Implement syntax highlighting.

Author: myronmarston

Changelog.md

@@ -52,6 +52,8 @@ Enhancements:
 * Enhance `fail_fast` option so it can take a number (e.g. `--fail-fast=3`)
   to force the run to abort after the specified number of failures.
   (Jack Scotti, #2065)
+* Syntax highlight the failure snippets in text formatters when `color`
+  is enabled and the `coderay` gem is installed. (Myron Marston, #2109)
 
 Bug Fixes:
 

lib/rspec/core/formatters/exception_presenter.rb

@@ -159,7 +159,7 @@ def failure_slash_error_lines
           if lines.count == 1
             lines[0] = "Failure/Error: #{lines[0].strip}"
           else
-            least_indentation = lines.map { |line| line[/^[ \t]*/] }.min
+            least_indentation = SnippetExtractor.least_indentation_from(lines)
             lines = lines.map { |line| line.sub(/^#{least_indentation}/, '  ') }
             lines.unshift('Failure/Error:')
           end
@@ -204,7 +204,8 @@ def read_failed_lines
 
           file_path, line_number = matching_line.match(/(.+?):(\d+)(|:\d+)/)[1..2]
           max_line_count = RSpec.configuration.max_displayed_failure_line_count
-          SnippetExtractor.extract_expression_lines_at(file_path, line_number.to_i, max_line_count)
+          lines = SnippetExtractor.extract_expression_lines_at(file_path, line_number.to_i, max_line_count)
+          RSpec.world.source_cache.syntax_highlighter.highlight(lines)
         rescue SnippetExtractor::NoSuchFileError
           ["Unable to find #{file_path} to read failed line"]
         rescue SnippetExtractor::NoSuchLineError

lib/rspec/core/formatters/snippet_extractor.rb

@@ -133,6 +133,10 @@ def self.extract_expression_lines_at(file_path, beginning_line_number, *)
           end
           # :nocov:
         end
+
+        def self.least_indentation_from(lines)
+          lines.map { |line| line[/^[ \t]*/] }.min
+        end
       end
     end
   end

lib/rspec/core/source.rb

@@ -1,4 +1,5 @@
 RSpec::Support.require_rspec_core 'source/node'
+RSpec::Support.require_rspec_core 'source/syntax_highlighter'
 RSpec::Support.require_rspec_core 'source/token'
 
 module RSpec
@@ -59,8 +60,11 @@ def inspect
 
       # @private
       class Cache
-        def initialize
+        attr_reader :syntax_highlighter
+
+        def initialize(configuration)
           @sources_by_path = {}
+          @syntax_highlighter = SyntaxHighlighter.new(configuration)
         end
 
         def source_from_file(path)

lib/rspec/core/source/syntax_highlighter.rb

@@ -0,0 +1,61 @@
+module RSpec
+  module Core
+    class Source
+      # @private
+      # Provides terminal syntax highlighting of code snippets
+      # when coderay is available.
+      class SyntaxHighlighter
+        def initialize(configuration)
+          @configuration = configuration
+        end
+
+        def highlight(lines)
+          implementation.highlight_syntax(lines)
+        end
+
+      private
+
+        def implementation
+          return color_enabled_implementation if @configuration.color_enabled?
+          ColorDisabledImplementation
+        end
+
+        def color_enabled_implementation
+          @color_enabled_implementation ||= begin
+            ::Kernel.require 'coderay'
+            CodeRayImplementation
+          rescue LoadError
+            NoCodeRayImplementation
+          end
+        end
+
+        module CodeRayImplementation
+          RESET_CODE = "\e[0m"
+
+          def self.highlight_syntax(lines)
+            highlighted = CodeRay.encode(lines.join("\n"), :ruby, :terminal)
+            highlighted.split("\n").map do |line|
+              line.sub(/\S/) { |char| char.insert(0, RESET_CODE) }
+            end
+          end
+        end
+
+        module NoCodeRayImplementation
+          INSTALL_CODERAY_COMMENT = "# Install the coderay gem to get syntax highlighting"
+
+          def self.highlight_syntax(lines)
+            return lines unless lines.size > 1
+            least_indentation = Formatters::SnippetExtractor.least_indentation_from(lines)
+            lines + ["#{least_indentation}#{INSTALL_CODERAY_COMMENT}"]
+          end
+        end
+
+        module ColorDisabledImplementation
+          def self.highlight_syntax(lines)
+            lines
+          end
+        end
+      end
+    end
+  end
+end

lib/rspec/core/world.rb

@@ -111,7 +111,7 @@ def reporter
       def source_cache
         @source_cache ||= begin
           RSpec::Support.require_rspec_core "source"
-          Source::Cache.new
+          Source::Cache.new(@configuration)
         end
       end
 

