Previously, the parser created `Literal` nodes for many things. This resulted in
information loss. Instead of being able to check the node type, we had to use
regexes to tell the different types of `Literal`s apart. That was a bit like
parsing literals twice: Once in the lexer, and once (or more) in the compiler.
It also caused problems, such as `` `this` `` and `this` being indistinguishable
(fixes#2009).
Instead returning `new Literal` in the grammar, subtypes of it are now returned
instead, such as `NumberLiteral`, `StringLiteral` and `IdentifierLiteral`. `new
Literal` by itself is only used to represent code chunks that fit no category.
(While mentioning `NumberLiteral`, there's also `InfinityLiteral` now, which is
a subtype of `NumberLiteral`.)
`StringWithInterpolations` has been added as a subtype of `Parens`, and
`RegexWithInterpolations` as a subtype of `Call`. This makes it easier for other
programs to make use of CoffeeScript's "AST" (nodes). For example, it is now
possible to distinguish between `"a #{b} c"` and `"a " + b + " c"`. Fixes#4192.
`SuperCall` has been added as a subtype of `Call`.
Note, though, that some information is still lost, especially in the lexer. For
example, there is no way to distinguish a heredoc from a regular string, or a
heregex without interpolations from a regular regex. Binary and octal number
literals are indistinguishable from hexadecimal literals.
After the new subtypes were added, they were taken advantage of, removing most
regexes in nodes.coffee. `SIMPLENUM` (which matches non-hex integers) had to be
kept, though, because such numbers need special handling in JavaScript (for
example in `1..toString()`).
An especially nice hack to get rid of was using `new String()` for the token
value for reserved identifiers (to be able to set a property on them which could
survive through the parser). Now it's a good old regular string.
In range literals, slices, splices and for loop steps when number literals
are involved, CoffeeScript can do some optimizations, such as precomputing the
value of, say, `5 - 3` (outputting `2` instead of `5 - 3` literally). As a side
bonus, this now also works with hexadecimal number literals, such as `0x02`.
Finally, this also improves the output of `coffee --nodes`:
# Before:
$ bin/coffee -ne 'while true
"#{a}"
break'
Block
While
Value
Bool
Block
Value
Parens
Block
Op +
Value """"
Value
Parens
Block
Value "a" "break"
# After:
$ bin/coffee -ne 'while true
"#{a}"
break'
Block
While
Value BooleanLiteral: true
Block
Value
StringWithInterpolations
Block
Op +
Value StringLiteral: ""
Value
Parens
Block
Value IdentifierLiteral: a
StatementLiteral: break
Testing with `'[object Array]' is Object::toString.call element` allows arrays from another JS context to be properly handled. The specific use case here is to support jest, which sets up JS contexts using Node/io.js's "vm" module. This approach works in ES3 environments in contrast with ES5's `Array.isArray`.
- Fix#3394: Unclosed single-quoted strings (both regular ones and heredocs)
used to pass through the lexer, causing a parsing error later, while
double-quoted strings caused an error already in the lexing phase. Now both
single and double-quoted unclosed strings error out in the lexer (which is the
more logical option) with consistent error messages. This also fixes the last
comment by @satyr in #3301.
- Similar to the above, unclosed heregexes also used to pass through the lexer
and not error until in the parsing phase, which resulted in confusing error
messages. This has been fixed, too.
- Fix#3348, by adding passing tests.
- Fix#3529: If a string starts with an interpolation, an empty string is no
longer emitted before the interpolation (unless it is needed to coerce the
interpolation into a string).
- Block comments cannot contain `*/`. Now the error message also shows exactly
where the offending `*/`. This improvement might seem unrelated, but I had to
touch that code anyway to refactor string and regex related code, and the
change was very trivial. Moreover, it's consistent with the next two points.
- Regexes cannot start with `*`. Now the error message also shows exactly where
the offending `*` is. (It might actually not be exatly at the start in
heregexes.) It is a very minor improvement, but it was trivial to add.
- Octal escapes in strings are forbidden in CoffeeScript (just like in
JavaScript strict mode). However, this used to be the case only for regular
strings. Now they are also forbidden in heredocs. Moreover, the errors now
point at the offending octal escape.
- Invalid regex flags are no longer allowed. This includes repeated modifiers
and unknown ones. Moreover, invalid modifiers do not stop a heregex from
being matched, which results in better error messages.
- Fix#3621: `///a#{1}///` compiles to `RegExp("a" + 1)`. So does
`RegExp("a#{1}")`. Still, those two code snippets used to generate different
tokens, which is a bit weird, but more importantly causes problems for
coffeelint (see clutchski/coffeelint#340). This required lots of tests in
test/location.coffee to be updated. Note that some updates to those tests are
unrelated to this point; some have been updated to be more consistent (I
discovered this because the refactored code happened to be seemingly more
correct).
- Regular regex literals used to erraneously allow newlines to be escaped,
causing invalid JavaScript output. This has been fixed.
- Heregexes may now be completely empty (`//////`), instead of erroring out with
a confusing message.
- Fix#2388: Heredocs and heregexes used to be lexed simply, which meant that
you couldn't nest a heredoc within a heredoc (double-quoted, that is) or a
heregex inside a heregex.
- Fix#2321: If you used division inside interpolation and then a slash later in
the string containing that interpolation, the division slash and the latter
slash was erraneously matched as a regex. This has been fixed.
- Indentation inside interpolations in heredocs no longer affect how much
indentation is removed from each line of the heredoc (which is more
intuitive).
- Whitespace is now correctly trimmed from the start and end of strings in a few
edge cases.
- Last but not least, the lexing of interpolated strings now seems to be more
efficient. For a regular double-quoted string, we used to use a custom
function to find the end of it (taking interpolations and interpolations
within interpolations etc. into account). Then we used to re-find the
interpolations and recursively lex their contents. In effect, the same string
was processed twice, or even more in the case of deeper nesting of
interpolations. Now the same string is processed just once.
- Code duplication between regular strings, heredocs, regular regexes and
heregexes has been reduced.
- The above two points should result in more easily read code, too.
This makes the "stack" property more useful when it's shown on other Node.js applications that compile CoffeeScript (e.g. testing libraries) and should fix#3023. A minimal example:
$ node -e 'require("coffee-script").compile("class class")'
/usr/lib/node_modules/coffee-script/lib/coffee-script/coffee-script.js:41
throw err;
^
[stdin]:1:7: error: unexpected CLASS
class class
^^^^^
Instead of throwing the syntax errors with their source file location and needing to then catch them and call a `prettyErrorMessage` function in order to get the formatted error message, now syntax errors know how to pretty-print themselves (their `toString` method gets overridden).
An intermediate `catch` & re-`throw` is needed at the level of `CoffeeScript.compile` and friends. But the benefit of this approach is that now libraries that use the `CoffeeScript` object directly don't need to bother catching the possible compilation errors and calling a special function in order to get the nice error messages; they can just print the error itself (or let it bubble up) and the error will know how to pretty-print itself.
