Do not report unreachable code after loops

closes #251

spec/ameba/ast/flow_expression_spec.cr

@@ -39,6 +39,22 @@ module Ameba::AST
           flow_expression.unreachable_nodes.should eq nodes.assign_nodes
         end
 
+        it "returns nil if there is no unreachable node after loop" do
+          nodes = as_nodes %(
+            def run
+              idx = items.size - 1
+              while 0 <= idx
+                return
+              end
+
+              puts "foo"
+            end
+          )
+          node = nodes.expressions_nodes.first
+          flow_expression = FlowExpression.new node, false
+          flow_expression.unreachable_nodes.empty?.should eq true
+        end
+
         it "returns nil if there is no unreachable node" do
           nodes = as_nodes %(
             def foobar

spec/ameba/rule/lint/unreachable_code_spec.cr

@@ -420,7 +420,7 @@ module Ameba::Rule::Lint
     end
 
     context "while/until" do
-      it "reports if there is unreachable code after while" do
+      it "does not report if there is no unreachable code after while" do
         s = Source.new %(
           def method
             while something
@@ -434,13 +434,10 @@ module Ameba::Rule::Lint
           end
         )
 
-        subject.catch(s).should_not be_valid
-
-        issue = s.issues.first
-        issue.location.to_s.should eq ":9:3"
+        subject.catch(s).should be_valid
       end
 
-      it "reports if there is unreachable code after until" do
+      it "does not report if there is no unreachable code after until" do
         s = Source.new %(
           def method
             until something
@@ -454,10 +451,7 @@ module Ameba::Rule::Lint
           end
         )
 
-        subject.catch(s).should_not be_valid
-
-        issue = s.issues.first
-        issue.location.to_s.should eq ":9:3"
+        subject.catch(s).should be_valid
       end
 
       it "doesn't report if there is reachable code after while with break" do

src/ameba/ast/flow_expression.cr

@@ -55,7 +55,7 @@ module Ameba::AST
         control_flow_found = false
         current_node.expressions.each do |exp|
           unreachable_nodes << exp if control_flow_found
-          control_flow_found ||= flow_expression?(exp, in_loop?)
+          control_flow_found ||= !loop?(exp) && flow_expression?(exp, in_loop?)
         end
       when Crystal::BinaryOp
         unreachable_nodes << current_node.right if flow_expression?(current_node.left, in_loop?)