Support for Ternary Operator assignments in var context

[MBoegers]

What problem are you trying to solve?

While developing #217 I discovered that handling, especially detecting ternary operator assignments, is hard.
With this issue, Rewrite become able to apply ´var´ to ternary operator assignments.

What precondition(s) should be checked before applying this recipe?

var should not be applied to variable declarations where:

• the type of the ternary operator and the left-hand side don't match
• the type is byte or short
• only null is assigned
• the declaration is outside a method declaration

Describe the situation before applying the recipe

class A {
    void foo(String bar) {
        int i1 = bar != null ? 3 : 5;
        Integer i2 = bar != null ? 3 : null;
        Integer i3 = bar == null ? null : bar.lenght();
        Integer i4 = bar != null ? throw new IlligalArgumentExcpetion() : -1;
        int i5 = bar != null ? bar.lenght() : 0;
        float f1 = bar != null ? 3f : 3.5;
    }
}

Describe the situation after applying the recipe

class A {
    void foo(String bar) {
        var i1 = bar != null ? 3 : 5;
        var i2 = bar != null ? 3 : null;
        var i3 = bar == null ? null : bar.lenght();
        var i4 = bar != null ? throw new IlligalArgumentExcpetion() : -1;
        var i5 = bar != null ? bar.lenght() : 0;
        var f1 = bar != null ? 3f : 3.5;
    }
}

Have you considered any alternatives or workarounds?

An alternative would be to skip every ternary operator, this would lead to no 100% local variable type inference for rewrite.

Any additional context

It would be nice to write a separate recipe for this and integrate them later on as global var refactoring.

Are you interested in contributing this recipe to OpenRewrite?

not now.