Initial indent at start of a file

[xixixao]

Is this is a language/compiler feature?

  a
ignored
  also ignored

compiles down to

a;

Or an uncaught syntax error?

[vendethiel]

seems like we should be avoiding that

[epidemian]

This is an awesome feature actually.

Want to comment a gigantic file? Just type TABnull at the start of the file and you're done!

/sarcasm

[xixixao]

I had a go at fixing it, but where @Nami-Doc pointed to is not the place to fix it, since leading indent is needed for interpolations (even though that seems like a hack as well). It should be fixed wherever CoffeeScript actually ignores the negatively indented code (and throw error), which is beyond my knowledge of the compiler.

[vendethiel]

We can easily disable initial indent

@jashkenas any reason we allow that?

[epidemian]

I think allowing initial indentation is quite handy in cases where you copy some code and want to, for example, paste it in coffeescript.org to see how it compiles. The copied code could have some level of indentation, but as long as that indentation is consistent, i don't see why the compiler should not allow it.

What should not be allowed is having an initial indentation in the first line of code and then having some other line going below that level of indentation (i'd expect and "unexpected DEDENT" error or something like that).

[vendethiel]

Ah, yeah, that's perfectly valid (saves so much time). We can keep track of "initial indent" in the lexer but we need to be sure we're not in an interpolation (we don't even flag the lexer yet), not in a string, not hacking with debts, etc.

It should be fixed wherever CoffeeScript actually ignores the negatively indented code (and throw error), which is beyond my knowledge of the compiler.

I'd say in the grammar. We have :

• Root:
  • (empty)
  • Body
  • Block TERMINATOR
• Body:
  • Line
  • Body TERMINATOR Line
  • Body TERMINATOR
• Line:
  • Expression
  • Statement
• Block:
  • INDENT OUTDENT
  • INDENT Body OUTDENT

So for ' 1\n2' will be lexed as :

[INDENT 1] [NUMBER 1] [OUTDENT 1] [TERMINATOR \n] [NUMBER 2] [TERMINATOR \n]

and Jison will give us these nodes :

Block
  Value "1"

Because Block isn't expecting a "side-block" (ie Block TERMINATOR Block)

Whereas if we have '1\n2', we'd get

[NUMBER 1] [TERMINATOR \n] [NUMBER 2] [TERMINATOR \n]

Generating the correct AST :

Block
  Value "1"
  Value "2"

[michaelficarra]

CoffeeScriptRedux handles this in the preprocessor with the notion of "base" indentation. Since the parser can't handle an indentation stack, the preprocessor adds the indent/dedent markers appropriately.

[vendethiel]

Would be easy if only we weren't creating new lexer instances, strange strings, newline suppression and some more. I tried to patch Lexer::lineToken to set @baseIndent if none was set and check size but sometimes I'd get really nasty error messages, like unexpected eval etc.

[michaelficarra]

So much statefulness!

[vendethiel]

Also, considering the order :

           @identifierToken() or
           @commentToken()    or
           @whitespaceToken() or
           @lineToken()       or

we'd need to set @baseIndent if not set in the 3 first, remove the or after @lineToken, set @baseIndent if not set, continue with our ors. Ugh. Coco allows it through the lexer (satyr/coco@4c034fe, test here).

[satyr]

Coco seems to ignore it

I specially allowed

  a
b

case for some weird reasons regarding string interpolation.

If we're disallowing it, an easy way is to append an EOF to the token list and make Root require that.

[vendethiel]

Edited my post with the relevant commit

[xixixao]

Checking for EOF seems to make the most sense to me (as grammars usually do).

[vendethiel]

But would not give a really good error message

[xixixao]

exp.coffee:2:1: error: unexpected IDENTIFIER
ignored
^^^^^^^

It is not entirely clear ( unexpected negative indent ) but it also isn't useless.

For some reason though, it breaks tabs in tabbed code test in literate. Follow up: of course it breaks the tabbed code test, because that test is ignored in current version.