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 <raykar.ath@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

11 files changed, 65 insertions, 0 deletions

diff --git a/t/t4018/scheme-class b/t/t4018/scheme-class
new file mode 100644
index 0000000000..e5e07b43fb
--- /dev/null
+++ b/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)))
diff --git a/t/t4018/scheme-def b/t/t4018/scheme-def
new file mode 100644
index 0000000000..1e2673da96
--- /dev/null
+++ b/t/t4018/scheme-def
@@ -0,0 +1,4 @@
+(def (some-func x y z) RIGHT
+  (let ((a x)
+        (b y))
+        (ChangeMe a b)))
diff --git a/t/t4018/scheme-def-variant b/t/t4018/scheme-def-variant
new file mode 100644
index 0000000000..d857a61d64
--- /dev/null
+++ 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))))
diff --git a/t/t4018/scheme-define-slash-public b/t/t4018/scheme-define-slash-public
new file mode 100644
index 0000000000..39a93a1600
--- /dev/null
+++ b/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)))
diff --git a/t/t4018/scheme-define-syntax b/t/t4018/scheme-define-syntax
new file mode 100644
index 0000000000..7d5e99e0fc
--- /dev/null
+++ b/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)))))))
diff --git a/t/t4018/scheme-define-variant b/t/t4018/scheme-define-variant
new file mode 100644
index 0000000000..911708854d
--- /dev/null
+++ b/t/t4018/scheme-define-variant
@@ -0,0 +1,4 @@
+(define* (some-func x y z) RIGHT
+  (let ((a x)
+        (b y))
+        (ChangeMe a b)))
diff --git a/t/t4018/scheme-library b/t/t4018/scheme-library
new file mode 100644
index 0000000000..82ea3df510
--- /dev/null
+++ 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))])))))
diff --git a/t/t4018/scheme-local-define b/t/t4018/scheme-local-define
new file mode 100644
index 0000000000..bc6d8aebbe
--- /dev/null
+++ b/t/t4018/scheme-local-define
@@ -0,0 +1,4 @@
+(define (higher-order)
+  (define local-function RIGHT
+    (lambda (x)
+     (car "this is" "ChangeMe"))))
diff --git a/t/t4018/scheme-module b/t/t4018/scheme-module
new file mode 100644
index 0000000000..edfae0ebf7
--- /dev/null
+++ b/t/t4018/scheme-module
@@ -0,0 +1,6 @@
+(module A RIGHT
+  (export with-display-exception)
+  (extern (display-exception display-exception ChangeMe))
+  (def (with-display-exception thunk)
+    (with-catch (lambda (e) (display-exception e (current-error-port)) e)
+      thunk)))
diff --git a/t/t4018/scheme-top-level-define b/t/t4018/scheme-top-level-define
new file mode 100644
index 0000000000..624743c22b
--- /dev/null
+++ b/t/t4018/scheme-top-level-define
@@ -0,0 +1,4 @@
+(define (some-func x y z) RIGHT
+  (let ((a x)
+        (b y))
+        (ChangeMe a b)))
diff --git a/t/t4018/scheme-user-defined-define b/t/t4018/scheme-user-defined-define
new file mode 100644
index 0000000000..35fe7cc9bf
--- /dev/null
+++ b/t/t4018/scheme-user-defined-define
@@ -0,0 +1,6 @@
+(define-test-suite record\ case-tests RIGHT
+  (record-case-1 (lambda (fail)
+                   (let ((a (make-foo 1 2)))
+                     (record-case a
+                       ((bar x) (ChangeMe))
+                       ((foo a b) (+ a b)))))))