Detect shadowing outer local vars

spec/ameba/rule/shadowing_local_outer_var_spec.cr

@@ -0,0 +1,140 @@
+require "../../spec_helper"
+
+module Ameba::Rule
+  describe ShadowingOuterLocalVar do
+    subject = ShadowingOuterLocalVar.new
+
+    it "doesn't report if there is no shadowing" do
+      source = Source.new %(
+        def some_method
+          foo = 1
+
+          3.times do |bar|
+            bar
+          end
+
+          -> (baz : Int32) {}
+
+          -> (bar : String) {}
+        end
+      )
+
+      subject.catch(source).should be_valid
+    end
+
+    it "reports if there is a shadowing in a block" do
+      source = Source.new %(
+        def some_method
+          foo = 1
+
+          3.times do |foo|
+          end
+        end
+      )
+      subject.catch(source).should_not be_valid
+    end
+
+    it "reports if there is a shadowing in a proc" do
+      source = Source.new %(
+        def some_method
+          foo = 1
+
+          -> (foo : Int32) {}
+        end
+      )
+      subject.catch(source).should_not be_valid
+    end
+
+    it "reports if there is a shadowing in an inner scope" do
+      source = Source.new %(
+        def foo
+          foo = 1
+
+          3.times do |i|
+            3.times { |foo| foo }
+          end
+        end
+      )
+      subject.catch(source).should_not be_valid
+    end
+
+    it "reports if variable is shadowed twice" do
+      source = Source.new %(
+        foo = 1
+
+        3.times do |foo|
+          -> (foo : Int32) { foo + 1 }
+        end
+      )
+      subject.catch(source).should_not be_valid
+
+      source.errors.size.should eq 2
+    end
+
+    it "reports if a splat block argument shadows local var" do
+      source = Source.new %(
+        foo = 1
+
+        3.times do |*foo|
+        end
+      )
+      subject.catch(source).should_not be_valid
+    end
+
+    it "reports if a &block argument is shadowed" do
+      source = Source.new %(
+        def method_with_block(a, &block)
+          3.times do |block|
+          end
+        end
+      )
+      subject.catch(source).should_not be_valid
+      source.errors.first.message.should eq "Shadowing outer local variable `block`"
+    end
+
+    it "reports if there are multiple args and one shadows local var" do
+      source = Source.new %(
+        foo = 1
+        [1, 2, 3].each_with_index do |i, foo|
+          i + foo
+        end
+      )
+      subject.catch(source).should_not be_valid
+      source.errors.first.message.should eq "Shadowing outer local variable `foo`"
+    end
+
+    it "doesn't report if an outer var is reassigned in a block" do
+      source = Source.new %(
+        def foo
+          foo = 1
+          3.times do |i|
+            foo = 2
+          end
+        end
+      )
+      subject.catch(source).should be_valid
+    end
+
+    it "doesn't report if an argument is a black hole '_'" do
+      source = Source.new %(
+        _ = 1
+        3.times do |_|
+        end
+      )
+      subject.catch(source).should be_valid
+    end
+
+    it "reports rule, location and message" do
+      source = Source.new %(
+        foo = 1
+        3.times { |foo| foo + 1 }
+      ), "source.cr"
+      subject.catch(source).should_not be_valid
+
+      error = source.errors.first
+      error.rule.should_not be_nil
+      error.location.to_s.should eq "source.cr:3:20"
+      error.message.should eq "Shadowing outer local variable `foo`"
+    end
+  end
+end