Datalog Scope Analysis

[Kixiron]

Scope analysis using ddlog. Implements incremental scope analysis using a datalog variant allowing concise and high-level descriptions of analyses, with future goals towards writing more complex analyses, code path analysis and even type checking within datalog.

(Un)implemented bits

• no-undef
• no-unused-vars
• no-use-before-define
• no-shadow
• typeof-undef
• no-unused-labels
• Exporting of scopes to allow other rules access to data
• Testing, lots of it
  • Per-rule tests
  • Make tests only enable the rules they're testing
  • Make tests that check combinations of errors instead of singular ones
• Nice(r) errors, preferably with suggestions
• Configuration of rules
• Dev docs

Code Structure

• crates/rslint_scope/ contains all analysis-related code
• src/analyzer/ contains the ast->ddlog translation code
• src/datalog.rs contains the ddlog program instance & the interface for interacting with it
• ddlog/ contains the written datalog rules
• generated/ contains the code generated by ddlog

Prior Art & Resources

• Doop - Pointer analysis for Java (github)
• On Fast Large-Scale Program Analysis in Datalog
• Differential Datalog
• Differential Dataflow
• Introduction to Datalog

[RDambrosio016]

I think instead of making the diagnostics ourselves, we should just return an additional structure, maybe ScopeFacts which just contains vectors with locations/extra info for these errors. I think computing some of the errors in ddlog is helpful but ddlog shouldnt be making diagnostics.

[Kixiron]

That's what I do currently, ddlog's output relations are combined into the DerivedFacts struct here which are then made into diagnostics here, ddlog has no knowledge of diagnostics (although it could potentially do so)

[RDambrosio016]

The current way of how errors are emitted and registered is very janky (although its temporary). Firstly, rslint_scope cannot depend on rslint_core, it needs to be the other way around, rules will grab the scope and emit errors based on that.

[Stupremee]

Don't forget to add the rslint_scope module in the dev docs in website/docs/dev/architecture.md

[Kixiron]

@RDambrosio016 @Stupremee Can y'all fancy up the rule impls, I'm not sure how to make the actually emitted errors good