TypeScript/src/compiler/sourcemapDecoder.ts

/* @internal */
namespace ts {
    export interface SourceFileLikeCache {
        get(path: Path): SourceFileLike | undefined;
    }

    export function createSourceFileLikeCache(host: { readFile?: (path: string) => string | undefined, fileExists?: (path: string) => boolean }): SourceFileLikeCache {
        const cached = createMap<SourceFileLike>();
        return {
            get(path: Path) {
                if (cached.has(path)) {
                    return cached.get(path);
                }
                if (!host.fileExists || !host.readFile || !host.fileExists(path)) return;
                // And failing that, check the disk
                const text = host.readFile(path)!; // TODO: GH#18217
                const file = {
                    text,
                    lineMap: undefined,
                    getLineAndCharacterOfPosition(pos: number) {
                        return computeLineAndCharacterOfPosition(getLineStarts(this), pos);
                    }
                } as SourceFileLike;
                cached.set(path, file);
                return file;
            }
        };
    }
}

/* @internal */
namespace ts.sourcemaps {
    export interface SourceMapData {
        version?: number;
        file?: string;
        sourceRoot?: string;
        sources: string[];
        sourcesContent?: (string | null)[];
        names?: string[];
        mappings: string;
    }

    export interface SourceMappableLocation {
        fileName: string;
        position: number;
    }

    export interface SourceMapper {
        getOriginalPosition(input: SourceMappableLocation): SourceMappableLocation;
        getGeneratedPosition(input: SourceMappableLocation): SourceMappableLocation;
    }

    export const identitySourceMapper = { getOriginalPosition: identity, getGeneratedPosition: identity };

    export interface SourceMapDecodeHost {
        readFile(path: string): string | undefined;
        fileExists(path: string): boolean;
        getCanonicalFileName(path: string): string;
        log(text: string): void;
    }

    export function decode(host: SourceMapDecodeHost, mapPath: string, map: SourceMapData, program?: Program, fallbackCache = createSourceFileLikeCache(host)): SourceMapper {
        const currentDirectory = getDirectoryPath(mapPath);
        const sourceRoot = map.sourceRoot || currentDirectory;
        let decodedMappings: ProcessedSourceMapPosition[];
        let generatedOrderedMappings: ProcessedSourceMapPosition[];
        let sourceOrderedMappings: ProcessedSourceMapPosition[];

        return {
            getOriginalPosition,
            getGeneratedPosition
        };

        function getGeneratedPosition(loc: SourceMappableLocation): SourceMappableLocation {
            const maps = getSourceOrderedMappings();
            if (!length(maps)) return loc;
            let targetIndex = binarySearch(maps, { sourcePath: loc.fileName, sourcePosition: loc.position }, identity, compareProcessedPositionSourcePositions);
            if (targetIndex < 0 && maps.length > 0) {
                // if no exact match, closest is 2's compliment of result
                targetIndex = ~targetIndex;
            }
            if (!maps[targetIndex] || comparePaths(loc.fileName, maps[targetIndex].sourcePath, sourceRoot) !== 0) {
                return loc;
            }
            return { fileName: toPath(map.file!, sourceRoot, host.getCanonicalFileName), position: maps[targetIndex].emittedPosition }; // Closest pos
        }

        function getOriginalPosition(loc: SourceMappableLocation): SourceMappableLocation {
            const maps = getGeneratedOrderedMappings();
            if (!length(maps)) return loc;
            let targetIndex = binarySearch(maps, { emittedPosition: loc.position }, identity, compareProcessedPositionEmittedPositions);
            if (targetIndex < 0 && maps.length > 0) {
                // if no exact match, closest is 2's compliment of result
                targetIndex = ~targetIndex;
            }
            return { fileName: toPath(maps[targetIndex].sourcePath, sourceRoot, host.getCanonicalFileName), position: maps[targetIndex].sourcePosition }; // Closest pos
        }

        function getSourceFileLike(fileName: string, location: string): SourceFileLike | undefined {
            // Lookup file in program, if provided
            const file = program && program.getSourceFile(fileName);
            if (!file) {
                // Otherwise check the cache (which may hit disk)
                const path = toPath(fileName, location, host.getCanonicalFileName);
                return fallbackCache.get(path);
            }
            return file;
        }

        function getPositionOfLineAndCharacterUsingName(fileName: string, directory: string, line: number, character: number) {
            const file = getSourceFileLike(fileName, directory);
            if (!file) {
                return -1;
            }
            return getPositionOfLineAndCharacter(file, line, character);
        }

        function getDecodedMappings() {
            return decodedMappings || (decodedMappings = calculateDecodedMappings(map, processPosition, host));
        }

