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/app/app-logs.ts

@@ -63,9 +63,24 @@ async function determineLogPath(
   const logFilePaths: {
     readonly [K in SupportedPlatform]: () => string;
   } = {
-    [SupportedPlatform.macOS]: () => join(process.env.HOME, 'Library', 'Logs', appName, `${logFileName}.log`),
-    [SupportedPlatform.Linux]: () => join(process.env.HOME, '.config', appName, 'logs', `${logFileName}.log`),
-    [SupportedPlatform.Windows]: () => join(process.env.USERPROFILE, 'AppData', 'Roaming', appName, 'logs', `${logFileName}.log`),
+    [SupportedPlatform.macOS]: () => {
+      if (!process.env.HOME) {
+        throw new Error('HOME environment variable is not defined');
+      }
+      return join(process.env.HOME, 'Library', 'Logs', appName, `${logFileName}.log`);
+    },
+    [SupportedPlatform.Linux]: () => {
+      if (!process.env.HOME) {
+        throw new Error('HOME environment variable is not defined');
+      }
+      return join(process.env.HOME, '.config', appName, 'logs', `${logFileName}.log`);
+    },
+    [SupportedPlatform.Windows]: () => {
+      if (!process.env.USERPROFILE) {
+        throw new Error('USERPROFILE environment variable is not defined');
+      }
+      return join(process.env.USERPROFILE, 'AppData', 'Roaming', appName, 'logs', `${logFileName}.log`);
+    },
   };
   const logFilePath = logFilePaths[CURRENT_PLATFORM]?.();
   if (!logFilePath) {

tests/checks/desktop-runtime-errors/check-desktop-runtime-errors/app/check-for-errors.ts

@@ -1,4 +1,4 @@
-import { splitTextIntoLines, indentText } from '../utils/text';
+import { splitTextIntoLines, indentText, filterEmpty } from '../utils/text';
 import { log, die } from '../utils/log';
 import { readAppLogFile } from './app-logs';
 import { STDERR_IGNORE_PATTERNS } from './error-ignore-patterns';
@@ -33,7 +33,7 @@ async function gatherErrors(
   if (!projectDir) { throw new Error('missing project directory'); }
   const { logFileContent: mainLogs, logFilePath: mainLogFile } = await readAppLogFile(projectDir, 'main');
   const { logFileContent: rendererLogs, logFilePath: rendererLogFile } = await readAppLogFile(projectDir, 'renderer');
-  const allLogs = [mainLogs, rendererLogs, stderr].filter(Boolean).join('\n');
+  const allLogs = filterEmpty([mainLogs, rendererLogs, stderr]).join('\n');
   return [
     verifyStdErr(stderr),
     verifyApplicationLogsExist('main', mainLogs, mainLogFile),
@@ -43,7 +43,7 @@ async function gatherErrors(
     ),
     verifyWindowTitle(windowTitles),
     verifyErrorsInLogs(allLogs),
-  ].filter(Boolean);
+  ].filter((error): error is ExecutionError => Boolean(error));
 }
 
 interface ExecutionError {

tests/checks/desktop-runtime-errors/check-desktop-runtime-errors/app/extractors/common/app-artifact-locator.ts

@@ -8,7 +8,7 @@ export async function findByFilePattern(
   pattern: string,
   directory: string,
   projectRootDir: string,
-): Promise<ArtifactLocation> {
+): Promise<ArtifactLocation | never> {
   if (!directory) { throw new Error('Missing directory'); }
   if (!pattern) { throw new Error('Missing file pattern'); }
 
@@ -42,5 +42,5 @@ function escapeRegExp(string: string) {
 }
 
 interface ArtifactLocation {
-  readonly absolutePath?: string;
+  readonly absolutePath: string;
 }

tests/checks/desktop-runtime-errors/check-desktop-runtime-errors/app/extractors/macos.ts

