support HTML comments

txexpr/base.rkt

@@ -4,7 +4,7 @@
          xml
          "private/define-provide-safe-match.rkt"
          (for-syntax racket/base syntax/parse))
-(provide cdata? cdata valid-char? xexpr->string xexpr?) ; from xml
+(provide cdata? cdata valid-char? xexpr->string xexpr? comment comment?) ; from xml
 (provide empty) ; from racket/list
 
 ;; Section 2.2 of XML 1.1
@@ -101,10 +101,10 @@
   (andmap
    (lambda (e)
      (cond
-       [(or (string? e) (symbol? e) (my-valid-char? e) (cdata? e)) #t]
+       [(or (string? e) (symbol? e) (my-valid-char? e) (cdata? e) (comment? e)) #t]
        [(and (list? e) (symbol? (first e)))
         (validate-txexpr e)]
-       [else (txexpr-error "element" "not a valid element (= txexpr, string, symbol, XML char, or cdata)" e tx)]))
+       [else (txexpr-error "element" "not a valid element (= txexpr, string, symbol, XML char, cdata, or comment)" e tx)]))
    elems))
   
 (define (txexpr-error noun has-problem bad tx)
@@ -306,15 +306,23 @@
 (define (cdata-string? x)
   (and (string? x) (regexp-match #rx"^<!\\[CDATA\\[.*\\]\\]>$" x) #true))
 
+(define comment-pattern #rx"^<!--(.*?)-->$")
+
+(define (string->comment x)
+  (match (regexp-match comment-pattern x)
+    [(list _ comment-payload) (comment comment-payload)]
+    [_ #false]))
+
 (define+provide+safe (xexpr->html x)
   (xexpr? . -> . string?)
   (xexpr->string
    (let loop ([x x])
-     (match x
-       [(? txexpr?)
+     (cond
+       [(txexpr? x)
         (define-values (tag attrs elements) (txexpr->values x))
         (define proc (if (memq tag '(script style)) ->cdata loop))
         ;; a little faster than `txexpr` since we know the pieces are valid
         (txexpr-unsafe tag attrs (map proc elements))]
-       [(? cdata-string?) (->cdata x)]
-       [_ x]))))
+       [(cdata-string? x) (->cdata x)]
+       [(and (string? x) (string->comment x))]
+       [else x]))))

txexpr/test/tests.rkt

@@ -94,7 +94,7 @@
  ;; Invalid element
  (check-validate-exn-msg
   '(p "foo" "bar" ((key "value")))
-  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, or cdata)\n  element: '((key \"value\"))\n  in: '(p \"foo\" \"bar\" ((key \"value\")))")
+  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, cdata, or comment)\n  element: '((key \"value\"))\n  in: '(p \"foo\" \"bar\" ((key \"value\")))")
 
  ;; Malformed attribute list
  (check-validate-exn-msg
@@ -114,17 +114,17 @@
  ;; Invalid element type
  (check-validate-exn-msg
   `(root ,(void))
-  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, or cdata)\n  element: #<void>\n  in: '(root #<void>)")
+  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, cdata, or comment)\n  element: #<void>\n  in: '(root #<void>)")
 
  ;; (Deeply nested) No name: error should pinpoint element in 'div txexpr 
  (check-validate-exn-msg
   '(fine-outer [[type "valid"]] (div (br) ("p" "foo" "bar")))
-  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, or cdata)\n  element: '(\"p\" \"foo\" \"bar\")\n  in: '(div (br) (\"p\" \"foo\" \"bar\"))")
+  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, cdata, or comment)\n  element: '(\"p\" \"foo\" \"bar\")\n  in: '(div (br) (\"p\" \"foo\" \"bar\"))")
 
  ;; (Deeply nested) Invalid element: error should pinpoint element in 'p txexpr
  (check-validate-exn-msg
   '(fine-outer [[type "valid"]] (div (br) (p "foo" "bar" ((key "value")))))
-  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, or cdata)\n  element: '((key \"value\"))\n  in: '(p \"foo\" \"bar\" ((key \"value\")))")
+  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, cdata, or comment)\n  element: '((key \"value\"))\n  in: '(p \"foo\" \"bar\" ((key \"value\")))")
 
  ;; (Deeply nested) Malformed attribute list: error should pinpoint attr in 'p txexpr
  (check-validate-exn-msg
@@ -144,7 +144,7 @@
  ;; (Deeply nested) Invalid element type: error should pinpoint element in 'p txexpr
  (check-validate-exn-msg
   `(fine-outer [[type "valid"]] (div (br) (p ,(void))))
-  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, or cdata)\n  element: #<void>\n  in: '(p #<void>)")
+  "validate-txexpr: element not a valid element (= txexpr, string, symbol, XML char, cdata, or comment)\n  element: #<void>\n  in: '(p #<void>)")
  
  (check-txexprs-equal? (make-txexpr 'p) '(p))
  (check-txexprs-equal? (make-txexpr 'p '((key "value"))) '(p ((key "value"))))
@@ -309,4 +309,16 @@
                "<root><script>3 > 2</script>Why is 3 &gt; 2?</root>")
 
  (check-equal? (xexpr->html '(root (div "<![CDATA[3 > 2]]>") "Why is 3 > 2?"))
-               "<root><div><![CDATA[3 > 2]]></div>Why is 3 &gt; 2?</root>"))
+               "<root><div><![CDATA[3 > 2]]></div>Why is 3 &gt; 2?</root>")
+ 
+ ;; comment
+ (check-equal? (xexpr->html '(root "<!-- comment -->" "Why is 3 > 2?"))
+               "<root><!-- comment -->Why is 3 &gt; 2?</root>")
+
+  ;; malformed comment: merged with next string
+ (check-equal? (xexpr->html '(root "<!-- comment -->Why is 3 > 2?"))
+               "<root>&lt;!-- comment --&gt;Why is 3 &gt; 2?</root>")
+
+ ;; malformed comment: missing double hyphen at end
+ (check-equal? (xexpr->html '(root "<!-- comment ->" "Why is 3 > 2?"))
+               "<root>&lt;!-- comment -&gt;Why is 3 &gt; 2?</root>"))