Fail lv:param-class-to-yields without relying on propagation

RELEASES.md

@@ -16,6 +16,11 @@ commits that introduce the changes.  To make a new release, run
 
 NEXT
 ====
+Compiler
+--------
+- `lv:param-class-to-yields` will now trigger a failure rather than relying
+  on propagating bad values, which may not result in failure if the symbol
+  is represented by another type (non-class) of object.
 
 Miscellaneous
 -------------

src/current/include/preproc/template.xsl

@@ -1264,16 +1264,11 @@
 
   <choose>
     <when test="not( $yields ) or $yields=''">
-      <message>
+      <preproc:error>
         <text>error: unable to determine @yields for class `</text>
         <value-of select="$as" />
         <text>' (has the class been imported?)</text>
-      </message>
-
-      <!-- just retain the name; it'll be used for an error message,
-           since it won't be foudn -->
-      <!-- TODO: this is dangerous; find a way to propagate the error -->
-      <value-of select="$as" />
+      </preproc:error>
     </when>
 
     <otherwise>