fix: issue with preserving new line characters in read-rule

.gitignore

@@ -1,3 +1,4 @@
 node_modules
 coverage
 lib
+.idea

.npmignore

@@ -1,3 +1,4 @@
 # If `lib` is ignored, then npm won’t publish it.
 coverage
 __tests__
+__mocks__

src/actions/__tests__/read-rule.test.js

@@ -9,9 +9,10 @@ const readRule = require('../../actions/read-rule')
 
 const description = 'Require that the file be empty'
 const name = 'require-empty'
+const heading = `# ${description} (${name})`
 const docs =
   `
-# ${description} (${name})
+${heading}
 
 This rule ensures great productivity by requiring that
 all files you write are completely empty.
@@ -74,4 +75,45 @@ describe('readRule()', () => {
       runReadRule(undefined, docs.replace('\n', '\r\n')).newDocs
     ).toMatchSnapshot()
   })
+
+  it('properly handles mixed Windows and Unix newlines', () => {
+    const docs = `${heading}\nSome random test:\r\n\r\n`
+
+    expect(runReadRule(undefined, docs).newDocs).toBe(docs)
+  })
+
+  it('properly handles multiple newlines before heading', () => {
+    const docs = `\n\n\n\n\r\n${heading}\n`
+    const outputDocs = `${heading}\n`
+
+    expect(runReadRule(undefined, docs).newDocs).toBe(outputDocs)
+  })
+
+  it('properly handles non heading text with new line', () => {
+    const docs = `\nTest\n`
+    const outputDocs = `${heading}\n\nTest\n`
+
+    expect(runReadRule(undefined, docs).newDocs).toBe(outputDocs)
+  })
+
+  it('properly handles non heading text without new line', () => {
+    const docs = `Test\n`
+    const outputDocs = `${heading}\nTest\n`
+
+    expect(runReadRule(undefined, docs).newDocs).toBe(outputDocs)
+  })
+
+  it('properly handles an single line heading', () => {
+    const docs = `# Test`
+    const outputDocs = `${heading}`
+
+    expect(runReadRule(undefined, docs).newDocs).toBe(outputDocs)
+  })
+
+  it('handles an empty file properly', () => {
+    const docs = ``
+    const outputDocs = `${heading}\n`
+
+    expect(runReadRule(undefined, docs).newDocs).toBe(outputDocs)
+  })
 })

src/actions/read-rule.js

@@ -15,11 +15,13 @@ module.exports = ({ rule, docs, friendlyDocPath }, name) => {
   const fixable = rule.meta.fixable
   const { description, extraDescription, recommended } = rule.meta.docs
 
-  const nl = detectNewline(docs)
+  const heading = `# ${description} (${name})`
 
-  const newDocs = [`# ${description} (${name})`]
-    .concat(docs.split(nl).slice(1))
-    .join(nl)
+  const headingRe = /^\s*#[^\r\n]*(\r?\n)?/
+
+  const newDocs = headingRe.test(docs)
+    ? docs.replace(headingRe, heading + `$1`)
+    : `${heading}${detectNewline(docs)}${docs}`
 
   if (newDocs !== docs) {
     const patch = diff(friendlyDocPath, 'generated', docs, newDocs)