Ridiculous number of compiler errors for a missing open { on top-level

[DavidSouther]

Compare:
https://dartpad.dartlang.org/8f24e1eb9c237c01bcb3

http://www.typescriptlang.org/Playground#src=%0Afunction%20main()%0A%20%20var%20lines%20%3D%20getLines()%3B%0A%0A%20%20%2F%2F%20If%20result%20is%20non-null%2C%20print%20it.%0A%20%20if(lines%20!%3D%3D%20null)%20%7B%0A%09lines.forEach((line)%20%3D%3E%20console.log(line))%3B%0A%20%20%7D%0A%7D%0A%0Afunction%20getLines()%3A%20string%5B%5D%20%7B%0A%09return%20%5B%22%22%5D%0A%7D

Both have the same syntax error, a missing { on the function body.

Dart prints 8 errors, 7 of which are completely useless noise and one is in completely the wrong place (a full 3 lines from where the error actually is).

Typescript prints two - one at the method I messed up on, and one (correctly) at the end brace for that method.

[bwilkerson]

@danrubel Another example of poor error recovery that we should look at for Fasta.

[danrubel]

Agreed. The scanner could have a flag indicating that there were unbalanced { } pairs, then the parser could quickly determine if it should run a special recovery pass over the tokens before the normal parsing begins.

[bwilkerson]

There's an even stronger signal here, which is that the quotes will be unbalanced if we assume they're part of the string interpolation expression, but balanced if we assume that they're not. That said, it isn't clear whether to assume the missing } should be inserted before the first, third, fifth, etc. ending quote. I suspect that this will be a hard case to recover from well.

[danrubel]

Um... I don't see any string interpolation in the dartpad example above. Am I missing something?

[bwilkerson]

Sorry, my mistake. I was confusing two issues.

Yes, we need to do a better job of recovering from mis-matched token pairs.