[Interest] How to prevent large qml forms from hitting javascript stack size?

[NIkolai Marchenko]

Relevant Qt version: 5.15

I've recently been investigating a weird "Range error: maximum call stack
size exceeded" in our application and I think I've tracked down what's
happening, but I don't know if there are ways of dealing with that.

In essence: when a form has a large amount of subforms and Components,
then, in the internals of qml engine, it is parsed and every piece of it is
assigned totalObjectCount which is accumulated recursively for big forms.
Then, in qjsengine sources this happens:

sharedState->allJavaScriptObjects =
scope.alloc(compilationUnit->totalObjectCount());

As far as I understand, this doesn't even allocate anything, just bumps
jsStackTop pointer to a new value. The problem with it is that once the
application tries to initialize a component from c++ (say, we have
triggered a c++ side attached property and it, in its constructor, tries
component instantiation) we end up calling

engine->jsStackTop += frame.requiredJSStackFrameSize();

and once we do `checkStackLimits` qt suddenly realizes that we're (already)
past the default javascript stack and issue a RangeError.  Funny thing is
that no range checking is seemingly happening when the form itself is
parsed and only when we try to add a new component from c++ the engine
suddenly realizes that our jsStackTop is already a fair bit past the
jsStackLimit.

The form that triggers this has a lot of components attached to it and not
all of them are instantiated at the same time, but qt seemingly bumps
jsStackTop to a value that accumulates all of their objectCounts which ends
up in the range of ~1 million.

Is there some kind of pattern that will let javascript engine handle it
more gracefully and not try to reserve stack for everything at once? Is it
possibly correct to just bump the JS stack size via environment variable
and forget about it?
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