Add a js_error! macro to create opaque errors (#3920)

* Add a js_error! macro to create opaque errors

And as a bonus since I needed it, simplify comparison of strings
and add PartialEq<&str> for JsString.

* Add PartialEq<str> for JsStr. PartialEq<&str> uses the other

* Cargo clippy

* Remove conversion of non-string literals and remove From<String> for JsValue

core/engine/src/error.rs

@@ -14,6 +14,48 @@ use boa_gc::{custom_trace, Finalize, Trace};
 use boa_macros::js_str;
 use thiserror::Error;
 
+/// Create an opaque error object from a value or string literal.
+///
+/// Can be used with an expression that converts into `JsValue` or a format
+/// string with arguments.
+///
+/// # Examples
+///
+/// ```
+/// # use boa_engine::{js_str, Context, JsValue};
+/// use boa_engine::{js_error};
+/// let context = &mut Context::default();
+///
+/// let error = js_error!("error!");
+/// assert!(error.as_opaque().is_some());
+/// assert_eq!(error.as_opaque().unwrap().to_string(context).unwrap(), "error!");
+///
+/// let error = js_error!("error: {}", 5);
+/// assert_eq!(error.as_opaque().unwrap().to_string(context).unwrap(), "error: 5");
+///
+/// // Non-string literals must be used as an expression.
+/// let error = js_error!({ true });
+/// assert_eq!(error.as_opaque().unwrap(), &JsValue::from(true));
+/// ```
+#[macro_export]
+macro_rules! js_error {
+    ($value: literal) => {
+        $crate::JsError::from_opaque($crate::JsValue::from(
+            $crate::js_string!($value)
+        ))
+    };
+    ($value: expr) => {
+        $crate::JsError::from_opaque(
+            $crate::JsValue::from($value)
+        )
+    };
+    ($value: literal $(, $args: tt)* $(,)?) => {
+        $crate::JsError::from_opaque($crate::JsValue::from(
+            $crate::JsString::from(format!($value $(, $args)*))
+        ))
+    };
+}
+
 /// The error type returned by all operations related
 /// to the execution of Javascript code.
 ///
@@ -352,7 +394,7 @@ impl JsError {
     ///
     /// assert!(error.as_native().is_some());
     ///
-    /// let error = JsError::from_opaque(JsValue::undefined().into());
+    /// let error = JsError::from_opaque(JsValue::undefined());
     ///
     /// assert!(error.as_native().is_none());
     /// ```

core/string/src/lib.rs

@@ -1073,19 +1073,14 @@ impl<const N: usize> PartialEq<[u16; N]> for JsString {
 impl PartialEq<str> for JsString {
     #[inline]
     fn eq(&self, other: &str) -> bool {
-        let utf16 = self.code_points();
-        let mut utf8 = other.chars();
-
-        for lhs in utf16 {
-            if let Some(rhs) = utf8.next() {
-                match lhs {
-                    CodePoint::Unicode(lhs) if lhs == rhs => continue,
-                    _ => return false,
-                }
+        self.as_str() == other
     }
-            return false;
 }
-        utf8.next().is_none()
+
+impl PartialEq<&str> for JsString {
+    #[inline]
+    fn eq(&self, other: &&str) -> bool {
+        self.as_str() == *other
     }
 }
 

core/string/src/str.rs

@@ -291,6 +291,23 @@ impl PartialEq for JsStr<'_> {
     }
 }
 
+impl PartialEq<str> for JsStr<'_> {
+    #[inline]
+    fn eq(&self, other: &str) -> bool {
+        match self.variant() {
+            JsStrVariant::Latin1(v) => v == other.as_bytes(),
+            JsStrVariant::Utf16(v) => other.encode_utf16().zip(v).all(|(a, b)| a == *b),
+        }
+    }
+}
+
+impl PartialEq<&str> for JsStr<'_> {
+    #[inline]
+    fn eq(&self, other: &&str) -> bool {
+        self == *other
+    }
+}
+
 impl<'a> PartialEq<JsStr<'a>> for [u16] {
     #[inline]
     fn eq(&self, other: &JsStr<'a>) -> bool {