Demonstration of ANTLR4 Go Explosive Memory Growth

This repo contains a grammar and code that reproduces issue antlr/antlr4#1901, which I've opened against the antlr4 repository. In here we have:

• ./parser
  • A grammar for Javascript ES5 with a Go target (I've just PR'ed to the grammars-v4 repo)
  • The code generated by antlr4 -Dlanguage=Go ECMAScript.g4 using the latest master.
• jstest.go
  • Accepts a filename of a Javascript file
  • Prints the text of every rule encountered in the file
  • Enables the Go profiler over HTTP port 6060
    • Useful profiler operations
• good.js
  • Sample JS code that parses correctly without issue
• bad.js
  • JS code that eventually parses and works, but not after first allocating almost 8GB RAM
• profile001.svg
  • Graphical heap profile taken when resident mem was ~2.3GB
  • To take your own heap snapshot, run the following while the test is running:
    • go tool pprof http://localhost:6060/debug/pprof/heap
    • In the CLI, run svg, or run top to see it in text form (svg is more comprehensive)

To reproduce first install dependencies:

go get github.com/antlr/antlr4/runtime/Go/antlr

To run the parser on the good JS file:

go run js.go -file good.js

To run the parser and cause the memory issue:

go run js.go -file bad.js

WARNING- Make sure you run this on a system with plenty of free memory!

The test takes a while- several minutes.