pub const ENV_VERSION: u32 = 3;Expand description
Bumped whenever the on-disk shape of BuildEnvironment changes.
BuildEnvironment::load discards (returns None for) any file whose
stored version doesn’t match current — mirroring Sphinx’s own
ENV_VERSION check, where a stale environment is simply rebuilt from
scratch rather than partially trusted.
Version 3: wave 4.5’s Span change (a line provenance field) alters
the shape of every serialized Node tree in tocs/titles. The same
wave later added the py field; a v3 env.bin written before it fails
to decode (the trailing bytes don’t parse as a PyDomainData) and is
rebuilt — only dev builds of this branch ever wrote one, so no second
bump.