Create new lazy Error type (#2283)

This is an experiment that tries to migrate the codebase from eager `Error` objects to lazy ones.

In short words, this redefines `JsResult = Result<JsValue, JsError>`, where `JsError` is a brand new type that stores only the essential part of an error type, and only transforms those errors to `JsObject`s on demand (when having to pass them as arguments to functions or store them inside async/generators).

This change is pretty big, because it unblocks a LOT of code from having to take a `&mut Context` on each call. It also paves the road for possibly making `JsError` a proper variant of `JsValue`, which can be a pretty big optimization for try/catch.

A downside of this is that it exposes some brand new error types to our public API. However, we can now implement `Error` on `JsError`, making our `JsResult` type a bit more inline with Rust's best practices.

~Will mark this as draft, since it's missing some documentation and a lot of examples, but~ it's pretty much feature complete. As always, any comments about the design are very much appreciated!

Note: Since there are a lot of changes which are essentially just rewriting `context.throw` to `JsNativeError::%type%`, I'll leave an "index" of the most important changes here:

- [boa_engine/src/error.rs](https://github.com/boa-dev/boa/pull/2283/files#diff-f15f2715655440626eefda5c46193d29856f4949ad37380c129a8debc6b82f26)
- [boa_engine/src/builtins/error/mod.rs](https://github.com/boa-dev/boa/pull/2283/files#diff-3eb1e4b4b5c7210eb98192a5277f5a239148423c6b970c4ae05d1b267f8f1084)
- [boa_tester/src/exec/mod.rs](https://github.com/boa-dev/boa/pull/2283/files#diff-fc3d7ad7b5e64574258c9febbe56171f3309b74e0c8da35238a76002f3ee34d9)

boa_cli/src/main.rs

@@ -118,7 +118,6 @@ impl Opt {
 #[derive(Debug, Clone, ValueEnum)]
 enum DumpFormat {
     /// The different types of format available for dumping.
-    ///
     // NOTE: This can easily support other formats just by
     // adding a field to this enum and adding the necessary
     // implementation. Example: Toml, Html, etc.
@@ -204,7 +203,7 @@ pub fn main() -> Result<(), io::Error> {
         } else {
             match context.eval(&buffer) {
                 Ok(v) => println!("{}", v.display()),
-                Err(v) => eprintln!("Uncaught {}", v.display()),
+                Err(v) => eprintln!("Uncaught {v}"),
             }
         }
     }
@@ -251,11 +250,7 @@ pub fn main() -> Result<(), io::Error> {
                         match context.eval(line.trim_end()) {
                             Ok(v) => println!("{}", v.display()),
                             Err(v) => {
-                                eprintln!(
-                                    "{}: {}",
-                                    "Uncaught".red(),
-                                    v.display().to_string().red()
-                                );
+                                eprintln!("{}: {}", "Uncaught".red(), v.to_string().red());
                             }
                         }
                     }

boa_engine/Cargo.toml

@@ -53,6 +53,7 @@ once_cell = "1.15.0"
 tap = "1.0.1"
 sptr = "0.3.2"
 static_assertions = "1.1.0"
+thiserror = "1.0.37"
 icu_locale_canonicalizer = { version = "0.6.0", features = ["serde"], optional = true }
 icu_locid = { version = "0.6.0", features = ["serde"], optional = true }
 icu_datetime = { version = "0.6.0", features = ["serde"], optional = true }

boa_engine/src/bigint.rs

@@ -1,6 +1,6 @@
 //! This module implements the JavaScript bigint primitive rust type.
 
-use crate::{builtins::Number, Context, JsValue};
+use crate::{builtins::Number, error::JsNativeError, JsResult};
 use num_integer::Integer;
 use num_traits::{pow::Pow, FromPrimitive, One, ToPrimitive, Zero};
 use std::{
@@ -148,11 +148,13 @@ impl JsBigInt {
     }
 
     #[inline]
-    pub fn pow(x: &Self, y: &Self, context: &mut Context) -> Result<Self, JsValue> {
+    pub fn pow(x: &Self, y: &Self) -> JsResult<Self> {
         let y = if let Some(y) = y.inner.to_biguint() {
             y
         } else {
-            return context.throw_range_error("BigInt negative exponent");
+            return Err(JsNativeError::range()
+                .with_message("BigInt negative exponent")
+                .into());
         };
 
         let num_bits = (x.inner.bits() as f64
@@ -161,14 +163,16 @@ impl JsBigInt {
             + 1f64;
 
         if num_bits > 1_000_000_000f64 {
-            return context.throw_range_error("Maximum BigInt size exceeded");
+            return Err(JsNativeError::range()
+                .with_message("Maximum BigInt size exceeded")
+                .into());
         }
 
         Ok(Self::new(x.inner.as_ref().clone().pow(y)))
     }
 
     #[inline]
-    pub fn shift_right(x: &Self, y: &Self, context: &mut Context) -> Result<Self, JsValue> {
+    pub fn shift_right(x: &Self, y: &Self) -> JsResult<Self> {
         if let Some(n) = y.inner.to_i32() {
             let inner = if n > 0 {
                 x.inner.as_ref().clone().shr(n as usize)
@@ -178,12 +182,14 @@ impl JsBigInt {
 
             Ok(Self::new(inner))
         } else {
-            context.throw_range_error("Maximum BigInt size exceeded")
+            Err(JsNativeError::range()
+                .with_message("Maximum BigInt size exceeded")
+                .into())
         }
     }
 
     #[inline]
-    pub fn shift_left(x: &Self, y: &Self, context: &mut Context) -> Result<Self, JsValue> {
+    pub fn shift_left(x: &Self, y: &Self) -> JsResult<Self> {
         if let Some(n) = y.inner.to_i32() {
             let inner = if n > 0 {
                 x.inner.as_ref().clone().shl(n as usize)
@@ -193,7 +199,9 @@ impl JsBigInt {
 
             Ok(Self::new(inner))
         } else {
-            context.throw_range_error("Maximum BigInt size exceeded")
+            Err(JsNativeError::range()
+                .with_message("Maximum BigInt size exceeded")
+                .into())
         }
     }
 

boa_engine/src/builtins/array/array_iterator.rs

@@ -1,5 +1,6 @@
 use crate::{
     builtins::{function::make_builtin_fn, iterable::create_iter_result_object, Array, JsValue},
+    error::JsNativeError,
     object::{JsObject, ObjectData},
     property::{PropertyDescriptor, PropertyNameKind},
     symbol::WellKnownSymbols,
@@ -72,7 +73,7 @@ impl ArrayIterator {
         let array_iterator = array_iterator
             .as_mut()
             .and_then(|obj| obj.as_array_iterator_mut())
-            .ok_or_else(|| context.construct_type_error("`this` is not an ArrayIterator"))?;
+            .ok_or_else(|| JsNativeError::typ().with_message("`this` is not an ArrayIterator"))?;
         let index = array_iterator.next_index;
         if array_iterator.done {
             return Ok(create_iter_result_object(
@@ -84,9 +85,11 @@ impl ArrayIterator {
 
         let len = if let Some(f) = array_iterator.array.borrow().as_typed_array() {
             if f.is_detached() {
-                return context.throw_type_error(
-                    "Cannot get value from typed array that has a detached array buffer",
-                );
+                return Err(JsNativeError::typ()
+                    .with_message(
+                        "Cannot get value from typed array that has a detached array buffer",
+                    )
+                    .into());
             }
 
             f.array_length()