhs.as_str();
+            let value = rhs.as_str().to_owned();
+            ExpressionKind::StringPattern { kind, value }
+        }
+        Rule::bare_string => ExpressionKind::String(first.as_str().to_owned()),
+        r => panic!("unexpected program or bare string rule: {r:?}"),
+    };
+    Ok(ExpressionNode::new(expr, span))
+}
+
 pub fn expect_no_arguments(function: &FunctionCallNode) -> FilesetParseResult<()> {
     if function.args.is_empty() {
         Ok(())
@@ -325,10 +355,20 @@ mod tests {
             .map_err(|err| err.kind)
     }
 
+    fn parse_maybe_bare_into_kind(text: &str) -> Result<ExpressionKind, FilesetParseErrorKind> {
+        parse_program_or_bare_string(text)
+            .map(|node| node.kind)
+            .map_err(|err| err.kind)
+    }
+
     fn parse_normalized(text: &str) -> FilesetParseResult<ExpressionNode> {
         parse_program(text).map(normalize_tree)
     }
 
+    fn parse_maybe_bare_normalized(text: &str) -> FilesetParseResult<ExpressionNode> {
+        parse_program_or_bare_string(text).map(normalize_tree)
+    }
+
     /// Drops auxiliary data from parsed tree so it can be compared with other.
     fn normalize_tree(node: ExpressionNode) -> ExpressionNode {
         fn empty_span() -> pest::Span<'static> {
@@ -561,6 +601,75 @@ mod tests {
         assert!(parse_normalized("foo(a,,b)").is_err());
     }
 
+    #[test]
+    fn test_parse_bare_string() {
+        // Valid expression should be parsed as such
+        assert_eq!(
+            parse_maybe_bare_into_kind(" valid "),
+            Ok(ExpressionKind::Identifier("valid"))
+        );
+        assert_eq!(
+            parse_maybe_bare_normalized("f(x)&y").unwrap(),
+            parse_normalized("f(x)&y").unwrap()
+        );
+
+        // Bare string
+        assert_eq!(
+            parse_maybe_bare_into_kind("Foo Bar.txt"),
+            Ok(ExpressionKind::String("Foo Bar.txt".to_owned()))
+        );
+        assert_eq!(
+            parse_maybe_bare_into_kind(r#"Windows\Path with space"#),
+            Ok(ExpressionKind::String(
+                r#"Windows\Path with space"#.to_owned()
+            ))
+        );
+        assert_eq!(
+            parse_maybe_bare_into_kind("柔 術 . j j"),
+            Ok(ExpressionKind::String("柔 術 . j j".to_owned()))
+        );
+        assert_eq!(
+            parse_maybe_bare_into_kind("Unicode emoji 💩"),
+            Ok(ExpressionKind::String("Unicode emoji 💩".to_owned()))
+        );
+        assert_eq!(
+            parse_maybe_bare_into_kind("looks like & expression"),
+            Err(FilesetParseErrorKind::SyntaxError)
+        );
+        assert_eq!(
+            parse_maybe_bare_into_kind("unbalanced_parens("),
+            Err(FilesetParseErrorKind::SyntaxError)
+        );
+
+        // Bare string pattern
+        assert_eq!(
+            parse_maybe_bare_into_kind("foo: bar baz"),
+            Ok(ExpressionKind::StringPattern {
+                kind: "foo",
+                value: " bar baz".to_owned()
+            })
+        );
+        assert_eq!(
+            parse_maybe_bare_into_kind("foo:bar:baz"),
+            Err(FilesetParseErrorKind::SyntaxError)
+        );
+        assert_eq!(
+            parse_maybe_bare_into_kind("foo:"),
+            Err(FilesetParseErrorKind::SyntaxError)
+        );
+        assert_eq!(
+            parse_maybe_bare_into_kind(r#"foo:"unclosed quote"#),
+            Err(FilesetParseErrorKind::SyntaxError)
+        );
+
+        // Surrounding spaces are simply preserved. They could be trimmed, but
+        // space is valid bare_string character.
+        assert_eq!(
+            parse_maybe_bare_into_kind(" No trim "),
+            Ok(ExpressionKind::String(" No trim ".to_owned()))
+        );
+    }
+
     #[test]
     fn test_parse_error() {
         insta::assert_snapshot!(parse_program("foo|").unwrap_err().to_string(), @r###"