Add PluginValue.docViewUpdate

FEATURE: View plugins can now provide a `docViewUpdate` method that
is called whenever the document view is updated.

src/docview.ts

@@ -9,7 +9,7 @@ import {getAttrs} from "./attributes"
 import {clientRectsFor, isEquivalentPosition, maxOffset, Rect, scrollRectIntoView,
         getSelection, hasSelection, textRange, DOMSelectionState} from "./dom"
 import {ViewUpdate, decorations as decorationsFacet, outerDecorations,
-        ChangedRange, ScrollTarget, getScrollMargins} from "./extension"
+        ChangedRange, ScrollTarget, getScrollMargins, requestMeasureOnDocUpdate} from "./extension"
 import {EditorView} from "./editorview"
 import {Direction} from "./bidi"
 

src/editorview.ts

@@ -322,6 +322,7 @@ export class EditorView {
       this.viewState.mustMeasureContent = true
     if (redrawn || attrsChanged || scrollTarget || this.viewState.mustEnforceCursorAssoc || this.viewState.mustMeasureContent)
       this.requestMeasure()
+    if (redrawn) this.docViewUpdate()
     if (!update.empty) for (let listener of this.state.facet(updateListener)) {
       try { listener(update) }
       catch (e) { logException(this.state, e, "update listener") }
@@ -391,6 +392,16 @@ export class EditorView {
     if (prevSpecs != specs) this.inputState.ensureHandlers(this.plugins)
   }
 
+  private docViewUpdate() {
+    for (let plugin of this.plugins) {
+      let val = plugin.value
+      if (val && val.docViewUpdate) {
+        try { val.docViewUpdate(this) }
+        catch(e) { logException(this.state, e, "doc view update listener") }
+      }
+    }
+  }
+
   /// @internal
   measure(flush = true) {
     if (this.destroyed) return
@@ -449,6 +460,7 @@ export class EditorView {
           this.inputState.update(update)
           this.updateAttrs()
           redrawn = this.docView.update(update)
+          if (redrawn) this.docViewUpdate()
         }
         for (let i = 0; i < measuring.length; i++) if (measured[i] != BadMeasure) {
           try {

src/extension.ts

@@ -99,6 +99,12 @@ export interface PluginValue extends Object {
   /// your code in a DOM reading phase if you need to.
   update?(update: ViewUpdate): void
 
+  /// Called when the document view is updated (due to content,
+  /// decoration, or viewport changes). Should not try to immediately
+  /// start another view update. Often useful for calling
+  /// [`requestMeasure`](#view.EditorView.requestMeasure).
+  docViewUpdate?(view: EditorView): void
+
   /// Called when the plugin is no longer going to be used. Should
   /// revert any changes the plugin made to the DOM.
   destroy?(): void