Various improvements to the JSON syntax (#246)

- add support for variables, generators, lists
- add support for macros
- add support for variable overrides
- added ScreenExample12

Author: camaelon

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

@@ -117,6 +117,11 @@ internal fun rememberConstraintLayoutMeasurePolicy(
                         }
                     }
                 }
+
+                override fun override(name: String, value: Float) : ConstraintSet {
+                    // nothing here yet
+                    return this
+                }
             }
             val layoutSize = measurer.performMeasure(
                 constraints,
@@ -1231,14 +1236,32 @@ interface ConstraintSet {
      * Applies the [ConstraintSet] to a state.
      */
     fun applyTo(state: State, measurables: List<Measurable>)
+
+    fun override(name: String, value: Float) : ConstraintSet
 }
 
 fun ConstraintSet(@Language("json5") content : String) = object : ConstraintSet {
+    private val overridedVariables = HashMap<String, Float>()
+
     override fun applyTo(state: State, measurables: List<Measurable>) {
         measurables.forEach { measurable ->
-            state.map((measurable.layoutId ?: createId()), measurable)
+            var layoutId = measurable.layoutId ?: measurable.constraintLayoutId ?: createId()
+            state.map(layoutId, measurable)
+            var tag = measurable.constraintLayoutTag
+            if (tag != null && tag is String && layoutId is String) {
+                state.setTag(layoutId, tag)
+            }
         }
-        parseJSON(content, state)
+        val layoutVariables = LayoutVariables()
+        for (name in overridedVariables.keys) {
+            layoutVariables.putOverride(name, overridedVariables[name]!!)
+        }
+        parseJSON(content, state, layoutVariables)
+    }
+
+    override fun override(name: String, value: Float) : ConstraintSet {
+        overridedVariables[name] = value
+        return this
     }
 }
 
@@ -1254,6 +1277,11 @@ fun ConstraintSet(description: ConstraintSetScope.() -> Unit) = object : Constra
         scope.description()
         scope.applyTo(state)
     }
+
+    override fun override(name: String, value: Float) : ConstraintSet {
+        // nothing yet
+        return this
+    }
 }
 
 /**

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

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2021 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.constraintlayout.compose
+
+import androidx.compose.runtime.Immutable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.layout.Measurable
+import androidx.compose.ui.layout.ParentDataModifier
+import androidx.compose.ui.layout.layoutId
+import androidx.compose.ui.platform.InspectorInfo
+import androidx.compose.ui.platform.InspectorValueInfo
+import androidx.compose.ui.platform.debugInspectorInfo
+import androidx.compose.ui.unit.Density
+
+fun Modifier.layoutId(layoutId: String, tag: String) = this.then(
+    ConstraintLayoutTag(
+        constraintLayoutId = layoutId,
+        constraintLayoutTag = tag,
+        inspectorInfo = debugInspectorInfo {
+            name = "constraintLayoutId"
+            value = layoutId
+        }
+    )
+)
+
+@Immutable
+private class ConstraintLayoutTag(
+    override val constraintLayoutTag: String,
+    override val constraintLayoutId: String,
+    inspectorInfo: InspectorInfo.() -> Unit
+) : ParentDataModifier, ConstraintLayoutTagParentData, InspectorValueInfo(inspectorInfo) {
+    override fun Density.modifyParentData(parentData: Any?): Any? {
+        return this@ConstraintLayoutTag
+    }
+
+    override fun hashCode(): Int =
+        constraintLayoutTag.hashCode()
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        val otherModifier = other as? ConstraintLayoutTag ?: return false
+        return constraintLayoutTag == otherModifier.constraintLayoutTag
+    }
+
+    override fun toString(): String =
+        "ConstraintLayoutTag(id=$constraintLayoutTag)"
+}
+
+interface ConstraintLayoutTagParentData {
+    val constraintLayoutId: String
+    val constraintLayoutTag: String
+}
+
+val Measurable.constraintLayoutTag: Any?
+    get() = (parentData as? ConstraintLayoutTagParentData)?.constraintLayoutTag
+
+val Measurable.constraintLayoutId: Any?
+    get() = (parentData as? ConstraintLayoutTagParentData)?.constraintLayoutId