jashkenas/coffeescript

Bug: Wrong `this` in bound methods of nested classes

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#5,222 opened on Jul 18, 2019

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 (1 comment) (5 reactions) (0 assignees)CoffeeScript (1,980 forks)batch import
bughelp wanted

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Description

While upgrading an application to CS2 we ran into the following issue in an obscure usage of nested classes.

Screenshot 2019-07-18 at 16 33 10

As you can see, the nested bound method thought its this is the parent class. This seems to happen on a "parse" level, because it's replaced in the code. This lead to tricky to catch bug on our side.

Contributor guide

Research direction
Examine how the CoffeeScript compiler resolves `this` in nested classes by inspecting the generated JavaScript or the parser's AST. Look for differences in binding between direct methods and bound methods.
Tech stack
javascript
Domain
compilers
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
CoffeeScriptJavaScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60