Signature help: restructure async work

sendRequest isn't an async function as 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.

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,
@@ -23,7 +23,6 @@ import { IntlShape } from "react-intl";
 import {
   MarkupContent,
   SignatureHelp,
-  SignatureHelpParams,
   SignatureHelpRequest,
 } from "vscode-languageserver-protocol";
 import { ApiReferenceMap } from "../../../documentation/mapping/content";
@@ -38,6 +37,10 @@ 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 +52,7 @@ class SignatureHelpState {
    * -1 for no signature help requested.
    */
   pos: number;
+
   /**
    * The latest result we want to display.
    *
@@ -77,44 +81,12 @@ 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 openSignatureHelp: Command = (view: EditorView) => {
-  triggerSignatureHelpRequest(view, view.state);
+  view.dispatch({
+    effects: [
+      setSignatureHelpRequestPosition.of(view.state.selection.main.from),
+    ],
+  });
   return true;
 };
 
@@ -138,12 +110,35 @@ 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);
+
+      // 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;
+          }
+        });
+      }
+
       if (state.pos === pos && state.result === result) {
         // Avoid pointless tooltip updates. If nothing else it makes e2e tests hard.
         return state;
@@ -191,30 +186,54 @@ export const signatureHelp = (
     extends BaseLanguageServerView
     implements PluginValue
   {
-    constructor(view: EditorView, private automatic: boolean) {
+    private destroyed = false;
+    private lastPos = -1;
+
+    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 { pos } = update.state.field(signatureHelpTooltipField);
+      if (this.lastPos !== pos) {
+        this.lastPos = pos;
+        if (this.lastPos !== -1) {
+          (async () => {
+            try {
+              const result = await client.connection.sendRequest(
+                SignatureHelpRequest.type,
+                {
+                  textDocument: { uri },
+                  position: offsetToPosition(state.doc, this.lastPos),
+                }
+              );
+              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 +325,11 @@ 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