thenIf modifier.

This modifier is more ergonomic than then "then" modifier.

Bug: 281871687
Test: as part of later CLs in this chain
Change-Id: Ifef4f85859720f9089f7d4e14048d9bb5c5aa58d

packages/SystemUI/compose/features/src/com/android/systemui/compose/modifiers/ConditionalModifiers.kt

@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2023 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 com.android.systemui.compose.modifiers
+
+import androidx.compose.ui.Modifier
+
+/**
+ * Concatenates this modifier with another if `condition` is true.
+ *
+ * @param condition Whether or not to apply the modifiers.
+ * @param factory Creates the modifier to concatenate with the current one.
+ * @return a Modifier representing this modifier followed by other in sequence.
+ * @see Modifier.then
+ *
+ * This method allows inline conditional addition of modifiers to a modifier chain. Instead of
+ * writing
+ *
+ * ```
+ * val aModifier = Modifier.a()
+ * val bModifier = if(condition) aModifier.b() else aModifier
+ * Composable(modifier = bModifier)
+ * ```
+ *
+ * You can instead write
+ *
+ * ```
+ * Composable(modifier = Modifier.a().thenIf(condition){
+ *  Modifier.b()
+ * }
+ * ```
+ *
+ * This makes the modifier chain easier to read.
+ *
+ * Note that unlike the non-factory version, the conditional modifier is recreated each time, and
+ * may never be created at all.
+ */
+inline fun Modifier.thenIf(condition: Boolean, crossinline factory: () -> Modifier): Modifier =
+    if (condition) this.then(factory()) else this