sourcemap.ts

import {
    arrayFrom,
    binarySearchKey,
    CharacterCodes,
    combinePaths,
    compareValues,
    Debug,
    DocumentPosition,
    DocumentPositionMapper,
    DocumentPositionMapperHost,
    EmitHost,
    emptyArray,
    every,
    getDirectoryPath,
    getNormalizedAbsolutePath,
    getPositionOfLineAndCharacter,
    getRelativePathToDirectoryOrUrl,
    identity,
    isArray,
    isString,
    LineAndCharacter,
    RawSourceMap,
    some,
    sortAndDeduplicate,
    SortedReadonlyArray,
    SourceMapGenerator,
} from "./_namespaces/ts.js";
import * as performance from "./_namespaces/ts.performance.js";

/** @internal */
export interface SourceMapGeneratorOptions {
    extendedDiagnostics?: boolean;
}

/** @internal */
export function createSourceMapGenerator(host: EmitHost, file: string, sourceRoot: string, sourcesDirectoryPath: string, generatorOptions: SourceMapGeneratorOptions): SourceMapGenerator {
    // Why var? It avoids TDZ checks in the runtime which can be costly.
    // See: https://github.com/microsoft/TypeScript/issues/52924
    /* eslint-disable no-var */
    var { enter, exit } = generatorOptions.extendedDiagnostics
        ? performance.createTimer("Source Map", "beforeSourcemap", "afterSourcemap")
        : performance.nullTimer;

    // Current source map file and its index in the sources list
    var rawSources: string[] = [];
    var sources: string[] = [];
    var sourceToSourceIndexMap = new Map<string, number>();
    var sourcesContent: (string | null)[] | undefined; // eslint-disable-line no-restricted-syntax

    var names: string[] = [];
    var nameToNameIndexMap: Map<string, number> | undefined;
    var mappingCharCodes: number[] = [];
    var mappings = "";

    // Last recorded and encoded mappings
    var lastGeneratedLine = 0;
    var lastGeneratedCharacter = 0;
    var lastSourceIndex = 0;
    var lastSourceLine = 0;
    var lastSourceCharacter = 0;
    var lastNameIndex = 0;
    var hasLast = false;

    var pendingGeneratedLine = 0;
    var pendingGeneratedCharacter = 0;
    var pendingSourceIndex = 0;
    var pendingSourceLine = 0;
    var pendingSourceCharacter = 0;
    var pendingNameIndex = 0;
    var hasPending = false;
    var hasPendingSource = false;
    var hasPendingName = false;
    /* eslint-enable no-var */

    return {
        getSources: () => rawSources,
        addSource,
        setSourceContent,
        addName,
        addMapping,
        appendSourceMap,
        toJSON,
        toString: () => JSON.stringify(toJSON()),
    };

    function addSource(fileName: string) {
        enter();
        const source = getRelativePathToDirectoryOrUrl(sourcesDirectoryPath, fileName, host.getCurrentDirectory(), host.getCanonicalFileName, /*isAbsolutePathAnUrl*/ true);

        let sourceIndex = sourceToSourceIndexMap.get(source);
        if (sourceIndex === undefined) {
            sourceIndex = sources.length;
            sources.push(source);
            rawSources.push(fileName);
            sourceToSourceIndexMap.set(source, sourceIndex);
        }
        exit();
        return sourceIndex;
    }

    /* eslint-disable no-restricted-syntax */
    function setSourceContent(sourceIndex: number, content: string | null) {
        enter();
        if (content !== null) {
            if (!sourcesContent) sourcesContent = [];
            while (sourcesContent.length < sourceIndex) {
                sourcesContent.push(null);
            }
            sourcesContent[sourceIndex] = content;
        }
        exit();
    }
    /* eslint-enable no-restricted-syntax */

    function addName(name: string) {
        enter();
        if (!nameToNameIndexMap) nameToNameIndexMap = new Map();
        let nameIndex = nameToNameIndexMap.get(name);
        if (nameIndex === undefined) {
            nameIndex = names.length;
            names.push(name);
            nameToNameIndexMap.set(name, nameIndex);
        }
        exit();
        return nameIndex;
    }

    function isNewGeneratedPosition(generatedLine: number, generatedCharacter: number) {
        return !hasPending
            || pendingGeneratedLine !== generatedLine
            || pendingGeneratedCharacter !== generatedCharacter;
    }

    function isBacktrackingSourcePosition(sourceIndex: number | undefined, sourceLine: number | undefined, sourceCharacter: number | undefined) {
        return sourceIndex !== undefined
            && sourceLine !== undefined
            && sourceCharacter !== undefined
            && pendingSourceIndex === sourceIndex
            && (pendingSourceLine > sourceLine
                || pendingSourceLine === sourceLine && pendingSourceCharacter > sourceCharacter);
    }

