typeof someFun() erroneously collapses to typeof globalVar when inlined #3498
Description
This is quite the corner case. It produces code that behaves differently depending on whether a function call is inlined or not.
Reproducer:
// ==ClosureCompiler==
// @compilation_level ADVANCED_OPTIMIZATIONS
// @output_file_name default.js
// @formatting pretty_print
// ==/ClosureCompiler==
function testInlined() {
return thisVarDoesNotExist;
}
/**
* @noinline
*/
function testNotInlined() {
return thisVarDoesNotExist;
}
function test(f) {
try {
console.log(f());
} catch (e) {
console.log(e);
}
}
test(() => typeof thisVarDoesNotExist);
test(() => typeof testInlined());
test(() => typeof testNotInlined());The (pretty-printed) compiled code is:
function a() {
return thisVarDoesNotExist;
}
function b(c) {
try {
console.log(c());
} catch (d) {
console.log(d);
}
}
b(function() {
return typeof thisVarDoesNotExist;
});
b(function() {
return typeof thisVarDoesNotExist;
});
b(function() {
return typeof a();
});The original code prints:
undefined
ReferenceError: thisVarDoesNotExist is not defined
ReferenceError: thisVarDoesNotExist is not defined
as it should, but the compiled code prints:
undefined
undefined
ReferenceError: thisVarDoesNotExist is not defined
The problem is that, when inlining testInlined() in the expression typeof testInlined(), the compiler forgot to protect the reference to the non-existent global reference to thisVarDoesNotExist, resulting in
typeof thisVarDoesNotExistThis changes the semantics of the evaluation, because a typeof whose direct argument is a reference to a non-existent global variable returns "undefined" instead of throwing a ReferenceError.
A correct translation would be to protect the inlined argument to typeof with:
typeof (0, thisVarDoesNotExist)