From ceb75fa8dc95e44bfe19f8f1de9126f91353d62b Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <piotr.github@karwasz.org>
Date: Fri, 10 Feb 2023 18:26:33 +0100
Subject: [PATCH] Use `System.lineSeparator()` on all systems

The current version of the `flatten-maven-plugin` switches between LF
and CRLF line endings based on the system name.

Reproducible builds require normalization of line endings on all
systems.  This PR allows to change the generated line endings by passing
an appropriate `-Dline.separator=...` option to Maven and therefore
allows to use LF line endings also on Windows machines.
---
 .../codehaus/mojo/flatten/FlattenMojo.java    |  4 +-
 .../mojo/flatten/KeepCommentsInPomTest.java   | 48 +++++++++++--------
 2 files changed, 30 insertions(+), 22 deletions(-)

diff --git a/src/main/java/org/codehaus/mojo/flatten/FlattenMojo.java b/src/main/java/org/codehaus/mojo/flatten/FlattenMojo.java
index 0825ab83..92cb61ea 100644
--- a/src/main/java/org/codehaus/mojo/flatten/FlattenMojo.java
+++ b/src/main/java/org/codehaus/mojo/flatten/FlattenMojo.java
@@ -537,9 +537,9 @@ protected void writePom( Model pom, File pomFile, String headerComment, KeepComm
     protected void writeStringToFile( String data, File file, String encoding )
         throws MojoExecutionException
     {
-        if ( System.getProperty( "os.name" ).contains( "Windows" ) )
+        if ( !"\n".equals( System.lineSeparator() ) )
         {
-            data = data.replace( "\n", "\r\n" );
+            data = data.replace( "\n", System.lineSeparator() );
         }
         byte[] binaryData;
 
diff --git a/src/test/java/org/codehaus/mojo/flatten/KeepCommentsInPomTest.java b/src/test/java/org/codehaus/mojo/flatten/KeepCommentsInPomTest.java
index ff17efbc..1621a06d 100644
--- a/src/test/java/org/codehaus/mojo/flatten/KeepCommentsInPomTest.java
+++ b/src/test/java/org/codehaus/mojo/flatten/KeepCommentsInPomTest.java
@@ -21,9 +21,10 @@
 
 import java.io.File;
 import java.io.IOException;
-import java.nio.charset.StandardCharsets;
-import java.nio.file.Files;
+import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.util.Scanner;
+import java.util.regex.Pattern;
 
 import org.apache.maven.plugin.testing.MojoRule;
 import org.apache.maven.project.MavenProject;
@@ -32,7 +33,7 @@
 import org.junit.Rule;
 import org.junit.Test;
 
-import static org.junit.Assert.assertEquals;
+import static org.assertj.core.api.Assertions.assertThat;
 
 /**
  * Test-Case for {@link FlattenMojo}.
@@ -48,6 +49,7 @@ public class KeepCommentsInPomTest
      * Expected result since jdk11 with updated xml header and properties sequence.
      */
     private static final String EXPECTED_FLATTENED_POM_JDK11 = PATH + "expected-flattened-pom-jdk11.xml";
+    private static final Pattern NEW_LINE_PATTERN = Pattern.compile( "\\n|\\r\\n?" );
 
     @Rule
     public MojoRule rule = new MojoRule();
@@ -77,18 +79,10 @@ public void keepsProfileActivationFile() throws Exception
         // execute writes new FLATTENED_POM
         flattenMojo.execute();
 
-        String tempExpectedContent;
-        if ( isJdk8() )
-        {
-            tempExpectedContent = getContent( EXPECTED_FLATTENED_POM );
-        }
-        else
-        {
-            tempExpectedContent = getContent( EXPECTED_FLATTENED_POM_JDK11 );
-        }
-        String tempActualContent = getContent( FLATTENED_POM );
-        assertEquals( "Expected POM does not match, see " + FLATTENED_POM, tempExpectedContent, tempActualContent );
-
+        Path expectedContentFile = Paths.get( isJdk8() ? EXPECTED_FLATTENED_POM : EXPECTED_FLATTENED_POM_JDK11 );
+        Path actualContentFile = Paths.get( FLATTENED_POM );
+        assertThat( actualContentFile ).hasSameTextualContentAs( expectedContentFile );
+        assertHasLineSeparator( actualContentFile , System.lineSeparator() );
     }
 
     /**
@@ -107,12 +101,26 @@ private boolean isJdk8()
         return false;
     }
 
-    /**
-     *
-     */
-    private String getContent( String aPomFile ) throws IOException
+    private static void assertHasLineSeparator( final Path file, final String expectedSeparator ) throws IOException
     {
-        return String.join( "\n", Files.readAllLines( Paths.get( aPomFile ), StandardCharsets.UTF_8 ) );
+        try ( Scanner scanner = new Scanner( file ) )
+        {
+            int lineNr = 0;
+            String actualSeparator;
+            while ( ( actualSeparator = scanner.findWithinHorizon( NEW_LINE_PATTERN, 0 ) ) != null )
+            {
+                lineNr++;
+                if ( !expectedSeparator.equals( actualSeparator ) )
+                {
+                    final String actualDesc = actualSeparator.replace( "\r", "CR" ).replace( "\n", "LF" );
+                    final String expectedDesc = expectedSeparator.replace( "\r", "CR" ).replace( "\n", "LF" );
+                    throw new AssertionError(
+                            String.format(
+                                    "\nLine %d of path %s has %s as line separator.\nExpected line separator: %s.",
+                                    lineNr, file, actualDesc, expectedDesc ) );
+                }
+            }
+        }
     }
 
 }