fix(objectionary#76): add exception for void attribute with base

src/main/resources/org/eolang/lints/errors/unknown-name.xsl

@@ -26,7 +26,7 @@ SOFTWARE.
   <xsl:output encoding="UTF-8" method="xml"/>
   <xsl:template match="/">
     <defects>
-      <xsl:for-each select="//o[@base and @base!='@' and @base!='&amp;' and @base!='Q' and @base!='^' and @base!='$' and @base!='&lt;' and not(@ref) and not(contains(@base, '.')) and not(@base = //meta[head='alias']/part[1])]">
+      <xsl:for-each select="//o[@base and @base!='∅' and @base!='@' and @base!='&amp;' and @base!='Q' and @base!='^' and @base!='$' and @base!='&lt;' and not(@ref) and not(contains(@base, '.')) and not(@base = //meta[head='alias']/part[1])]">
         <xsl:element name="defect">
           <xsl:attribute name="line">
             <xsl:value-of select="if (@line) then @line else '0'"/>

src/test/resources/org/eolang/lints/xmir-packs/unknown-name/void-attr-with-base.yaml

@@ -0,0 +1,34 @@
+# The MIT License (MIT)
+#
+# Copyright (c) 2016-2024 Objectionary.com
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included
+# in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+---
+xsls:
+  - /org/eolang/lints/errors/unknown-name.xsl
+tests:
+  - /defects[count(defect[@severity='error'])=0]
+xmir: |
+  <program>
+    <objects>
+      <o name="main">
+        <o base="∅" name="foo"/>
+      </o>
+    </objects>
+  </program>