resolves #4368 redo loop rather than using recursion to locate next line to process (PR #4372)

3 files changed, 55 insertions, 10 deletions

diff --git a/CHANGELOG.adoc b/CHANGELOG.adoc
index 3f0d6ede..dc57c5a9 100644
--- a/CHANGELOG.adoc
+++ b/CHANGELOG.adoc
@@ -57,6 +57,10 @@ Improvements::
   * Set linenums option on source block when line numbering is enabled (#3313)
   * Warn if include target is remote and `allow-uri-read` attribute is not set (#2284)
 
+Bug Fixes::
+
+  * Redo loop rather than using recursion to locate next line to process; prevents stack limit error (#4368)
+
 == 2.0.18 (2022-10-15) - @mojavelinux
 
 Improvements::
diff --git a/lib/asciidoctor/reader.rb b/lib/asciidoctor/reader.rb
index d74fbd23..c101fd9d 100644
--- a/lib/asciidoctor/reader.rb
+++ b/lib/asciidoctor/reader.rb
@@ -129,16 +129,20 @@ class Reader
   # Returns the next line of the source data as a String if there are lines remaining.
   # Returns nothing if there is no more data.
   def peek_line direct = false
-    if direct || @look_ahead > 0
-      @unescape_next_line ? ((line = @lines[-1]).slice 1, line.length) : @lines[-1]
-    elsif @lines.empty?
-      @look_ahead = 0
-      nil
-    else
-      # FIXME the problem with this approach is that we aren't
-      # retaining the modified line (hence the @unescape_next_line tweak)
-      # perhaps we need a stack of proxied lines
-      (process_line @lines[-1]) || peek_line
+    while true
+      next_line = @lines[-1]
+      return @unescape_next_line ? (next_line.slice 1, next_line.length) : next_line if direct || @look_ahead > 0
+      if next_line
+        # FIXME the problem with this approach is that we aren't
+        # retaining the modified line (hence the @unescape_next_line tweak)
+        # perhaps we need a stack of proxied lines
+        if (line = process_line next_line)
+          return line
+        end
+      else
+        @look_ahead = 0
+        return
+      end
     end
   end
 
diff --git a/test/reader_test.rb b/test/reader_test.rb
index 9014fa1f..21cd8bd9 100644
--- a/test/reader_test.rb
+++ b/test/reader_test.rb
@@ -146,6 +146,10 @@ class ReaderTest < Minitest::Test
         assert reader.next_line_empty?
       end
 
+      test 'peek_line should return nil if next entry is nil' do
+        assert_nil (Asciidoctor::Reader.new [nil]).peek_line
+      end
+
       test 'peek_line should return next line if there are lines remaining' do
         reader = Asciidoctor::Reader.new SAMPLE_DATA
         assert_equal SAMPLE_DATA.first, reader.peek_line
@@ -2819,6 +2823,39 @@ class ReaderTest < Minitest::Test
           assert_empty logger
         end
       end
+
+      test 'should not fail to process preprocessor directive that evaluates to false and has a large number of lines' do
+        lines = (%w(data) * 5000) * ?\n
+        input = <<~EOS
+        before
+
+        ifdef::attribute-not-set[]
+        #{lines}
+        endif::attribute-not-set[]
+
+        after
+        EOS
+
+        doc = Asciidoctor.load input
+        assert_equal 2, doc.blocks.size
+        assert_equal 'before', doc.blocks[0].source
+        assert_equal 'after', doc.blocks[1].source
+      end
+
+      test 'should not fail to process lines if reader contains a nil entry' do
+        input = ['before', '', '', '', 'after']
+        doc = Asciidoctor.load input, extensions: proc {
+          preprocessor do
+            process do |_, reader|
+              reader.source_lines[2] = nil
+              nil
+            end
+          end
+        }
+        assert_equal 2, doc.blocks.size
+        assert_equal 'before', doc.blocks[0].source
+        assert_equal 'after', doc.blocks[1].source
+      end
     end
   end
 end