Revert to recently focused document if the current one was immedietal…

…ly closed

Some clients when using peek functionality might send didOpen and didClose notifications immediately one after the other. In this case we don't actually want to change the focused document so we revert to the one that was most recently focused.

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

@@ -27,4 +27,9 @@ final class ActiveFiles(time: Time) {
   def isRecentlyActive(path: AbsolutePath): Boolean = {
     paths.asScala.exists(p => p.isActive && p.path == path)
   }
+
+  def pollRecent(): Option[AbsolutePath] = {
+    paths.removeIf(_.isStale)
+    Option(paths.poll()).map(_.path)
+  }
 }

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

@@ -146,6 +146,7 @@ class MetalsLanguageServer(
     Option.empty[BspSession]
   private val savedFiles = new ActiveFiles(time)
   private val openedFiles = new ActiveFiles(time)
+  private val recentlyFocusedFiles = new ActiveFiles(time)
   private val languageClient = new DelegatingLanguageClient(NoopLanguageClient)
   var userConfig: UserConfiguration = UserConfiguration()
   val excludedPackageHandler: ExcludedPackagesHandler =
@@ -928,6 +929,9 @@ class MetalsLanguageServer(
   @JsonNotification("textDocument/didOpen")
   def didOpen(params: DidOpenTextDocumentParams): CompletableFuture[Unit] = {
     val path = params.getTextDocument.getUri.toAbsolutePath
+    // In some cases like peeking definition didOpen might be followed up by close
+    // and we would lose the notion of the focused document
+    focusedDocument.foreach(recentlyFocusedFiles.add)
     focusedDocument = Some(path)
     openedFiles.add(path)
 
@@ -1050,6 +1054,9 @@ class MetalsLanguageServer(
   @JsonNotification("textDocument/didClose")
   def didClose(params: DidCloseTextDocumentParams): Unit = {
     val path = params.getTextDocument.getUri.toAbsolutePath
+    if (focusedDocument.contains(path)) {
+      focusedDocument = recentlyFocusedFiles.pollRecent()
+    }
     buffers.remove(path)
     compilers.didClose(path)
     trees.didClose(path)