Unification error

[ggeoffrey]

Impacts the master branch.

@witek 2:11 PM
Hi. I discovered strange behavior using rcf in my shadow-cljs app.

(tests "mytest" "x" := "y")

yields this error in the browser console:

react_devtools_backend.js:4049 mytest
react_devtools_backend.js:4049   actual:
react_devtools_backend.js:4049 RangeError: Maximum call stack size exceeded
    at Object.eval [as cljs$core$ILookup$_lookup$arity$3] (core.cljs:9183)
    at Object.eval [as cljs$core$ILookup$_lookup$arity$2] (core.cljs:9250)
    at Object.eval [as cljs$core$IFn$_invoke$arity$1] (core.cljs:9262)
    at Object.hyperfiddle$rcf$unify$wildcard_QMARK_ [as wildcard_QMARK_] (unify.cljc:60)
    at Function.eval [as cljs$core$IFn$_invoke$arity$5] (unify.cljc:76)
    at Function.eval [as cljs$core$IFn$_invoke$arity$5] (unify.cljc:82)
    at Function.eval [as cljs$core$IFn$_invoke$arity$5] (unify.cljc:82)
    at Function.eval [as cljs$core$IFn$_invoke$arity$5] (unify.cljc:82)
    at Function.eval [as cljs$core$IFn$_invoke$arity$5] (unify.cljc:82)
    at Function.eval [as cljs$core$IFn$_invoke$arity$5] (unify.cljc:82)
overrideMethod @ react_devtools_backend.js:4049
eval @ reporters.cljs:43
eval @ core.cljs:11198
eval @ core.cljs:11184
cljs$test$do_report @ test.cljs:425
eval @ utils.cljs:286
eval @ test.cljs:476
cljs$test$run_block @ test.cljs:448
cljs$test$test_var @ test.cljs:500
spark$utils$RCF__spark_utils__286 @ utils.cljs:286
eval @ utils.cljs:286
goog.globalEval @ main.js:486
shadow$cljs$devtools$client$browser$script_eval @ browser.cljs:24
shadow$cljs$devtools$client$browser$do_js_load @ browser.cljs:36
eval @ browser.cljs:57
eval @ env.cljs:248
shadow$cljs$devtools$client$env$do_js_reload_STAR_ @ env.cljs:220
eval @ env.cljs:256
shadow$cljs$devtools$client$browser$do_js_reload @ browser.cljs:43
eval @ browser.cljs:93
eval @ shared.cljs:32
shadow$remote$runtime$shared$process @ shared.cljc:164
eval @ shared.cljs:289
shadow$cljs$devtools$client$shared$remote_msg @ shared.cljs:16
eval @ websocket.cljs:16
react_devtools_backend.js:4049 expected: (hyperfiddle.rcf/unifies? := "x" "y")

[ggeoffrey]

I could reproduce a similar issue compiling to the node-test target:

🔥example.cljc:55:1
  mytest
    actual:
  RangeError: Maximum call stack size exceeded
      at Object.hyperfiddle$rcf$unify$ignore_variable_QMARK_ [as ignore_variable_QMARK_] (/Users/geoffrey/Documents/hyperfiddle/fabric/vendor/rcf/.shadow-cljs/builds/test/dev/out/cljs-runtime/hyperfiddle/rcf/unify.cljc:16:1)
      at hyperfiddle$rcf$unify$lvar_QMARK_ (/Users/geoffrey/Documents/hyperfiddle/fabric/vendor/rcf/.shadow-cljs/builds/test/dev/out/cljs-runtime/hyperfiddle/rcf/unify.cljc:20:1)
      at Function.cljs$core$IFn$_invoke$arity$5 (/Users/geoffrey/Documents/hyperfiddle/fabric/vendor/rcf/.shadow-cljs/builds/test/dev/out/cljs-runtime/hyperfiddle/rcf/unify.cljc:71:6)
      at Function.cljs$core$IFn$_invoke$arity$5 (/Users/geoffrey/Documents/hyperfiddle/fabric/vendor/rcf/.shadow-cljs/builds/test/dev/out/cljs-runtime/hyperfiddle/rcf/unify.cljc:78:33)
      at Function.cljs$core$IFn$_invoke$arity$5 (/Users/geoffrey/Documents/hyperfiddle/fabric/vendor/rcf/.shadow-cljs/builds/test/dev/out/cljs-runtime/hyperfiddle/rcf/unify.cljc:78:33)
      at Function.cljs$core$IFn$_invoke$arity$5 (/Users/geoffrey/Documents/hyperfiddle/fabric/vendor/rcf/.shadow-cljs/builds/test/dev/out/cljs-runtime/hyperfiddle/rcf/unify.cljc:78:33)
      at Function.cljs$core$IFn$_invoke$arity$5 (/Users/geoffrey/Documents/hyperfiddle/fabric/vendor/rcf/.shadow-cljs/builds/test/dev/out/cljs-runtime/hyperfiddle/rcf/unify.cljc:78:33)
      at Function.cljs$core$IFn$_invoke$arity$5 (/Users/geoffrey/Documents/hyperfiddle/fabric/vendor/rcf/.shadow-cljs/builds/test/dev/out/cljs-runtime/hyperfiddle/rcf/unify.cljc:78:33)
      at Function.cljs$core$IFn$_invoke$arity$5 (/Users/geoffrey/Documents/hyperfiddle/fabric/vendor/rcf/.shadow-cljs/builds/test/dev/out/cljs-runtime/hyperfiddle/rcf/unify.cljc:78:33)
      at Function.cljs$core$IFn$_invoke$arity$5 (/Users/geoffrey/Documents/hyperfiddle/fabric/vendor/rcf/.shadow-cljs/builds/test/dev/out/cljs-runtime/hyperfiddle/rcf/unify.cljc:78:33)
  expected: (hyperfiddle.rcf/unifies? := "x" "y")

Only ClojureScript is impacted.

[ggeoffrey]

Unification will recurse on composite values. Collections and strings are examples of composite values. In Clojure, strings are made of chars (first "str") := \s, but JavaScript doesn’t have chars. So strings are made of strings of size 1.

"a"[0] := 'a'
"a"[0][0] … := StackOverflow