Release 1.4.0

A feature release on top of 1.3.0, backwards compatible with
respect to rule language, build description, repository description,
and wire protocols. However, the internal representation in local
build root has changed; it is therefore recommended to remove the
local build root on upgrade.

New features

• just serve now also works together with a compatible remote-execution
  endpoint. This uses an extended version of the serve protocol, so
  both, just-mr and just serve need to be at the new version.
• User-defined rules, as well as the built-in rule "generic" can
  now specify a subdirectory in which an action is to be executed.
• just-mr now supports garbage collection for repository roots
  via the gc-repo subcommand. This follows the same two-generation
  approach as garbage collection for the cache-CAS pair; in
  other words, everything is cleaned up that was not used since
  the last call to gc-repo. To accommodate this, the layout in
  the local build root had to be changed. The directory git as
  well as *-map directories are now located in the subdirectory
  repositories/generation-0. On upgrade those have to be manually
  moved there if they should be continued to be used; removing the
  whole local build root is, of course, also a valid upgrade path,
  however losing the whole cache. Not doing anything on upgrade
  will not lead to an inconsistent state; however, the directories
  at the old location will not be used anymore while still using
  disk space.
• The expression language has been extended to contain quote
  and quasi-quote expressions, as well as new built-in functions
  "from_subdir", "nub_left".

Fixes

• The built-in rule "generic" now properly enforces that the
  obtained outputs form a well-formed artifact stage; a conflicting
  arrangement of artifacts was possilbe beforehand.
• The built-in expression functions "join" and "join_cmd"
  now properly enforce that the argument is a list of strings.
  So far, they used to accept a single string, treating it as a
  singleton list.
• A bug was fixed that cased just serve to fail with an internal
  error when building against ignore-special roots.
• just now accurately reports internal errors that occurred on
  the serve endpoint.
• Target-level cache entries are only written if all export targets
  depended upon are also written to or found in cache; previously,
  it was assumed that all export targets not analysed locally
  were local cache hits, an assumption that no longer holds in
  the presence of serve endpoints. This fixes a cache consistency
  problem if the same remote-execution endpoint is used both, with
  and without a serve endpoint.
• A race condition in reconstructing executables from large CAS
  has been removed that could lead to an open file descriptor being
  kept alive for too long, resulting EBUSY failures of actions
  using this binary.
• Internal code clean up, reducing memory footprint, in particular
  for simultaneous upload of a large number of blobs.
• Avoidence of duplicate requests and performance improvements when
  synchronizing artifacts with another CAS.
• Dependencies have been updated to also build with gcc 14.
• Portability improvements of the code by not relying on implementation
  details of the compiler.
• Local execution no longer has the requirement that there exist
  no more files with identical content than the hardlink limit of
  the underlying file system.
• Inside action descriptions, paths are always normalized; this improves
  compatibility with existing remote-execution implementations.
• The size of large object entries has been reduced. The cache
  and CAS must be cleaned up since stable versions before 1.4.0
  cannot use the new format.
• The way of storing intermediate keys of the action cache has
  been changed. The cache must be cleaned up since stable versions
  before 1.4.0 cannot use the new format.
• Various improvements to the tests: dispatching of the summary
  action is now possible, tests are independent of a .just-mrrc
  file the user might have in their home directory
• Various improvements of the documentation.