Render one arrow at between modules if compound=1

lib/diver_down/web/definition_to_dot.rb

@@ -88,6 +88,7 @@ def initialize(definition, compound: false, concentrate: false)
         @io = DiverDown::IndentedStringIo.new
         @indent = 0
         @compound = compound
+        @compound_map = Hash.new { |h, k| h[k] = Set.new } # { ltail => Set<lhead> }
         @concentrate = concentrate
       end
 
@@ -122,14 +123,25 @@ def insert_source(source)
 
         source.dependencies.each do
           attributes = {}
-
-          if @compound
-            ltail = module_label(*source.modules)
-            lhead = module_label(*definition.source(_1.source_name).modules)
-
-            attributes.merge!(ltail:, lhead:)
+          ltail = module_label(*source.modules)
+          lhead = module_label(*definition.source(_1.source_name).modules)
+          skip_rendering = false
+
+          if @compound && (ltail || lhead)
+            # Rendering of dependencies between modules is done only once
+            between_modules = ltail != lhead
+            skip_rendering ||= @compound_map[ltail].include?(lhead) if between_modules
+            @compound_map[ltail].add(lhead)
+
+            attributes.merge!(
+              ltail:,
+              lhead:,
+              minlen: (between_modules ? 3 : nil) # Between modules is prominently distanced
+            )
           end
 
+          next if skip_rendering
+
           io.write(%("#{source.source_name}" -> "#{_1.source_name}"))
           io.write(%( #{build_attributes(**attributes)}), indent: false) unless attributes.empty?
           io.write("\n")
@@ -176,10 +188,10 @@ def insert_modules(source)
       # rubocop:disable Lint/UnderscorePrefixedVariableName
       # attrsの参考 https://qiita.com/rubytomato@github/items/51779135bc4b77c8c20d
       def build_attributes(_wrap: '[]', **attrs)
-        attrs_str = attrs.filter_map { %(#{_1}="#{_2}") if _2 }.join(ATTRIBUTE_DELIMITER)
-        attrs.merge!(label: 'a-b', headlabel: 'head', taillabel: 'tail')
+        attrs = attrs.reject { _2.nil? || _2 == '' }
+        return if attrs.empty?
 
-        return if attrs_str.empty?
+        attrs_str = attrs.map { %(#{_1}="#{_2}") }.join(ATTRIBUTE_DELIMITER)
 
         if _wrap
           "#{_wrap[0]}#{attrs_str}#{_wrap[1]}"

spec/diver_down/web/definition_to_dot_spec.rb

@@ -54,13 +54,17 @@ def build_definition(title: 'title', sources: [])
                   },
                 ],
               },
+              {
+                source_name: 'b.rb',
+              }
             ]
           )
 
           expect(described_class.new(definition).to_s).to eq(<<~DOT)
             strict digraph "title" {
               "a.rb" [label="a.rb"]
               "a.rb" -> "b.rb"
+              "b.rb" [label="b.rb"]
             }
           DOT
         end
@@ -79,7 +83,7 @@ def build_definition(title: 'title', sources: [])
                     module_name: 'B',
                   },
                 ],
-              },
+              }
             ]
           )
 
@@ -137,8 +141,7 @@ def build_definition(title: 'title', sources: [])
               subgraph "cluster_A" {
                 label="A" "a.rb" [label="a.rb"]
               }
-              "a.rb" -> "b.rb" [ltail="cluster_A" lhead="cluster_B"]
-              "a.rb" -> "c.rb" [ltail="cluster_A" lhead="cluster_B"]
+              "a.rb" -> "b.rb" [ltail="cluster_A" lhead="cluster_B" minlen="3"]
               subgraph "cluster_B" {
                 label="B" "b.rb" [label="b.rb"]
               }