[PATCH] fast-import: accept invalid timezones so we can import existing repos

From: Elijah Newren <newren@gmail.com>

There are multiple repositories in the wild with random, invalid timezones. Most notably is a commit from rails.git with a timezone of "+051800"[1]. However, a few searches found other repos with that same invalid timezone. Further, Peff reports that GitHub relaxed their fsck checks in August 2011 to accept any timezone value[2], and there have been multiple reports to filter-repo about fast-import crashing while trying to import their existing repositories since they had timezone values such as "-7349423" and "-43455309"[3].

It is not clear what created these invalid timezones, but since git has permitted their use and worked with these repositories for years at this point, it seems pointless to make fast-import be the only thing that disallows them. Relax the parsing to allow these timezones when using raw import format; when using --date-format=rfc2822 (which is not the default), we can continue being more strict about timezones.

[1] https://github.com/rails/rails/commit/4cf94979c9f4d6683c9338d694d5eb3106a4e734 [2] https://lore.kernel.org/git/20200521195513.GA1542632@coredump.intra.peff.net/ [3] https://github.com/newren/git-filter-repo/issues/88

Signed-off-by: Elijah Newren <newren@gmail.com>
---
    fast-import: accept invalid timezones so we can import existing repos
    
    Note: this is not a fix for a regression, so you can ignore it for 2.27;
    it can sit in pu.
    
    Peff leaned towards normalizing these timezones in fast-export[1], but
    (A) it's not clear what "valid" timezone we should randomly pick and
    regardless of what we pick, it seems it'll be wrong for most cases, (B)
    it would provide yet another way that "git fast-export --all | git
    fast-import" would not preserve the original history, as users sometimes
    expect[2], and (C) that'd prevent users from passing a special callback
    to filter-repo to fix up these values[3].
    
    Since I'm not a fan of picking a random value to reassign these to (in
    either fast-export or fast-import), I went the route of relaxing the
    requirements in fast-import, similar to what Peff reports GitHub did
    about 9 years ago in their incoming fsck checks.
    
    [1] 
    https://lore.kernel.org/git/20200521195513.GA1542632@coredump.intra.peff.net/
    [2] 
    https://lore.kernel.org/git/CABPp-BFLJ48BZ97Y9mr4i3q7HMqjq18cXMgSYdxqD1cMzH8Spg@mail.gmail.com/
    [3] Example: 
    https://github.com/newren/git-filter-repo/issues/88#issuecomment-629706776

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-795%2Fnewren%2Floosen-fast-import-timezone-parsing-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-795/newren/loosen-fast-import-timezone-parsing-v1
Pull-Request: https://github.com/git/git/pull/795

 fast-import.c          |  7 +++----
 t/t9300-fast-import.sh | 17 +++++++++++++++++
 2 files changed, 20 insertions(+), 4 deletions(-)