Signature help: restructure async work (#1198)

sendRequest isn't an async function and it can synchronously throw errors
so we need something to prevent reentrant updates in the error case.

Otherwise though we don't needed it if we move more work into the state.

I've also calculated line/column ASAP - I'm not sure this is necessary but it
feels obviously correct / straightforward which is a win in this code.

Author: microbit-matt-hillsdon

src/editor/codemirror/language-server/signatureHelp.ts

@@ -7,7 +7,7 @@
  *
  * SPDX-License-Identifier: MIT
  */
-import { EditorState, StateEffect, StateField } from "@codemirror/state";
+import { Facet, StateEffect, StateField } from "@codemirror/state";
 import {
   Command,
   EditorView,
@@ -22,8 +22,8 @@ import {
 import { IntlShape } from "react-intl";
 import {
   MarkupContent,
+  Position,
   SignatureHelp,
-  SignatureHelpParams,
   SignatureHelpRequest,
 } from "vscode-languageserver-protocol";
 import { ApiReferenceMap } from "../../../documentation/mapping/content";
@@ -38,6 +38,10 @@ import {
 import { nameFromSignature, removeFullyQualifiedName } from "./names";
 import { offsetToPosition } from "./positions";
 
+export const automaticFacet = Facet.define<boolean, boolean>({
+  combine: (values) => values[values.length - 1] ?? true,
+});
+
 export const setSignatureHelpRequestPosition = StateEffect.define<number>({});
 
 export const setSignatureHelpResult = StateEffect.define<SignatureHelp | null>(
@@ -49,6 +53,12 @@ class SignatureHelpState {
    * -1 for no signature help requested.
    */
   pos: number;
+
+  /**
+   * The LSP position for pos.
+   */
+  position: Position | null;
+
   /**
    * The latest result we want to display.
    *
@@ -57,11 +67,16 @@ class SignatureHelpState {
    */
   result: SignatureHelp | null;
 
-  constructor(pos: number, result: SignatureHelp | null) {
+  constructor(
+    pos: number,
+    position: Position | null,
+    result: SignatureHelp | null
+  ) {
     if (result && pos === -1) {
       throw new Error("Invalid state");
     }
     this.pos = pos;
+    this.position = position;
     this.result = result;
   }
 }
@@ -77,44 +92,22 @@ const signatureHelpToolTipBaseTheme = EditorView.baseTheme({
   },
 });
 
-const triggerSignatureHelpRequest = async (
-  view: EditorView,
-  state: EditorState
-): Promise<void> => {
-  const uri = state.facet(uriFacet)!;
-  const client = state.facet(clientFacet)!;
-  const pos = state.selection.main.from;
-  const params: SignatureHelpParams = {
-    textDocument: { uri },
-    position: offsetToPosition(state.doc, pos),
-  };
-  try {
-    // Must happen before other event handling that might dispatch more
-    // changes that invalidate our position.
-    queueMicrotask(() => {
-      view.dispatch({
-        effects: [setSignatureHelpRequestPosition.of(pos)],
-      });
-    });
-    const result = await client.connection.sendRequest(
-      SignatureHelpRequest.type,
-      params
-    );
-    view.dispatch({
-      effects: [setSignatureHelpResult.of(result)],
-    });
-  } catch (e) {
-    if (!isErrorDueToDispose(e)) {
-      logException(state, e, "signature-help");
-    }
-    view.dispatch({
-      effects: [setSignatureHelpResult.of(null)],
-    });
+const positionEq = (a: Position | null, b: Position | null): boolean => {
+  if (a === null) {
+    return b === null;
+  }
+  if (b === null) {
+    return a === null;
   }
+  return a.character === b.character && a.line === b.line;
 };
 
 const openSignatureHelp: Command = (view: EditorView) => {
-  triggerSignatureHelpRequest(view, view.state);
+  view.dispatch({
+    effects: [
+      setSignatureHelpRequestPosition.of(view.state.selection.main.from),
+    ],
+  });
   return true;
 };
 
@@ -124,7 +117,7 @@ export const signatureHelp = (
   apiReferenceMap: ApiReferenceMap
 ) => {
   const signatureHelpTooltipField = StateField.define<SignatureHelpState>({
-    create: () => new SignatureHelpState(-1, null),
+    create: () => new SignatureHelpState(-1, null, null),
     update(state, tr) {
       let { pos, result } = state;
       for (const effect of tr.effects) {
@@ -138,17 +131,45 @@ export const signatureHelp = (
           }
         }
       }
+
       // Even if we just got a result, if the position has been cleared we don't want it.
       if (pos === -1) {
         result = null;
       }
 
