resolves asciidoctor#4024 suppress missing attribute warning when sub…

…stituting value for doctitle attribute

suppress missing attribute warning when applying substitutions to implicit document title to assign to doctitle attribute

CHANGELOG.adoc

@@ -18,6 +18,7 @@ For a detailed view of what has changed, refer to the {uri-repo}/commits/master[
 Bug Fixes::
 
   * Ensure mtime of input file honors TZ environment variable on JRuby for Windows (affects value of docdatetime attribute) (#3550)
+  * Suppress missing attribute warning when applying substitutions to implicit document title to assign to doctitle attribute (#4024)
 
 Improvements::
 

lib/asciidoctor/parser.rb

@@ -144,7 +144,9 @@ def self.parse_document_header(reader, document)
         l0_section_title = nil
       else
         document.title = l0_section_title
-        doc_attrs['doctitle'] = doctitle_attr_val = document.apply_header_subs l0_section_title
+        if (doc_attrs['doctitle'] = doctitle_attr_val = document.sub_specialchars l0_section_title).include? ATTR_REF_HEAD
+          doc_attrs['doctitle'] = doctitle_attr_val = document.sub_attributes doctitle_attr_val, attribute_missing: 'skip'
+        end
       end
       document.header.source_location = source_location if source_location
       # default to compat-mode if document has setext doctitle

test/document_test.rb

@@ -691,16 +691,48 @@
       assert_xpath '//*[@id="preamble"]//p[text()="Override"]', doc.convert, 1
     end
 
-    test 'header substitutions should be applied to the value of the doctitle attribute' do
+    test 'should apply header substitutions to value of the doctitle attribute assigned from implicit doctitle' do
       input = <<~'EOS'
-      = <Foo> & <Bar>
+      = <Foo> {plus} <Bar>
 
       The name of the game is {doctitle}.
       EOS
 
       doc = document_from_string input
-      assert_equal '&lt;Foo&gt; &amp; &lt;Bar&gt;', (doc.attr 'doctitle')
-      assert_includes doc.blocks[0].content, '&lt;Foo&gt; &amp; &lt;Bar&gt;'
+      assert_equal '&lt;Foo&gt; &#43; &lt;Bar&gt;', (doc.attr 'doctitle')
+      assert_includes doc.blocks[0].content, '&lt;Foo&gt; &#43; &lt;Bar&gt;'
+    end
+
+    test 'should substitute attribute reference in implicit document title for attribute defined earlier in header' do
+      using_memory_logger do |logger|
+        input = <<~'EOS'
+        :project-name: ACME
+        = {project-name} Docs
+
+        {doctitle}
+        EOS
+        doc = document_from_string input, attributes: { 'attribute-missing' => 'warn' }
+        assert_empty logger
+        assert_equal 'ACME Docs', (doc.attr 'doctitle')
+        assert_equal 'ACME Docs', doc.doctitle
+        assert_xpath '//p[text()="ACME Docs"]', doc.convert, 1
+      end
+    end
+
+    test 'should not warn if implicit document title contains attribute reference for attribute defined later in header' do
+      using_memory_logger do |logger|
+        input = <<~'EOS'
+        = {project-name} Docs
+        :project-name: ACME
+
+        {doctitle}
+        EOS
+        doc = document_from_string input, attributes: { 'attribute-missing' => 'warn' }
+        assert_empty logger
+        assert_equal '{project-name} Docs', (doc.attr 'doctitle')
+        assert_equal 'ACME Docs', doc.doctitle
+        assert_xpath '//p[text()="{project-name} Docs"]', doc.convert, 1
+      end
     end
 
     test 'should recognize document title when preceded by blank lines' do