spec/rspec/core/formatters/exception_presenter_spec.rb

@@ -187,6 +187,24 @@ module RSpec::Core
           end
         end
 
+        describe "syntax highlighting" do
+          let(:expression) do
+            expect('RSpec').to be_a(Integer)
+          end
+
+          it 'uses our syntax highlighter on the code snippet to format it nicely' do
+            syntax_highlighter = instance_double(Source::SyntaxHighlighter)
+            allow(syntax_highlighter).to receive(:highlight) do |lines|
+              lines.map { |l| "<highlighted>#{l.strip}</highlighted>" }
+            end
+
+            allow(RSpec.world.source_cache).to receive_messages(:syntax_highlighter => syntax_highlighter)
+
+            formatted = presenter.fully_formatted(1)
+            expect(formatted).to include("<highlighted>expect('RSpec').to be_a(Integer)</highlighted>")
+          end
+        end
+
         context 'with single line expression and single line RSpec exception message' do
           let(:expression) do
             expect('RSpec').to be_a(Integer)

spec/rspec/core/source/syntax_highlighter_spec.rb

@@ -0,0 +1,95 @@
+require 'rspec/core/source/syntax_highlighter'
+
+class RSpec::Core::Source
+  RSpec.describe SyntaxHighlighter do
+    let(:config)      { RSpec::Core::Configuration.new.tap { |c| c.color = true } }
+    let(:highlighter) { SyntaxHighlighter.new(config)  }
+
+    def be_highlighted
+      include("\e[32m")
+    end
+
+    context "when CodeRay is available" do
+      before { expect { require 'coderay' }.not_to raise_error }
+
+      it 'highlights the syntax of the provided lines' do
+        highlighted = highlighter.highlight(['[:ok, "ok"]'])
+        expect(highlighted.size).to eq(1)
+        expect(highlighted.first).to be_highlighted.and include(":ok")
+      end
+
+      it 'prefixes the each line with a reset escape code so it can be interpolated in a colored string without affecting the syntax highlighting of the snippet' do
+        highlighted = highlighter.highlight(['a = 1', 'b = 2'])
+        expect(highlighted).to all start_with("\e[0m")
+      end
+
+      it 'leaves leading spaces alone so it can be re-indented as needed without the leading reset code interfering' do
+        highlighted = highlighter.highlight(['  a = 1', '  b = 2'])
+        expect(highlighted).to all start_with("  \e[0m")
+      end
+
+      it 'returns the provided lines unmodified if color is disabled' do
+        config.color = false
+        expect(highlighter.highlight(['[:ok, "ok"]'])).to eq(['[:ok, "ok"]'])
+      end
+
+      it 'dynamically adjusts to changing color config' do
+        config.color = false
+        expect(highlighter.highlight(['[:ok, "ok"]']).first).not_to be_highlighted
+        config.color = true
+        expect(highlighter.highlight(['[:ok, "ok"]']).first).to be_highlighted
+        config.color = false
+        expect(highlighter.highlight(['[:ok, "ok"]']).first).not_to be_highlighted
+      end
+    end
+
+    context "when CodeRay is unavailable" do
+      before do
+        allow(::Kernel).to receive(:require).with("coderay").and_raise(LoadError)
+      end
+
+      it 'does not highlight the syntax' do
+        unhighlighted = highlighter.highlight(['[:ok, "ok"]'])
+        expect(unhighlighted.size).to eq(1)
+        expect(unhighlighted.first).not_to be_highlighted
+      end
+
+      it 'adds a comment explaining the user can get syntax highlighting by installing coderay' do
+        lines = ["a = 1", "b = 2"]
+        expect(highlighter.highlight(lines)).to eq([
+          "a = 1",
+          "b = 2",
+          "# Install the coderay gem to get syntax highlighting"
+        ])
+      end
+
+      it 'indents the "install coderay" comment to match the snippet' do
+        lines = ["  a = 1", "    b = 2"]
+        expect(highlighter.highlight(lines)).to eq([
+          "  a = 1",
+          "    b = 2",
+          "  # Install the coderay gem to get syntax highlighting"
+        ])
+      end
+
+      it 'does not mutate the input array' do
+        lines = ["a = 1", "b = 2"]
+        expect { highlighter.highlight(lines) }.not_to change { lines }
+      end
+
+      it 'does not add the comment about coderay if the snippet is only one line as we do not want to convert it to multiline just for the comment' do
+        expect(highlighter.highlight(["a = 1"])).to eq(["a = 1"])
+      end
+
+      it 'does not add the comment about coderay if given no lines' do
+        expect(highlighter.highlight([])).to eq([])
+      end
+
+      it 'does not add the comment about coderay if color id disabled even when given a multiline snippet' do
+        config.color = false
+        lines = ["a = 1", "b = 2"]
+        expect(highlighter.highlight(lines)).to eq(lines)
+      end
+    end
+  end
+end