chore(transformer): Enforce definitive signature for getDeclarationKeyMap and add a comment to why we can do that

src/transformer/descriptor/typeParameter/typeParameter.ts

@@ -20,13 +20,7 @@ export function GetTypeParameterDescriptor(node: ts.TypeParameterDeclaration, sc
     throw new Error(`Failed to determine the owner (parent) of the type parameter: \`${declaration.getText()}'.`);
   }
 
-  const genericKey: string | undefined = MockDefiner.instance.getDeclarationKeyMap(typeDeclaration);
-
-  if (!genericKey) {
-    throw new Error(
-      `Failed to look up generic key in MockDefiner for \`${typeDeclaration.getText()}'.`,
-    );
-  }
+  const genericKey: string = MockDefiner.instance.getDeclarationKeyMap(typeDeclaration);
 
   return createFunctionToAccessToGenericValue(genericKey + node.name.escapedText, descriptor);
 }

src/transformer/mockDefiner/mockDefiner.ts

@@ -110,13 +110,7 @@ export class MockDefiner {
   public createMockFactory(declaration: ts.Declaration): void {
     const thisFileName: string = this._fileName;
 
-    const key: string | undefined = this.getDeclarationKeyMap(declaration);
-
-    if (!key) {
-      throw new Error(
-        `Failed to obtain key while creating mock factory for \`${declaration.getText()}'.`,
-      );
-    }
+    const key: string = this.getDeclarationKeyMap(declaration);
 
     this._factoryCache.set(declaration, key);
 
@@ -152,24 +146,22 @@ export class MockDefiner {
     return this._getCallGetFactory(key);
   }
 
-  public getDeclarationKeyMap(declaration: ts.Declaration): string | undefined {
+  public getDeclarationKeyMap(declaration: ts.Declaration): string {
+    let key: string | undefined;
+
     if (!this._declarationCache.has(declaration)) {
-      const key: string = this._factoryUniqueName.createForDeclaration(declaration as PossibleDeclaration);
+      key = this._factoryUniqueName.createForDeclaration(declaration as PossibleDeclaration);
 
       this._declarationCache.set(declaration, key);
     }
 
-    return this._declarationCache.get(declaration);
+    // NOTE: TypeScript does not support inference through has/get, but we know
+    // for a fact that the result here is a string!
+    return (key || this._declarationCache.get(declaration)) as string;
   }
 
   public storeRegisterMockFor(declaration: ts.Declaration, factory: ts.FunctionExpression): void {
-    const key: string | undefined = this.getDeclarationKeyMap(declaration);
-
-    if (!key) {
-      throw new Error(
-        `Failed to obtain key while storing mock for \`${declaration.getText()}'.`,
-      );
-    }
+    const key: string = this.getDeclarationKeyMap(declaration);
 
     this._registerMockFactoryCache.set(declaration, key);
 
@@ -207,13 +199,7 @@ export class MockDefiner {
       return cachedFactory;
     }
 
-    const key: string | undefined = this.getDeclarationKeyMap(declaration);
-
-    if (!key) {
-      throw new Error(
-        `Failed to obtain key while resolving factory identifier (internal) for \`${declaration.getText()}'.`,
-      );
-    }
+    const key: string = this.getDeclarationKeyMap(declaration);
 
     this._factoryCache.set(declaration, key);
 

src/transformer/mockFactoryCall/mockFactoryCall.ts

@@ -30,13 +30,7 @@ export function GetMockFactoryCallIntersection(intersection: ts.IntersectionType
   const declarations: ts.Declaration[] | ts.TypeLiteralNode[] = intersection.types.map((type: ts.TypeNode) => {
     if (ts.isTypeReferenceNode(type)) {
       const declaration: ts.Declaration = TypescriptHelper.GetDeclarationFromNode(type.typeName);
-      const declarationKey: string | undefined = MockDefiner.instance.getDeclarationKeyMap(declaration);
-
-      if (!declarationKey) {
-        throw new Error(
-          `Failed to look up declaration key in MockDefiner for \`${declaration.getText()}'.`,
-        );
-      }
+      const declarationKey: string = MockDefiner.instance.getDeclarationKeyMap(declaration);
 
       genericDeclaration.addFromTypeReferenceNode(type, declarationKey);