Merge predictive-back fixes

CHANGELOG.md

@@ -58,6 +58,16 @@ are no binary releases; "version" tracks the shared `version` in the root build
 
 ### Fixed
 
+- **`identity`** — A committed predictive back no longer snaps the surface back
+  to full size before it leaves. `Modifier.predictiveBack()` now holds the
+  preview transform after `onBack`, and the new `predictiveBackExit()` exit
+  fades and keeps shrinking from there; pair them on the surface's
+  `AnimatedVisibility` instead of a full-size slide-out. Pass that
+  `AnimatedVisibility`'s `visible` to `predictiveBack(visible = …)` (or
+  `CollapsingScaffold(visible = …)`) so the preview is dropped as soon as the
+  surface is shown again — reopened mid-exit it no longer appears shrunk — and
+  settles back when a back leaves it in place. Without it the preview is held
+  for a fixed second.
 - **`core-crash`** — The prefilled crash issue is filed in English again. Its
   title and body came from string resources, so a crash on a French phone
   opened the tracker with a French issue — unreadable to whoever has to triage

components/src/main/kotlin/de/jeanlucmakiola/floret/components/CollapsingScaffold.kt

@@ -45,7 +45,9 @@ import de.jeanlucmakiola.floret.identity.predictiveBack
  * Optional extras, all defaulting to the bare scaffold so existing callers are
  * unchanged: [actions] adds trailing app-bar items; [snackbarHost] hosts
  * transient messages; [predictiveBack] (off by default) wires the gesture
- * preview to [onBack] for full-screen surfaces that want it.
+ * preview to [onBack] for full-screen surfaces that want it, with [visible]
+ * passed through to [Modifier.predictiveBack] for a surface that is shown and
+ * hidden in place.
  *
  * Set [scrollable] to false when [content] brings its own scrolling container.
  * The default column scrolls as a whole, which composes every row up front —
@@ -65,6 +67,7 @@ fun CollapsingScaffold(
     modifier: Modifier = Modifier,
     largeTopBar: Boolean = true,
     predictiveBack: Boolean = false,
+    visible: Boolean? = null,
     scrollable: Boolean = true,
     actions: @Composable RowScope.() -> Unit = {},
     snackbarHost: @Composable () -> Unit = {},
@@ -77,7 +80,7 @@ fun CollapsingScaffold(
     }
     Scaffold(
         modifier = modifier
-            .then(if (predictiveBack) Modifier.predictiveBack(onBack = onBack) else Modifier)
+            .then(if (predictiveBack) Modifier.predictiveBack(onBack = onBack, visible = visible) else Modifier)
             .fillMaxSize()
             .background(MaterialTheme.colorScheme.surface)
             .nestedScroll(scrollBehavior.nestedScrollConnection),

identity/src/main/kotlin/de/jeanlucmakiola/floret/identity/Motion.kt

@@ -3,22 +3,31 @@ package de.jeanlucmakiola.floret.identity
 import android.provider.Settings
 import androidx.activity.BackEventCompat
 import androidx.activity.compose.PredictiveBackHandler
+import androidx.compose.animation.ExitTransition
 import androidx.compose.animation.animateContentSize
 import androidx.compose.animation.core.Animatable
 import androidx.compose.animation.core.FastOutSlowInEasing
+import androidx.compose.animation.fadeOut
+import androidx.compose.animation.scaleOut
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material3.ExperimentalMaterial3ExpressiveApi
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberUpdatedState
 import androidx.compose.runtime.setValue
+import androidx.compose.runtime.withFrameNanos
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.graphicsLayer
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.unit.IntSize
 import androidx.compose.ui.unit.dp
+import kotlinx.coroutines.NonCancellable
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.withContext
 import kotlin.coroutines.cancellation.CancellationException
 
