Add ObjectPath query language

crates/pile-config/src/objectpath/mod.rs

@@ -0,0 +1,95 @@
+use std::{fmt, str::FromStr};
+
+use serde::{
+	Deserialize, Deserializer,
+	de::{self, Visitor},
+};
+use smartstring::{LazyCompact, SmartString};
+use thiserror::Error;
+
+use crate::Label;
+
+mod parser;
+mod tokenizer;
+
+#[derive(Debug, Error, PartialEq)]
+pub enum PathParseError {
+	#[error("invalid syntax at index {position}")]
+	Syntax { position: usize },
+
+	#[error("path string must start with $")]
+	MustStartWithRoot { position: usize },
+
+	#[error("invalid field {str:?} at {position}")]
+	InvalidField {
+		position: usize,
+		str: SmartString<LazyCompact>,
+	},
+
+	#[error("invalid index {str:?} at {position}")]
+	InvalidIndexString {
+		position: usize,
+		str: SmartString<LazyCompact>,
+	},
+
+	#[error("non-ascii character {char:?} at index {position}")]
+	NonAsciiChar { position: usize, char: char },
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum PathSegment {
+	/// Go to root node (`$` identifier)
+	Root,
+
+	/// Go to a child of the current object
+	Field(Label),
+
+	/// Go to an element of the current list
+	Index(i64),
+}
+
+/// A path to aPathSegment::Field inside a nested object,
+/// This is a subset of the rfc9535 jsonpath.
+///
+/// Format:
+/// - `$` refers to the root object
+/// - `.<name>` selects aPathSegment::Field of an object
+/// - `[n]` selects an item of an array
+#[derive(Debug, Clone)]
+pub struct ObjectPath {
+	pub segments: Vec<PathSegment>,
+}
+
+impl<'de> Deserialize<'de> for ObjectPath {
+	fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
+		struct PathVisitor;
+
+		impl Visitor<'_> for PathVisitor {
+			type Value = ObjectPath;
+
+			fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+				f.write_str("an objectpath")
+			}
+
+			fn visit_str<E: de::Error>(self, v: &str) -> Result<Self::Value, E> {
+				v.parse().map_err(de::Error::custom)
+			}
+		}
+
+		deserializer.deserialize_str(PathVisitor)
+	}
+}
+
+impl FromStr for ObjectPath {
+	type Err = PathParseError;
+
+	fn from_str(source: &str) -> Result<Self, Self::Err> {
+		let tk = tokenizer::Tokenizer::new();
+		let tk = tk.tokenize(source)?;
+
+		let ps = parser::Parser::new();
+		let segments = ps.parse(source, &tk)?;
+
+		return Ok(Self { segments });
+	}
+}