Add Lint/StaticComparison rule

spec/ameba/rule/lint/static_comparison_spec.cr

@@ -0,0 +1,51 @@
+require "../../../spec_helper"
+
+module Ameba::Rule::Lint
+  subject = StaticComparison.new
+
+  describe StaticComparison do
+    it "passes for valid cases" do
+      expect_no_issues subject, <<-CRYSTAL
+        /foo/ === "foo"
+        "foo" == foo
+        foo == "foo"
+        CRYSTAL
+    end
+
+    it "reports if there is a static comparison evaluating to true" do
+      expect_issue subject, <<-CRYSTAL
+        "foo" == "foo"
+        # ^^^^^^^^^^^^ error: Comparison always evaluates to true
+        CRYSTAL
+    end
+
+    it "reports if there is a static comparison evaluating to false" do
+      expect_issue subject, <<-CRYSTAL
+        "foo" != "foo"
+        # ^^^^^^^^^^^^ error: Comparison always evaluates to false
+        CRYSTAL
+    end
+
+    context "macro" do
+      it "reports in macro scope" do
+        expect_issue subject, <<-CRYSTAL
+          {{ "foo" == "foo" }}
+           # ^^^^^^^^^^^^^^ error: Comparison always evaluates to true
+          CRYSTAL
+      end
+    end
+
+    it "reports rule, pos and message" do
+      s = Source.new %(
+        "foo" == "foo"
+      ), "source.cr"
+      subject.catch(s).should_not be_valid
+      issue = s.issues.first
+
+      issue.rule.should_not be_nil
+      issue.location.to_s.should eq "source.cr:1:1"
+      issue.end_location.to_s.should eq "source.cr:1:14"
+      issue.message.should eq "Comparison always evaluates to true"
+    end
+  end
+end