FIR LT: fix line offsets calculations for text files with crlf

#KT-55886 fixed

compiler/frontend.common/src/org/jetbrains/kotlin/KtSourceFileLinesMapping.kt

@@ -91,7 +91,7 @@ fun InputStreamReader.readSourceFileWithMapping(): Pair<CharSequence, KtSourceFi
             charsRead++
             when {
                 c == '\n' && skipNextLf -> {
-                    lineOffsets[lineOffsets.size - 1] = charsRead
+                    charsRead--
                     skipNextLf = false
                 }
                 c == '\n' || c == '\r' -> {

compiler/tests/org/jetbrains/kotlin/lightTree/LightTreeParsingTest.kt

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.lightTree
+
+import com.intellij.lang.LighterASTNode
+import com.intellij.openapi.util.Ref
+import com.intellij.util.diff.FlyweightCapableTreeStructure
+import org.jetbrains.kotlin.fir.lightTree.LightTree2Fir
+import org.jetbrains.kotlin.readSourceFileWithMapping
+import org.junit.Assert
+import org.junit.Test
+import java.io.ByteArrayInputStream
+
+class LightTreeParsingTest {
+
+    @Test
+    fun testLightTreeReadLineEndings() {
+        fun String.makeCodeMappingAndLines() = run {
+            val (code, mapping) = ByteArrayInputStream(toByteArray()).reader().readSourceFileWithMapping()
+            val lines =
+                LightTree2Fir.buildLightTree(code).getChildrenAsArray().mapNotNull { it?.startOffset }.map { mapping.getLineByOffset(it) }
+            Triple(code, mapping, lines)
+        }
+
+        val (codeFromTextWithLf, mappingFromTextWithLf, linesFromTextWithLf) = MULTILINE_SOURCE.makeCodeMappingAndLines()
+
+        val (codeFromTextWithCrLf, mappingFromTextWithCrLf, linesFromTextWithCrLf) =
+            MULTILINE_SOURCE.replace("\n", "\r\n").makeCodeMappingAndLines()
+
+        // classic Mac OS line endings are probably not to be found in the wild, but checking the support nevertheless
+        val (codeFromTextWithCr, mappingFromTextWithCr, linesFromTextWithCr) =
+            MULTILINE_SOURCE.replace("\n", "\r").makeCodeMappingAndLines()
+
+        Assert.assertEquals(codeFromTextWithLf.toString(), codeFromTextWithCrLf.toString())
+        Assert.assertEquals(codeFromTextWithLf.toString(), codeFromTextWithCr.toString())
+
+        Assert.assertEquals(mappingFromTextWithLf.linesCount, mappingFromTextWithCrLf.linesCount)
+        Assert.assertEquals(mappingFromTextWithLf.linesCount, mappingFromTextWithCr.linesCount)
+
+        Assert.assertEquals(linesFromTextWithLf, linesFromTextWithCrLf)
+        Assert.assertEquals(linesFromTextWithLf, linesFromTextWithCr)
+
+        Assert.assertEquals(mappingFromTextWithLf.lastOffset, mappingFromTextWithCrLf.lastOffset)
+        Assert.assertEquals(mappingFromTextWithLf.lastOffset, mappingFromTextWithCr.lastOffset)
+    }
+}
+
+private fun FlyweightCapableTreeStructure<LighterASTNode>.getChildrenAsArray(): Array<out LighterASTNode?> {
+    val kidsRef = Ref<Array<LighterASTNode?>>()
+    getChildren(root, kidsRef)
+    return kidsRef.get()
+}
+
+private const val MULTILINE_SOURCE = """
+val a = 1
+ val b = 2 
+  val c = 3
+   val d = 4
+"""