Allow limiting count of displayed failed lines

Author: yujinakayama

lib/rspec/core/configuration.rb

@@ -332,6 +332,11 @@ def treat_symbols_as_metadata_keys_with_true_values=(_value)
       # Currently this will place a mutex around memoized values such as let blocks.
       add_setting :threadsafe
 
+      # @macro add_setting
+      # Maximum count of failed source lines to display in the failure reports.
+      # (default `10`).
+      add_setting :max_displayed_failure_line_count
+
       # @private
       add_setting :tty
       # @private
@@ -387,6 +392,7 @@ def initialize
         @libs = []
         @derived_metadata_blocks = FilterableItemRepository::QueryOptimized.new(:any?)
         @threadsafe = true
+        @max_displayed_failure_line_count = 10
 
         define_built_in_hooks
       end

lib/rspec/core/formatters/exception_presenter.rb

@@ -192,8 +192,9 @@ def read_failed_lines
           end
 
           file_path, line_number = matching_line.match(/(.+?):(\d+)(|:\d+)/)[1..2]
+          max_line_count = RSpec.configuration.max_displayed_failure_line_count
           RSpec::Support.require_rspec_core "formatters/snippet_extractor"
-          SnippetExtractor.extract_expression_lines_at(file_path, line_number.to_i)
+          SnippetExtractor.extract_expression_lines_at(file_path, line_number.to_i, max_line_count)
         rescue SnippetExtractor::NoSuchFileError
           ["Unable to find #{file_path} to read failed line"]
         rescue SnippetExtractor::NoSuchLineError

lib/rspec/core/formatters/snippet_extractor.rb

@@ -30,20 +30,30 @@ def self.source_from_file(path)
             :on_heredoc_beg => :on_heredoc_end
           }
 
-          attr_reader :source, :beginning_line_number
-
-          def self.extract_expression_lines_at(file_path, beginning_line_number)
-            source = source_from_file(file_path)
-            new(source, beginning_line_number).expression_lines
+          attr_reader :source, :beginning_line_number, :max_line_count
+
+          def self.extract_expression_lines_at(file_path, beginning_line_number, max_line_count=nil)
+            if max_line_count == 1
+              [extract_line_at(file_path, beginning_line_number)]
+            else
+              source = source_from_file(file_path)
+              new(source, beginning_line_number, max_line_count).expression_lines
+            end
           end
 
-          def initialize(source, beginning_line_number)
+          def initialize(source, beginning_line_number, max_line_count=nil)
             @source = source
             @beginning_line_number = beginning_line_number
+            @max_line_count = max_line_count
           end
 
           def expression_lines
             line_range = line_range_of_expression
+
+            if max_line_count && line_range.count > max_line_count
+              line_range = (line_range.begin)..(line_range.begin + max_line_count - 1)
+            end
+
             source.lines[(line_range.begin - 1)..(line_range.end - 1)]
           rescue NoExpressionAtLineError
             [self.class.extract_line_at(source.path, beginning_line_number)]
@@ -118,7 +128,7 @@ def location_nodes_at_beginning_line
           end
         else
           # :nocov:
-          def self.extract_expression_lines_at(file_path, beginning_line_number)
+          def self.extract_expression_lines_at(file_path, beginning_line_number, *)
             [extract_line_at(file_path, beginning_line_number)]
           end
           # :nocov:

spec/rspec/core/configuration_spec.rb

@@ -2172,6 +2172,17 @@ def emulate_not_configured_expectation_framework
       end
     end
 
+    describe '#max_displayed_failure_line_count' do
+      it 'defaults to 10' do
+        expect(config.max_displayed_failure_line_count).to eq 10
+      end
+
+      it 'is configurable' do
+        config.max_displayed_failure_line_count = 5
+        expect(config.max_displayed_failure_line_count).to eq 5
+      end
+    end
+
     # assigns files_or_directories_to_run and triggers post-processing
     # via `files_to_run`.
     def assign_files_or_directories_to_run(*value)

spec/rspec/core/formatters/exception_presenter_spec.rb

@@ -177,18 +177,35 @@ def read_failed_lines
       context 'when the failed expression spans multiple lines', :if => RSpec::Support::RubyFeatures.ripper_supported? do
         let(:exception) do
           begin
-            expect('RSpec').to start_with('R').
+            expect('RSpec').to be_a(String).
+                           and start_with('R').
                            and end_with('z')
           rescue RSpec::Expectations::ExpectationNotMetError => exception
             exception
           end
         end
 
-        it 'returns all the lines' do
-          expect(read_failed_lines).to eq([
-            "            expect('RSpec').to start_with('R').",
-            "                           and end_with('z')"
-          ])
+        context 'and the line count does not exceed RSpec.configuration.max_displayed_failure_line_count' do
+          it 'returns all the lines' do
+            expect(read_failed_lines).to eq([
+              "            expect('RSpec').to be_a(String).",
+              "                           and start_with('R').",
+              "                           and end_with('z')"
+            ])
+          end
+        end
+
+        context 'and the line count exceeds RSpec.configuration.max_displayed_failure_line_count' do
+          before do
+            RSpec.configuration.max_displayed_failure_line_count = 2
+          end
+
+          it 'returns the lines without exceeding the max count' do
+            expect(read_failed_lines).to eq([
+              "            expect('RSpec').to be_a(String).",
+              "                           and start_with('R')."
+            ])
+          end
         end
       end
 

spec/rspec/core/formatters/snippet_extractor_spec.rb

@@ -3,7 +3,7 @@
 module RSpec::Core::Formatters
   RSpec.describe SnippetExtractor do
     subject(:expression_lines) do
-      SnippetExtractor.extract_expression_lines_at(file_path, line_number)
+      SnippetExtractor.extract_expression_lines_at(file_path, line_number, max_line_count)
     end
 
     let(:file_path) do
@@ -24,6 +24,10 @@ module RSpec::Core::Formatters
       location
     end
 
+    let(:max_line_count) do
+      nil
+    end
+
     let(:error) do
       begin
         source
@@ -245,6 +249,51 @@ def another_expression(*)
           ])
         end
       end
+
+      context 'when max line count is given' do
+        let(:max_line_count) do
+          2
+        end
+
+        let(:source) do
+          do_something_fail "line1", [
+            "line2",
+            "line3"
+          ]
+        end
+
+        it 'returns the lines without exceeding the given count' do
+          expect(expression_lines).to eq([
+            '          do_something_fail "line1", [',
+            '            "line2",'
+          ])
+        end
+      end
+
+      context 'when max line count is 1' do
+        let(:max_line_count) do
+          1
+        end
+
+        let(:source) do
+          do_something_fail "line1", [
+            "line2",
+            "line3"
+          ]
+        end
+
+        before do
+          RSpec.reset # Clear source cache
+        end
+
+        it 'returns the line without parsing the source for efficiency' do
+          require 'ripper'
+          expect(Ripper).not_to receive(:sexp)
+          expect(expression_lines).to eq([
+            '          do_something_fail "line1", ['
+          ])
+        end
+      end
     end
 
     context 'in Ripper unsupported environment', :unless => RSpec::Support::RubyFeatures.ripper_supported? do