Refactor to enforce strictNullChecks

This commit applies `strictNullChecks` to the entire codebase to improve
maintainability and type safety. Key changes include:

- Remove some explicit null-checks where unnecessary.
- Add necessary null-checks.
- Refactor static factory functions for a more functional approach.
- Improve some test names and contexts for better debugging.
- Add unit tests for any additional logic introduced.
- Refactor `createPositionFromRegexFullMatch` to its own function as the
  logic is reused.
- Prefer `find` prefix on functions that may return `undefined` and
  `get` prefix for those that always return a value.

tests/checks/desktop-runtime-errors/check-desktop-runtime-errors/utils/npm.ts

@@ -70,13 +70,14 @@ const appNameCache = new Map<string, string>();
 
 export async function getAppName(projectDir: string): Promise<string> {
   if (!projectDir) { throw new Error('missing project directory'); }
-  if (appNameCache.has(projectDir)) {
-    return appNameCache.get(projectDir);
+  const cachedName = appNameCache.get(projectDir);
+  if (cachedName) {
+    return cachedName;
   }
   const packageData = await readPackageJsonContents(projectDir);
   try {
     const packageJson = JSON.parse(packageData);
-    const name = packageJson.name as string;
+    const name = packageJson.name as string | undefined;
     if (!name) {
       return die(`The \`package.json\` file doesn't specify a name: ${packageData}`);
     }

tests/checks/desktop-runtime-errors/check-desktop-runtime-errors/utils/platform.ts

@@ -15,7 +15,7 @@ const NODE_PLATFORM_MAPPINGS: {
   [SupportedPlatform.Windows]: 'win32',
 };
 
-function findCurrentPlatform(): SupportedPlatform | undefined {
+function getCurrentPlatform(): SupportedPlatform | never {
   const nodePlatform = platform();
 
   for (const key of Object.keys(NODE_PLATFORM_MAPPINGS)) {
@@ -28,4 +28,4 @@ function findCurrentPlatform(): SupportedPlatform | undefined {
   return die(`Unsupported platform: ${nodePlatform}`);
 }
 
-export const CURRENT_PLATFORM: SupportedPlatform = findCurrentPlatform();
+export const CURRENT_PLATFORM: SupportedPlatform = getCurrentPlatform();

tests/checks/desktop-runtime-errors/check-desktop-runtime-errors/utils/run-command.ts

@@ -37,7 +37,7 @@ export interface CommandResult {
 
 function formatError(
   command: string,
-  error: ExecException | undefined,
+  error: ExecException | null,
   stdout: string | undefined,
   stderr: string | undefined,
 ) {

tests/checks/desktop-runtime-errors/check-desktop-runtime-errors/utils/text.ts

@@ -15,6 +15,11 @@ export function splitTextIntoLines(text: string): string[] {
     .split(/[\r\n]+/);
 }
 
+export function filterEmpty(texts: readonly (string | undefined | null)[]): string[] {
+  return texts
+    .filter((title): title is string => Boolean(title));
+}
+
 function validateText(text: string): void {
   if (typeof text !== 'string') {
     throw new Error(`text is not a string. It is: ${typeof text}\n${text}`);