profiles: align type of index into string table

[florianl]

With Mapping.filename, Function.name, Label.key and others, the type of the index into the string table is always int64. For consistency align the type of Location.type_index, which is also an index into the string table, to int64.

type_index is an element introduced by the OTel Profiling SIG and was added to message Location. Changing this type does not break compatibility with the original pprof, as the original pprof does not have this element in message Location.

FYI: @petethepig @open-telemetry/profiling-maintainers

[felixge]

Works for me. There might be some concerns around memory usage here, but we can come back to this if it turns out to be problematic.

[tigrannajaryan]

Changing this type does not break compatibility with the original pprof, as the original pprof does not have this element in message Location.

Does it still meet the requirement of "every valid pprof profile is also a valid Otel profile"?

[florianl]

Does it still meet the requirement of "every valid pprof profile is also a valid Otel profile"?

@tigrannajaryan - yes it does. As type_index was introduced by the OTel Profiling SIG it does not affect original pprof profiles. In general original pprof profiles use int64 as index type and this PR aligns the OTel Profiling SIG introduced element to also use int64 as its type.

[javierhonduco]

Love this change! – are there any blockers to iron out before it can be merged?

[florianl]

friendly ping @open-telemetry/specs-approvers - can this change get merged?

@felixge , @petethepig and @christos68k from the @open-telemetry/profiling-maintainers group approved this change already.