[Row & Column feature parity] LastBaseline alignment experiment

constraintlayout/compose/src/main/java/androidx/constraintlayout/compose/ConstrainScope.kt

@@ -21,6 +21,7 @@ import androidx.compose.foundation.layout.LayoutScopeMarker
 import androidx.compose.runtime.Stable
 import androidx.compose.ui.graphics.TransformOrigin
 import androidx.compose.ui.layout.FirstBaseline
+import androidx.compose.ui.layout.LastBaseline
 import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
 import androidx.constraintlayout.core.parser.CLArray
@@ -83,6 +84,11 @@ class ConstrainScope internal constructor(
      */
     val baseline: BaselineAnchorable = ConstraintBaselineAnchorable(containerObject)
 
+    /**
+     * The [LastBaseline] of the layout - can be constrained using [LastBaselineAnchorable.linkTo].
+     */
+    val lastBaseline: LastBaselineAnchorable = ConstraintLastBaselineAnchorable(containerObject)
+
     /**
      * The width of the [ConstraintLayout] child.
      */
@@ -399,6 +405,7 @@ class ConstrainScope internal constructor(
         containerObject.remove("top")
         containerObject.remove("bottom")
         containerObject.remove("baseline")
+        containerObject.remove("lastBaseline")
     }
 
     /**
@@ -523,6 +530,23 @@ private class ConstraintBaselineAnchorable constructor(
         containerObject.put("baseline", constraintArray)
     }
 
+    /**
+     * Adds a link towards a [ConstraintLayoutBaseScope.LastBaselineAnchor].
+     */
+    override fun linkTo(
+        anchor: ConstraintLayoutBaseScope.LastBaselineAnchor,
+        margin: Dp,
+        goneMargin: Dp
+    ) {
+        val constraintArray = CLArray(charArrayOf()).apply {
+            add(CLString.from(anchor.id.toString()))
+            add(CLString.from("lastBaseline"))
+            add(CLNumber(margin.value))
+            add(CLNumber(goneMargin.value))
+        }
+        containerObject.put("baseline", constraintArray)
+    }
+
     /**
      * Adds a link towards a [ConstraintLayoutBaseScope.HorizontalAnchor].
      */
@@ -540,4 +564,64 @@ private class ConstraintBaselineAnchorable constructor(
         }
         containerObject.put("baseline", constraintArray)
     }
+}
+
+/**
+ * Represents the [LastBaseline] of a layout that can be anchored
+ * using [linkTo] in their `Modifier.constrainAs` blocks.
+ */
+private class ConstraintLastBaselineAnchorable constructor(
+    private val containerObject: CLObject
+) : LastBaselineAnchorable {
+    /**
+     * Adds a link towards a [ConstraintLayoutBaseScope.BaselineAnchor].
+     */
+    override fun linkTo(
+        anchor: ConstraintLayoutBaseScope.BaselineAnchor,
+        margin: Dp,
+        goneMargin: Dp
+    ) {
+        val constraintArray = CLArray(charArrayOf()).apply {
+            add(CLString.from(anchor.id.toString()))
+            add(CLString.from("baseline"))
+            add(CLNumber(margin.value))
+            add(CLNumber(goneMargin.value))
+        }
+        containerObject.put("lastBaseline", constraintArray)
+    }
+
+    /**
+     * Adds a link towards a [ConstraintLayoutBaseScope.LastBaselineAnchor].
+     */
+    override fun linkTo(
+        anchor: ConstraintLayoutBaseScope.LastBaselineAnchor,
+        margin: Dp,
+        goneMargin: Dp
+    ) {
+        val constraintArray = CLArray(charArrayOf()).apply {
+            add(CLString.from(anchor.id.toString()))
+            add(CLString.from("lastBaseline"))
+            add(CLNumber(margin.value))
+            add(CLNumber(goneMargin.value))
+        }
+        containerObject.put("lastBaseline", constraintArray)
+    }
+
+    /**
+     * Adds a link towards a [ConstraintLayoutBaseScope.HorizontalAnchor].
+     */
+    override fun linkTo(
+        anchor: ConstraintLayoutBaseScope.HorizontalAnchor,
+        margin: Dp,
+        goneMargin: Dp
+    ) {
+        val targetAnchorName = AnchorFunctions.horizontalAnchorIndexToAnchorName(anchor.index)
+        val constraintArray = CLArray(charArrayOf()).apply {
+            add(CLString.from(anchor.id.toString()))
+            add(CLString.from(targetAnchorName))
+            add(CLNumber(margin.value))
+            add(CLNumber(goneMargin.value))
+        }
+        containerObject.put("lastBaseline", constraintArray)
+    }
 }

constraintlayout/compose/src/main/java/androidx/constraintlayout/compose/ConstraintLayout.kt

@@ -55,6 +55,7 @@ import androidx.compose.ui.graphics.TransformOrigin
 import androidx.compose.ui.graphics.drawscope.DrawScope
 import androidx.compose.ui.layout.AlignmentLine
 import androidx.compose.ui.layout.FirstBaseline
+import androidx.compose.ui.layout.LastBaseline
 import androidx.compose.ui.layout.LayoutIdParentData
 import androidx.compose.ui.layout.Measurable
 import androidx.compose.ui.layout.MeasurePolicy
@@ -1210,6 +1211,8 @@ internal open class Measurer(
         val baseline =
             if (currentPlaceable != null && state.isBaselineNeeded(constraintWidget)) {
                 currentPlaceable[FirstBaseline]
+            } else if (currentPlaceable != null && state.isLastBaselineNeeded(constraintWidget)) {
+                currentPlaceable[LastBaseline]
             } else {
                 AlignmentLine.Unspecified
             }

constraintlayout/compose/src/main/java/androidx/constraintlayout/compose/ConstraintLayoutBaseScope.kt

