chloe: ensure self-closing tags are self-closing

This gets us much closer to HTML5 compatibility, while not breaking the
existing XHTML functionality. (Indeed, the entire reason this is necessary is
that XHTML, being an XML derivative, treats `<foo></foo>` and `<foo />`
equivalently, whereas HTML5 does not.)

basis/html/templates/chloe/compiler/compiler.factor

@@ -2,7 +2,7 @@
 ! See http://factorcode.org/license.txt for BSD license.
 USING: assocs namespaces make kernel sequences accessors
 combinators strings splitting io io.streams.string present
-xml.writer xml.data xml.entities html.forms
+sets ascii xml.writer xml.data xml.entities html.forms
 html.templates html.templates.chloe.syntax ;
 IN: html.templates.chloe.compiler
 
@@ -60,6 +60,11 @@ DEFER: compile-element
         "\"" [write]
     ] assoc-each ;
 
+: compile-self-closing-tag ( tag -- )
+    "<" [write]
+    [ name>string [write] ] [ attrs>> compile-attrs ] bi
+    " />" [write] ;
+
 : compile-start-tag ( tag -- )
     "<" [write]
     [ name>string [write] ] [ attrs>> compile-attrs ] bi
@@ -74,17 +79,38 @@ SYMBOL: string-context?
 
 ERROR: tag-not-allowed-here ;
 
+CONSTANT: self-closing-tags {
+        "area"
+        "base"
+        "br"
+        "embed"
+        "hr"
+        "iframe"
+        "img"
+        "input"
+        "link"
+        "meta"
+        "param"
+        "source"
+        "track"
+    }
+
 : check-tag ( -- )
     string-context? get [ tag-not-allowed-here ] when ;
 
-: compile-tag ( tag -- )
+: (compile-tag) ( tag -- )
-    check-tag
+    dup name>string >lower self-closing-tags in?
-    {
+    [ compile-self-closing-tag ]
-        [ main>> tag-stack get push ]
+    [
         [ compile-start-tag ]
         [ compile-children ]
-        [ compile-end-tag ]
+        [ compile-end-tag ] tri
-    } cleave
+    ] if ;
+
+: compile-tag ( tag -- )
+    check-tag
+    [ main>> tag-stack get push ]
+    [ (compile-tag) ] bi
     tag-stack get pop* ;
 
 ERROR: unknown-chloe-tag tag ;