Add XPath parser/evaluator (#34463)

* Add XPath parser/evaluator

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

* Correctly annotate XPathEvaluator IDL

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

* [PR review]: have bindings pass in `can_gc`

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

* [PR review]: add docstrings

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

* [PR review]: implement PartialEq for Value for readability

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

* [PR review]: add docstrings for CoreFunctions

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

* [PR review]: simplify node test code

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

* [PR review]: add unit tests for string handling xpath functions

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

* put xpath features behind dom.xpath.enabled pref

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

* [PR review] remove rstest and insta dev-deps

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

* update wpt test expectations

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

* [PR review]: tweak metadata files

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

* update wpt test expectations AGAIN

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

---------

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

components/script/xpath/mod.rs

@@ -0,0 +1,73 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use context::EvaluationCtx;
+use eval::Evaluatable;
+pub use eval_value::{NodesetHelpers, Value};
+use parser::OwnedParserError;
+pub use parser::{parse as parse_impl, Expr};
+
+use super::dom::node::Node;
+
+mod context;
+mod eval;
+mod eval_function;
+mod eval_value;
+mod parser;
+
+/// The failure modes of executing an XPath.
+#[derive(Debug, PartialEq)]
+pub enum Error {
+    /// The XPath was syntactically invalid
+    Parsing { source: OwnedParserError },
+    /// The XPath could not be executed
+    Evaluating { source: eval::Error },
+}
+
+impl std::fmt::Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self {
+            Error::Parsing { source } => write!(f, "Unable to parse XPath: {}", source),
+            Error::Evaluating { source } => write!(f, "Unable to evaluate XPath: {}", source),
+        }
+    }
+}
+
+impl std::error::Error for Error {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Error::Parsing { source } => Some(source),
+            Error::Evaluating { source } => Some(source),
+        }
+    }
+}
+
+/// Parse an XPath expression from a string
+pub fn parse(xpath: &str) -> Result<Expr, Error> {
+    match parse_impl(xpath) {
+        Ok(expr) => {
+            debug!("Parsed XPath: {:?}", expr);
+            Ok(expr)
+        },
+        Err(e) => {
+            debug!("Unable to parse XPath: {}", e);
+            Err(Error::Parsing { source: e })
+        },
+    }
+}
+
+/// Evaluate an already-parsed XPath expression
+pub fn evaluate_parsed_xpath(expr: &Expr, context_node: &Node) -> Result<Value, Error> {
+    let context = EvaluationCtx::new(context_node);
+    match expr.evaluate(&context) {
+        Ok(v) => {
+            debug!("Evaluated XPath: {:?}", v);
+            Ok(v)
+        },
+        Err(e) => {
+            debug!("Unable to evaluate XPath: {}", e);
+            Err(Error::Evaluating { source: e })
+        },
+    }
+}