[terminal] IJPL-182482 Report backend document update latency

Report it with the length of the updated text.

GitOrigin-RevId: bb89d8c5ad1d666147b1b431430608f050fccd70

plugins/terminal/backend/src/com/intellij/terminal/backend/StateAwareTerminalSession.kt

@@ -16,6 +16,7 @@ import org.jetbrains.plugins.terminal.block.reworked.*
 import org.jetbrains.plugins.terminal.block.ui.TerminalUiUtils
 import org.jetbrains.plugins.terminal.fus.ReworkedTerminalUsageCollector
 import kotlin.coroutines.cancellation.CancellationException
+import kotlin.time.TimeSource
 
 /**
  * TerminalSession implementation that stores the state of the [delegate] session output.
@@ -81,9 +82,8 @@ internal class StateAwareTerminalSession(private val delegate: TerminalSession)
   private fun handleEvent(event: TerminalOutputEvent) {
     when (event) {
       is TerminalContentUpdatedEvent -> {
-        val styles = event.styles.map { it.toStyleRange() }
         val model = getCurrentOutputModel()
-        model.updateContent(event.startLineLogicalIndex, event.text, styles)
+        updateOutputModelContent(model, event)
 
         val latency = event.readTime?.elapsedNow()
         if (latency != null) {
@@ -128,4 +128,16 @@ internal class StateAwareTerminalSession(private val delegate: TerminalSession)
   private fun getCurrentOutputModel(): TerminalOutputModel {
     return if (sessionModel.terminalState.value.isAlternateScreenBuffer) alternateBufferModel else outputModel
   }
+
+  private fun updateOutputModelContent(model: TerminalOutputModel, event: TerminalContentUpdatedEvent) {
+    val startTime = TimeSource.Monotonic.markNow()
+
+    val styles = event.styles.map { it.toStyleRange() }
+    model.updateContent(event.startLineLogicalIndex, event.text, styles)
+
+    ReworkedTerminalUsageCollector.logBackendDocumentUpdateLatency(
+      textLength = event.text.length,
+      duration = startTime.elapsedNow(),
+    )
+  }
 }

plugins/terminal/src/org/jetbrains/plugins/terminal/fus/ReworkedTerminalUsageCollector.kt

@@ -75,6 +75,12 @@ object ReworkedTerminalUsageCollector : CounterUsagesCollector() {
     DURATION_FIELD,
   )
 
+  private val backendDocumentUpdateLatencyEvent = GROUP.registerVarargEvent(
+    "terminal.backend.document.update.latency",
+    TEXT_LENGTH_FIELD,
+    DURATION_FIELD,
+  )
+
   @JvmStatic
   fun logLocalShellStarted(project: Project, shellCommand: Array<String>) {
     localShellStartedEvent.log(project,
@@ -135,4 +141,11 @@ object ReworkedTerminalUsageCollector : CounterUsagesCollector() {
       DURATION_FIELD with duration
     )
   }
+
+  fun logBackendDocumentUpdateLatency(textLength: Int, duration: Duration) {
+    backendDocumentUpdateLatencyEvent.log(
+      TEXT_LENGTH_FIELD with textLength,
+      DURATION_FIELD with duration
+    )
+  }
 }