@@ -19,6 +19,7 @@ package androidx.constraintlayout.compose
 import androidx.compose.runtime.Immutable
 import androidx.compose.runtime.Stable
 import androidx.compose.ui.layout.FirstBaseline
+import androidx.compose.ui.layout.LastBaseline
 import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
 import androidx.constraintlayout.core.parser.CLArray
@@ -105,6 +106,19 @@ abstract class ConstraintLayoutBaseScope internal constructor(extendFrom: CLObje
         val reference: LayoutReference
     )
 
+    /**
+     * Represents a horizontal anchor corresponding to the [LastBaseline] of a layout that other
+     * layouts can link to in their `Modifier.constrainAs` or `constrain` blocks.
+     *
+     * @param reference The [LayoutReference] that this anchor belongs to.
+     */
+    // TODO(popam): investigate if this can be just a HorizontalAnchor
+    @Stable
+    data class LastBaselineAnchor internal constructor(
+        internal val id: Any,
+        val reference: LayoutReference
+    )
+
     /**
      * Specifies additional constraints associated to the horizontal chain identified with [ref].
      */
@@ -1740,6 +1754,12 @@ class ConstrainedLayoutReference(override val id: Any) : LayoutReference(id) {
      */
     @Stable
     val baseline = ConstraintLayoutBaseScope.BaselineAnchor(id, this)
+
+    /**
+     * The lastBaseline anchor of this layout.
+     */
+    @Stable
+    val lastBaseline = ConstraintLayoutBaseScope.LastBaselineAnchor(id, this)
 }
 
 /**
@@ -1918,6 +1938,7 @@ class VerticalAlign internal constructor(
         val Bottom = VerticalAlign("bottom")
         val Center = VerticalAlign("center")
         val Baseline = VerticalAlign("baseline")
+        val LastBaseline = VerticalAlign("lastBaseline")
     }
 }
 

constraintlayout/compose/src/main/java/androidx/constraintlayout/compose/ConstraintScopeCommon.kt

@@ -18,6 +18,7 @@ package androidx.constraintlayout.compose
 
 import android.util.Log
 import androidx.compose.ui.layout.FirstBaseline
+import androidx.compose.ui.layout.LastBaseline
 import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
 import androidx.constraintlayout.core.parser.CLArray
@@ -64,6 +65,15 @@ interface HorizontalAnchorable {
         margin: Dp = 0.dp,
         goneMargin: Dp = 0.dp
     )
+
+    /**
+     * Adds a link towards a [ConstraintLayoutBaseScope.LastBaselineAnchor].
+     */
+    fun linkTo(
+        anchor: ConstraintLayoutBaseScope.LastBaselineAnchor,
+        margin: Dp = 0.dp,
+        goneMargin: Dp = 0.dp
+    )
 }
 
 @JvmDefaultWithCompatibility
@@ -81,6 +91,49 @@ interface BaselineAnchorable {
         goneMargin: Dp = 0.dp
     )
 
+    /**
+     * Adds a link towards a [ConstraintLayoutBaseScope.LastBaselineAnchor].
+     */
+    fun linkTo(
+        anchor: ConstraintLayoutBaseScope.LastBaselineAnchor,
+        margin: Dp = 0.dp,
+        goneMargin: Dp = 0.dp
+    )
+
+    /**
+     * Adds a link towards a [ConstraintLayoutBaseScope.HorizontalAnchor].
+     */
+    fun linkTo(
+        anchor: ConstraintLayoutBaseScope.HorizontalAnchor,
+        margin: Dp = 0.dp,
+        goneMargin: Dp = 0.dp
+    )
+}
+
+@JvmDefaultWithCompatibility
+/**
+ * Represents the [LastBaseline] of a layout that can be anchored
+ * using [linkTo] in their `Modifier.constrainAs` blocks.
+ */
+interface LastBaselineAnchorable {
+    /**
+     * Adds a link towards a [ConstraintLayoutBaseScope.BaselineAnchor].
+     */
+    fun linkTo(
+        anchor: ConstraintLayoutBaseScope.BaselineAnchor,
+        margin: Dp = 0.dp,
+        goneMargin: Dp = 0.dp
+    )
+
+    /**
+     * Adds a link towards a [ConstraintLayoutBaseScope.LastBaselineAnchor].
+     */
+    fun linkTo(
+        anchor: ConstraintLayoutBaseScope.LastBaselineAnchor,
+        margin: Dp = 0.dp,
+        goneMargin: Dp = 0.dp
+    )
+
     /**
      * Adds a link towards a [ConstraintLayoutBaseScope.HorizontalAnchor].
      */
@@ -147,6 +200,20 @@ internal abstract class BaseHorizontalAnchorable(
         }
         containerObject.put(anchorName, constraintArray)
     }
+
+    final override fun linkTo(
+        anchor: ConstraintLayoutBaseScope.LastBaselineAnchor,
+        margin: Dp,
+        goneMargin: Dp
+    ) {
+        val constraintArray = CLArray(charArrayOf()).apply {
+            add(CLString.from(anchor.id.toString()))
+            add(CLString.from("lastBaseline"))
+            add(CLNumber(margin.value))
+            add(CLNumber(goneMargin.value))
+        }
+        containerObject.put(anchorName, constraintArray)
+    }
 }
 
 internal object AnchorFunctions {