        function getSourceOrderedMappings() {
            return sourceOrderedMappings || (sourceOrderedMappings = getDecodedMappings().slice().sort(compareProcessedPositionSourcePositions));
        }

        function getGeneratedOrderedMappings() {
            return generatedOrderedMappings || (generatedOrderedMappings = getDecodedMappings().slice().sort(compareProcessedPositionEmittedPositions));
        }

        function compareProcessedPositionSourcePositions(a: ProcessedSourceMapPosition, b: ProcessedSourceMapPosition) {
            return comparePaths(a.sourcePath, b.sourcePath, sourceRoot) ||
                compareValues(a.sourcePosition, b.sourcePosition);
        }

        function compareProcessedPositionEmittedPositions(a: ProcessedSourceMapPosition, b: ProcessedSourceMapPosition) {
            return compareValues(a.emittedPosition, b.emittedPosition);
        }

        function processPosition(position: RawSourceMapPosition): ProcessedSourceMapPosition {
            const sourcePath = map.sources[position.sourceIndex];
            return {
                emittedPosition: getPositionOfLineAndCharacterUsingName(map.file!, currentDirectory, position.emittedLine, position.emittedColumn),
                sourcePosition: getPositionOfLineAndCharacterUsingName(sourcePath, sourceRoot, position.sourceLine, position.sourceColumn),
                sourcePath,
                // TODO: Consider using `name` field to remap the expected identifier to scan for renames to handle another tool renaming oout output
                // name: position.nameIndex ? map.names[position.nameIndex] : undefined
            };
        }
    }

    /*@internal*/
    export interface MappingsDecoder extends Iterator<SourceMapSpan> {
        readonly decodingIndex: number;
        readonly error: string | undefined;
        readonly lastSpan: SourceMapSpan;
    }

    /*@internal*/
    export function decodeMappings(map: SourceMapData): MappingsDecoder {
        const state: DecoderState = {
            encodedText: map.mappings,
            currentNameIndex: undefined,
            sourceMapNamesLength: map.names ? map.names.length : undefined,
            currentEmittedColumn: 0,
            currentEmittedLine: 0,
            currentSourceColumn: 0,
            currentSourceLine: 0,
            currentSourceIndex: 0,
            decodingIndex: 0
        };
        function captureSpan(): SourceMapSpan {
            return {
                emittedColumn: state.currentEmittedColumn,
                emittedLine: state.currentEmittedLine,
                sourceColumn: state.currentSourceColumn,
                sourceIndex: state.currentSourceIndex,
                sourceLine: state.currentSourceLine,
                nameIndex: state.currentNameIndex
            };
        }
        return {
            get decodingIndex() { return state.decodingIndex; },
            get error() { return state.error; },
            get lastSpan() { return captureSpan(); },
            next() {
                if (hasCompletedDecoding(state) || state.error) return { done: true, value: undefined as never };
                if (!decodeSinglePosition(state)) return { done: true, value: undefined as never };
                return { done: false, value: captureSpan() };
            }
        };
    }

    function calculateDecodedMappings<T>(map: SourceMapData, processPosition: (position: RawSourceMapPosition) => T, host?: { log?(s: string): void }): T[] {
        const decoder = decodeMappings(map);
        const positions = arrayFrom(decoder, processPosition);
        if (decoder.error) {
            if (host && host.log) {
                host.log(`Encountered error while decoding sourcemap: ${decoder.error}`);
            }
            return [];
        }
        return positions;
    }

    interface ProcessedSourceMapPosition {
        emittedPosition: number;
        sourcePosition: number;
        sourcePath: string;
    }

    interface RawSourceMapPosition {
        emittedLine: number;
        emittedColumn: number;
        sourceLine: number;
        sourceColumn: number;
        sourceIndex: number;
        nameIndex?: number;
    }

    interface DecoderState {
        decodingIndex: number;
        currentEmittedLine: number;
        currentEmittedColumn: number;
        currentSourceLine: number;
        currentSourceColumn: number;
        currentSourceIndex: number;
        currentNameIndex: number | undefined;
        encodedText: string;
        sourceMapNamesLength?: number;
        error?: string;
    }

    function hasCompletedDecoding(state: DecoderState) {
        return state.decodingIndex === state.encodedText.length;
    }

    function decodeSinglePosition(state: DecoderState): boolean {
        while (state.decodingIndex < state.encodedText.length) {
            const char = state.encodedText.charCodeAt(state.decodingIndex);
            if (char === CharacterCodes.semicolon) {
                // New line
                state.currentEmittedLine++;
                state.currentEmittedColumn = 0;
                state.decodingIndex++;
                continue;
            }

            if (char === CharacterCodes.comma) {
                // Next entry is on same line - no action needed
                state.decodingIndex++;
                continue;
            }

