Refactored preprocess for readability

Author: ehrencrona

src/compiler/preprocess/decode_sourcemap.ts

@@ -0,0 +1,88 @@
+import { decode as decode_mappings } from 'sourcemap-codec';
+import { Processed } from './types';
+
+/**
+ * Import decoded sourcemap from mozilla/source-map/SourceMapGenerator
+ * Forked from source-map/lib/source-map-generator.js
+ * from methods _serializeMappings and toJSON.
+ * We cannot use source-map.d.ts types, because we access hidden properties.
+ */
+function decoded_sourcemap_from_generator(generator: any) {
+	let previous_generated_line = 1;
+	const converted_mappings = [[]];
+	let result_line;
+	let result_segment;
+	let mapping;
+
+	const source_idx = generator._sources.toArray()
+		.reduce((acc, val, idx) => (acc[val] = idx, acc), {});
+
+	const name_idx = generator._names.toArray()
+		.reduce((acc, val, idx) => (acc[val] = idx, acc), {});
+
+	const mappings = generator._mappings.toArray();
+	result_line = converted_mappings[0];
+
+	for (let i = 0, len = mappings.length; i < len; i++) {
+		mapping = mappings[i];
+
+		if (mapping.generatedLine > previous_generated_line) {
+			while (mapping.generatedLine > previous_generated_line) {
+				converted_mappings.push([]);
+				previous_generated_line++;
+			}
+			result_line = converted_mappings[mapping.generatedLine - 1]; // line is one-based
+		} else if (i > 0) {
+			const previous_mapping = mappings[i - 1];
+			if (
+				// sorted by selectivity
+				mapping.generatedColumn === previous_mapping.generatedColumn &&
+				mapping.originalColumn === previous_mapping.originalColumn &&
+				mapping.name === previous_mapping.name &&
+				mapping.generatedLine === previous_mapping.generatedLine &&
+				mapping.originalLine === previous_mapping.originalLine &&
+				mapping.source === previous_mapping.source
+		) {
+				continue;
+			}
+		}
+		result_line.push([mapping.generatedColumn]);
+		result_segment = result_line[result_line.length - 1];
+
+		if (mapping.source != null) {
+			result_segment.push(...[
+				source_idx[mapping.source],
+				mapping.originalLine - 1, // line is one-based
+				mapping.originalColumn
+			]);
+			if (mapping.name != null) {
+				result_segment.push(name_idx[mapping.name]);
+			}
+		}
+	}
+
+	const map = {
+		version: generator._version,
+		sources: generator._sources.toArray(),
+		names: generator._names.toArray(),
+		mappings: converted_mappings
+	};
+	if (generator._file != null) {
+		(map as any).file = generator._file;
+	}
+	// not needed: map.sourcesContent and map.sourceRoot
+	return map;
+}
+
+export function decode_map(processed: Processed) {
+	let decoded_map = typeof processed.map === 'string' ? JSON.parse(processed.map) : processed.map;
+	if (typeof(decoded_map.mappings) === 'string') {
+		decoded_map.mappings = decode_mappings(decoded_map.mappings);
+	}
+	if ((decoded_map as any)._mappings && decoded_map.constructor.name === 'SourceMapGenerator') {
+		// import decoded sourcemap from mozilla/source-map/SourceMapGenerator
+		decoded_map = decoded_sourcemap_from_generator(decoded_map);
+	}
+
+	return decoded_map;
+}