Rather than printing them to stderr directly the parser now keeps a
Vector<Error>, which allows the "owner" of the parser to consume them
individually after parsing.
The Error struct has a message, line number, column number and a
to_string() helper function to format this information into a meaningful
error message.
The Function() constructor will now include an error message when
throwing a SyntaxError.
Giving the lexer the ability to generate errors adds unnecessary
complexity - also it only calls its syntax_error() function in one place
anyway ("unterminated string literal"). But since the lexer *also* emits
tokens like Eof or UnterminatedStringLiteral, it should be up to the
consumer of these tokens to decide what to do.
Also remove the option to not print errors to stderr as that's not
relevant anymore.
There are many cases which shouldn't even parse, like
null = ...
true = ...
false = ...
123 = ...
"foo" = ...
However this *is* valid syntax:
foo() = ...
So we still have to keep the current code doing a runtime check if the
LHS value is a resolvable reference. I believe this was declared valid
syntax to *in theory* allow functions returning references - though in
practice that isn't a thing.
Fixes#2204.
The ECMAScript spec defines multiple equality operations which are used
all over the spec; this patch introduces them. Of course, the two
primary equality operations are AbtractEquals ('==') and StrictEquals
('==='), which have been renamed to 'abstract_eq' and 'strict_eq' in
this patch.
In support of the two operations mentioned above, the following have
also been added: SameValue, SameValueZero, and SameValueNonNumeric.
These are important to have, because they are used elsewhere in the spec
aside from the two primary equality comparisons.
This required 2 changes:
1. In the parser, create a new variable scope, so the variable is
declared in it instead of the scope in which the 'for' is found.
2. On execute, push the variable into the newly created block. Existing
code created an empty block (no variables, no arguments) which
allows Interpreter::enter_scope() to skip the creation of a new
environment, therefore when the variable initializer is executed, it
sets the variable to the outer scope. By attaching the variable to
the new block, the block gets a new environment.
This is only needed for 'let' / 'const' declarations, since 'var'
declarations are expected to leak.
Fixes: #2103
"[Function.length is] the number of formal parameters. This number
excludes the rest parameter and only includes parameters before
the first one with a default value." - MDN
To make processing tagged template literals easier, template literals
will now add one empty StringLiteral before and after each template
expression *if* there's no other string - e.g.:
`${foo}` -> "", foo, ""
`test${foo}${bar}test` -> "test", foo, "", bar, "test"
This also matches the behaviour of many other parsers.
A regression was introduced in dc9b4da where the parser would
incorrectly parse the assignment of arrow functions to (non-declaration)
variables. For example, consider:
a = () => {}
Because the parser was aware of default parameters, in
try_parse_arrow_function, the equals sign would be interpreted as a
default argument, leading to incorrect parsing of the overall
expression. Also resulted in some funny behavior
(a = () => {} => {} worked just fine!).
The simple fix is to only look for default parameters if the arrow
function is required to have parenthesis.
Now, you can optionally specify a ConsoleClient, to customise the
behaviour of the LibJS Console.
To customise the console, create a new ConsoleClient class that inherits
from JS::ConsoleClient and override all the abstract methods.
When Console::log() is called, if Console has a ConsoleClient,
ConsoleClient::log() is called instead.
These abstract methods are Value(void) functions: you can return a Value
which will be returned by the JavaScript function which calls that
method, in JavaScript.
Console methods are now Value(void) functions.
JavaScript functions in the JavaScript ConsoleObject are now implemented
as simple wrappers around Console methods.
This will make it possible for LibJS users to easily override the
default behaviour of JS console functions (even their return value!)
once we add a way to override Console behaviour.
This now matches the output of
Program
(Variables)
...
(Children)
...
or
FunctionDeclaration 'foo'
(Parameters)
...
(Body)
...
etc.
Also don't print each consequent statement index, it doesn't add any
value.
Adds fully functioning template literals. Because template literals
contain expressions, most of the work has to be done in the Lexer rather
than the Parser. And because of the complexity of template literals
(expressions, nesting, escapes, etc), the Lexer needs to have some
template-related state.
When entering a new template literal, a TemplateLiteralStart token is
emitted. When inside a literal, all text will be parsed up until a '${'
or '`' (or EOF, but that's a syntax error) is seen, and then a
TemplateLiteralExprStart token is emitted. At this point, the Lexer
proceeds as normal, however it keeps track of the number of opening
and closing curly braces it has seen in order to determine the close
of the expression. Once it finds a matching curly brace for the '${',
a TemplateLiteralExprEnd token is emitted and the state is updated
accordingly.
When the Lexer is inside of a template literal, but not an expression,
and sees a '`', this must be the closing grave: a TemplateLiteralEnd
token is emitted.
The state required to correctly parse template strings consists of a
vector (for nesting) of two pieces of information: whether or not we
are in a template expression (as opposed to a template string); and
the count of the number of unmatched open curly braces we have seen
(only applicable if the Lexer is currently in a template expression).
TODO: Add support for template literal newlines in the JS REPL (this will
cause a syntax error currently):
> `foo
> bar`
'foo
bar'
We already skipped random semicolons in Parser::parse_program(), but now
they are properly matched and parsed as empty statements - and thus
recognized as a valid body of an if / else / while / ... statement.
Adds the ability for function arguments to have default values. This
works for standard functions as well as arrow functions. Default values
are not printed in a <function>.toString() call, as nodes cannot print
their source string representation.
