Fix SkiaParagraph.getLineForVerticalPosition (#1012)

compose/material/material/build.gradle

@@ -167,6 +167,11 @@ if(AndroidXComposePlugin.isMultiplatformEnabled(project)) {
                 implementation(libs.testUiautomator)
             }
 
+            commonTest.dependencies {
+                implementation(kotlin("test"))
+                implementation(project(":compose:ui:ui-test"))
+            }
+
             desktopTest.dependencies {
                 implementation(project(":compose:ui:ui-test-junit4"))
                 implementation(libs.truth)

compose/material/material/src/commonTest/kotlin/androidx/compose/material/TextLayout.kt

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package androidx.compose.material
+
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.text.BasicTextField
+import androidx.compose.runtime.remember
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.test.ExperimentalTestApi
+import androidx.compose.ui.test.runComposeUiTest
+import androidx.compose.ui.text.TextLayoutResult
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+/**
+ * Tests text layout in text fields.
+ */
+@OptIn(ExperimentalTestApi::class)
+class TextLayout {
+    @Test
+    fun getLineForOffsetReturnsLastLineWhenOffsetIsBeyondLast() = runComposeUiTest {
+        lateinit var textLayoutResult: TextLayoutResult
+
+        setContent {
+            val text = remember { "X\n".repeat(100) }
+
+            BasicTextField(
+                value = text,
+                onValueChange = {},
+                onTextLayout = { textLayoutResult = it },
+                modifier = Modifier.fillMaxSize()
+            )
+        }
+
+        assertEquals(100, textLayoutResult.getLineForOffset(Int.MAX_VALUE))
+    }
+
+    @Test
+    fun getLineForVerticalPositionReturnsLastLineWhenPositionIsBeyondLastLine() = runComposeUiTest {
+        lateinit var textLayoutResult: TextLayoutResult
+
+        setContent {
+            val text = remember { "Compose rules!\n".repeat(100) }
+
+            BasicTextField(
+                value = text,
+                onValueChange = {},
+                onTextLayout = { textLayoutResult = it },
+                modifier = Modifier.fillMaxSize()
+            )
+        }
+
+        assertEquals(100, textLayoutResult.getLineForVerticalPosition(Float.MAX_VALUE))
+    }
+}

compose/ui/ui-text/src/skikoMain/kotlin/androidx/compose/ui/text/SkiaParagraph.skiko.kt

@@ -187,17 +187,10 @@ internal class SkiaParagraph(
 
     private fun lineMetricsForOffset(offset: Int): LineMetrics? {
         checkOffsetIsValid(offset)
-        val metrics = lineMetrics
-        if (metrics.isEmpty()) {
-            return null
-        }
 
-        val index = metrics.asList().binarySearch {
-            if (offset >= it.endIncludingNewline) -1 else 1
+        return lineMetrics.binarySearchFirstMatchingOrLast {
+            offset < it.endIncludingNewline
         }
-
-        // The search will always return a negative value because the comparison never returns 0
-        return metrics[(-index - 1).coerceAtMost(metrics.lastIndex)]
     }
 
     override fun getLineHeight(lineIndex: Int) =
@@ -239,7 +232,7 @@ internal class SkiaParagraph(
     }
 
     private fun getLineMetricsForVerticalPosition(vertical: Float): LineMetrics? {
-        return lineMetrics.firstOrNull { vertical < it.baseline + it.descent }
+        return lineMetrics.binarySearchFirstMatchingOrLast { vertical < it.baseline + it.descent }
     }
 
     override fun getHorizontalPosition(offset: Int, usePrimaryDirection: Boolean): Float {
@@ -613,3 +606,23 @@ private fun LineMetrics.copy(
 )
 
 private fun IRange.toTextRange() = TextRange(start, end)
+
+/**
+ * Returns the first item satisfying [predicate], or the last item in the array if none satisfy it.
+ *
+ * Returns `null` if the array is empty.
+ */
+private inline fun <T> Array<out T>.binarySearchFirstMatchingOrLast(
+    crossinline predicate: (T) -> Boolean): T?
+{
+    if (this.isEmpty()) {
+        return null
+    }
+
+    val index = this.asList().binarySearch {
+        if (predicate(it)) 1 else -1
+    }
+
+    // The search will always return a negative value because the comparison never returns 0
+    return this[(-index - 1).coerceAtMost(this.lastIndex)]
+}