Stop rescanning message bodies for emoji only on every recomposition (#7531)

Deciding whether a text message is emoji only compares the formatted body to
the plain one and runs a grapheme scan over the whole message. Nothing was
remembered, so both ran again on every recomposition of every visible message.

Remember the decision against the body and the formatted body. The preview
branch moves into the same computation, so the composable wrapper around
containsOnlyEmojis, which had a single caller and existed only to read
LocalInspectionMode, is no longer needed.

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/timeline/components/event/TimelineItemTextView.kt

@@ -15,7 +15,9 @@ import androidx.compose.material3.LocalContentColor
 import androidx.compose.material3.LocalTextStyle
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalInspectionMode
 import androidx.compose.ui.semantics.contentDescription
 import androidx.compose.ui.semantics.semantics
 import androidx.compose.ui.tooling.preview.Preview
@@ -23,6 +25,7 @@ import androidx.compose.ui.tooling.preview.PreviewParameter
 import io.element.android.compound.theme.ElementTheme
 import io.element.android.features.messages.impl.timeline.components.layout.ContentAvoidingLayout
 import io.element.android.features.messages.impl.timeline.components.layout.ContentAvoidingLayoutData
+import io.element.android.features.messages.impl.timeline.model.event.AN_EMOJI_ONLY_TEXT
 import io.element.android.features.messages.impl.timeline.model.event.TimelineItemTextBasedContent
 import io.element.android.features.messages.impl.timeline.model.event.TimelineItemTextBasedContentPreviewParam
 import io.element.android.features.messages.impl.timeline.model.event.aTimelineItemTextContent
@@ -47,8 +50,13 @@ fun TimelineItemTextView(
     // The View <-> Compose interop is not working well with Compose UI tests (it loops indefinitely), so we skip it in the UI test mode.
     if (LocalUiTestMode.current) return
 
-    val emojiOnly = content.formattedBody.toString() == content.body &&
-        content.body.replace(" ", "").containsOnlyEmojis()
+    val isInPreview = LocalInspectionMode.current
+    val emojiOnly = remember(content.body, content.formattedBody, isInPreview) {
+        content.formattedBody.toString() == content.body &&
+            content.body.replace(" ", "").let { body ->
+                if (isInPreview) body == AN_EMOJI_ONLY_TEXT else body.containsOnlyEmojis()
+            }
+    }
     val textStyle = when {
         emojiOnly -> ElementTheme.typography.fontHeadingXlRegular
         else -> ElementTheme.typography.fontBodyLgRegular

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/utils/Emoji.kt

@@ -8,25 +8,15 @@
 
 package io.element.android.features.messages.impl.utils
 
-import androidx.compose.runtime.Composable
-import androidx.compose.ui.platform.LocalInspectionMode
 import com.sigpwned.emoji4j.core.Grapheme.Type.EMOJI
 import com.sigpwned.emoji4j.core.Grapheme.Type.PICTOGRAPHIC
 import com.sigpwned.emoji4j.core.GraphemeMatchResult
 import com.sigpwned.emoji4j.core.GraphemeMatcher
-import io.element.android.features.messages.impl.timeline.model.event.AN_EMOJI_ONLY_TEXT
 
 /**
  * Returns true if the string consists exclusively of "emoji or pictographic graphemes".
  */
-@Composable
-fun String.containsOnlyEmojis(): Boolean {
-    if (LocalInspectionMode.current) return this == AN_EMOJI_ONLY_TEXT
-    if (isEmpty()) return false
-    return containsOnlyEmojisInternal()
-}
-
-internal fun String.containsOnlyEmojisInternal(): Boolean {
+internal fun String.containsOnlyEmojis(): Boolean {
     val matcher = GraphemeMatcher(this)
     var m: GraphemeMatchResult? = null
     var contiguous = true

features/messages/impl/src/test/kotlin/io/element/android/features/messages/impl/utils/EmojiTest.kt

@@ -16,23 +16,23 @@ class EmojiTest {
     @Test
     fun validEmojis() {
         // Simple single/multiple single-codepoint emojis per string
-        assertTrue("👍".containsOnlyEmojisInternal())
-        assertTrue("😀".containsOnlyEmojisInternal())
-        assertTrue("🙂🙁".containsOnlyEmojisInternal())
-        assertTrue("👁❤️🍝".containsOnlyEmojisInternal()) // 👁 is a pictographic
-        assertTrue("👨‍👩‍👦1️⃣🚀👳🏾‍♂️🪩".containsOnlyEmojisInternal())
-        assertTrue("🌍🌎🌏".containsOnlyEmojisInternal())
+        assertTrue("👍".containsOnlyEmojis())
+        assertTrue("😀".containsOnlyEmojis())
+        assertTrue("🙂🙁".containsOnlyEmojis())
+        assertTrue("👁❤️🍝".containsOnlyEmojis()) // 👁 is a pictographic
+        assertTrue("👨‍👩‍👦1️⃣🚀👳🏾‍♂️🪩".containsOnlyEmojis())
+        assertTrue("🌍🌎🌏".containsOnlyEmojis())
 
         // Awkward multi-codepoint graphemes
-        assertTrue("🧑‍🧑‍🧒‍🧒".containsOnlyEmojisInternal())
-        assertTrue("🏴‍☠".containsOnlyEmojisInternal())
-        assertTrue("👩🏿‍🔧".containsOnlyEmojisInternal())
+        assertTrue("🧑‍🧑‍🧒‍🧒".containsOnlyEmojis())
+        assertTrue("🏴‍☠".containsOnlyEmojis())
+        assertTrue("👩🏿‍🔧".containsOnlyEmojis())
 
-        Assert.assertFalse("".containsOnlyEmojisInternal())
-        Assert.assertFalse(" ".containsOnlyEmojisInternal())
-        Assert.assertFalse("🙂 🙁".containsOnlyEmojisInternal())
-        Assert.assertFalse(" 🙂 🙁 ".containsOnlyEmojisInternal())
-        Assert.assertFalse("Hello".containsOnlyEmojisInternal())
-        Assert.assertFalse("Hello 👋".containsOnlyEmojisInternal())
+        Assert.assertFalse("".containsOnlyEmojis())
+        Assert.assertFalse(" ".containsOnlyEmojis())
+        Assert.assertFalse("🙂 🙁".containsOnlyEmojis())
+        Assert.assertFalse(" 🙂 🙁 ".containsOnlyEmojis())
+        Assert.assertFalse("Hello".containsOnlyEmojis())
+        Assert.assertFalse("Hello 👋".containsOnlyEmojis())
     }
 }