Prevent line separators to be changed from CRLF to LF (#2752)

When running on Windows, and `end_of_line` property not set in `.editorconfig` the line separators should not be changed from CRLF to LF whenever the file does not contain any lint violation that can be autocorrected.

Closes #2747

ktlint-api-consumer/src/test/kotlin/com/pinterest/ktlint/api/consumer/KtLintRuleEngineTest.kt

@@ -272,7 +272,7 @@ class KtLintRuleEngineTest {
     @Nested
     inner class `Format with KtLintRuleEngine` {
         @Nested
-        inner class `Given a file that does not contain an error` {
+        inner class `Given a file that containing some errors` {
             @Test
             fun `Given defaultAutocorrect is not set`(
                 @TempDir
@@ -402,7 +402,7 @@ class KtLintRuleEngineTest {
         }
 
         @Nested
-        inner class `Given a kotlin code snippet that does contain an indentation error` {
+        inner class `Given a kotlin code snippet containing some errors` {
             @Test
             fun `Given defaultAutocorrect is not set`() {
                 val lintErrors = mutableListOf<LintError>()
@@ -511,7 +511,7 @@ class KtLintRuleEngineTest {
         }
 
         @Nested
-        inner class `Given a kotlin script code snippet that does contain an indentation error` {
+        inner class `Given a kotlin script code snippet containing some errors` {
             @Test
             fun `Given defaultAutocorrect is not set`() {
                 val lintErrors = mutableListOf<LintError>()
@@ -662,6 +662,51 @@ class KtLintRuleEngineTest {
                 """.trimIndent(),
             )
         }
+
+        @Test
+        fun `Issue 2747 - Given some code with crlf separators instead of lfs, but not containing any lint error, then do no reformat the line separators`(
+            @TempDir
+            tempDir: Path,
+        ) {
+            val codeWithCrlfSeparators =
+                """
+                fun bar() {
+                    // FOO
+                    // BAR
+                }
+                """.trimIndent().replace("\n", "\r\n")
+            val filePath = "$tempDir/Code.kt"
+            FileWriter(filePath).use {
+                it.write(codeWithCrlfSeparators)
+            }
+
+            val lintErrors = mutableListOf<LintError>()
+            val actual =
+                KtLintRuleEngine(
+                    ruleProviders =
+                        setOf(
+                            RuleProvider { IndentationRule() },
+                            RuleProvider { RuleWithAutocorrectApproveHandler() },
+                            RuleProvider { RuleWithoutAutocorrectApproveHandler() },
+                        ),
+                    editorConfigOverride =
+                        EditorConfigOverride.from(
+                            // Do not set END_OF_LINE_PROPERTY explicitly!
+                            RULE_WITHOUT_AUTOCORRECT_APPROVE_HANDLER.createRuleExecutionEditorConfigProperty() to RuleExecution.enabled,
+                            RULE_WITH_AUTOCORRECT_APPROVE_HANDLER.createRuleExecutionEditorConfigProperty() to RuleExecution.enabled,
+                        ),
+                    fileSystem = ktlintTestFileSystem.fileSystem,
+                ).format(
+                    code = Code.fromFile(File(filePath)),
+                    defaultAutocorrect = true,
+                ) { lintError ->
+                    lintErrors.add(lintError)
+                    ALLOW_AUTOCORRECT
+                }
+
+            assertThat(lintErrors).isEmpty()
+            assertThat(actual).isEqualTo(codeWithCrlfSeparators)
+        }
     }
 
     @Test

ktlint-rule-engine/src/main/kotlin/com/pinterest/ktlint/rule/engine/internal/CodeFormatter.kt

@@ -10,6 +10,7 @@ import com.pinterest.ktlint.rule.engine.core.api.Rule
 import com.pinterest.ktlint.rule.engine.core.api.editorconfig.END_OF_LINE_PROPERTY
 import io.github.oshai.kotlinlogging.KotlinLogging
 import org.ec4j.core.model.PropertyType
+import org.jetbrains.kotlin.util.prefixIfNot
 
 private val LOGGER = KotlinLogging.logger {}.initKtLintKLogger()
 
@@ -30,7 +31,7 @@ internal class CodeFormatter(
             .sortedWith(lintErrorLineAndColumnComparator { it.first })
             .forEach { (e, corrected) -> callback(e, corrected) }
 
-        return (code.utf8Bom() + formattedCode).also {
+        return (formattedCode.prefixIfNot(code.utf8Bom())).also {
             LOGGER.debug { "Finished with processing file '${code.fileNameOrStdin()}'" }
         }
     }
@@ -71,8 +72,13 @@ internal class CodeFormatter(
                     }
                 }
             }
-            val lineSeparator = code.determineLineSeparator(editorConfig[END_OF_LINE_PROPERTY])
-            return Pair(formattedCode(lineSeparator), errors)
+            return if (mutated || formatRunCount > 1) {
+                val lineSeparator = code.determineLineSeparator(editorConfig[END_OF_LINE_PROPERTY])
+                Pair(formattedCode(lineSeparator), errors)
+            } else {
+                // None of the format runs has found
+                Pair(code.content, errors)
+            }
         }
     }
 
@@ -149,9 +155,9 @@ internal class CodeFormatter(
             eolEditorConfigProperty == PropertyType.EndOfLineValue.crlf ||
                 eolEditorConfigProperty != PropertyType.EndOfLineValue.lf &&
                 doesNotContain('\r') ->
-                "\r\n".also { LOGGER.debug { "line separator: ${eolEditorConfigProperty.name} --> CRLF" } }
+                "\r\n".also { LOGGER.trace { "line separator: ${eolEditorConfigProperty.name} --> CRLF" } }
 
-            else -> "\n".also { LOGGER.debug { "line separator: ${eolEditorConfigProperty.name} --> LF" } }
+            else -> "\n".also { LOGGER.trace { "line separator: ${eolEditorConfigProperty.name} --> LF" } }
         }
 
     private fun Code.doesNotContain(char: Char) = content.lastIndexOf(char) != -1