Fix couple of edge-cases in VerboseBlock rule

spec/ameba/rule/style/verbose_block_spec.cr

@@ -14,6 +14,18 @@ module Ameba::Rule::Style
       subject.catch(source).should be_valid
     end
 
+    it "passes if the block argument is used within the body" do
+      source = Source.new %(
+        (1..3).map { |i| i * i }
+        (1..3).map { |j| j * j.to_i64 }
+        (1..3).map { |k| k.to_i64 * k }
+        (1..3).map { |l| l.to_i64 * l.to_i64 }
+        (1..3).map { |m| m.to_s[start: m.to_i64, count: 3]? }
+        (1..3).map { |n| n.to_s.split.map { |z| n.to_i * z.to_i }.join }
+      )
+      subject.catch(source).should be_valid
+    end
+
     it "reports if there is a call with a collapsible block" do
       source = Source.new %(
         (1..3).any? { |i| i.odd? }

src/ameba/rule/style/verbose_block.cr

@@ -80,6 +80,27 @@ module Ameba::Rule::Style
       true
     end
 
+    protected def reference_count(node, obj : Crystal::Var)
+      i = 0
+      case node
+      when Crystal::Call
+        i += reference_count(node.obj, obj)
+        i += reference_count(node.block, obj)
+
+        node.args.each do |arg|
+          i += reference_count(arg, obj)
+        end
+        node.named_args.try &.each do |arg|
+          i += reference_count(arg.value, obj)
+        end
+      when Crystal::Block
+        i += reference_count(node.body, obj)
+      when Crystal::Var
+        i += 1 if node == obj
+      end
+      i
+    end
+
     protected def node_to_s(node : Crystal::Call)
       case name = node.name
       when "[]"
@@ -143,6 +164,11 @@ module Ameba::Rule::Style
       # ```
       return unless (block = node.block) && block.args.size == 1
 
+      arg = block.args.first
+
+      # we skip auto-generated blocks - `(1..3).any?(&.odd?)`
+      return if arg.name.starts_with?("__arg")
+
       # we filter out the blocks that are of call type - `i.to_i64.odd?`
       return unless (body = block.body).is_a?(Crystal::Call)
 
@@ -155,10 +181,10 @@ module Ameba::Rule::Style
       return unless obj.is_a?(Crystal::Var)
 
       # only calls with a first argument used as a receiver are the valid game
-      return unless (arg = block.args.first) == obj
+      return unless obj == arg
 
-      # we skip auto-generated blocks - `(1..3).any?(&.odd?)`
+      # we bail out if the block node include the block argument
-      return if arg.name.starts_with?("__arg")
+      return if reference_count(body, arg) > 1
 
       # add issue if the given nodes pass all of the checks
       issue_for_valid source, node, body