Add Performance/ExcessiveAllocations rule

spec/ameba/rule/performance/excessive_allocations_spec.cr

@@ -0,0 +1,57 @@
+require "../../../spec_helper"
+
+module Ameba::Rule::Performance
+  subject = ExcessiveAllocations.new
+
+  describe ExcessiveAllocations do
+    it "passes if there is no potential performance improvements" do
+      expect_no_issues subject, <<-CRYSTAL
+        "Alice".chars.each(arg) { |c| puts c }
+        "Alice".chars(arg).each { |c| puts c }
+        "Alice\nBob".lines.each(arg) { |l| puts l }
+        "Alice\nBob".lines(arg).each { |l| puts l }
+        CRYSTAL
+    end
+
+    it "reports if there is a collection method followed by each" do
+      source = expect_issue subject, <<-CRYSTAL
+        "Alice".chars.each { |c| puts c }
+              # ^^^^^^^^^^ error: Use `each_char {...}` instead of `chars.each {...}` to avoid excessive allocation
+        "Alice\nBob".lines.each { |l| puts l }
+           # ^^^^^^^^^^ error: Use `each_line {...}` instead of `lines.each {...}` to avoid excessive allocation
+        CRYSTAL
+
+      expect_correction source, <<-CRYSTAL
+        "Alice".each_char { |c| puts c }
+        "Alice\nBob".each_line { |l| puts l }
+        CRYSTAL
+    end
+
+    it "does not report if source is a spec" do
+      expect_no_issues subject, <<-CRYSTAL, "source_spec.cr"
+        "Alice".chars.each { |c| puts c }
+        CRYSTAL
+    end
+
+    context "properties" do
+      it "#call_names" do
+        rule = ExcessiveAllocations.new
+        rule.call_names = {
+          "children" => "each_child",
+        }
+
+        expect_no_issues rule, <<-CRYSTAL
+          "Alice".chars.each { |c| puts c }
+          CRYSTAL
+      end
+    end
+
+    context "macro" do
+      it "doesn't report in macro scope" do
+        expect_no_issues subject, <<-CRYSTAL
+          {{ "Alice".chars.each { |c| puts c } }}
+          CRYSTAL
+      end
+    end
+  end
+end