Provide infix compareTo extension for Comparable<T> #KT-46423

libraries/stdlib/api/js-v1/kotlin.kt

@@ -193,6 +193,10 @@ public inline fun <T> T.also(block: (T) -> kotlin.Unit): T
 @kotlin.internal.InlineOnly
 public inline fun <T> T.apply(block: T.() -> kotlin.Unit): T
 
+@kotlin.internal.InlineOnly
+@kotlin.SinceKotlin(version = "1.6")
+public inline infix fun <T> kotlin.Comparable<T>.compareTo(other: T): kotlin.Int
+
 @kotlin.SinceKotlin(version = "1.4")
 @kotlin.WasExperimental(markerClass = {kotlin.ExperimentalStdlibApi::class})
 @kotlin.internal.InlineOnly

libraries/stdlib/api/js/kotlin.kt

@@ -156,6 +156,10 @@ public inline fun <T> T.also(block: (T) -> kotlin.Unit): T
 @kotlin.internal.InlineOnly
 public inline fun <T> T.apply(block: T.() -> kotlin.Unit): T
 
+@kotlin.internal.InlineOnly
+@kotlin.SinceKotlin(version = "1.6")
+public inline infix fun <T> kotlin.Comparable<T>.compareTo(other: T): kotlin.Int
+
 @kotlin.SinceKotlin(version = "1.4")
 @kotlin.WasExperimental(markerClass = {kotlin.ExperimentalStdlibApi::class})
 @kotlin.internal.InlineOnly

libraries/stdlib/src/kotlin/comparisons/compareTo.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2010-2021 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 kotlin
+
+import kotlin.internal.InlineOnly
+
+/**
+ * Compares this object with the specified object for order. Returns zero if this object is equal
+ * to the specified [other] object, a negative number if it's less than [other], or a positive number
+ * if it's greater than [other].
+ *
+ * This function delegates to [Comparable.compareTo] and allows to call it in infix form.
+ */
+@InlineOnly
+@SinceKotlin("1.6")
+public inline infix fun <T> Comparable<T>.compareTo(other: T): Int =
+    this.compareTo(other)

libraries/stdlib/test/collections/ArraysTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2021 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.
  */
 
@@ -2129,7 +2129,7 @@ class ArraysTest {
     }
 
     private data class Text(val data: String) : Comparable<Text> {
-        override fun compareTo(other: Text): Int = data.compareTo(other.data)
+        override fun compareTo(other: Text): Int = data compareTo other.data
     }
 
     private fun testStableSort(stableSort: Array<Text>.() -> Unit, intSort: Array<Int>.() -> Unit) {

libraries/stdlib/test/collections/IterableTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2021 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.
  */
 
@@ -578,13 +578,13 @@ fun <T> Iterator<T>.assertSorted(isInOrder: (T, T) -> Boolean) {
 }
 
 data class Sortable<K : Comparable<K>>(val key: K, val index: Int) : Comparable<Sortable<K>> {
-    override fun compareTo(other: Sortable<K>): Int = this.key.compareTo(other.key)
+    override fun compareTo(other: Sortable<K>): Int = this.key compareTo other.key
 }
 
 
 fun <K : Comparable<K>> Iterator<Sortable<K>>.assertStableSorted(descending: Boolean = false) {
     assertSorted { a, b ->
-        val relation = a.key.compareTo(b.key)
+        val relation = a.key compareTo b.key
         (if (descending) relation > 0 else relation < 0) || relation == 0 && a.index < b.index
     }
 }

libraries/stdlib/test/comparisons/OrderingTest.kt

@@ -28,6 +28,8 @@ class OrderingTest {
     fun compareByCompareTo() {
         val diff = v1.compareTo(v2)
         assertTrue(diff < 0)
+        val infixDiff = v1 compareTo v2
+        assertEquals(diff, infixDiff)
     }
 
     @Test
@@ -60,7 +62,7 @@ class OrderingTest {
 
     @Test
     fun sortComparatorThenComparator() {
-        val comparator = Comparator<Item> { a, b -> a.name.compareTo(b.name) }.thenComparator { a, b -> a.rating.compareTo(b.rating) }
+        val comparator = Comparator<Item> { a, b -> a.name compareTo b.name }.thenComparator { a, b -> a.rating compareTo b.rating }
 
         val diff = comparator.compare(v1, v2)
         assertTrue(diff > 0)

libraries/stdlib/test/utils/KotlinVersionTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2021 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.
  */
 
@@ -20,7 +20,7 @@ class KotlinVersionTest {
         val anotherCurrent = KotlinVersion.CURRENT.run { KotlinVersion(major, minor, patch) }
         assertEquals(KotlinVersion.CURRENT, anotherCurrent)
         assertEquals(KotlinVersion.CURRENT.hashCode(), anotherCurrent.hashCode())
-        assertEquals(0, KotlinVersion.CURRENT.compareTo(anotherCurrent))
+        assertEquals(0, KotlinVersion.CURRENT compareTo anotherCurrent)
     }
 
     @Test fun componentValidation() {