Fix coverage ICE because fn_sig can have a span that crosses file bou…

[richkadel]

Fixes: #83792

MIR InstrumentCoverage assumed the FnSig span was contained within a
single file, but this is not always the case. Some macro constructions
can result in a span that starts in one SourceFile and ends in a
different one.

The FnSig span is included in coverage results as long as that span is
in the same SourceFile and the same macro context, but by assuming the
FnSig span's hi() and lo() were in the same file, I took this for
granted, and checked only that the FnSig hi() was in the same
SourceFile as the body_span.

I actually drop the hi() though, and extend the FnSig span to the
body_span.lo(), so I really should have simply checked that the
FnSig span's lo() was in the SourceFile of the body_span.

r? @tmandry
cc: @wesleywiser

[richkadel]

@tmandry - If the first email for this PR did not match the title, please ignore it. (An older PR's description was added in error, but I've updated it.)

This is the correct description:

Fix coverage ICE because fn_sig can have a span that crosses file boundaries

Fixes: #83792

MIR InstrumentCoverage assumed the FnSig span was contained within a
single file, but this is not always the case. Some macro constructions
can result in a span that starts in one SourceFile and ends in a
different one.

The FnSig span is included in coverage results as long as that span is
in the same SourceFile and the same macro context, but by assuming the
FnSig span's hi() and lo() were in the same file, I took this for
granted, and checked only that the FnSig hi() was in the same
SourceFile as the body_span.

I actually drop the hi() though, and extend the FnSig span to the
body_span.lo(), so I really should have simply checked that the
FnSig span's lo() was in the SourceFile of the body_span.

[tmandry]

@bors r+ rollup

[bors]

📌 Commit 31cba57 has been approved by tmandry

[bors]

⌛ Testing commit 31cba57 with merge e188693...

[bors]

☀️ Test successful - checks-actions
Approved by: tmandry
Pushing e188693 to master...