IssueTracker

Small bump for Tor :) Still the case with AGP 4.1 and now that CL 2.0 is out it triggers a lot more false warnings as this is used a lot more.

Following example will trigger unused id view1 when it's actually used.

    <Space
        android:id="@+id/view1"
        android:layout_width="0dp"
        android:layout_height="0dp" />

    <androidx.constraintlayout.helper.widget.Flow
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:constraint_referenced_ids="view1"
        app:flow_maxElementsWrap="3"
        app:flow_wrapMode="aligned" />

Fixed by Change-Id: Id116185535fc955bc7de091e318cdcd7bbd00343 for 4.2. Also considering cherry-pick into 4.1 RC. Thanks for the bump and sorry for the delay.

When we use lint gradle command (gradlew :app:lint) then we receive exactly the same issue:

Error: This view is not constrained. It only has designtime positions,
so it will jump to (0,0) at runtime unless you add the constraints [MissingConstraints]

Tested with Android Gradle Plugin 4.1.2 and 4.2.0-beta04

Is there any way you can create a reproducible scenario for this?

The simplest reproductible scenario in Android Studio 4.1.2 (but probably also in 4.2.0-beta04) is:

1. Create a new project with Empty Activity
2. Modify activity_main layout to use Flow with constraint_referenced_ids and remove unnecessary constraints from TextView

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.constraintlayout.helper.widget.Flow
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:constraint_referenced_ids="someTextView"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/someTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />

</androidx.constraintlayout.widget.ConstraintLayout>

3. In terminal run gradlew :app:lint

Thanks for the repro project! I can reproduce this in 4.2 but not in 7.0. Let me see if I can find the fix and evaluate whether it's safe enough to put into 4.2.

Uhm no, that fix is way too risky this late in the 4.2 cycle; it basically switched us over from batch collection of id declarations to using the resource repository -- it's a 4000+ line plus CL (https://cs.android.com/android-studio/platform/tools/base/+/64857dabc30ce1ac5fe64c4c89439f93854a47cc), which itself sits on top of other required CLs.

I think what I'll do for 4.2 is to try to disable part or all of that check.

Actually, I went to look into this and I realized that we're talking about different things.

This bug was about the unused resource detector not realizing that a view referenced from a constraint_referenced_ids attribute is actually used.

However, the bug I reproduced with your example is a separate one, the MissingConstraints one, which complains if you haven't both horizontally and vertically constrained your id.

I've filed a new bug to track this, here: https://issuetracker.google.com/181056543

Marking this (unused resource handling for constraint_referenced_ids again).