fix macro hygiene for kwargs with name conflicts (#34329)

src/macroexpand.scm

@@ -297,10 +297,9 @@
              (append!
               pairs
               (filter (lambda (v) (not (assq (car v) env)))
-                      (append!
-                       (pair-with-gensyms v)
-                       (map (lambda (v) (cons v v))
-                            (diff (keywords-introduced-by x) globals))))
+                      (pair-with-gensyms v))
+              (map (lambda (v) (cons v v))
+                   (keywords-introduced-by x))
               env)))))))
 
 (define (resolve-expansion-vars-with-new-env x env m parent-scope inarg (outermost #f))

test/syntax.jl

@@ -1971,3 +1971,18 @@ end
 # issue #33987
 f33987(args::(Vararg{Any, N} where N); kwargs...) = args
 @test f33987(1,2,3) === (1,2,3)
+
+macro id_for_kwarg(x); x; end
+Xo65KdlD = @id_for_kwarg let x = 1
+    function f(; x)
+        x
+    end
+end
+@test_throws UndefKeywordError(:x) Xo65KdlD()
+i0xb23hG = @id_for_kwarg let x = 1
+    function f(; x=2)
+        x
+    end
+end
+@test i0xb23hG() == 2
+@test i0xb23hG(x=10) == 10