Nonsense error messages, such as 'Line 1, column 3: Expected "a" but "a" found'.

[chrisdew]

I keep coming across nonsense error messages with PEG.js, of the form:

Line 1, column 3: Expected "a" but "a" found.

when parsing bda.

Typically I see them when parsing text which begins with a parseable expression, but adds unneeded text onto the end.

A simple example is:

start
  = presingle single
  / preplural plural

presingle
  = "a"
  / "b"

preplural
  = "b"
  / "c"

single
  = "d"
  / "e"

plural
  = "dd"
  / "ee"

Could there be a more sane error message, such as 'too much text' instead?

Thanks,

Chris.

[chrisdew]

I think the correct error should be: Line 1, column 2: Expected "d" but "da" found.

[dmajda]

@chrisdew I reduced the testcase further:

Grammar

start = "a" / "b"

Input

bc

With both 0.7.0 and the current development version, the error message is:

Line 1, column 2: Expected "a" but "c" found.

It should be:

Line 1, column 2: Expected end of input but "c" found.

When I change the grammar to:

start = "a" / "b" "d"?

the message changes to:

Line 1, column 2: Expected "d" but "c" found.

It should be:

Line 1, column 2: Expected "d" or end of input but "c" found.

In short — this is a valid bug and I'll fix it. Thanks for reporting it.

[chrisdew]

Thanks for writing this library, I look forward to a fix.

[chrisdew]

Hi, any news on this bug?

[dmajda]

@chrisdew Sorry this took so long. I wanted to redesign the error reporting first. Once done, the fix (or rather, its core) was trivial.

[chrisdew]

@dmajda Thanks for the fix - I'll have a look soon.