simplify expressions that could be type-casts

[erik-krogh]

Fixes the issues identified by this QL-for-QL query.

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Consider the below:

predicate even(int i) { exists(Even even | even = i) }

That is basically just a type-cast, so we might as well simplify it as such:

predicate even(int i) { i instanceof Even }

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There are also some cases where the resulting type-cast would be redundant.
Here's an example:

predicate hasAttribute(string name) { exists(XMLAttribute a | a = this.getAttribute(name)) }

The getAttribute predicate has XMLAttribute as its result type, so adding a type-cast would be redundant.
It is therefore simplified as follows:

predicate hasAttribute(string name) { exists(this.getAttribute(name)) }

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The patch was generated automatically by a tool.
(GitHub people: you can see how in the backref below).

[nickrolfe]

👍 for Ruby

[smowton]

Java 👍

[tausbn]

Python 👍

[yoff]

I wonder if the line

exists(DataFlow::Node r | r = requestNode.getAMethodCall("body") | result = r)

could also be simplified to

result = requestNode.getAMethodCall("body")

if the query was extended slightly? (We know that result has type DataFlow::Node in this case.)

[erik-krogh]

It could, and originally my query did just that (see the discussion in the PR).
But that had too many FPs, so I dropped it.

[hvitved]

C# 👍