@@ -36,7 +36,10 @@ async function mountDmg(
     die(`Failed to mount DMG file at ${dmgFile}.\n${error}`);
   }
   const mountPathMatch = hdiutilOutput.match(/\/Volumes\/[^\n]+/);
-  const mountPath = mountPathMatch ? mountPathMatch[0] : null;
+  if (!mountPathMatch || mountPathMatch.length === 0) {
+    die(`Could not find mount path from \`hdiutil\` output:\n${hdiutilOutput}`);
+  }
+  const mountPath = mountPathMatch[0];
   return {
     mountPath,
   };
@@ -52,7 +55,10 @@ async function findMacAppExecutablePath(
     return die(`Failed to find executable path at mount path ${mountPath}\n${error}`);
   }
   const appFolder = findOutput.trim();
-  const appName = appFolder.split('/').pop().replace('.app', '');
+  const appName = appFolder.split('/').pop()?.replace('.app', '');
+  if (!appName) {
+    die(`Could not extract app path from \`find\` output: ${findOutput}`);
+  }
   const appPath = `${appFolder}/Contents/MacOS/${appName}`;
   if (await exists(appPath)) {
     log(`Application is located at ${appPath}`);

tests/checks/desktop-runtime-errors/check-desktop-runtime-errors/app/runner.ts

@@ -20,6 +20,7 @@ export function runApplication(
 
   logDetails(appFile, executionDurationInSeconds);
 
+  const process = spawn(appFile);
   const processDetails: ApplicationProcessDetails = {
     stderrData: '',
     stdoutData: '',
@@ -27,15 +28,15 @@ export function runApplication(
     windowTitles: [],
     isCrashed: false,
     isDone: false,
-    process: undefined,
+    process,
     resolve: () => { /* NOOP */ },
   };
 
-  const process = spawn(appFile);
-  processDetails.process = process;
-
   return new Promise((resolve) => {
     processDetails.resolve = resolve;
+    if (process.pid === undefined) {
+      throw new Error('Unknown PID');
+    }
     beginCapturingTitles(process.pid, processDetails);
     handleProcessEvents(
       processDetails,
@@ -54,13 +55,14 @@ interface ApplicationExecutionResult {
 }
 
 interface ApplicationProcessDetails {
+  readonly process: ChildProcess;
+
   stderrData: string;
   stdoutData: string;
   explicitlyKilled: boolean;
   windowTitles: Array<string>;
   isCrashed: boolean;
   isDone: boolean;
-  process: ChildProcess;
   resolve: (value: ApplicationExecutionResult) => void;
 }
 
@@ -85,7 +87,7 @@ function beginCapturingTitles(
     const titles = await captureWindowTitles(processId);
 
     (titles || []).forEach((title) => {
-      if (!title?.length) {
+      if (!title) {
         return;
       }
       if (!processDetails.windowTitles.includes(title)) {
@@ -109,10 +111,10 @@ function handleProcessEvents(
   executionDurationInSeconds: number,
 ): void {
   const { process } = processDetails;
-  process.stderr.on('data', (data) => {
+  process.stderr?.on('data', (data) => {
     processDetails.stderrData += data.toString();
   });
-  process.stdout.on('data', (data) => {
+  process.stdout?.on('data', (data) => {
     processDetails.stdoutData += data.toString();
   });
 
@@ -130,7 +132,7 @@ function handleProcessEvents(
 }
 
 async function onProcessExit(
-  code: number,
+  code: number | null,
   processDetails: ApplicationProcessDetails,
   enableScreenshot: boolean,
   screenshotPath: string,

tests/checks/desktop-runtime-errors/check-desktop-runtime-errors/app/system-capture/window-title-capture.ts

@@ -1,6 +1,7 @@
 import { runCommand } from '../../utils/run-command';
 import { log, LogLevel } from '../../utils/log';
 import { SupportedPlatform, CURRENT_PLATFORM } from '../../utils/platform';
+import { filterEmpty } from '../../utils/text';
 
 export async function captureWindowTitles(processId: number) {
   if (!processId) { throw new Error('Missing process ID.'); }
@@ -67,7 +68,7 @@ async function captureTitlesOnLinux(processId: number): Promise<string[]> {
     return titleOutput.trim();
   }));
 
-  return titles.filter(Boolean);
+  return filterEmpty(titles);
 }
 
 let hasAssistiveAccessOnMac = true;