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Negated Types: Remove the concept of control-flow made "fresh" negations - #65286
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…t literal handling
Deduplicate fresh negations against their regular counterparts during union collection and intersection insertion. Preserve the first intersection position and ordered-set membership when replacing a fresh member, while leaving standalone fresh negations eligible for widening. Add compiler coverage for explicit exclusions, generic array narrowing, both union operand orders, and fresh-only widening.
…ntial structures, broaden negation reduction applicability
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This change allows full negated types to be created in control flow, not just "fresh" ones that widen away when a position isn't contextually typed by something implying a need for a negation.
This is going to break any "exact" type matching (eg, DT) on locations where these negations are introduced, but logically shouldn't be too breaky otherwise. The other potential downside is possible performance costs - by unconditionally introducing negations, we're unconditionally growing the number of elements in control-flow produced types, in all branches.