Refactor sidecars

crates/pile-config/src/pattern/parser.rs

@@ -0,0 +1,195 @@
+use smartstring::{LazyCompact, SmartString};
+
+use crate::{objectpath::ObjectPath, pattern::GroupPatternParseError};
+
+#[cfg_attr(test, derive(PartialEq))]
+#[derive(Debug, Clone)]
+pub enum GroupSegment {
+	Path(ObjectPath),
+	Literal(SmartString<LazyCompact>),
+}
+
+pub struct Parser {}
+
+impl Parser {
+	pub fn new() -> Self {
+		Self {}
+	}
+
+	/// Parse a pattern string of the form `{path}.literal{path}...`.
+	///
+	/// - `{...}` delimiters are parsed as [`ObjectPath`] expressions.
+	///   Nested `{}` inside a path are allowed; depth is tracked to find the
+	///   matching closing brace.
+	/// - Everything outside `{...}` is a `Literal` segment.
+	/// - A bare `}` in literal position (depth == 0) is a syntax error.
+	/// - An unclosed `{` is a syntax error.
+	pub fn parse(self, source: &str) -> Result<Vec<(usize, GroupSegment)>, GroupPatternParseError> {
+		let mut tokens = Vec::new();
+
+		// `depth` > 0 means we are currently inside a `{...}` path expression.
+		let mut depth: usize = 0;
+		// Start of the current segment (literal text or path content).
+		let mut window_start: usize = 0;
+		// Source position of the opening `{` for the current path (used for error reporting).
+		let mut open_brace: usize = 0;
+
+		for (i, c) in source.char_indices() {
+			match c {
+				'{' => {
+					if depth == 0 {
+						// Emit any accumulated literal.
+						if i > window_start {
+							tokens.push((
+								window_start,
+								GroupSegment::Literal(source[window_start..i].into()),
+							));
+						}
+						open_brace = i;
+						// Path content starts after the opening brace.
+						window_start = i + 1;
+						depth = 1;
+					} else {
+						// Nested brace inside a path — keep counting.
+						depth += 1;
+					}
+				}
+
+				'}' => {
+					if depth == 0 {
+						// Unmatched `}` outside any path.
+						return Err(GroupPatternParseError::Syntax { position: i });
+					}
+					depth -= 1;
+					if depth == 0 {
+						// Closing brace of the outermost path expression — parse as ObjectPath.
+						let path_str = &source[window_start..i];
+						let path = path_str.parse::<ObjectPath>().map_err(|e| {
+							GroupPatternParseError::InvalidObjectPath {
+								start: open_brace,
+								end: i + 1,
+								path: path_str.into(),
+								source: e,
+							}
+						})?;
+						tokens.push((open_brace, GroupSegment::Path(path)));
+						// Literal content (if any) starts after this `}`.
+						window_start = i + 1;
+					}
+				}
+
+				_ => {}
+			}
+		}
+
+		// Unclosed `{`.
+		if depth > 0 {
+			return Err(GroupPatternParseError::Syntax {
+				position: open_brace,
+			});
+		}
+
+		// Emit any trailing literal.
+		if window_start < source.len() {
+			tokens.push((
+				window_start,
+				GroupSegment::Literal(source[window_start..].into()),
+			));
+		}
+
+		Ok(tokens)
+	}
+}
+
+//
+// MARK: tests
+//
+
+#[expect(clippy::unwrap_used)]
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	fn parse(source: &str) -> Result<Vec<(usize, GroupSegment)>, GroupPatternParseError> {
+		Parser::new().parse(source)
+	}
+
+	fn path(s: &str) -> GroupSegment {
+		GroupSegment::Path(s.parse().unwrap())
+	}
+
+	fn lit(s: &str) -> GroupSegment {
+		GroupSegment::Literal(s.into())
+	}
+
+	#[test]
+	fn single_path() {
+		assert_eq!(parse("{$.foo}").unwrap(), vec![(0, path("$.foo"))]);
+	}
+
+	#[test]
+	fn single_literal() {
+		assert_eq!(parse("hello").unwrap(), vec![(0, lit("hello"))]);
+	}
+
+	#[test]
+	fn path_then_literal() {
+		assert_eq!(
+			parse("{$.foo}.txt").unwrap(),
+			vec![(0, path("$.foo")), (7, lit(".txt"))]
+		);
+	}
+
+	#[test]
+	fn literal_then_path() {
+		assert_eq!(
+			parse("prefix/{$.foo}").unwrap(),
+			vec![(0, lit("prefix/")), (7, path("$.foo"))]
+		);
+	}
+
+	#[test]
+	fn interleaved() {
+		assert_eq!(
+			parse("{$.a}.sep.{$.b}").unwrap(),
+			vec![(0, path("$.a")), (5, lit(".sep.")), (10, path("$.b")),]
+		);
+	}
+
+	#[test]
+	fn unmatched_open_brace_error() {
+		assert_eq!(
+			parse("{$.foo"),
+			Err(GroupPatternParseError::Syntax { position: 0 })
+		);
+	}
+
+	#[test]
+	fn unmatched_close_brace_in_literal_error() {
+		assert_eq!(
+			parse("foo}bar"),
+			Err(GroupPatternParseError::Syntax { position: 3 })
+		);
+	}
+
+	#[test]
+	fn invalid_path_error() {
+		assert_eq!(
+			parse("{not-a-path}"),
+			Err(GroupPatternParseError::InvalidObjectPath {
+				start: 0,
+				end: 12,
+				path: "not-a-path".into(),
+				source: crate::objectpath::PathParseError::MustStartWithRoot { position: 0 },
+			})
+		);
+	}
+
+	#[test]
+	fn literal_between_paths() {
+		assert_eq!(
+			parse("foo{$.x}bar").unwrap(),
+			vec![(0, lit("foo")), (3, path("$.x")), (8, lit("bar")),]
+		);
+	}
+}