Assert creation of scope handlers (#2684)

## Checklist

- [/] I have added
[tests](https://www.cursorless.org/docs/contributing/test-case-recorder/)
- [/] I have updated the
[docs](https://github.com/cursorless-dev/cursorless/tree/main/docs) and
[cheatsheet](https://github.com/cursorless-dev/cursorless/tree/main/cursorless-talon/src/cheatsheet)
- [/] I have not broken the cheatsheet

Author: AndreasArvidsson

packages/cursorless-engine/src/processTargets/modifiers/ContainingScopeStage.ts

@@ -34,7 +34,7 @@ export class ContainingScopeStage implements ModifierStage {
   run(target: Target): Target[] {
     const { scopeType, ancestorIndex = 0 } = this.modifier;
 
-    const scopeHandler = this.scopeHandlerFactory.create(
+    const scopeHandler = this.scopeHandlerFactory.maybeCreate(
       scopeType,
       target.editor.document.languageId,
     );

packages/cursorless-engine/src/processTargets/modifiers/EveryScopeStage.ts

@@ -39,7 +39,7 @@ export class EveryScopeStage implements ModifierStage {
     const { scopeType } = this.modifier;
     const { editor, isReversed } = target;
 
-    const scopeHandler = this.scopeHandlerFactory.create(
+    const scopeHandler = this.scopeHandlerFactory.maybeCreate(
       scopeType,
       editor.document.languageId,
     );
@@ -108,7 +108,7 @@ export class EveryScopeStage implements ModifierStage {
     scopeHandlerFactory: ScopeHandlerFactory,
     target: Target,
   ): Range[] {
-    const iterationScopeHandler = scopeHandlerFactory.create(
+    const iterationScopeHandler = scopeHandlerFactory.maybeCreate(
       scopeHandler.iterationScopeType,
       target.editor.document.languageId,
     );

packages/cursorless-engine/src/processTargets/modifiers/PreferredScopeStage.ts

@@ -46,10 +46,6 @@ export class PreferredScopeStage implements ModifierStage {
       target.editor.document.languageId,
     );
 
-    if (scopeHandler == null) {
-      throw Error(`Couldn't create scope handler for: ${scopeType.type}`);
-    }
-
     const closestTargets = getClosestScopeTargets(target, scopeHandler);
 
     if (closestTargets == null) {

packages/cursorless-engine/src/processTargets/modifiers/RelativeScopeStage.ts

@@ -31,7 +31,7 @@ export class RelativeScopeStage implements ModifierStage {
   ) {}
 
   run(target: Target): Target[] {
-    const scopeHandler = this.scopeHandlerFactory.create(
+    const scopeHandler = this.scopeHandlerFactory.maybeCreate(
       this.modifier.scopeType,
       target.editor.document.languageId,
     );

packages/cursorless-engine/src/processTargets/modifiers/scopeHandlers/BoundedScopeHandler.ts

@@ -35,14 +35,14 @@ abstract class BoundedBaseScopeHandler extends BaseScopeHandler {
     this.targetScopeHandler = this.scopeHandlerFactory.create(
       this.targetScopeType,
       this.languageId,
-    )!;
+    );
     this.surroundingPairInteriorScopeHandler = this.scopeHandlerFactory.create(
       {
         type: "surroundingPairInterior",
         delimiter: "any",
       },
       this.languageId,
-    )!;
+    );
   }
 
   get iterationScopeType(): ScopeType {

packages/cursorless-engine/src/processTargets/modifiers/scopeHandlers/NestedScopeHandler.ts

@@ -63,7 +63,7 @@ export abstract class NestedScopeHandler extends BaseScopeHandler {
       this._searchScopeHandler = this.scopeHandlerFactory.create(
         this.searchScopeType,
         this.languageId,
-      )!;
+      );
     }
 
     return this._searchScopeHandler;

packages/cursorless-engine/src/processTargets/modifiers/scopeHandlers/OneOfScopeHandler.ts

@@ -24,25 +24,18 @@ export class OneOfScopeHandler extends BaseScopeHandler {
     languageId: string,
   ): ScopeHandler {
     const scopeHandlers: ScopeHandler[] = scopeType.scopeTypes.map(
-      (scopeType) => {
-        const handler = scopeHandlerFactory.create(scopeType, languageId);
-        if (handler == null) {
-          throw new Error(`No available scope handler for '${scopeType.type}'`);
-        }
-        return handler;
-      },
+      (scopeType) => scopeHandlerFactory.create(scopeType, languageId),
     );
 
     const iterationScopeType = (): CustomScopeType => ({
       type: "custom",
       scopeHandler: new OneOfScopeHandler(
         undefined,
-        scopeHandlers.map(
-          (scopeHandler) =>
-            scopeHandlerFactory.create(
-              scopeHandler.iterationScopeType,
-              languageId,
-            )!,
+        scopeHandlers.map((scopeHandler) =>
+          scopeHandlerFactory.create(
+            scopeHandler.iterationScopeType,
+            languageId,
+          ),
         ),
         () => {
           throw new Error("Not implemented");

packages/cursorless-engine/src/processTargets/modifiers/scopeHandlers/ScopeHandlerFactory.ts

@@ -2,8 +2,13 @@ import type { ScopeType } from "@cursorless/common";
 import type { CustomScopeType, ScopeHandler } from "./scopeHandler.types";
 
 export interface ScopeHandlerFactory {
-  create(
+  maybeCreate(
     scopeType: ScopeType | CustomScopeType,
     languageId: string,
   ): ScopeHandler | undefined;
+
+  create(
+    scopeType: ScopeType | CustomScopeType,
+    languageId: string,
+  ): ScopeHandler;
 }

packages/cursorless-engine/src/processTargets/modifiers/scopeHandlers/ScopeHandlerFactoryImpl.ts

@@ -45,10 +45,11 @@ import type { CustomScopeType, ScopeHandler } from "./scopeHandler.types";
  */
 export class ScopeHandlerFactoryImpl implements ScopeHandlerFactory {
   constructor(private languageDefinitions: LanguageDefinitions) {
+    this.maybeCreate = this.maybeCreate.bind(this);
     this.create = this.create.bind(this);
   }
 
-  create(
+  maybeCreate(
     scopeType: ScopeType | CustomScopeType,
     languageId: string,
   ): ScopeHandler | undefined {
@@ -114,4 +115,15 @@ export class ScopeHandlerFactoryImpl implements ScopeHandlerFactory {
           ?.getScopeHandler(scopeType);
     }
   }
+
+  create(
+    scopeType: ScopeType | CustomScopeType,
+    languageId: string,
+  ): ScopeHandler {
+    const handler = this.maybeCreate(scopeType, languageId);
+    if (handler == null) {
+      throw new Error(`Couldn't create scope handler for '${scopeType.type}'`);
+    }
+    return handler;
+  }
 }

packages/cursorless-engine/src/processTargets/modifiers/scopeHandlers/SurroundingPairScopeHandler/SurroundingPairInteriorScopeHandler.ts

@@ -24,7 +24,7 @@ export class SurroundingPairInteriorScopeHandler extends BaseScopeHandler {
         requireStrongContainment: true,
       },
       this.languageId,
-    )!;
+    );
   }
 
   get iterationScopeType() {