ci(covr): install xml2 from r-lib/xml2#479 to fix multi-hour coverage runs

[krlmlr]

Problem

The coverage job on GitHub Actions takes ~5 hours. The time is spent entirely after the last Moving gcov outputs to covr directory. message — i.e. in covr::to_cobertura(cov), which the covr action runs after package_coverage().

to_cobertura() builds the Cobertura report by appending one <line> XML node per covered source line. With released xml2, xml_add_child() defaults to .where = length(xml_children(.x)), which re-enumerates all existing siblings on every append → O(n²) per file. For RSQLite's bundled sqlite3.c (~67k covered lines under a single <lines> node) that is ~4.5 billion operations.

Evidence

Profiling the real coverage object (74,017 entries; sqlite3.c = 67,619) showed everything up to and including package_coverage() finishing in ~1.2 min, while to_cobertura() dominated, with Rprof attributing 94% of time to xml_add_child → xml_children/xml_nodeset.

Fix

The root cause is in xml2 and is fixed upstream by r-lib/xml2#479, which makes the default append O(1).

This PR installs xml2 from that PR at the start of the covr action, so the fast path is used only for coverage runs:

- name: Install xml2 with O(1) xml_add_child() (r-lib/xml2#479)
  run: pak::pak("r-lib/xml2#479")
  shell: Rscript {0}

pak is already provisioned by setup-r-dependencies in this job, so no extra setup is required.

Verified

With xml2 installed from the PR, the unmodified, released to_cobertura() processes the full RSQLite coverage data in ~25 seconds (down from ~5 hours).

Note

This pins coverage to a PR build of xml2. Once r-lib/xml2#479 is merged and released, this step can be dropped (or switched to r-lib/xml2 / the released version).

🤖 Generated with Claude Code

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Generated by Claude Code