Add the asApiLink function to verify if the API link is valid and if we trigger or not the warning

Author: Dedelweiss

scaladoc/src/dotty/tools/scaladoc/renderers/SiteRenderer.scala

@@ -46,16 +46,26 @@ trait SiteRenderer(using DocContext) extends Locations:
         resolveLink(pageDri, str.stripPrefix("/"))
       )
       def asStaticSite: Option[String] = tryAsDri(str)
+      def asApiLink: Option[String] =
+        {
+        val strWithoutHtml = str.stripSuffix(".html").stripPrefix("/")
+        val sourceDir = Paths.get("src", "main", "scala")
+        val scalaPath = sourceDir.resolve(s"$strWithoutHtml.scala")
+        val scalaDirPath = sourceDir.resolve(strWithoutHtml)
+        Option.when(Files.exists(scalaPath)|| Files.exists(scalaDirPath))(resolveLink(pageDri, str))
+      }
 
       /* Link resolving checks performs multiple strategies with following priority:
         1. We check if the link is a valid URL e.g. http://dotty.epfl.ch
         2. We check if the link leads to other static site
         3. We check if the link leads to existing asset e.g. images/logo.svg -> <static-site-root>/_assets/images/logo.svg
+        4. We check if the link leads to existing API page
       */
 
       asValidURL
         .orElse(asStaticSite)
         .orElse(asAsset)
+        .orElse(asApiLink)
         .getOrElse {
           report.warn(s"Unable to resolve link '$str'", content.template.templateFile.file)
           str