Create :pre snapshot if none already exist

lib/nanoc/rule_dsl/rule_memory_calculator.rb

@@ -84,6 +84,9 @@ def new_rule_memory_for_rep(rep)
       unless rule_memory.snapshot_actions.any? { |sa| sa.snapshot_name == :last }
         executor.snapshot(:last)
       end
+      unless rule_memory.snapshot_actions.any? { |sa| sa.snapshot_name == :pre }
+        executor.snapshot(:pre)
+      end
 
       assign_paths_to_mem(rule_memory, rep: rep)
     end

spec/nanoc/regressions/gh_1064_spec.rb

@@ -0,0 +1,18 @@
+describe 'GH-1064', site: true, stdio: true do
+  before do
+    File.write('content/foo.erb', '*<%= @items["/bar.*"].compiled_content(snapshot: :pre) %>*')
+    File.write('content/bar.erb', 'Bar!')
+
+    File.write('Rules', <<EOS)
+  compile '/*' do
+    filter :erb
+    write item.identifier
+  end
+EOS
+  end
+
+  it 'does not reuse old content' do
+    Nanoc::CLI.run(%w(compile))
+    expect(File.read('output/foo.erb')).to eql('*Bar!*')
+  end
+end

spec/nanoc/rule_dsl/rule_memory_calculator_spec.rb

@@ -96,7 +96,11 @@
           expect(subject[1].snapshot_name).to eql(:last)
           expect(subject[1].path).to be_nil
 
-          expect(subject.size).to eql(2)
+          expect(subject[2]).to be_a(Nanoc::Int::ProcessingActions::Snapshot)
+          expect(subject[2].snapshot_name).to eql(:pre)
+          expect(subject[2].path).to be_nil
+
+          expect(subject.size).to eql(3)
         end
       end
 
@@ -122,7 +126,11 @@
           expect(subject[1].snapshot_name).to eql(:last)
           expect(subject[1].path).to eq('/foo.md')
 
-          expect(subject.size).to eql(2)
+          expect(subject[2]).to be_a(Nanoc::Int::ProcessingActions::Snapshot)
+          expect(subject[2].snapshot_name).to eql(:pre)
+          expect(subject[2].path).to be_nil
+
+          expect(subject.size).to eql(3)
         end
       end
 
@@ -148,7 +156,11 @@
           expect(subject[1].snapshot_name).to eql(:last)
           expect(subject[1].path).to be_nil
 
-          expect(subject.size).to eql(2)
+          expect(subject[2]).to be_a(Nanoc::Int::ProcessingActions::Snapshot)
+          expect(subject[2].snapshot_name).to eql(:pre)
+          expect(subject[2].path).to be_nil
+
+          expect(subject.size).to eql(3)
         end
       end
     end