userdiff: add support for Scheme

Add a diff driver for Scheme-like languages which recognizes top level
and local `define` forms, whether it is a function definition, binding,
syntax definition or a user-defined `define-xyzzy` form.

Also supports R6RS `library` forms, `module` forms along with class and
struct declarations used in Racket (PLT Scheme).

Alternate "def" syntax such as those in Gerbil Scheme are also
supported, like defstruct, defsyntax and so on.

The rationale for picking `define` forms for the hunk headers is because
it is usually the only significant form for defining the structure of
the program, and it is a common pattern for schemers to have local
function definitions to hide their visibility, so it is not only the top
level `define`'s that are of interest. Schemers also extend the language
with macros to provide their own define forms (for example, something
like a `define-test-suite`) which is also captured in the hunk header.

Since it is common practice to extend syntax with variants of a form
like `module+`, `class*` etc, those have been supported as well.

The word regex is a best-effort attempt to conform to R7RS[1] valid
identifiers, symbols and numbers.

[1] https://small.r7rs.org/attachment/r7rs.pdf (section 2.1)

Signed-off-by: Atharva Raykar <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: tfidfwastaken

Documentation/gitattributes.txt

@@ -845,6 +845,8 @@ patterns are available:
 
 - `rust` suitable for source code in the Rust language.
 
+- `scheme` suitable for source code in the Scheme language.
+
 - `tex` suitable for source code for LaTeX documents.
 
 

t/t4018-diff-funcname.sh

@@ -48,6 +48,7 @@ diffpatterns="
 	python
 	ruby
 	rust
+	scheme
 	tex
 	custom1
 	custom2

t/t4018/scheme-class

@@ -0,0 +1,7 @@
+(define book-class%
+  (class* () object% RIGHT
+    (field (pages 5))
+    (field (ChangeMe 5))
+    (define/public (letters)
+      (* pages 500))
+    (super-new)))

t/t4018/scheme-def

@@ -0,0 +1,4 @@
+(def (some-func x y z) RIGHT
+  (let ((a x)
+        (b y))
+        (ChangeMe a b)))

t/t4018/scheme-def-variant

@@ -0,0 +1,4 @@
+(defmethod {print point} RIGHT
+  (lambda (self)
+    (with ((point x y) self)
+      (printf "{ChangeMe x:~a y:~a}~n" x y))))

t/t4018/scheme-define-slash-public

@@ -0,0 +1,7 @@
+(define bar-class%
+  (class object%
+    (field (info 5))
+    (define/public (foo) RIGHT
+      (+ info 42)
+      (* info ChangeMe))
+    (super-new)))

t/t4018/scheme-define-syntax

@@ -0,0 +1,8 @@
+(define-syntax define-test-suite RIGHT
+  (syntax-rules ()
+    ((_ suite-name (name test) ChangeMe ...)
+     (define suite-name
+       (let ((tests
+              `((name . ,test) ...)))
+         (lambda ()
+           (run-suite 'suite-name tests)))))))

t/t4018/scheme-define-variant

@@ -0,0 +1,4 @@
+(define* (some-func x y z) RIGHT
+  (let ((a x)
+        (b y))
+        (ChangeMe a b)))

t/t4018/scheme-library

@@ -0,0 +1,11 @@
+(library (my-helpers id-stuff) RIGHT
+  (export find-dup)
+  (import (ChangeMe))
+  (define (find-dup l)
+    (and (pair? l)
+         (let loop ((rest (cdr l)))
+           (cond
+            [(null? rest) (find-dup (cdr l))]
+            [(bound-identifier=? (car l) (car rest))
+             (car rest)]
+            [else (loop (cdr rest))])))))

t/t4018/scheme-local-define

@@ -0,0 +1,4 @@
+(define (higher-order)
+  (define local-function RIGHT
+    (lambda (x)
+     (car "this is" "ChangeMe"))))