improvement: ignore create or modify file watcher event, when content…

… of the file is not changed

metals/src/main/scala/scala/meta/internal/metals/ProjectMetalsLspService.scala

@@ -1,11 +1,13 @@
 package scala.meta.internal.metals
 
+import java.io.IOException
 import java.util
 import java.util.concurrent.CompletableFuture
 import java.util.concurrent.Executors
 import java.util.concurrent.ScheduledExecutorService
 import java.util.concurrent.atomic.AtomicReference
 
+import scala.collection.concurrent.TrieMap
 import scala.concurrent.ExecutionContext
 import scala.concurrent.ExecutionContextExecutorService
 import scala.concurrent.Future
@@ -20,6 +22,7 @@ import scala.meta.internal.builds.BuildServerProvider
 import scala.meta.internal.builds.BuildTools
 import scala.meta.internal.builds.ScalaCliBuildTool
 import scala.meta.internal.builds.ShellRunner
+import scala.meta.internal.io.FileIO
 import scala.meta.internal.metals.MetalsEnrichments._
 import scala.meta.internal.metals.ammonite.Ammonite
 import scala.meta.internal.metals.clients.language.ConfiguredLanguageClient
@@ -28,6 +31,7 @@ import scala.meta.internal.metals.doctor.MetalsServiceInfo
 import scala.meta.internal.metals.watcher.FileWatcherEvent
 import scala.meta.internal.metals.watcher.FileWatcherEvent.EventType
 import scala.meta.internal.metals.watcher.ProjectFileWatcher
+import scala.meta.internal.mtags.MD5
 import scala.meta.internal.mtags.SemanticdbPath
 import scala.meta.internal.mtags.Semanticdbs
 import scala.meta.internal.tvp.FolderTreeViewProvider
@@ -411,7 +415,8 @@ class ProjectMetalsLspService(
       isScalaOrJava &&
       !path.isDirectory &&
       !savedFiles.isRecentlyActive(path) &&
-      !buffers.contains(path)
+      !buffers.contains(path) &&
+      didContentChange(event)
     ) {
       event.eventType match {
         case EventType.CreateOrModify => onCreate(path)
@@ -436,6 +441,34 @@ class ProjectMetalsLspService(
     }
   }
 
+  private val previousCreateOrModify = TrieMap[AbsolutePath, String]()
+
+  // If code is genereted we might get a lot of `CreateOrModify`
+  // events, even if the code doesn't really change
+  private def didContentChange(event: FileWatcherEvent): Boolean = {
+    val path = AbsolutePath(event.path)
+    event.eventType match {
+      case EventType.CreateOrModify =>
+        try {
+          val md5 = MD5.bytesToHex(FileIO.readAllBytes(path))
+          previousCreateOrModify.synchronized {
+            if (previousCreateOrModify.get(path).exists(_ == md5)) false
+            else {
+              previousCreateOrModify.put(path, md5)
+              true
+            }
+          }
+        } catch {
+          case e: IOException =>
+            scribe.warn(s"Failed to read contents of $path", e)
+            false
+        }
+      case _ =>
+        previousCreateOrModify.remove(path)
+        true
+    }
+  }
+
   private val ammonite: Ammonite = register {
     val amm = new Ammonite(
       buffers,