coverage: Store signature/body spans and branch spans in the expansion tree

[Zalathar]

In order to support coverage instrumentation of expansion regions, we need to reduce the amount of code that assumes we're only instrumenting a flat function body. Moving more data into expansion tree nodes is an incremental step in that direction.

There should be no change to compiler output.

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[rustbot]

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[oli-obk]

Preexisting, but are there tests for the signature coming from a macro def, but the body from the invocation site? Or where the outer block is also part of the macro and the statements inside are from the call site?

I see the code "handling" it, but not sure what the effects are

[Zalathar]

Preexisting, but are there tests for the signature coming from a macro def, but the body from the invocation site? Or where the outer block is also part of the macro and the statements inside are from the call site?

I see the code "handling" it, but not sure what the effects are

Instrumentation of macro expansions has pretty poor test coverage overall, but it was easy enough to add a new test for those specific cases.

The other changes in this PR don't seem to affect the new tests, which is reassuring.

[oli-obk]

r? @oli-obk

@bors r+ rollup

[bors]

📌 Commit ac43716 has been approved by oli-obk

It is now in the queue for this repository.