Option to strip trailing CR (#344)

* Basic option for ignoring CR when doing linediff

* Add tests for supporting `stripTrailingCr` in createPatch

* Update documentation for createPatch

* Improve english of README changes

* Only remove one \r to match GNU diff behaviour

* Fix the same bad english in other place in README

Author: oBusk

README.md

@@ -37,6 +37,8 @@ npm install diff --save
 
     Options
     * `ignoreWhitespace`: `true` to ignore leading and trailing whitespace. This is the same as `diffTrimmedLines`
+    * `stripTrailingCr`: `true` to remove all trailing CR (`\r`) characters before perfoming the diff. 
+      This helps to get a useful diff when diffing UNIX text files against Windows text files.
     * `newlineIsToken`: `true` to treat newline characters as separate tokens.  This allows for changes to the newline structure to occur independently of the line content and to be treated as such. In general this is the more human friendly form of `diffLines` and `diffLines` is better suited for patches and other computer friendly output.
 
     Returns a list of [change objects](#change-objects).
@@ -81,6 +83,8 @@ npm install diff --save
       - `context` describes how many lines of context should be included.
       - `ignoreWhitespace`: `true` to ignore leading and trailing whitespace.
       - `newlineIsToken`: `true` to treat newline characters as separate tokens. This allows for changes to the newline structure to occur independently of the line content and to be treated as such. In general this is the more human friendly form of `diffLines` and `diffLines` is better suited for patches and other computer friendly output.
+      - `stripTrailingCr`: `true` to remove all trailing CR (`\r`) characters before perfoming the diff. 
+        This helps to get a useful diff when diffing UNIX text files against Windows text files.
 
 * `Diff.createPatch(fileName, oldStr, newStr, oldHeader, newHeader)` - creates a unified diff patch.
 

src/diff/line.js

@@ -3,6 +3,11 @@ import {generateOptions} from '../util/params';
 
 export const lineDiff = new Diff();
 lineDiff.tokenize = function(value) {
+  if(this.options.stripTrailingCr) {
+    // remove one \r before \n to match GNU diff's --strip-trailing-cr behavior
+    value = value.replace(/\r\n/g, '\n');
+  }
+
   let retLines = [],
       linesAndNewlines = value.split(/(\n|\r\n)/);
 

test/diff/line.js

@@ -106,4 +106,10 @@ describe('diff/line', function() {
       {value: '\nhello', count: 2, added: true, removed: undefined}
     ]);
   });
+
+  describe('Strip trailing CR', function() {
+    expect(diffLines('line\nline', 'line\r\nline', {stripTrailingCr: true})).to.eql([
+      {value: 'line\nline', count: 2}
+    ]);
+  });
 });

test/patch/create.js

@@ -705,6 +705,45 @@ describe('patch/create', function() {
     });
   });
 
+  describe('stripTrailingCr', function() {
+    it('stripTrailingCr: false', function() {
+      const expectedResult =
+      '===================================================================\n'
+      + '--- foo\n'
+      + '+++ bar\n'
+      + '@@ -1,2 +1,2 @@\n'
+      + '\-line\n'
+      + '\+line\r\n'
+      + '\ line\n'
+      + '\\ No newline at end of file\n';
+      expect(createTwoFilesPatch(
+        'foo',
+        'bar',
+        'line\nline',
+        'line\r\nline',
+        undefined,
+        undefined,
+        {stripTrailingCr: false}
+      )).to.equal(expectedResult);
+    });
+
+    it('stripTrailingCr: true', function() {
+      const expectedResult =
+        '===================================================================\n'
+        + '--- foo\n'
+        + '+++ bar\n';
+      expect(createTwoFilesPatch(
+        'foo',
+        'bar',
+        'line\nline',
+        'line\r\nline',
+        undefined,
+        undefined,
+        {stripTrailingCr: true}
+      )).to.equal(expectedResult);
+    });
+  });
+
   describe('#structuredPatch', function() {
     it('should handle files with the last line changed', function() {
       const res = structuredPatch(