Variable scope & useless assignments (#41)

* AST::Visitor -> AST::NodeVisitor

* Scope & ScopeVisitor

* Useless assignment rule

* Instance vars and useless assignments

* Multiple assigns one by one

* Support outer scope

* Variable used in the useless assignment

* Support OpAssign & MultiAssign

* Captured by block

* Variable, Assignment, Reference & Refactoring

* Variable has references, Assignment can be referenced

* Branch entity

* Handle useless assignments in branches

* Handle assignments in a loop

* Handle branch equality

* Handle special var `$?` assignment

* Improve captured by block stuff

* Avoid assignments in property definitions

(UselessAssign rule reports an warning)

* Support MacroIf and MacroFor branches

* Handle assignments with shadowed vars in inner scopes

* Add method arguments as scope variables

* Handle case if branch is blank

* Top level scope

* Handle case when branch is nop?

spec/ameba/ast/visitors/node_visitor_spec.cr

@@ -0,0 +1,18 @@
+require "../../../spec_helper"
+
+module Ameba::AST
+  rule = DummyRule.new
+  source = Source.new ""
+
+  describe NodeVisitor do
+    {% for name in NODES %}
+      describe "{{name}}" do
+        it "allow to visit {{name}} node" do
+          visitor = NodeVisitor.new rule, source
+          nodes = Crystal::Parser.new("").parse
+          nodes.accept visitor
+        end
+      end
+    {% end %}
+  end
+end

spec/ameba/ast/visitors/scope_visitor_spec.cr

@@ -0,0 +1,58 @@
+require "../../../spec_helper"
+
+module Ameba::AST
+  describe ScopeVisitor do
+    it "creates a scope for the def" do
+      rule = ScopeRule.new
+      ScopeVisitor.new rule, Source.new %(
+        def method
+        end
+      )
+      rule.scopes.size.should eq 1
+    end
+
+    it "creates a scope for the proc" do
+      rule = ScopeRule.new
+      ScopeVisitor.new rule, Source.new %(
+        -> {}
+      )
+      rule.scopes.size.should eq 1
+    end
+
+    it "creates a scope for the block" do
+      rule = ScopeRule.new
+      ScopeVisitor.new rule, Source.new %(
+        3.times {}
+      )
+      rule.scopes.size.should eq 2
+    end
+
+    context "inner scopes" do
+      it "creates scope for block inside def" do
+        rule = ScopeRule.new
+        ScopeVisitor.new rule, Source.new %(
+          def method
+            3.times {}
+          end
+        )
+        rule.scopes.size.should eq 2
+        rule.scopes.last.outer_scope.should_not be_nil
+        rule.scopes.first.outer_scope.should eq rule.scopes.last
+      end
+
+      it "creates scope for block inside block" do
+        rule = ScopeRule.new
+        ScopeVisitor.new rule, Source.new %(
+          3.times do
+            2.times {}
+          end
+        )
+        rule.scopes.size.should eq 3
+        inner_block = rule.scopes.first
+        outer_block = rule.scopes.last
+        inner_block.outer_scope.should_not eq outer_block
+        outer_block.outer_scope.should be_nil
+      end
+    end
+  end
+end