commonmark / commonmark/commonmark-java
Implement methods to go backwards and look backwards inside Scanner
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Description
Is your feature request related to a problem? Please describe.
I'm trying to implement an InlineContentParser for images from a custom markdown spec from a certain website. Given I already parsed the opener, the spec requires me to look for the first whitespace character or end of text, then going backwards from there, look for the first ). Everything between the opener and ) is considered the image link.
This is a bit annoying to implement with the current limited set of methods Scanner has, and I also imagine the performance would be worse when instead of going backwards from the closer, you go forward from the opener via scanner.find(')') and perform an additional find to see if you just found the last ).
Describe the solution you'd like
I would like for there to be similar methods to next and find that would instead look back from the current Scanner position, i.e prev, and findPrev. Then I could just do the following (sorry that the code is in Kotlin as I don't regularly write Java, I hope the intent is clear):
val start = scanner.position() // position after the opener has been parsed
scanner.find { char -> char.isWhitespace() } // scanner gets moved to first whitespace or very end if there is none
scanner.findPrev(')') // scanner gets moved backwards until the position is at ')'. Ideally there would also be an overload that takes a position until which it should move, so i could pass the `start` to it and it would early exit if it doesn't find one by then
val end = scanner.position()
val imageLink = scanner.getSource(start, end).getContent()
Describe alternatives you've considered
As stated above I have considered iterating forward from the current position to find the next ) and check if there's another one to see if I'd found the last one.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start at the Scanner entry point and compare the existing next and find behavior described in the issue. Define backward equivalents that update the scanner position as requested, including the bounded search behavior, and verify that the image-link parsing use case can obtain the expected range.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- java
- Domain
- compilers
- Issue type
- Feature
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100