 /**
@@ -59,7 +68,10 @@ fun Modifier.animateContentSizeMotion(reduceMotion: Boolean = rememberReduceMoti
  * The standard Android predictive-back transform for a full-screen surface: as
  * the back gesture is dragged, the surface scales toward ~90%, shifts toward the
  * swiped edge and rounds its corners, previewing what's behind. Completing the
- * gesture invokes [onBack]; cancelling springs it back.
+ * gesture invokes [onBack] and keeps the preview transform, so the surface
+ * leaves from where the finger let go instead of snapping back to full size —
+ * pair it with [predictiveBackExit] on the surface's own exit. Cancelling
+ * springs it back.
  *
  * A drop-in replacement for a screen's own `BackHandler(onBack)` — register it
  * once and apply the returned [Modifier] to that screen's root so the preview
@@ -70,15 +82,27 @@ fun Modifier.animateContentSizeMotion(reduceMotion: Boolean = rememberReduceMoti
  *
  * @param enabled gate the handler — e.g. set false while a screen's own inner
  *   back (a sub-section) should take the gesture instead.
+ * @param visible whether the surface is currently shown — typically the
+ *   `visible` of the `AnimatedVisibility` it lives in. The preview is held while
+ *   the surface leaves and dropped the moment it is shown again, so reopening it
+ *   mid-exit never starts from the shrunk state; a back that leaves it visible
+ *   settles back. Null when the caller doesn't track it: the preview is then held
+ *   for a fixed time before settling back.
  */
 @Composable
 fun Modifier.predictiveBack(
     onBack: () -> Unit,
     enabled: Boolean = true,
+    visible: Boolean? = null,
     reduceMotion: Boolean = rememberReduceMotion(),
 ): Modifier {
     val progress = remember { Animatable(0f) }
     var fromLeftEdge by remember { mutableStateOf(true) }
+    val currentVisible by rememberUpdatedState(visible)
+
+    LaunchedEffect(visible) {
+        if (visible == true) progress.snapTo(0f)
+    }
 
     PredictiveBackHandler(enabled = enabled) { events ->
         try {
@@ -87,9 +111,18 @@ fun Modifier.predictiveBack(
                 progress.snapTo(FastOutSlowInEasing.transform(event.progress))
             }
             onBack()
-            progress.snapTo(0f)
-        } catch (_: CancellationException) {
-            progress.animateTo(0f)
+            if (currentVisible == null) {
+                delay(COMMIT_SETTLE_DELAY_MILLIS)
+                progress.animateTo(0f)
+            } else {
+                // Two frames guarantee the recomposition that onBack triggered.
+                repeat(2) { withFrameNanos { } }
+                if (currentVisible == true) progress.animateTo(0f)
+            }
+        } catch (e: CancellationException) {
+            // A cancelled gesture also cancels this job, so the spring-back must not be.
+            withContext(NonCancellable) { progress.animateTo(0f) }
+            throw e
         }
     }
 
@@ -104,3 +137,26 @@ fun Modifier.predictiveBack(
         clip = p > 0f
     }
 }
+
+/**
+ * How long a committed preview is held before it settles back when the caller
+ * doesn't pass `visible` — past any exit the surface would play.
+ */
+private const val COMMIT_SETTLE_DELAY_MILLIS = 1_000L
+
+/**
+ * The exit for a surface closed through [predictiveBack]: it fades while it keeps
+ * shrinking from the preview's scale, rather than growing back and sliding off
+ * at full size. Also reads right for a close without a gesture. Fade only under
+ * reduced motion.
+ */
+@OptIn(ExperimentalMaterial3ExpressiveApi::class)
+@Composable
+fun predictiveBackExit(reduceMotion: Boolean = rememberReduceMotion()): ExitTransition {
+    val fade = fadeOut(MaterialTheme.motionScheme.defaultEffectsSpec())
+    return if (reduceMotion) {
+        fade
+    } else {
+        fade + scaleOut(MaterialTheme.motionScheme.defaultSpatialSpec(), targetScale = 0.9f)
+    }
+}