Subject: [PATCH 0/4] diff: reject negative context values

From: "Michael Montalbo via GitGitGadget" <[email-masked]>
Date: Tue, 05 May 2026 23:02:20 +0000

Negative values for -U and --inter-hunk-context are silently accepted
and produce structurally invalid diff output.

Malformed hunk headers:

$ wc -l GIT-VERSION-GEN
106
$ git log -1 -p -U-500 -- GIT-VERSION-GEN | grep '^@@'                                                         
@@ -503,999- +503,999- @@

Line 503 of a 106-line file, count "999-" is not a valid integer.

Overlapping hunks that cannot be applied:

$ git log -1 -p -U3 --inter-hunk-context=100 791aeddfa2 \                                                      
    -- git-compat-util.h | git apply --check --reverse
(success)                                                                                                      
                                                                                                             
$ git log -1 -p -U3 --inter-hunk-context=-100 791aeddfa2 \                                                     
    -- git-compat-util.h | git apply --check --reverse                                                       
error: patch failed: git-compat-util.h:118                                                                     
error: git-compat-util.h: patch does not apply                                                               

Both options were originally parsed via opt_arg() which gated on
isdigit(), making negative values impossible. When they were converted
to OPT_INTEGER_F / OPT_CALLBACK in d473e2e0e8 (diff.c: convert
-U|--unified, 2019-01-27) and 16ed6c97cc (diff-parseopt: convert
--inter-hunk-context, 2019-03-24), the implicit rejection was lost.
PARSE_OPT_NONEG was added but only prevents the --no-* boolean form,
not negative numeric arguments.

This series restores the original invariant with stronger guarantees:

1/4  diff: reject negative values for --inter-hunk-context                                                     
     Change type to unsigned int, switch to OPT_UNSIGNED.                                                    
                                                                                                               
2/4  diff: reject negative values for -U/--unified                                                             
     Change type to unsigned int, add range check in callback.                                                 
                                                                                                               
3/4  xdiff: guard against negative context lengths                                                           
     BUG() in xdl_get_hunk() as defense in depth.
                                                                                                               
4/4  parse-options: clarify PARSE_OPT_NONEG does not reject                                                    
     negative numbers                                                                                          
     Documentation fix.                                                                                        

The config variables diff.context and diff.interHunkContext have
always rejected negative values. This series brings the CLI options in line.

Michael Montalbo (4):
  diff: reject negative values for --inter-hunk-context
  diff: reject negative values for -U/--unified
  xdiff: guard against negative context lengths
  parse-options: clarify PARSE_OPT_NONEG does not reject negative
    numbers

 diff.c                             | 25 ++++++++++++++-----------
 diff.h                             |  4 ++--
 parse-options.h                    |  5 ++++-
 t/t4032-diff-inter-hunk-context.sh |  6 ++++++
 t/t4055-diff-context.sh            |  5 +++++
 xdiff/xemit.c                      | 16 ++++++++++++----
 6 files changed, 43 insertions(+), 18 deletions(-)

base-commit: 94f057755b7941b321fd11fec1b2e3ca5313a4e0
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2105%2Fmmontalbo%2Fmm%2Freject-negative-interhunk-context-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2105/mmontalbo/mm/reject-negative-interhunk-context-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/2105
-- 
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