Keep single-line Android placeholders from inflating field height

docs/api-migrations.md

@@ -13,6 +13,21 @@ inventory check is temporarily deferred until that inventory recognizes
 that renderer. The MyGo, Web, Apple, Android and shared ABI regressions remain
 covered separately.
 
+## Unreleased: Android single-line text placeholders
+
+Android placeholders now follow their control's line policy: `text-field`,
+`secure-field`, `input`, `search-field` and `combobox` keep placeholders on one
+line and ellipsize overflow. `textarea` placeholders continue to wrap. Previously
+a narrow or zero-width field could wrap its placeholder character by character,
+inflating a single-line control and its containing row to hundreds of dp even
+though the editable text itself was single-line.
+
+The wire format, default control height and `grow` behavior are unchanged. For
+example, keep sending `{"op":"set-prop","id":2,"property":"placeholder","value":"Search this book…"}`;
+no fixed height or placeholder rewrite is necessary. Applications must still
+provide usable width or responsive toolbar alternatives: this correction does
+not make a field usable when other row children consume all available width.
+
 ## Unreleased: Apple normalizes all floating wire properties
 
 Apple now normalizes integral JSON numbers to its floating retained value for

platform/android/lui/src/main/kotlin/dev/lui/LuiNodeView.kt

@@ -1279,7 +1279,13 @@ private fun LuiTextControl(
         }
     }
     val placeholderContent: (@Composable () -> Unit)? =
-        node.propString("placeholder")?.let { p -> { Text(p) } }
+        node.propString("placeholder")?.let { p -> {
+            Text(
+                p,
+                maxLines = if (multiline) Int.MAX_VALUE else 1,
+                overflow = if (multiline) TextOverflow.Clip else TextOverflow.Ellipsis,
+            )
+        } }
     val transformation = if (secure) {
         androidx.compose.ui.text.input.PasswordVisualTransformation()
     } else {

platform/android/lui/src/test/kotlin/dev/lui/LuiTextControlLayoutTest.kt

@@ -0,0 +1,63 @@
+package dev.lui
+
+import androidx.compose.foundation.layout.Box
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.layout.onGloballyPositioned
+import androidx.compose.ui.platform.ComposeView
+import androidx.compose.ui.platform.LocalView
+import androidx.compose.ui.semantics.SemanticsNode
+import androidx.compose.ui.semantics.SemanticsOwner
+import androidx.compose.ui.semantics.SemanticsProperties
+import androidx.compose.ui.semantics.getOrNull
+import app.cash.paparazzi.DeviceConfig
+import app.cash.paparazzi.Paparazzi
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Rule
+import org.junit.Test
+
+class LuiTextControlLayoutTest {
+    @get:Rule val paparazzi = Paparazzi(deviceConfig = DeviceConfig.PIXEL_5.copy(softButtons = false))
+
+    private fun nodes(root: SemanticsNode): List<SemanticsNode> =
+        listOf(root) + root.children.flatMap(::nodes)
+
+    @Test fun narrowPlaceholderRespectsTextControlLinePolicy() {
+        for (kind in listOf("text-field", "secure-field", "input", "search-field", "combobox", "textarea")) {
+            val backend = LuiBackend()
+            val ops = mutableListOf("""{"op":"create-node","id":1,"kind":"column"}""")
+            for (id in 2..3) {
+                ops.add("""{"op":"create-node","id":$id,"kind":"$kind"}""")
+                ops.add("""{"op":"set-prop","id":$id,"property":"width","value":80}""")
+                ops.add("""{"op":"insert-child","parent":1,"child":$id,"index":${id - 2}}""")
+            }
+            ops.add("""{"op":"set-prop","id":3,"property":"placeholder","value":"A long placeholder that cannot fit in one narrow line"}""")
+            assertTrue(backend.applyBatch("""{"generation":1,"ops":[${ops.joinToString(",")}]}"""))
+            var heights = emptyList<Int>()
+            val view = ComposeView(paparazzi.context).apply { setContent {
+                val native = LocalView.current
+                LuiTheme {
+                    Box(Modifier.onGloballyPositioned {
+                        val owner = native.javaClass.methods.first { it.name == "getSemanticsOwner" }
+                            .invoke(native) as SemanticsOwner
+                        heights = nodes(owner.unmergedRootSemanticsNode)
+                            .filter { it.config.getOrNull(SemanticsProperties.EditableText) != null }
+                            .map { it.size.height }
+                    }) { backend.Content(1) }
+                }
+            } }
+            try {
+                paparazzi.snapshot(view, name = "narrow-$kind-placeholder")
+                assertEquals("both $kind controls were measured", 2, heights.size)
+                assertTrue("empty $kind has an intrinsic height", heights[0] > 0)
+                if (kind == "textarea") {
+                    assertTrue("textarea placeholder still wraps: $heights", heights[1] > heights[0])
+                } else {
+                    assertEquals("single-line $kind placeholder must not inflate height", heights[0], heights[1])
+                }
+            } finally {
+                view.disposeComposition()
+            }
+        }
+    }
+}