Tom Saeger rightly pointed out [1] that the prefetch task ignores custom
refspecs. This can lead to downloading more data than requested, and it
doesn't even help the future foreground fetches that use that custom
refspec.

[1]
https://lore.kernel.org/git/20210401184914.qmr7jhjbhp2mt3h6@dhcp-10-154-148-175.vpn.oracle.com/

This series fixes this problem by carefully replacing the start of each
refspec's destination with "refs/prefetch/". If the destination already
starts with "refs/", then that is replaced. Otherwise "refs/prefetch/" is
just prepended.

In order to accomplish this safely, a new refspec_item_format() method is
created and tested.

Patch 1 is just a preparation patch that makes the code simpler (and in
hindsight it should have been written this way from the start).

Patch 2 is a simplification of test_subcommand that removes the need for
escaping glob characters. Thanks, Eric Sunshine, for the tip of why my tests
were failing on FreeBSD.

Patches 3-4 add refspec_item_format().

Patch 5 finally modifies the logic in the prefetch task to translate these
refspecs.

Thanks, -Stolee

Derrick Stolee (5):
  maintenance: simplify prefetch logic
  test-lib: use exact match for test_subcommand
  refspec: output a refspec item
  test-tool: test refspec input/output
  maintenance: allow custom refspecs during prefetch

 Documentation/git-maintenance.txt |  3 +-
 Makefile                          |  1 +
 builtin/gc.c                      | 63 +++++++++++++++++++------------
 refspec.c                         | 25 ++++++++++++
 refspec.h                         |  5 +++
 t/helper/test-refspec.c           | 39 +++++++++++++++++++
 t/helper/test-tool.c              |  1 +
 t/helper/test-tool.h              |  1 +
 t/t5511-refspec.sh                | 41 ++++++++++++++++++++
 t/t7900-maintenance.sh            | 43 ++++++++++++++++++---
 t/test-lib-functions.sh           |  4 +-
 11 files changed, 192 insertions(+), 34 deletions(-)
 create mode 100644 t/helper/test-refspec.c

base-commit: 2e36527f23b7f6ae15e6f21ac3b08bf3fed6ee48

Submitted-As: https://lore.kernel.org/git/pull.924.git.1617627856.gitgitgadget@gmail.com