From dc7a28c201bd1c3aaf672f86fa4e179fea400a57 Mon Sep 17 00:00:00 2001
From: Manjunath <manjunath@clearstack.io>
Date: Fri, 6 Aug 2021 17:40:41 +0530
Subject: [PATCH] Hash#update() vs Hash#[]=

---
 .fasterer.yml                                 |  1 +
 README.md                                     |  1 +
 lib/fasterer/offense.rb                       |  3 +++
 lib/fasterer/scanners/method_call_scanner.rb  | 13 ++++++++++++
 .../17_hash_update_vs_hash_brackets_spec.rb   | 11 ++++++++++
 .../17_hash_update_vs_hash_brackets.rb        | 21 +++++++++++++++++++
 6 files changed, 50 insertions(+)
 create mode 100644 spec/lib/fasterer/analyzer/17_hash_update_vs_hash_brackets_spec.rb
 create mode 100644 spec/support/analyzer/17_hash_update_vs_hash_brackets.rb

diff --git a/.fasterer.yml b/.fasterer.yml
index c125758..08ffd51 100644
--- a/.fasterer.yml
+++ b/.fasterer.yml
@@ -12,6 +12,7 @@ speedups:
   fetch_with_argument_vs_block: true
   keys_each_vs_each_key: true
   hash_merge_bang_vs_hash_brackets: true
+  hash_update_vs_hash_brackets: true
   block_vs_symbol_to_proc: true
   proc_call_vs_yield: true
   gsub_vs_tr: true
diff --git a/README.md b/README.md
index 59c941a..57597da 100644
--- a/README.md
+++ b/README.md
@@ -69,6 +69,7 @@ speedups:
   fetch_with_argument_vs_block: true
   keys_each_vs_each_key: true
   hash_merge_bang_vs_hash_brackets: true
+  hash_update_vs_hash_brackets: true
   block_vs_symbol_to_proc: true
   proc_call_vs_yield: true
   gsub_vs_tr: true
diff --git a/lib/fasterer/offense.rb b/lib/fasterer/offense.rb
index 883b7b1..11001da 100644
--- a/lib/fasterer/offense.rb
+++ b/lib/fasterer/offense.rb
@@ -52,6 +52,9 @@ def explanation
       hash_merge_bang_vs_hash_brackets:
         'Hash#merge! with one argument is slower than Hash#[]',
 
+      hash_update_vs_hash_brackets:
+        'Hash#update with one argument is slower than Hash#[]',
+
       block_vs_symbol_to_proc:
         'Calling argumentless methods within blocks is slower than using symbol to proc',
 
diff --git a/lib/fasterer/scanners/method_call_scanner.rb b/lib/fasterer/scanners/method_call_scanner.rb
index a8f976e..7eb5b90 100644
--- a/lib/fasterer/scanners/method_call_scanner.rb
+++ b/lib/fasterer/scanners/method_call_scanner.rb
@@ -39,6 +39,8 @@ def check_offense
         check_fetch_offense
       when :merge!
         check_merge_bang_offense
+      when :update
+        check_update_offense
       when :last
         check_last_offense
       when :include?
@@ -149,6 +151,17 @@ def check_merge_bang_offense
       end
     end
 
+    def check_update_offense
+      return unless method_call.arguments.count == 1
+
+      first_argument = method_call.arguments.first
+      return unless first_argument.type == :hash
+
+      if first_argument.element.drop(1).count == 2 # each key and value is an item by itself.
+        add_offense(:hash_update_vs_hash_brackets)
+      end
+    end
+
     def check_last_offense
       return method_call unless method_call.receiver.is_a?(MethodCall)
 
diff --git a/spec/lib/fasterer/analyzer/17_hash_update_vs_hash_brackets_spec.rb b/spec/lib/fasterer/analyzer/17_hash_update_vs_hash_brackets_spec.rb
new file mode 100644
index 0000000..6df092a
--- /dev/null
+++ b/spec/lib/fasterer/analyzer/17_hash_update_vs_hash_brackets_spec.rb
@@ -0,0 +1,11 @@
+require 'spec_helper'
+
+describe Fasterer::Analyzer do
+  let(:test_file_path) { RSpec.root.join('support', 'analyzer', '17_hash_update_vs_hash_brackets.rb') }
+
+  it 'should detect keys each 3 times' do
+    analyzer = Fasterer::Analyzer.new(test_file_path)
+    analyzer.scan
+    expect(analyzer.errors[:hash_update_vs_hash_brackets].count).to eq(3)
+  end
+end
diff --git a/spec/support/analyzer/17_hash_update_vs_hash_brackets.rb b/spec/support/analyzer/17_hash_update_vs_hash_brackets.rb
new file mode 100644
index 0000000..252f680
--- /dev/null
+++ b/spec/support/analyzer/17_hash_update_vs_hash_brackets.rb
@@ -0,0 +1,21 @@
+h.update(item: 1, item2: 3)
+
+h.update
+
+h.update(item, item: 1)
+
+h.update(item: 1)
+
+ENUM.each_with_object({}) do |e, h|
+  h.update(e => e)
+end
+
+ENUM.each_with_object({}) do |e, h|
+  h[e] = e
+end
+
+h.update(item: 1)
+
+h.update({item: 1})
+
+h.update({})