Handle gems installed with --user-install (#27)

When you install gems with `--user-install`, they will go in `~/.gem`
instead of in, e.g. `~/.rbenv` (or wherever your default GEM_PATH is).

This is a relatively uncommon way for gems to be installed, but it's
technically supported by bundler & rubygems, and it causes issues with
`uncruft`'s ability to resolve `$GEM_HOME` in ignorefile entries. This
PR adds an additional check against `Gem.user_dir` and treats it as
equivalent to `$GEM_HOME` (since the ignorefile is designed to work
across multiple systems, and should not care where the gems are
installed).

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    uncruft (0.4.0)
+    uncruft (0.5.0)
       railties (>= 6.1.0)
 
 GEM

gemfiles/rails_6_1.gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: ..
   specs:
-    uncruft (0.4.0)
+    uncruft (0.5.0)
       railties (>= 6.1.0)
 
 GEM

gemfiles/rails_7_0.gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: ..
   specs:
-    uncruft (0.4.0)
+    uncruft (0.5.0)
       railties (>= 6.1.0)
 
 GEM

gemfiles/rails_7_1.gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: ..
   specs:
-    uncruft (0.4.0)
+    uncruft (0.5.0)
       railties (>= 6.1.0)
 
 GEM

lib/uncruft/deprecation_handler.rb

@@ -44,6 +44,10 @@ def normalize_callstack_path(message)
         message.gsub!(gem_home, '$GEM_PATH')
       end
 
+      if (user_install = user_install(message)).present?
+        message.gsub!(user_install, '$GEM_PATH')
+      end
+
       if message.include?(bin_dir)
         message.gsub!(bin_dir, '$BIN_PATH')
       end
@@ -70,7 +74,11 @@ def remove_line_number(message)
     end
 
     def gem_home(message)
-      message.match(%r{(?i:c)alled from( .+ at)? (#{ENV['GEM_HOME']}/(.+/)*gems)})&.[](2) # rubocop:disable Style/FetchEnvVar
+      message.match(%r{(?i:c)alled from( .+ at)? (#{ENV.fetch('GEM_HOME', nil)}/(.+/)*gems)})&.[](2).presence
+    end
+
+    def user_install(message)
+      message.match(%r{(?i:c)alled from( .+ at)? (#{Gem.user_dir}/(.+/)*gems)})&.[](2).presence
     end
 
     def absolute_path(message)

lib/uncruft/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Uncruft
-  VERSION = '0.4.0'
+  VERSION = '0.5.0'
 end

spec/uncruft/deprecation_handler_spec.rb

@@ -91,6 +91,7 @@
       let(:expected_ignorefile_entry) { 'Warning: BAD called from <global scope> at $BIN_PATH/rake' }
 
       before do
+        allow(RbConfig::CONFIG).to receive(:[]).and_call_original
         allow(RbConfig::CONFIG).to receive(:[]).with('bindir').and_return bin_dir
       end
 
@@ -114,8 +115,9 @@
       let(:expected_ignorefile_entry) { "Warning: BAD called from <something> at $GEM_PATH/chicken/nuggets.rb" }
 
       before do
-        allow(ENV).to receive(:[]).and_call_original
-        allow(ENV).to receive(:[]).with('GEM_HOME').and_return('/banana/banana/banana')
+        allow(ENV).to receive(:fetch).and_call_original
+        allow(ENV).to receive(:fetch).with('GEM_HOME', nil).and_return('/banana/banana/banana')
+        allow(Gem).to receive(:user_dir).and_return('/apple/apple/apple')
       end
 
       it 'sanitizes the message and raises an error' do
@@ -130,6 +132,14 @@
         end
       end
 
+      context 'when gem is installed in the --user-install path' do
+        let(:absolute_path) { Pathname.new('/apple/apple/apple/ohno/gems/chicken/nuggets.rb') }
+
+        it 'sanitizes the message and raises an error' do
+          expect { subject.call(message, '') }.to raise_error(RuntimeError, expected_error_message)
+        end
+      end
+
       context 'when gem is vendored' do
         let(:absolute_path) { Rails.root.join('vendor/cache/chicken/nuggets.rb') }