fix: replace type assertion with type guard (#4302)

* fix: replace type assertion with type guard

* replace another assertion with type guard

* Review comments

Co-authored-by: Lukas Taegert-Atkinson <lukastaegert@users.noreply.github.com>
Co-authored-by: Lukas Taegert-Atkinson <lukas.taegert-atkinson@tngtech.com>

src/Bundle.ts

@@ -307,10 +307,10 @@ function validateOptionsForMultiChunkOutput(
 
 function getIncludedModules(modulesById: Map<string, Module | ExternalModule>): Module[] {
 	return [...modulesById.values()].filter(
-		module =>
+		(module): module is Module =>
 			module instanceof Module &&
 			(module.isIncluded() || module.info.isEntry || module.includedDynamicImporters.length > 0)
-	) as Module[];
+	);
 }
 
 function addModuleToManualChunk(

src/utils/getOriginalLocation.ts

@@ -4,10 +4,9 @@ export function getOriginalLocation(
 	sourcemapChain: DecodedSourceMapOrMissing[],
 	location: { column: number; line: number; name?: string; source?: string }
 ): { column: number; line: number } {
-	// This cast is guaranteed. If it were a missing Map, it wouldn't have a mappings.
 	const filteredSourcemapChain = sourcemapChain.filter(
-		sourcemap => sourcemap.mappings
-	) as ExistingDecodedSourceMap[];
+		(sourcemap): sourcemap is ExistingDecodedSourceMap => !!sourcemap.mappings
+	);
 
 	while (filteredSourcemapChain.length > 0) {
 		const sourcemap = filteredSourcemapChain.pop()!;