[PATCH v6 0/3] Convert USE_NSEC to runtime config

Topic name: dk/use-nsec-runtime (applied)

Topic summary: Expose USE_NSEC as a runtime configuration, since build-time is too early for distributing Git [1]. As a result, common index-related options, like git-diff, are less likely to hit "racy git" problems on supported filesystems.

[1]: https://git.github.io/rev_news/2026/07/31/edition-137/

Built on master (2c78326f81 (The 11th batch, 2026-08-05)).

Changes in v5:

- improve message flow in patch 2

Changes in v4:

- fix message typo
- change #ifdef strategy: only ignore the config variable.
  Otherwise, use the use_nanosec member unconditionally. Also clarify
  that config might be ignore depending on build options in the docs.
- mention potential platform unsafety directly in config doc in
  addition to the link to Racy Git

Changes in v3:

- #ifdef out use_nanosec when NO_NSEC is requested

As I have heard no comments about the "Todo" lines below, which perhaps could more clearly be marked "RFC"/"RFH", I've added this line to call them out ;) and renamed them "Comments welcome"

Changes in v2:

- move Best-viewed-with trailer into message body as descriptive
  text.
- read core.useNanosec through struct repo instead of parsing
  config strings. The test suite passes locally this way, though that
  skipped 151 tests.
    - CI run: https://github.com/benknoble/git/actions/runs/31701945211

Original cover letter:

Hi all, this series follows up on the previous racy Git/USE_NSEC conversations.

- The first patch is a mostly-unrelated documentation fix for Meson, but
  it came out of something I spotted while reviewing the outputs of the
  final (main) patch.
- The second patch is a preliminary no-op reorganization of
  repo_config_values_init.
- The third patch is the meat, converting USE_NSEC into core.useNanosec.

There is a small textual and semantic conflict with 'ty/repo-config-cleanups' in 'seen', since that branch removes the comments in 'struct repo_config_values' which this series adds to. (The semantic conflict is that, if we drop those comments, we should probably not add them to repo_config_values_init like I do in patch 2.)

Comments welcome: I haven't touched any tests; I saw a bunch of hits for "git grep racy t" but wasn't sure how to fit this particular change in, especially since it won't be equally valid on all systems? Advice welcome.

Comments welcome: I wonder if "useNanosec" paints us into too much of a
corner; that is (slightly more abstractly), we are using *extended
precision* in the index. Maybe the name and documentation should reflect
that, so we aren't too committed to "nanoseconds"?
    - Some platforms could offer extended precision that is not as
      precise as nanoseconds
    - Some could offer precision _beyond_ nanoseconds

idk.

v1: <cover.1786103607.git.ben.knoble@gmail.com> v2: <cover.1786710807.git.ben.knoble@gmail.com> v3: <cover.1787065125.git.ben.knoble@gmail.com> v4: <cover.1787231825.git.ben.knoble@gmail.com> v5: <cover.1788010335.git.ben.knoble@gmail.com>

[1/3] meson: expose knob for xmlto relative links in manuals [2/3] environment: align repo_config_values_init with struct declaration [3/3] core: convert build-time USE_NSEC into runtime core.useNanosec

 Documentation/config/core.adoc        |  7 +++++++
 Documentation/meson.build             |  7 ++++++-
 Documentation/technical/racy-git.adoc | 11 ++++++-----
 Makefile                              | 12 +-----------
 builtin/update-index.c                |  2 +-
 compat/posix.h                        |  1 -
 configure.ac                          |  6 ------
 environment.c                         | 27 ++++++++++++++++++++-------
 environment.h                         |  1 +
 meson_options.txt                     |  2 ++
 read-cache.c                          | 15 ++++++---------
 statinfo.c                            | 14 +++++++-------
 12 files changed, 57 insertions(+), 48 deletions(-)

Diff-intervalle contre v5 :
1:  d612de6c2d = 1:  d612de6c2d meson: expose knob for xmlto relative links in manuals
2:  12974e07d0 = 2:  12974e07d0 environment: align repo_config_values_init with struct declaration
3:  01cd487cd2 ! 3:  0a611f6140 core: convert build-time USE_NSEC into runtime core.useNanosec
    @@ builtin/update-index.c: static void xrmdir(const char *path)
      {
      	/*
     -	 * not use if we could usleep(10) if USE_NSEC is defined. The
    -+	 * not use if we could usleep(10) if core.useNanosec is defined. The
    ++	 * not use if we could usleep(10) if core.useNanosec is enabled. The
      	 * field nsec could be there, but the OS could choose to
      	 * ignore it?
      	 */

base-commit: 2c78326f810173a4f3aefd8021f1e07575412481