How to use the sourcemap-codec.decode function in sourcemap-codec

modules.forEach(module => {
		if (!/\.css$/.test(module)) return;

		const css = css_map.get(module);

		const { code, map } = extract_sourcemap(css, module);

		parts.push(code);

		if (map) {
			const lines = codec.decode(map.mappings);

			if (combined_map.sources.length > 0 || combined_map.names.length > 0) {
				lines.forEach(line => {
					line.forEach(segment => {
						// adjust source index
						segment[1] += combined_map.sources.length;

						// adjust name index
						if (segment[4]) segment[4] += combined_map.names.length;
					});
				});
			}

			combined_map.sources.push(...map.sources);
			combined_map.sourcesContent.push(...map.sourcesContent);
			combined_map.names.push(...map.names);

function fixMappings( mappings ) {
	if ( typeof mappings !== 'string' ) {
		return '';
	}

	mappings = decode( mappings );

	mappings[ 0 ].forEach( ( line, index ) => {
		// If the line has only one segment with only one item,
		// just drop the whole line.
		if ( line && line.length === 1 ) {
			mappings[ 0 ].splice( index, 1 );
		}
	} );

	return encode( mappings );
}

export default function check ( magicString, ast ) {
	const code = magicString.toString();

	try {
		parse( code, {
			ecmaVersion: 8,
			sourceType: 'module'
		});
	} catch ( err ) {
		const map = magicString.generateMap();
		const { line, column } = err.loc;
		const snippet = code.slice( Math.max( 0, err.pos - 35 ), Math.min( code.length, err.pos + 35 ) );

		const mappings = decode( map.mappings );
		const segments = mappings[ line - 1 ];

		for ( let i = 0; i < segments.length; i += 1 ) {
			const segment = segments[i];
			if ( segment[0] >= column ) {
				const sourceCodeLine = segment[2];
				const sourceCodeColumn = segment[3];

				err.message = `Butternut generated invalid JS: code in source file near (${sourceCodeLine + 1}:${sourceCodeColumn}) became\n...${snippet}...`;

				try {
					const repro = createRepro( magicString.original, ast, sourceCodeLine, sourceCodeColumn );
					if ( repro ) err.repro = repro;
				} catch (err) {
					// do nothing
				}

function Link ( map, sources ) {
	if ( !map ) throw new Error( 'Cannot generate a sourcemap if non-sourcemap-generating transformers are used' );

	this.sources = sources;
	this.names = map.names;
	this.mappings = decode( map.mappings );
}

export default function decodeMappings ( mappings ) {
	let checksum = crc32( mappings );

	if ( !cache[ checksum ] ) {
		cache[ checksum ] = decode( mappings );
	}

	return cache[ checksum ];
}

let result = '';

				const mappings = [];
				const sources = [];
				const sourcesContent = [];

				for (let chunk of cssLookup.values()) {
					if (!chunk.code) continue;
					result += chunk.code + '\n';

					if (chunk.map) {
						const i = sources.length;
						sources.push(chunk.map.sources[0]);
						sourcesContent.push(chunk.map.sourcesContent[0]);

						const decoded = decode(chunk.map.mappings);

						if (i > 0) {
							decoded.forEach(line => {
								line.forEach(segment => {
									segment[1] = i;
								});
							});
						}

						mappings.push(...decoded);
					}
				}

				const writer = new CssWriter(result, {
					sources,
					sourcesContent,

function trace(loc, map) {
	const mappings = decode(map.mappings);
	const segments = mappings[loc.line - 1];

	for (let i = 0; i < segments.length; i += 1) {
		const segment = segments[i];
		if (segment[0] === loc.column) {
			const [, sourceIndex, line, column] = segment;
			const source = map.sources[sourceIndex].slice(2);

			return { source, line: line + 1, column };
		}
	}

	return null;
}

function addNewLine( code, map, banner ) {
	map = Object.assign( {}, map );

	code = code.replace( banner, `${ banner }\n` );

	const mappings = decodeSourceMap( map.mappings );

	let codeStart = banner.match( /\n/g );
	codeStart = codeStart ? codeStart.length + 1 : 1;

	let whitespaceAtStart = code.replace( `${ banner }\n`, '' ).match( /^(\s)+/g );
	whitespaceAtStart = whitespaceAtStart ? whitespaceAtStart.length : 0;

	mappings.unshift( [] );

	if ( Array.isArray( mappings[ codeStart ] ) && mappings[ codeStart ].length ) {
		const offset = mappings[ codeStart ][ 0 ][ 0 ] - whitespaceAtStart;

		mappings[ codeStart ].forEach( ( segment ) => {
			segment[ 0 ] -= offset;
		} );
	}

return getMap( this, sourceMapByPath ).then( map => {
				if ( !map ) return null;

				this.map = map;

				let decodingStart = process.hrtime();
				this.mappings = decode( map.mappings );
				let decodingTime = process.hrtime( decodingStart );
				this._stats.decodingTime = 1e9 * decodingTime[0] + decodingTime[1];

				const sourcesContent = map.sourcesContent || [];

				const sourceRoot = resolve( dirname( this.file ), map.sourceRoot || '' );

				this.sources = map.sources.map( ( source, i ) => {
					return new Node({
						file: source ? resolve( sourceRoot, source ) : null,
						content: sourcesContent[i]
					});
				});

				const promises = this.sources.map( node => node.load( sourcesContentByPath, sourceMapByPath ) );
				return Promise.all( promises );