IllegalStateException in VarCheck: Unexpected variable

[rohanpadhye]

Input for SIMPLE_OPTIMIZATIONS:

while ((l_0)){ while ((l_0)){ if ((l_0)) { break;;var l_0;continue }{ break;var l_0 } } }

Throws:

Unexpected variable l_0
  Node(NAME l_0): stdin:1:8
while ((l_0)){ while ((l_0)){ if ((l_0)) { break;;var l_0;continue }{ break;var l_0 } } }
  Parent(FOR): stdin:1:0
while ((l_0)){ while ((l_0)){ if ((l_0)) { break;;var l_0;continue }{ break;var l_0 } } }

	at com.google.javascript.jscomp.VarCheck.visit(VarCheck.java:222)
	at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:772)
	at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:843)
	at com.google.javascript.jscomp.NodeTraversal.traverseBlockScope(NodeTraversal.java:858)
	at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:766)
	at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:843)
	at com.google.javascript.jscomp.NodeTraversal.handleScript(NodeTraversal.java:724)
	at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:749)
	at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:843)
	at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:768)
	at com.google.javascript.jscomp.NodeTraversal.traverseRoots(NodeTraversal.java:323)
	at com.google.javascript.jscomp.VarCheck.process(VarCheck.java:145)
	at com.google.javascript.jscomp.PhaseOptimizer$NamedPass.process(PhaseOptimizer.java:303)
	at com.google.javascript.jscomp.PhaseOptimizer.process(PhaseOptimizer.java:230)
	at com.google.javascript.jscomp.Compiler.performOptimizations(Compiler.java:2541)
	at com.google.javascript.jscomp.Compiler$3.call(Compiler.java:833)
	at com.google.javascript.jscomp.Compiler$3.call(Compiler.java:829)
	at com.google.javascript.jscomp.CompilerExecutor$2.call(CompilerExecutor.java:101)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.IllegalStateException: Unexpected variable l_0

Affects: v20180204 and current SNAPSHOT

Test-case was automatically generated using JQF.

[lauraharker]

Simplified repro:
https://closure-compiler-debugger.appspot.com/#input0%3Dwhile%2520(a)%257B%250A%2520%2520if%2520(a)%2520%257B%250A%2520%2520%2520%2520break%253B%250A%2520%2520%2520%2520var%2520a%253B%250A%2520%2520%2520%2520continue%253B%250A%2520%2520%257D%250A%252F%252F%2520%2520break%253B%250A%257D%26input1%26conformanceConfig%26externs%26refasterjs-template%26TRANSPILE%3Dtrue%26CHECK_TYPES%3Dtrue%26FOLD_CONSTANTS%3Dtrue%26CLOSURE_PASS%3Dtrue%26PRESERVE_TYPE_ANNOTATIONS%3Dtrue%26PRETTY_PRINT%3Dtrue

Enabling FOLD_CONSTANTS in the debugger causes the crash

[lauraharker]

Wrong link - this one crashes

https://closure-compiler-debugger.appspot.com/#input0%3Dwhile%2520(a)%257B%250A%2520%2520if%2520(a)%2520%257B%250A%2520%2520%2520%2520break%253B%250A%2520%2520%2520%2520var%2520a%253B%250A%2520%2520%2520%2520continue%253B%250A%2520%2520%257D%250A%2520%2520break%253B%250A%257D%26input1%26conformanceConfig%26externs%26refasterjs-template%26TRANSPILE%3Dtrue%26CHECK_TYPES%3Dtrue%26FOLD_CONSTANTS%3Dtrue%26CLOSURE_PASS%3Dtrue%26PRESERVE_TYPE_ANNOTATIONS%3Dtrue%26PRETTY_PRINT%3Dtrue

[MatrixFrog]

Cool! We've tried a couple fuzzing tools before but I don't think we were very successful at finding compiler bugs. We should look into this one more.