            // Read the current position
            // 1. Column offset from prev read jsColumn
            state.currentEmittedColumn += base64VLQFormatDecode();
            // Incorrect emittedColumn dont support this map
            if (createErrorIfCondition(state.currentEmittedColumn < 0, "Invalid emittedColumn found")) {
                return false;
            }
            // Dont support reading mappings that dont have information about original source and its line numbers
            if (createErrorIfCondition(isSourceMappingSegmentEnd(state.encodedText, state.decodingIndex), "Unsupported Error Format: No entries after emitted column")) {
                return false;
            }

            // 2. Relative sourceIndex
            state.currentSourceIndex += base64VLQFormatDecode();
            // Incorrect sourceIndex dont support this map
            if (createErrorIfCondition(state.currentSourceIndex < 0, "Invalid sourceIndex found")) {
                return false;
            }
            // Dont support reading mappings that dont have information about original source position
            if (createErrorIfCondition(isSourceMappingSegmentEnd(state.encodedText, state.decodingIndex), "Unsupported Error Format: No entries after sourceIndex")) {
                return false;
            }

            // 3. Relative sourceLine 0 based
            state.currentSourceLine += base64VLQFormatDecode();
            // Incorrect sourceLine dont support this map
            if (createErrorIfCondition(state.currentSourceLine < 0, "Invalid sourceLine found")) {
                return false;
            }
            // Dont support reading mappings that dont have information about original source and its line numbers
            if (createErrorIfCondition(isSourceMappingSegmentEnd(state.encodedText, state.decodingIndex), "Unsupported Error Format: No entries after emitted Line")) {
                return false;
            }

            // 4. Relative sourceColumn 0 based
            state.currentSourceColumn += base64VLQFormatDecode();
            // Incorrect sourceColumn dont support this map
            if (createErrorIfCondition(state.currentSourceColumn < 0, "Invalid sourceLine found")) {
                return false;
            }
            // 5. Check if there is name:
            if (!isSourceMappingSegmentEnd(state.encodedText, state.decodingIndex)) {
                if (state.currentNameIndex === undefined) {
                    state.currentNameIndex = 0;
                }
                state.currentNameIndex += base64VLQFormatDecode();
                // Incorrect nameIndex dont support this map
                // TODO: If we start using `name`s, issue errors when they aren't correct in the sourcemap
                // if (createErrorIfCondition(state.currentNameIndex < 0 || state.currentNameIndex >= state.sourceMapNamesLength, "Invalid name index for the source map entry")) {
                //    return;
                // }
            }
            // Dont support reading mappings that dont have information about original source and its line numbers
            if (createErrorIfCondition(!isSourceMappingSegmentEnd(state.encodedText, state.decodingIndex), "Unsupported Error Format: There are more entries after " + (state.currentNameIndex === undefined ? "sourceColumn" : "nameIndex"))) {
                return false;
            }

            // Entry should be complete
            return true;
        }

        createErrorIfCondition(/*condition*/ true, "No encoded entry found");
        return false;

        function createErrorIfCondition(condition: boolean, errormsg: string) {
            if (state.error) {
                // An error was already reported
                return true;
            }

            if (condition) {
                state.error = errormsg;
            }

            return condition;
        }

        function base64VLQFormatDecode(): number {
            let moreDigits = true;
            let shiftCount = 0;
            let value = 0;

            for (; moreDigits; state.decodingIndex++) {
                if (createErrorIfCondition(state.decodingIndex >= state.encodedText.length, "Error in decoding base64VLQFormatDecode, past the mapping string")) {
                    return undefined!; // TODO: GH#18217
                }

                // 6 digit number
                const currentByte = base64FormatDecode(state.encodedText.charAt(state.decodingIndex));

                // If msb is set, we still have more bits to continue
                moreDigits = (currentByte & 32) !== 0;

                // least significant 5 bits are the next msbs in the final value.
                value = value | ((currentByte & 31) << shiftCount);
                shiftCount += 5;
            }

            // Least significant bit if 1 represents negative and rest of the msb is actual absolute value
            if ((value & 1) === 0) {
                // + number
                value = value >> 1;
            }
            else {
                // - number
                value = value >> 1;
                value = -value;
            }

            return value;
        }
    }

    function base64FormatDecode(char: string) {
        return "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".indexOf(char);
    }

    function isSourceMappingSegmentEnd(encodedText: string, pos: number) {
        return (pos === encodedText.length ||
            encodedText.charCodeAt(pos) === CharacterCodes.comma ||
            encodedText.charCodeAt(pos) === CharacterCodes.semicolon);
    }
}