+      // By default map the previous position forward
       pos = pos === -1 ? -1 : tr.changes.mapPos(pos);
-      if (state.pos === pos && state.result === result) {
+
+      // Did the selection moved while open? We'll re-request but keep the old result for now.
+      if (pos !== -1 && tr.selection) {
+        pos = tr.selection.main.from;
+      }
+
+      // Automatic triggering cases
+      const automatic = tr.state.facet(automaticFacet).valueOf();
+      if (
+        automatic &&
+        ((tr.docChanged && tr.isUserEvent("input")) ||
+          tr.isUserEvent("dnd.drop.call"))
+      ) {
+        tr.changes.iterChanges((_fromA, _toA, _fromB, _toB, inserted) => {
+          if (inserted.sliceString(0).trim().endsWith("()")) {
+            // Triggered
+            pos = tr.newSelection.main.from;
+          }
+        });
+      }
+
+      const position = pos === -1 ? null : offsetToPosition(tr.state.doc, pos);
+      if (
+        state.pos === pos &&
+        state.result === result &&
+        positionEq(state.position, position)
+      ) {
         // Avoid pointless tooltip updates. If nothing else it makes e2e tests hard.
         return state;
       }
-      return new SignatureHelpState(pos, result);
+      return new SignatureHelpState(pos, position, result);
     },
     provide: (f) =>
       showTooltip.from(f, (val) => {
@@ -191,30 +212,54 @@ export const signatureHelp = (
     extends BaseLanguageServerView
     implements PluginValue
   {
-    constructor(view: EditorView, private automatic: boolean) {
+    private destroyed = false;
+    private lastPosition: Position | null = null;
+
+    constructor(view: EditorView) {
       super(view);
     }
     update(update: ViewUpdate) {
-      if (
-        (update.docChanged || update.selectionSet) &&
-        this.view.state.field(signatureHelpTooltipField).pos !== -1
-      ) {
-        triggerSignatureHelpRequest(this.view, update.state);
-      } else if (this.automatic && update.docChanged) {
-        const last = update.transactions[update.transactions.length - 1];
-
-        // This needs to trigger for autocomplete adding function parens
-        // as well as normal user input with `closebrackets` inserting
-        // the closing bracket.
-        if (last.isUserEvent("input") || last.isUserEvent("dnd.drop.call")) {
-          last.changes.iterChanges((_fromA, _toA, _fromB, _toB, inserted) => {
-            if (inserted.sliceString(0).trim().endsWith("()")) {
-              triggerSignatureHelpRequest(this.view, update.state);
+      const { view, state } = update;
+      const uri = state.facet(uriFacet)!;
+      const client = state.facet(clientFacet)!;
+      const { position } = update.state.field(signatureHelpTooltipField);
+      if (!positionEq(this.lastPosition, position)) {
+        this.lastPosition = position;
+        if (position !== null) {
+          (async () => {
+            try {
+              const result = await client.connection.sendRequest(
+                SignatureHelpRequest.type,
+                {
+                  textDocument: { uri },
+                  position,
+                }
+              );
+              if (!this.destroyed) {
+                view.dispatch({
+                  effects: [setSignatureHelpResult.of(result)],
+                });
+              }
+            } catch (e) {
+              if (!isErrorDueToDispose(e)) {
+                logException(state, e, "signature-help");
+              }
+              // The sendRequest call can fail synchronously when disposed so we need to ensure our clean-up doesn't happen inside the CM update call.
+              queueMicrotask(() => {
+                if (!this.destroyed) {
+                  view.dispatch({
+                    effects: [setSignatureHelpResult.of(null)],
+                  });
+                }
+              });
             }
-          });
+          })();
         }
       }
     }
+    destroy(): void {
+      this.destroyed = true;
+    }
   }
 
   const formatSignatureHelp = (
@@ -306,10 +351,11 @@ export const signatureHelp = (
 
   return [
     // View only handles automatic triggering.
-    ViewPlugin.define((view) => new SignatureHelpView(view, automatic)),
+    ViewPlugin.define((view) => new SignatureHelpView(view)),
     signatureHelpTooltipField,
     signatureHelpToolTipBaseTheme,
     keymap.of(signatureHelpKeymap),
+    automaticFacet.of(automatic),
     EditorView.domEventHandlers({
       blur(event, view) {
         // Close signature help as it interacts badly with drag and drop if