Subject: [PATCH v3 0/2] userdiff: extend Scheme support to cover other Lisp dialects

From: "Scott L. Burson via GitGitGadget" <[email-masked]>
Date: Thu, 15 Jan 2026 23:18:38 +0000

Common Lisp, Emacs Lisp, and other dialects have some top-level forms, most
importantly 'defun', that are not matched by the current Scheme pattern.
Also, it is common in these dialects, when defining user macros intended as
top-level forms, to prefix their names with "def" instead of "define"; such
forms are also not currently matched. Some such forms don't even begin with
"def".

On the other hand, it is an established formatting convention in the Lisp
community that only top-level forms start at the left margin. So matching
any unindented line starting with an open parenthesis is an acceptable
heuristic; false positives will be rare.

However, there are also cases where notionally top-level forms are grouped
together within some containing form. At least in the Common Lisp community,
it is conventional to indent these by two spaces, or sometimes one. But
matching just an open parenthesis indented by two spaces would be too broad;
so the pattern added by this commit requires an indented form to start with
"(def". It is believed that this strikes a good balance between potential
false positives and false negatives.

This commit disjoins a regexp employing these heuristics to the existing
Scheme regexp, so it will still match everything that it did previously.

Johannes Sixt (1):
  userdiff: tighten word-diff test case of the scheme driver

Scott L. Burson (1):
  userdiff: extend Scheme support to cover other Lisp dialects

 Documentation/gitattributes.adoc           |  1 +
 t/t4018/scheme-lisp-defun-a                |  4 ++++
 t/t4018/scheme-lisp-defun-b                |  4 ++++
 t/t4018/scheme-lisp-eval-when              |  4 ++++
 t/t4018/{scheme-module => scheme-module-a} |  0
 t/t4018/scheme-module-b                    |  6 ++++++
 t/t4034/scheme/expect                      |  5 +++--
 t/t4034/scheme/post                        |  3 ++-
 t/t4034/scheme/pre                         |  3 ++-
 userdiff.c                                 | 22 ++++++++++++++++------
 10 files changed, 42 insertions(+), 10 deletions(-)
 create mode 100644 t/t4018/scheme-lisp-defun-a
 create mode 100644 t/t4018/scheme-lisp-defun-b
 create mode 100644 t/t4018/scheme-lisp-eval-when
 rename t/t4018/{scheme-module => scheme-module-a} (100%)
 create mode 100644 t/t4018/scheme-module-b

base-commit: 8745eae506f700657882b9e32b2aa00f234a6fb6
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2000%2Fslburson%2Flisp-userdiff_driver-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2000/slburson/lisp-userdiff_driver-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/2000

Range-diff vs v2:

 1:  da99bb0bcd < -:  ---------- diff: "lisp" userdiff_driver
 2:  86315aa3e3 < -:  ---------- merge with Scheme regexp; fix bugs
 -:  ---------- > 1:  e20ac5b6a6 userdiff: tighten word-diff test case of the scheme driver
 -:  ---------- > 2:  fb4c8dc5d4 userdiff: extend Scheme support to cover other Lisp dialects

-- 
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