D015 - A census of absences needs a control in both directions

decided · 2026-08-19

900-surface/control probes one symbol that must resolve and one that must not, through exactly the path real entries use. It runs first in the section.

Written because the first run made the problem obvious. All 246 symbols reported absent, every library red - which is the correct answer on a host that implements none of the platform, and also precisely what a completely broken presence test would produce. The two are indistinguishable from the output, and the case where they are indistinguishable is the normal case for an emulator early in its life.

The control symbol is defined in a different translation unit from the census, so it exercises real weak resolution rather than short-circuiting within one file. If the control fails, the section says outright that every other number in it is meaningless.