My Emacs configuration https://git.cjennings.net/dotemacs/atom?h=main 2026-06-21T07:19:08+00:00 2026-06-21T07:19:08+00:00 Craig Jennings c@cjennings.net 2026-06-21T07:19:08+00:00 urn:sha1:a249e415c7199e3d4698f1956687fa351296a357 Re-enabling native-comp surfaced a suite-wide fragility. When a test redefines a C primitive (or a native-compiled function), native-comp routes native callers through a trampoline that calls the mock with the primitive's maximum arity. A fixed-arity mock narrower than the primitive then throws wrong-number-of-arguments, intermittently, as the eln-cache fills. I swept every arity-narrow subr mock to append &rest _ (188 sites, preserving any named args the body uses), and added tests/test-meta-subr-mock-arity.el, which fails make test on any subr mock too narrow for the primitive's arity. The rule isn't "never mock a subr". The suite mocks message and completing-read freely. It's "a subr mock must accept the primitive's arity." Background, the three failure modes, and the research are in docs/native-comp-subr-mocking.org.