Another related issue: we should allow any code in ${} , not only values.
For instance the following does not work ATM:
'${ var str = ""; str; }' while the following works : '${{ var str = ""; str; }}'

Another last issue is that quoted chars in sub format strings are unquoted.

That's actually quite complex and requires a lot of testing. Any volunteer to take over this task ? @Simn @nadako ?

I think we should first find a better way to communicate the quoted status (" or ') for strings, which would make this a Haxe 4 issue.

you mean inside the string itself ? this should not be required, given that we have all the information needed to correctly lex it

'${ '${x}'}' does not work (the inner string is not considered a format string)

This suggests to me that the information is lost somewhere. I'm not very familiar with the current implementation, but in general inner format strings should be handled without any additional effort via normal expression recursion.

Yes, I agree, this is normally done directly in lexer.mll (string2, code_string) which should unquote things as they should, but doesn't

Don't we need a stack in order to lex nested structures like this? At the moment we only have buf which is reset on new strings/comments/regexes, so that really doesn't support any notion of "string in string".

Eh, I guess we don't because we dump everything into the same buffer and deal with it while typing.

I fixed the spacing issue. As for this:

Another related issue: we should allow any code in ${} , not only values.
For instance the following does not work ATM:
'${ var str = ""; str; }' while the following works : '${{ var str = ""; str; }}'

I consider that a fair limitation. If you want a block you have to start a block. Sure it looks a bit funny because interpolation also uses {} as delimiters, but I don't see why we should imply blocks here.

Another last issue is that quoted chars in sub format strings are unquoted.

Any example of that?

'${'\''}' should be ok, but it's not. I think that requires an entirely different way of processing format strings.

Related issues:

• typer.ml Assertion not failed #3974
• [display] string interpolation vs newlines #5985
• '${"\\\\"}' #8888 - '${"\\\\"}' should produce two backslashes, but only produces one
• String interpolation ignores trailing invalid syntaxes #10287 - '${foo()blah}', blah is completely ignored
• Escaped quotation mark inside string interpolation fails to compile #10463 - '${'\''}'

And here is a new one:

class Main {
  public static function main():Void {
    var foo = "hello";
    trace('${'${foo}'}'); // outputs hello
    trace('\n${'${foo}'}'); // outputs ${foo}
  }
}

I'm going to revive my old branch with the "mini-ast" and probably do what is suggested in #9370 (comment).