[PATCH v8 0/9] config API: make "multi" safe, fix segfaults, propagate "ret"

This series fixes numerous segfaults in config API users, because they didn't expect *_get_multi() to hand them a string_list with a NULL in it given config like "[a] key" (note, no "="'s).

A larger general overview at v1[1], but note the API changes in v2[2]. Changes since v7[3]:

* A trivial documentation change to 3/9, to clarify which doc in
  config.h refer to what. As noted in the v7 discussion I think that
  config.h could use some larger cleanups in this area, but let's
  leave that for some future topic.

Branch & passing CI for this at: https://github.com/avar/git/tree/avar/have-git_configset_get_value-use-dest-and-int-pattern-8

1. https://lore.kernel.org/git/cover-00.10-00000000000-20221026T151328Z-avarab@gmail.com/
2. https://lore.kernel.org/git/cover-v2-0.9-00000000000-20221101T225822Z-avarab@gmail.com/
3. https://lore.kernel.org/git/cover-v7-0.9-00000000000-20230308T090513Z-avarab@gmail.com/

Ævar Arnfjörð Bjarmason (9):
  config tests: cover blind spots in git_die_config() tests
  config tests: add "NULL" tests for *_get_value_multi()
  config API: add and use a "git_config_get()" family of functions
  versioncmp.c: refactor config reading next commit
  config API: have *_multi() return an "int" and take a "dest"
  for-each-repo: error on bad --config
  config API users: test for *_get_value_multi() segfaults
  config API: add "string" version of *_value_multi(), fix segfaults
  for-each-repo: with bad config, don't conflate <path> and <cmd>

 builtin/for-each-repo.c              |  14 ++--
 builtin/gc.c                         |  15 ++--
 builtin/log.c                        |   6 +-
 builtin/submodule--helper.c          |   7 +-
 builtin/worktree.c                   |   3 +-
 config.c                             | 109 ++++++++++++++++++++++-----
 config.h                             |  72 +++++++++++++++---
 pack-bitmap.c                        |   6 +-
 submodule.c                          |   3 +-
 t/helper/test-config.c               |  28 ++++++-
 t/t0068-for-each-repo.sh             |  19 +++++
 t/t1308-config-set.sh                | 108 +++++++++++++++++++++++++-
 t/t3309-notes-merge-auto-resolve.sh  |   7 +-
 t/t4202-log.sh                       |  15 ++++
 t/t5304-prune.sh                     |  12 ++-
 t/t5310-pack-bitmaps.sh              |  20 +++++
 t/t5552-skipping-fetch-negotiator.sh |  16 ++++
 t/t7004-tag.sh                       |  17 +++++
 t/t7413-submodule-is-active.sh       |  16 ++++
 t/t7900-maintenance.sh               |  38 ++++++++++
 versioncmp.c                         |  22 ++++--
 21 files changed, 481 insertions(+), 72 deletions(-)

Range-diff against v7:
 1:  9f297a35e14 =  1:  b600354c0f6 config tests: cover blind spots in git_die_config() tests
 2:  45d483066ef =  2:  49908f0bcf3 config tests: add "NULL" tests for *_get_value_multi()
 3:  a977b7b188f !  3:  d163b3d04ff config API: add and use a "git_config_get()" family of functions
    @@ config.h: void git_configset_clear(struct config_set *cs);
       * value in the 'dest' pointer.
       */
      
    ++/**
    ++ * git_configset_get() returns negative values on error, see
    ++ * repo_config_get() below.
    ++ */
     +RESULT_MUST_BE_USED
     +int git_configset_get(struct config_set *cs, const char *key);
     +
 4:  3a5a323cd91 =  4:  d7dfedb7225 versioncmp.c: refactor config reading next commit
 5:  dced12a40d2 =  5:  840fb9d5c74 config API: have *_multi() return an "int" and take a "dest"
 6:  d910f7e3a27 =  6:  75a68b14217 for-each-repo: error on bad --config
 7:  57db0fcd91f =  7:  a78056e2748 config API users: test for *_get_value_multi() segfaults
 8:  b374a716555 =  8:  686b512c3df config API: add "string" version of *_value_multi(), fix segfaults
 9:  6791e1f6f85 =  9:  6fce633493b for-each-repo: with bad config, don't conflate <path> and <cmd>