From c7ab26a2092dfb1cafc9b80ec42fce3833e84c48 Mon Sep 17 00:00:00 2001
From: Jake Zerrer <him@jakezerrer.com>
Date: Mon, 14 Sep 2026 11:44:12 -0400
Subject: [PATCH] Merge shorthand classes when the attribute map has no :class
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`merge-attrs` only merged the shorthand classes from a tag like
`:div.card` when the attribute map ALSO carried a `:class` key — the
outer `if-let` tested the map's class, not the shorthand's. So

    [:div.card {:id "a"}]   =>  <div id="a"></div>

silently lost the class, while

    [:div.card {:class "big"}]  =>  <div class="card big"></div>

worked.

The same expression also interpolated at macroexpansion time, so a
`:class` bound to anything non-constant rendered the symbol's NAME:

    (let [x "big"] [:div.card {:class x}])  =>  class="card x"
---
 CHANGELOG.md                 |  4 ++++
 src/borkdude/html.cljc       | 21 +++++++++++----------
 test/borkdude/html_test.cljc | 13 +++++++++++++
 3 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 803b8d2..e97b8ee 100644
--- a/CHANGELOG.md
+++ b/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))
diff --git a/src/borkdude/html.cljc b/src/borkdude/html.cljc
index b0652ef..ae41c26 100644
--- a/src/borkdude/html.cljc
+++ b/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]))
diff --git a/test/borkdude/html_test.cljc b/test/borkdude/html_test.cljc
index 9db71d4..b93bdca 100644
--- a/test/borkdude/html_test.cljc
+++ b/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}}])