use custom JsonAdapter to be compatible with instances that have a custom subscribing feature

app/src/main/java/com/keylesspalace/tusky/entity/Relationship.kt

@@ -15,7 +15,9 @@
 
 package com.keylesspalace.tusky.entity
 
+import com.google.gson.annotations.JsonAdapter
 import com.google.gson.annotations.SerializedName
+import com.keylesspalace.tusky.json.GuardedBooleanAdapter
 
 data class Relationship(
     val id: String,
@@ -26,7 +28,11 @@ data class Relationship(
     @SerializedName("muting_notifications") val mutingNotifications: Boolean,
     val requested: Boolean,
     @SerializedName("showing_reblogs") val showingReblogs: Boolean,
-    val subscribing: Boolean? = null, // Pleroma extension
+    /* Pleroma extension, same as 'notifying' on Mastodon.
+     * Some instances like qoto.org have a custom subscription feature where 'subscribing' is a json object,
+     * so we use the custom GuardedBooleanAdapter to ignore the field if it is not a boolean.
+     */
+    @JsonAdapter(GuardedBooleanAdapter::class) val subscribing: Boolean? = null,
     @SerializedName("domain_blocking") val blockingDomain: Boolean,
     val note: String?, // nullable for backward compatibility / feature detection
     val notifying: Boolean? // since 3.3.0rc

app/src/main/java/com/keylesspalace/tusky/json/GuardedBooleanAdapter.kt

@@ -0,0 +1,33 @@
+/* Copyright 2022 Tusky Contributors
+ *
+ * This file is a part of Tusky.
+ *
+ * This program is free software; you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation; either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * Tusky is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
+ * the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with Tusky; if not,
+ * see <http://www.gnu.org/licenses>. */
+
+package com.keylesspalace.tusky.json
+
+import com.google.gson.JsonDeserializationContext
+import com.google.gson.JsonDeserializer
+import com.google.gson.JsonElement
+import com.google.gson.JsonParseException
+import java.lang.reflect.Type
+
+class GuardedBooleanAdapter : JsonDeserializer<Boolean?> {
+    @Throws(JsonParseException::class)
+    override fun deserialize(json: JsonElement, typeOfT: Type, context: JsonDeserializationContext): Boolean? {
+        return if (json.isJsonObject) {
+            null
+        } else {
+            json.asBoolean
+        }
+    }
+}

app/src/test/java/com/keylesspalace/tusky/json/GuardedBooleanAdapterTest.kt

@@ -0,0 +1,130 @@
+package com.keylesspalace.tusky.json
+
+import com.google.gson.Gson
+import com.keylesspalace.tusky.entity.Relationship
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class GuardedBooleanAdapterTest {
+
+    private val gson = Gson()
+
+    @Test
+    fun `should deserialize Relationship when attribute 'subscribing' is a boolean`() {
+        val jsonInput = """
+            {
+              "id": "1",
+              "following": true,
+              "showing_reblogs": true,
+              "notifying": false,
+              "followed_by": true,
+              "blocking": false,
+              "blocked_by": false,
+              "muting": false,
+              "muting_notifications": false,
+              "requested": false,
+              "domain_blocking": false,
+              "endorsed": false,
+              "note": "Hi",
+              "subscribing": true
+            }
+        """.trimIndent()
+
+        assertEquals(
+            Relationship(
+                id = "1",
+                following = true,
+                followedBy = true,
+                blocking = false,
+                muting = false,
+                mutingNotifications = false,
+                requested = false,
+                showingReblogs = true,
+                subscribing = true,
+                blockingDomain = false,
+                note = "Hi",
+                notifying = false
+            ),
+            gson.fromJson(jsonInput, Relationship::class.java)
+        )
+    }
+
+    @Test
+    fun `should deserialize Relationship when attribute 'subscribing' is an object`() {
+        val jsonInput = """
+            {
+              "id": "2",
+              "following": true,
+              "showing_reblogs": true,
+              "notifying": false,
+              "followed_by": true,
+              "blocking": false,
+              "blocked_by": false,
+              "muting": false,
+              "muting_notifications": false,
+              "requested": false,
+              "domain_blocking": false,
+              "endorsed": false,
+              "note": "Hi",
+              "subscribing": { }
+            }
+        """.trimIndent()
+
+        assertEquals(
+            Relationship(
+                id = "2",
+                following = true,
+                followedBy = true,
+                blocking = false,
+                muting = false,
+                mutingNotifications = false,
+                requested = false,
+                showingReblogs = true,
+                subscribing = null,
+                blockingDomain = false,
+                note = "Hi",
+                notifying = false
+            ),
+            gson.fromJson(jsonInput, Relationship::class.java)
+        )
+    }
+
+    @Test
+    fun `should deserialize Relationship when attribute 'subscribing' does not exist`() {
+        val jsonInput = """
+            {
+              "id": "3",
+              "following": true,
+              "showing_reblogs": true,
+              "notifying": false,
+              "followed_by": true,
+              "blocking": false,
+              "blocked_by": false,
+              "muting": false,
+              "muting_notifications": false,
+              "requested": false,
+              "domain_blocking": false,
+              "endorsed": false,
+              "note": "Hi"
+            }
+        """.trimIndent()
+
+        assertEquals(
+            Relationship(
+                id = "3",
+                following = true,
+                followedBy = true,
+                blocking = false,
+                muting = false,
+                mutingNotifications = false,
+                requested = false,
+                showingReblogs = true,
+                subscribing = null,
+                blockingDomain = false,
+                note = "Hi",
+                notifying = false
+            ),
+            gson.fromJson(jsonInput, Relationship::class.java)
+        )
+    }
+}