userdiff: extend Scheme support to cover other Lisp dialects

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           |  3 ++-
 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, 43 insertions(+), 11 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: 9e8f4e9c04e3efa494e78b710e0c5f6cc77a0a5e
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2000%2Fslburson%2Flisp-userdiff_driver-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2000/slburson/lisp-userdiff_driver-v4
Pull-Request: https://github.com/gitgitgadget/git/pull/2000

Range-diff vs v3:

 1:  e20ac5b6a6 = 1:  8e0b1e3d01 userdiff: tighten word-diff test case of the scheme driver
 2:  fb4c8dc5d4 ! 2:  0bd51e02ba userdiff: extend Scheme support to cover other Lisp dialects

@@ Commit message

## Documentation/gitattributes.adoc ##
@@ Documentation/gitattributes.adoc: patterns are available:
+
- rust suitable for source code in the Rust language.

- - scheme suitable for source code in the Scheme language. -+Also handles Emacs Lisp, Common Lisp, and most other dialects. +-- scheme suitable for source code in the Scheme language. ++- scheme suitable for source code in most Lisp dialects, ++ including Scheme, Emacs Lisp, Common Lisp, and Clojure.

- tex suitable for source code for LaTeX documents.

@@ t/t4034/scheme/expect
; This is a <RED>really<RESET><GREEN>(moderately)<RESET> cool function. (<RED>this\place<RESET><GREEN>that\place<RESET> (+ 3 4))
- (define <RED>|the greeting|<RESET><GREEN>|a greeting|<RESET> "hello")
-+ (define <RED>|the \greeting|<RESET><GREEN>|a \greeting|<RESET> |hello there|)
++ (define <RED>|the \| \greeting|<RESET><GREEN>|a \greeting|<RESET> |hello there|)
({<RED>}<RESET>(([<RED>]<RESET>(func-n)<RED>[<RESET>]))<RED>{<RESET>})
(let ((c (<RED>+ a b<RESET><GREEN>add1 first<RESET>)))
(format "one more than the total is %d" (<RED>add1<RESET><GREEN>+<RESET> c <GREEN>second<RESET>))))
@@ t/t4034/scheme/pre
; This is a really cool function.
(this\place (+ 3 4))
- (define |the greeting| "hello")
-+ (define |the \greeting| |hello there|)
++ (define |the \| \greeting| |hello there|)
({}(([](func-n)[])){})
(let ((c (+ a b)))
(format "one more than the total is %d" (add1 c))))

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