Add `first` filter for to allow for first in both array and string

2 files changed, 17 insertions, 0 deletions

diff --git a/doc-tool/src/dotty/tools/dottydoc/staticsite/LiquidTemplate.scala b/doc-tool/src/dotty/tools/dottydoc/staticsite/LiquidTemplate.scala
index a86a5bb54..87209b47a 100644
--- a/doc-tool/src/dotty/tools/dottydoc/staticsite/LiquidTemplate.scala
+++ b/doc-tool/src/dotty/tools/dottydoc/staticsite/LiquidTemplate.scala
@@ -15,6 +15,7 @@ case class LiquidTemplate(contents: String) extends ResourceFinder {
 
   /** Register filters to static container */
   Filter.registerFilter(new Reverse)
+  Filter.registerFilter(new First)
 
   // For some reason, liqp rejects a straight conversion using `.asJava`
   private def toJavaMap(map: Map[String, AnyRef]): HashMap[String, Object] =
diff --git a/doc-tool/src/dotty/tools/dottydoc/staticsite/filters.scala b/doc-tool/src/dotty/tools/dottydoc/staticsite/filters.scala
index 2239f5a50..1569d3873 100644
--- a/doc-tool/src/dotty/tools/dottydoc/staticsite/filters.scala
+++ b/doc-tool/src/dotty/tools/dottydoc/staticsite/filters.scala
@@ -23,4 +23,20 @@ object filters {
       else array.reverse
     }
   }
+
+  /** Used to get the first element of arrays and strings:
+    *
+    * ```html
+    * {% assign array = "1,2,3,4,5" | split: "," %}
+    * {{ array | first }}
+    * ```
+    * The above snippet will render "1"
+    */
+  final class First extends Filter("first") {
+    override def apply(value: Any, params: AnyRef*): AnyRef = value match {
+      case str: String if str.nonEmpty => str.charAt(0).toString
+      case xs: Array[String] if xs.nonEmpty => xs.head
+      case _ => null
+    }
+  }
 }