fix(logger): fix possibly-null property access in logger-typescript.ts (#3627)

This fixes a small issue where we were accessing a possibly-undefined
property on a TypeScript Diagnostic record.

This relates to the issue reported in #3443.

Author: alicewriteswrongs

src/utils/logger/logger-typescript.ts

@@ -93,7 +93,14 @@ export const loadTypeScriptDiagnostics = (tsDiagnostics: readonly Diagnostic[])
   return diagnostics;
 };
 
-export const loadTypeScriptDiagnostic = (tsDiagnostic: Diagnostic) => {
+/**
+ * Convert a TypeScript diagnostic object into our internal, Stencil-specific
+ * diagnostic format
+ *
+ * @param tsDiagnostic a TypeScript diagnostic message record
+ * @returns a Stencil diagnostic, suitable for showing an error to the user
+ */
+export const loadTypeScriptDiagnostic = (tsDiagnostic: Diagnostic): d.Diagnostic => {
   const d: d.Diagnostic = {
     level: 'warn',
     type: 'typescript',
@@ -164,15 +171,27 @@ export const loadTypeScriptDiagnostic = (tsDiagnostic: Diagnostic) => {
   return d;
 };
 
-const flattenDiagnosticMessageText = (tsDiagnostic: Diagnostic, diag: string | DiagnosticMessageChain | undefined) => {
+/**
+ * Flatten a TypeScript diagnostic object into a string which can be easily
+ * included in a Stencil diagnostic record.
+ *
+ * @param tsDiagnostic a TypeScript diagnostic record
+ * @param diag a {@link DiagnosticMessageChain} or a string with further info
+ * @returns a string with the relevant error message
+ */
+const flattenDiagnosticMessageText = (
+  tsDiagnostic: Diagnostic,
+  diag: string | DiagnosticMessageChain | undefined
+): string => {
   if (typeof diag === 'string') {
     return diag;
   } else if (diag === undefined) {
     return '';
   }
 
   const ignoreCodes: number[] = [];
-  const isStencilConfig = tsDiagnostic.file.fileName.includes('stencil.config');
+  // `tsDiagnostic.file` can be `undefined`, so we need to be a little careful here
+  const isStencilConfig = (tsDiagnostic.file?.fileName ?? '').includes('stencil.config');
   if (isStencilConfig) {
     ignoreCodes.push(2322);
   }