For expansion region support, we will want to be able to convert and check
spans before creating a corresponding local file ID.
If we create local file IDs eagerly, but some expansion turns out to have no
successfully-converted spans, LLVM will complain about that expansion's file ID
having no regions.
This reflects the fact that we can't compute meaningful info for a function
that wasn't instrumented and therefore doesn't have `function_coverage_info`.
In codegen, a used function with `FunctionCoverageInfo` but no mappings has
historically indicated a bug. However, that will no longer be the case after
moving some fallible span-processing steps into codegen.
This patch dismantles what was left of `FunctionCoverage` in `map_data.rs`,
replaces `function_coverage_map` with a set, and overhauls how we prepare
covfun records for unused functions.
The checks in `is_eligible_for_coverage` include `is_fn_like`, but will also
exclude various function-like things that cannot possibly have coverage
instrumentation.
This query (`coverage_ids_info`) already determines which counter/expression
IDs are unused, so it only takes a little extra effort to also determine which
counters/expressions must have a value of zero.
This is currently handled automatically by the fact that codegen doesn't visit
coverage statements in unused functions, but that will no longer be the case
when unused IDs are identified by a separate query instead.
A used function with no mappings has historically indicated a bug, but that
will no longer be the case after moving some fallible span-processing steps
into codegen.
coverage: Restrict empty-span expansion to only cover `{` and `}`
Coverage instrumentation has some tricky code for converting a coverage-relevant `Span` into a set of start/end line/byte-column coordinates that will be embedded in the CGU's coverage metadata.
A big part of this complexity is special code for handling empty spans, which are expanded into non-empty spans (if possible) because LLVM's coverage reporter does not handle empty spans well.
This PR simplifies that code by restricting it to only apply in two specific situations: when the character after the empty span is `{`, or the character before the empty span is `}`.
(As an added benefit, this means that the expanded spans no longer extend awkwardly beyond the end of a physical line, which was common under the previous implementation.)
Along the way, this PR also removes some unhelpful code for dealing with function source code spread across multiple files. Functions currently can't have coverage spans in multiple files, and if that ever changes (e.g. to properly support expansion regions) then this code will need to be completely overhauled anyway.
Functions currently can't have mappings in multiple files, and if that ever
changes (e.g. to properly support expansion regions), this code will need to be
completely overhauled anyway.
We already had a dedicated `LocalFileId` index type, but previously we used a
raw `u32` for global file IDs, because index types were harder to pass through
FFI.
