- NewString (allocates a new PrimitiveString from the GC heap)
- GetVariable (retrieves a variable in the current scope)
- SetVariable (assigns a variable in the current scope)
This patch begins the work of implementing JavaScript execution in a
bytecode VM instead of an AST tree-walk interpreter.
It's probably quite naive, but we have to start somewhere.
The basic idea is that you call Bytecode::Generator::generate() on an
AST node and it hands you back a Bytecode::Block filled with
instructions that can then be interpreted by a Bytecode::Interpreter.
This first version only implements two instructions: Load and Add. :^)
Each bytecode block has infinity registers, and the interpreter resizes
its register file to fit the block being executed.
Two new `js` options are added in this patch as well:
`-d` will dump the generated bytecode
`-b` will execute the generated bytecode
Note that unless `-d` and/or `-b` are specified, none of the bytecode
related stuff in LibJS runs at all. This is implemented in parallel
with the existing AST interpreter. :^)
This fixes an issue where this would be bound to the global object
by default when operating in strict mode.
According to the specification, the expected value for |this| when
no binding is provided is undefined.
The TryStatement handler execution creates a new LexicalEnvironment
without a current function set, which we were not accounting for when
trying to get the super constructor while executing a SuperExpression.
This makes it work but isn't pretty - this needs some refactoring to be
close to the spec for that to happen.
Fixes#7045.
In HackStudio's Debugger a custom GlobalObject is used to reflect
debugger variables into the JS scope by overriding GlobalObject's
get method. However, when throwing a custom error during that lookup
it was replaced with the generic "not found" js exception. This patch
makes it instead pass along the custom error.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
This has the nice side effect of giving us a decent error message for
something like undefined.foo() - another useless "ToObject on null or
undefined" gone. :^)
Also turn the various ternary operators into two separate if branches,
they don't really share that much.
Sometimes we just want to set m_exception to some value we stored
previously, without really "throwing" it again - that's what
set_exception() does now. Since we have clear_exception(), it does take
a reference, i.e. you don't set_exception(nullptr). For consistency I
updated throw_exception() to do the same.
Previously we would always return the result of executing the finalizer,
however the spec dictates the finalizer result must only be returned for
a non-normal completion.
I added some more comments along the way, which should make it more
clear what's going on - the unwinding and exception flow isn't super
straightforward here.
This implements the missing step 6a of 14.7.5.6 ForIn/OfHeadEvaluation:
a. If exprValue is undefined or null, then
i. Return Completion { [[Type]]: break, [[Value]]: empty, [[Target]]: empty }.
In other words, this should just do nothing instead of throwing during
the undefined to object coercion:
for (const x in undefined);
This replaces the current 'function plus boolean indicating the type'
API, which makes it easier to set both getter and setter at once.
This was already possible before but required two calls of this
function, which wasn't intuitive:
define_accessor(name, getter, true, ...);
define_accessor(name, setter, false, ...);
Which now becomes:
define_accessor(name, getter, setter, ...);
Letting these create and return a JS::Array directly is pretty awkward
since we then need to go through the indexed properties for iteration.
Just use a MarkedValueList (i.e. Vector<Value>) for this and add a new
Array::create_from() function to turn the Vector into a returnable
Array as we did before.
This brings it a lot closer to the spec as well, which uses the
CreateArrayFromList abstract operation to do exactly this.
There's an optimization opportunity for the future here, since we know
the Vector's size we could prepare the newly created Array accordingly,
e.g. by switching to generic storage upfront if needed.
Object::get_own_properties() is a bit unwieldy to use - especially as
StringOnly is about to no longer be the default value. The spec has an
abstract operation specifically for this (EnumerateObjectProperties),
so let's use that. No functionality change.
Specifically:
- Object::get_own_properties()
- Object::put_own_property()
- Object::put_own_property_by_index()
These APIs make no sense (and are inconsistent, get_own_property()
didn't have this parameter, for example) - and as expected we were
always passing in the same object we were calling the method on anyway.
Not sure if this regressed at some point or just never worked, it
definitely wasn't tested at all. We would always return undefined when
returning from a try statement block, handler, or finalizer.
We should be able to get the 'typeof' string for any value directly, so
this is now a standalone Value::typeof() method instead of being part of
UnaryExpression::execute().
The auto naming of function expressions is a purely syntactic
decision, so shouldn't be decided based on the dynamic type of
an assignment. This moves the decision making into the parser.
One icky hack is that we add a field to FunctionExpression to
indicate whether we can autoname. The real solution is to actually
generate a CompoundExpression node so that the parser can make
the correct decision, however this would have a potentially
significant run time cost.
This does not correct the behaviour for class expressions.
Patch from Anonymous.
We now store 32-bit integers as 32-bit integers directly which avoids
having to convert them from doubles when they're only used as 32-bit
integers anyway. :^)
This patch feels a bit incomplete and there's a lot of opportunities
to take advantage of this information. We'll have to find and exploit
them eventually.
Previously we would generate function names for anonymous functions
on every AssignmentExpression, even if we weren't assigning a function.
We were also setting names of anonymous functions in arrays, which is
apparently a SpiderMonkey specific behavior not supported by V8, JSC
or required by ECMA262. This patch removes that behavior.
This is a huge performance improvement on the CanvasCycle demo! :^)
For various statements the spec states:
Return NormalCompletion(empty).
In those cases we have been returning undefined so far, which is
incorrect.
In other cases it states:
Return Completion(UpdateEmpty(stmtCompletion, undefined)).
Which essentially means a statement is evaluated and its completion
value returned if non-empty, and undefined otherwise.
While not actually noticeable in normal scripts as the VM's "last value"
can't be accessed from JS code directly (with the exception of eval(),
see below), it provided an inconsistent experience in the REPL:
> if (true) 42;
42
> if (true) { 42; }
undefined
This also fixes the case where eval() would return undefined if the last
executed statement is not a value-producing one:
eval("1;;;;;")
eval("1;{}")
eval("1;var a;")
As a consequence of the changes outlined above, these now all correctly
return 1.
See https://tc39.es/ecma262/#sec-block-runtime-semantics-evaluation,
"NOTE 2".
Fixes#3609.
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
If it's missing we get an empty value, but we can't use that with
to_string_without_side_effects() so we have to use undefined as the
default.
Fixes#5142.
If we have a function as class extends value, we still cannot assume
that it has a prototype property and that property has a function or
null as its value - blindly calling to_object() on it may fail.
Fixes#5075.
Without this, the oss-fuzz build says:
../Userland/Libraries/LibJS/AST.cpp:58:34: error: member access into incomplete type 'const std::type_info'
return demangle(typeid(*this).name()).substring(4);
^
