Treat LoadErrors for known gems as trivial

nanoc/lib/nanoc/cli/error_handler.rb

@@ -58,12 +58,16 @@ def handle_while(exit_on_error:)
     rescue Interrupt
       exit(1)
     rescue StandardError, ScriptError => e
-      if trivial?(e)
-        $stderr.puts "Error: #{e.message}"
-        resolution = resolution_for(e)
+      handle_error(e, exit_on_error: exit_on_error)
+    end
+
+    def handle_error(error, exit_on_error:)
+      if trivial?(error)
+        $stderr.puts "Error: #{error.message}"
+        resolution = resolution_for(error)
         $stderr.puts resolution if resolution
       else
-        print_error(e)
+        print_error(error)
       end
       exit(1) if exit_on_error
     end
@@ -148,6 +152,18 @@ def forwards_stack_trace?
       feature_enabled || ruby_2_5_used
     end
 
+    # @api private
+    def trivial?(error)
+      case error
+      when Nanoc::Int::Errors::GenericTrivial, Errno::EADDRINUSE
+        true
+      when LoadError
+        GEM_NAMES.keys.include?(gem_name_from_load_error(error))
+      else
+        false
+      end
+    end
+
     protected
 
     # @return [Hash<String, Array>] A hash containing the gem names as keys and gem versions as value
@@ -196,15 +212,6 @@ def gems_and_versions
       'w3c_validators' => 'w3c_validators',
     }.freeze
 
-    def trivial?(error)
-      case error
-      when Nanoc::Int::Errors::GenericTrivial, Errno::EADDRINUSE
-        true
-      else
-        false
-      end
-    end
-
     # Attempts to find a resolution for the given error, or nil if no
     # resolution can be automatically obtained.
     #
@@ -216,12 +223,8 @@ def resolution_for(error)
 
       case error
       when LoadError
-        # Get gem name
-        matches = error.message.match(/(no such file to load|cannot load such file) -- ([^\s]+)/)
-        return nil if matches.nil?
-        gem_name = GEM_NAMES[matches[2]]
+        gem_name = gem_name_from_load_error(error)
 
-        # Build message
         if gem_name
           if using_bundler?
             'Make sure the gem is added to Gemfile and run `bundle install`.'
@@ -241,6 +244,12 @@ def resolution_for(error)
       end
     end
 
+    def gem_name_from_load_error(error)
+      matches = error.message.match(/(no such file to load|cannot load such file) -- ([^\s]+)/)
+      return nil if matches.nil?
+      GEM_NAMES[matches[2]]
+    end
+
     def using_bundler?
       defined?(Bundler) && Bundler::SharedHelpers.in_bundle?
     end

nanoc/spec/nanoc/cli/error_handler_spec.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-describe Nanoc::CLI::ErrorHandler do
+describe Nanoc::CLI::ErrorHandler, stdio: true do
   subject(:error_handler) { described_class.new }
 
   describe '#forwards_stack_trace?' do
@@ -40,4 +40,138 @@
       end
     end
   end
+
+  describe '#trivial?' do
+    subject { error_handler.trivial?(error) }
+
+    context 'LoadError of known gem' do
+      let(:error) do
+        begin
+          raise LoadError, 'cannot load such file -- nokogiri'
+        rescue LoadError => e
+          return e
+        end
+      end
+
+      it { is_expected.to be(true) }
+    end
+
+    context 'LoadError of unknown gem' do
+      let(:error) do
+        begin
+          raise LoadError, 'cannot load such file -- whatever'
+        rescue LoadError => e
+          return e
+        end
+      end
+
+      it { is_expected.to be(false) }
+    end
+
+    context 'random error' do
+      let(:error) do
+        begin
+          raise 'stuff'
+        rescue => e
+          return e
+        end
+      end
+
+      it { is_expected.to be(false) }
+    end
+
+    context 'Errno::EADDRINUSE' do
+      let(:error) do
+        begin
+          raise Errno::EADDRINUSE
+        rescue => e
+          return e
+        end
+      end
+
+      it { is_expected.to be(true) }
+    end
+
+    context 'GenericTrivial' do
+      let(:error) do
+        begin
+          raise Nanoc::Int::Errors::GenericTrivial, 'oh just a tiny thing'
+        rescue => e
+          return e
+        end
+      end
+
+      it { is_expected.to be(true) }
+    end
+  end
+
+  describe '#handle_error' do
+    subject { error_handler.handle_error(error, exit_on_error: exit_on_error) }
+
+    let(:error) do
+      begin
+        raise 'Bewm'
+      rescue => e
+        return e
+      end
+    end
+
+    let(:exit_on_error) { false }
+
+    describe 'exit behavior' do
+      context 'exit on error' do
+        let(:exit_on_error) { true }
+
+        it 'exits on error' do
+          expect { subject }.to raise_error(SystemExit)
+        end
+      end
+
+      context 'no exit on error' do
+        let(:exit_on_error) { false }
+
+        it 'does not exit on error' do
+          expect { subject }.not_to raise_error
+        end
+      end
+    end
+
+    describe 'printing behavior' do
+      context 'trivial error with no resolution' do
+        let(:error) do
+          begin
+            raise Nanoc::Int::Errors::GenericTrivial, 'asdf'
+          rescue => e
+            return e
+          end
+        end
+
+        it 'prints summary' do
+          expect { subject }.to output("Error: asdf\n").to_stderr
+        end
+      end
+
+      context 'trivial error with resolution' do
+        let(:error) do
+          begin
+            raise LoadError, 'cannot load such file -- nokogiri'
+          rescue LoadError => e
+            return e
+          end
+        end
+
+        it 'prints summary' do
+          expected_output = <<~OUT
+            Error: cannot load such file -- nokogiri
+            Make sure the gem is added to Gemfile and run `bundle install`.
+          OUT
+          expect { subject }.to output(expected_output).to_stderr
+        end
+      end
+
+      context 'non-trivial error' do
+        # …
+      end
+    end
+  end
 end