[code style] [prettier] WEB-74445: Add prepareForFormatting to PrettierFormattingService, avoid unnecessary file saves

(cherry picked from commit 51d6dc4ffdfcb565cb1edb12084d35babe3a122b)

IJ-CR-173729

GitOrigin-RevId: 917bbc7ca1f9ccbdb70b48b556666a5966df5fda

platform/code-style-api/api-dump.txt

@@ -303,6 +303,7 @@ a:com.intellij.formatting.service.AsyncDocumentFormattingService
 - p:getTimeout():java.time.Duration
 - p:getTimeoutActions(com.intellij.formatting.FormattingContext):com.intellij.openapi.actionSystem.AnAction[]
 - p:needToUpdate():Z
+- p:prepareForFormatting(com.intellij.openapi.editor.Document,com.intellij.formatting.FormattingContext):V
 p:com.intellij.formatting.service.AsyncDocumentFormattingService$FormattingTask
 - java.lang.Runnable
 - a:cancel():Z

platform/code-style-api/src/com/intellij/formatting/service/AsyncDocumentFormattingService.java

@@ -72,6 +72,7 @@ public abstract class AsyncDocumentFormattingService extends AbstractDocumentFor
         return;
       }
     }
+    prepareForFormatting(document, formattingContext);
     FormattingRequestImpl formattingRequest = new FormattingRequestImpl(formattingContext, document, formattingRanges,
                                                                          canChangeWhiteSpaceOnly, quickFormat);
     FormattingTask formattingTask = createFormattingTask(formattingRequest);
@@ -134,6 +135,14 @@ public abstract class AsyncDocumentFormattingService extends AbstractDocumentFor
    */
   protected abstract @NotNull @NlsSafe String getName();
 
+  /**
+   * Hook called before creating a formatting request. Default implementation saves the document
+   * to ensure external formatters working with IO files see the latest content.
+   */
+  protected void prepareForFormatting(@NotNull Document document, @NotNull FormattingContext formattingContext) {
+    FileDocumentManager.getInstance().saveDocument(document);
+  }
+
   /**
    * @return A duration to wait for the service to respond (call either {@code onTextReady()} or {@code onError()}).
    */
@@ -177,7 +186,6 @@ public abstract class AsyncDocumentFormattingService extends AbstractDocumentFor
       myRanges = ranges;
       myCanChangeWhitespaceOnly = canChangeWhitespaceOnly;
       myQuickFormat = quickFormat;
-      FileDocumentManager.getInstance().saveDocument(myDocument);
       myInitialModificationStamp = document.getModificationStamp();
     }