Make var"#self#" also work for callable structs

src/julia-syntax.scm

@@ -172,6 +172,22 @@
 (define (method-lambda-expr argl body rett)
   (let ((argl (map arg-name argl))
         (body (blockify body)))
+    ;; If the method body mentions |#self#| but no parameter is called
+    ;; |#self#|, introduce a local alias so var"#self#" works for
+    ;; callable objects as it does for ordinary functions.
+    (let* ((have-self-arg? (memq '|#self#| argl))
+           (first          (and (pair? argl) (car argl)))
+           (needs-alias?
+             (and (not have-self-arg?)
+                  (expr-contains-p
+                    (lambda (x) (eq? x '|#self#|))
+                    body))))
+      (when needs-alias?
+        (set! body
+              (insert-after-meta
+               body
+               `((local |#self#|)
+                 (= |#self#| ,first))))))
     `(lambda ,argl ()
              (scope-block
               ,(if (equal? rett '(core Any))

test/syntax.jl

@@ -4351,3 +4351,40 @@ let f = NoSpecClosure.K(1)
     @test f(2) == 1
     @test typeof(f).parameters == Core.svec()
 end
+
+# var"#self#"
+# regular functions can use var"#self#" to refer to the function itself
+regular_func() = var"#self#"
+@test regular_func() === regular_func
+
+# callable structs can also use var"#self#", which will refer to the struct instance
+struct CallableStruct
+    value::Int
+end
+(obj::CallableStruct)() = var"#self#"
+(obj::CallableStruct)(x) = var"#self#".value + x
+
+let cs = CallableStruct(42)
+    @test cs() === cs
+    @test cs(10) === 52
+end
+
+struct RecursiveCallableStruct; end
+(::RecursiveCallableStruct)(n) = n <= 1 ? n : var"#self#"(n-1) + var"#self#"(n-2)
+
+@test RecursiveCallableStruct()(10) === 55
+
+# In closures, var"#self#" should refer to the enclosing function,
+# NOT the enclosing struct instance
+struct CallableStruct2; end
+function (obj::CallableStruct2)()
+    function inner_func()
+        var"#self#"
+    end
+    inner_func
+end
+
+let cs = CallableStruct2()
+    @test cs()() === cs()
+    @test cs()() !== cs
+end