fix(compiler-cli): avoid fatal diagnostics for invalid module schemas

In the event of an invalid `schemas` field for an Angular module, an
empty schema array will now be used instead of a fatal error occurring.
A build will still fail in this case with the error reported as a
diagnostic. However, for the language service, this allows the module
to exist in the compiler registry and prevents cascading diagnostics
within an IDE due to "missing" modules/components. The originating
schema related errors will still be reported in the IDE.

Author: clydin

packages/compiler-cli/src/ngtsc/annotations/ng_module/src/handler.ts

@@ -466,10 +466,26 @@ export class NgModuleDecoratorHandler
       }
     }
 
-    const schemas =
-      this.compilationMode !== CompilationMode.LOCAL && ngModule.has('schemas')
-        ? extractSchemas(ngModule.get('schemas')!, this.evaluator, 'NgModule')
-        : [];
+    let schemas: SchemaMetadata[] | undefined;
+    try {
+      schemas =
+        this.compilationMode !== CompilationMode.LOCAL && ngModule.has('schemas')
+          ? extractSchemas(ngModule.get('schemas')!, this.evaluator, 'NgModule')
+          : [];
+    } catch (e) {
+      if (e instanceof FatalDiagnosticError) {
+        diagnostics.push(e.toDiagnostic());
+
+        // Use an empty schema array if schema extract fails.
+        // A build will still fail in this case. However, for the language service,
+        // this allows the module to exist in the compiler registry and prevents
+        // cascading diagnostics within an IDE due to "missing" components. The
+        // originating schema related errors will still be reported in the IDE.
+        schemas = [];
+      } else {
+        throw e;
+      }
+    }
 
     let id: Expression | null = null;
     if (ngModule.has('id')) {