a8cf1a0352
Allow `parseString()` to return an empty `StringRef` when the delimiter appears at position 0. This enables parsing pre-aggregated profile addresses with an omitted buildid but preserved colon (`:addr` format), where the empty buildid corresponds to the main binary. Previously, `parseString()` rejected zero-length fields by treating `StringEnd == 0` the same as `StringRef::npos` (delimiter not found). These are distinct situations: `npos` means no delimiter exists, while `0` means the field before the delimiter is empty. The fix removes the `StringEnd == 0` sub-condition so only the missing-delimiter case errors. The existing test for buildid-prefixed addresses is extended to also verify that `:addr` input produces identical output to the plain-address and non-empty-buildid variants. Test Plan: Added empty-buildid input file and extended `pre-aggregated-perf-buildid.test` to run perf2bolt with `:addr` format and diff the fdata output against the existing buildid-prefixed result.
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