Fix multiline string diff with blank lines

Author: jas14

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Features
 
 - Improve inspection of Module. [#263](https://github.com/splitwise/super_diff/pull/263) by [@phorsuedzie](https://github.com/phorsuedzie)
+- Fix multiline string diff with blank lines. [#266](https://github.com/splitwise/super_diff/pull/263)
 
 ## 0.13.0 - 2024-09-22
 

lib/super_diff/basic/operation_tree_builders/multiline_string.rb

@@ -42,7 +42,7 @@ def build_operation_tree
         attr_reader :sequence_matcher, :original_expected, :original_actual
 
         def split_into_lines(string)
-          string.scan(/.+(?:\r|\n|\r\n|\Z)/)
+          string.scan(/.*(?:\r|\n|\r\n|\Z)/)
         end
 
         def opcodes

spec/unit/basic/operation_tree_builders/multiline_string_spec.rb

@@ -0,0 +1,117 @@
+require "spec_helper"
+
+RSpec.describe SuperDiff, type: :unit do
+  describe ".diff" do
+    subject(:diff) { SuperDiff.diff(expected, actual) }
+
+    let(:expected) { <<~STRING }
+        This here is a string.
+        It contains separate lines.
+        What else can I say?
+      STRING
+    let(:actual) { <<~STRING }
+        This here is a string.
+        It contains separate lines.
+        What else can I say?
+      STRING
+
+    context "with extra blank lines in the middle of expected" do
+      let(:expected) { <<~STRING }
+          This here is a string.
+
+          It contains separate lines.
+
+
+          What else can I say?
+        STRING
+
+      it "removes the extra blank lines" do
+        expected_output =
+          SuperDiff::Core::Helpers
+            .style(color_enabled: true) do
+              plain_line "  This here is a string.\\n"
+              expected_line "- \\n"
+              plain_line "  It contains separate lines.\\n"
+              expected_line "- \\n"
+              expected_line "- \\n"
+              plain_line "  What else can I say?\\n"
+            end
+            .to_s
+            .chomp
+        expect(diff).to eq(expected_output)
+      end
+    end
+
+    context "with extra blank lines in the middle of actual" do
+      let(:actual) { <<~STRING }
+          This here is a string.
+
+          It contains separate lines.
+
+
+          What else can I say?
+        STRING
+
+      it "adds the extra blank lines" do
+        expected_output =
+          SuperDiff::Core::Helpers
+            .style(color_enabled: true) do
+              plain_line "  This here is a string.\\n"
+              actual_line "+ \\n"
+              plain_line "  It contains separate lines.\\n"
+              actual_line "+ \\n"
+              actual_line "+ \\n"
+              plain_line "  What else can I say?\\n"
+            end
+            .to_s
+            .chomp
+        expect(diff).to eq(expected_output)
+      end
+    end
+
+    context "with two trailing newlines in expected but only one in actual" do
+      let(:expected) { <<~STRING }
+          This here is a string.
+          It contains separate lines.
+          What else can I say?
+
+        STRING
+
+      it "removes the trailing newline" do
+        expected_output =
+          SuperDiff::Core::Helpers
+            .style(color_enabled: true) do
+              plain_line "  This here is a string.\\n"
+              plain_line "  It contains separate lines.\\n"
+              plain_line "  What else can I say?\\n"
+              expected_line "- \\n"
+            end
+            .to_s
+            .chomp
+        expect(diff).to eq(expected_output)
+      end
+    end
+
+    context "with one trailing newline in expected but none in actual" do
+      let(:actual) { <<~STRING.chomp }
+          This here is a string.
+          It contains separate lines.
+          What else can I say?
+        STRING
+
+      it "removes the trailing newline" do
+        expected_output =
+          SuperDiff::Core::Helpers
+            .style(color_enabled: true) do
+              plain_line "  This here is a string.\\n"
+              plain_line "  It contains separate lines.\\n"
+              expected_line "- What else can I say?\\n"
+              actual_line "+ What else can I say?"
+            end
+            .to_s
+            .chomp
+        expect(diff).to eq(expected_output)
+      end
+    end
+  end
+end