Merge shorthand classes when the attribute map has no :class

CHANGELOG.md

@@ -4,6 +4,10 @@ Unreleased changes are available via `io.github.borkdude/html {:git/sha "..."}`
 
 [html](https://github.com/borkdude/html): Produce HTML from hiccup in Clojure and ClojureScript
 
+## Unreleased
+
+- Fix shorthand classes being dropped when the attribute map has no `:class`: `[:div.card {:id "a"}]` rendered `<div id="a">`. The same path interpolated a symbol's _name_ when `:class` was bound to an expression, so `(let [x "big"] [:div.card {:class x}])` rendered `class="card x"`.
+
 ## 0.2.6
 
 - Fix [#17](https://github.com/borkdude/html/issues/17): inline `style` map emitted a literal `\n` between declarations via `pr-str`, producing invalid CSS that dropped every declaration after the first ([@cycl1st](https://github.com/cycl1st))

src/borkdude/html.cljc

@@ -93,14 +93,16 @@
        (.substring tag (unchecked-inc-int class-index)))]))
 
 (defn merge-attrs [attrs short-attrs]
-  (let [attrs (if-let [c (:class attrs)]
-                       (if-let [sc (:class short-attrs)]
-                         (assoc attrs :class (str sc " " c))
-                         attrs)
-                       attrs)
+  (let [attrs (if-let [sc (:class short-attrs)]
+                (if-let [c (:class attrs)]
+                  (assoc attrs :class (if (constant? c)
+                                        (str sc " " c)
+                                        `(str ~sc " " ~c)))
+                  (assoc attrs :class sc))
+                attrs)
         attrs (if-let [id (:id short-attrs (:id attrs))]
-                  (assoc attrs :id id)
-                  attrs)]
+                (assoc attrs :id id)
+                attrs)]
     attrs))
 
 (defn- ->html [opts form]
@@ -174,8 +176,7 @@
   (html [:div [:<> "hello " "there"]])
   (html [:div [[:<>script]]])
   (html [:div [:$ [:<>script]]])
-  (macroexpand-all '(html [:div ]))
+  (macroexpand-all '(html [:div]))
   (macroexpand-all '(html [:div "Hello"]))
   (html [:br])
-  (xml [:br])
-  )
+  (xml [:br]))

test/borkdude/html_test.cljc

@@ -94,6 +94,19 @@
     "<a class=\"bar baz quux\" id=\"foo\"></a>"
     (html [:a#foo.bar.baz {:class "quux"}])
 
+    "<div id=\"a\" class=\"card\"></div>"
+    (html [:div.card {:id "a"}])
+
+    "<div class=\"card\"></div>"
+    (html [:div.card {}])
+
+    "<div class=\"card big\"></div>"
+    (let [x "big"]
+      (html [:div.card {:class x}]))
+
+    "<div class=\"card big\"></div>"
+    (html [:div.card {:class (str "bi" "g")}])
+
     "<div style=\"color: blue;\"></div>"
     (html [:div {:style {:color :blue}}])