    function addMapping(generatedLine: number, generatedCharacter: number, sourceIndex?: number, sourceLine?: number, sourceCharacter?: number, nameIndex?: number) {
        Debug.assert(generatedLine >= pendingGeneratedLine, "generatedLine cannot backtrack");
        Debug.assert(generatedCharacter >= 0, "generatedCharacter cannot be negative");
        Debug.assert(sourceIndex === undefined || sourceIndex >= 0, "sourceIndex cannot be negative");
        Debug.assert(sourceLine === undefined || sourceLine >= 0, "sourceLine cannot be negative");
        Debug.assert(sourceCharacter === undefined || sourceCharacter >= 0, "sourceCharacter cannot be negative");
        enter();
        // If this location wasn't recorded or the location in source is going backwards, record the mapping
        if (
            isNewGeneratedPosition(generatedLine, generatedCharacter) ||
            isBacktrackingSourcePosition(sourceIndex, sourceLine, sourceCharacter)
        ) {
            commitPendingMapping();
            pendingGeneratedLine = generatedLine;
            pendingGeneratedCharacter = generatedCharacter;
            hasPendingSource = false;
            hasPendingName = false;
            hasPending = true;
        }

        if (sourceIndex !== undefined && sourceLine !== undefined && sourceCharacter !== undefined) {
            pendingSourceIndex = sourceIndex;
            pendingSourceLine = sourceLine;
            pendingSourceCharacter = sourceCharacter;
            hasPendingSource = true;
            if (nameIndex !== undefined) {
                pendingNameIndex = nameIndex;
                hasPendingName = true;
            }
        }
        exit();
    }

    function appendSourceMap(generatedLine: number, generatedCharacter: number, map: RawSourceMap, sourceMapPath: string, start?: LineAndCharacter, end?: LineAndCharacter) {
        Debug.assert(generatedLine >= pendingGeneratedLine, "generatedLine cannot backtrack");
        Debug.assert(generatedCharacter >= 0, "generatedCharacter cannot be negative");
        enter();
        // First, decode the old component sourcemap
        const sourceIndexToNewSourceIndexMap: number[] = [];
        let nameIndexToNewNameIndexMap: number[] | undefined;
        const mappingIterator = decodeMappings(map.mappings);
        for (const raw of mappingIterator) {
            if (
                end && (
                    raw.generatedLine > end.line ||
                    (raw.generatedLine === end.line && raw.generatedCharacter > end.character)
                )
            ) {
                break;
            }

            if (
                start && (
                    raw.generatedLine < start.line ||
                    (start.line === raw.generatedLine && raw.generatedCharacter < start.character)
                )
            ) {
                continue;
            }
            // Then reencode all the updated mappings into the overall map
            let newSourceIndex: number | undefined;
            let newSourceLine: number | undefined;
            let newSourceCharacter: number | undefined;
            let newNameIndex: number | undefined;
            if (raw.sourceIndex !== undefined) {
                newSourceIndex = sourceIndexToNewSourceIndexMap[raw.sourceIndex];
                if (newSourceIndex === undefined) {
                    // Apply offsets to each position and fixup source entries
                    const rawPath = map.sources[raw.sourceIndex];
                    const relativePath = map.sourceRoot ? combinePaths(map.sourceRoot, rawPath) : rawPath;
                    const combinedPath = combinePaths(getDirectoryPath(sourceMapPath), relativePath);
                    sourceIndexToNewSourceIndexMap[raw.sourceIndex] = newSourceIndex = addSource(combinedPath);
                    if (map.sourcesContent && typeof map.sourcesContent[raw.sourceIndex] === "string") {
                        setSourceContent(newSourceIndex, map.sourcesContent[raw.sourceIndex]);
                    }
                }

                newSourceLine = raw.sourceLine;
                newSourceCharacter = raw.sourceCharacter;
                if (map.names && raw.nameIndex !== undefined) {
                    if (!nameIndexToNewNameIndexMap) nameIndexToNewNameIndexMap = [];
                    newNameIndex = nameIndexToNewNameIndexMap[raw.nameIndex];
                    if (newNameIndex === undefined) {
                        nameIndexToNewNameIndexMap[raw.nameIndex] = newNameIndex = addName(map.names[raw.nameIndex]);
                    }
                }
            }

            const rawGeneratedLine = raw.generatedLine - (start ? start.line : 0);
            const newGeneratedLine = rawGeneratedLine + generatedLine;
            const rawGeneratedCharacter = start && start.line === raw.generatedLine ? raw.generatedCharacter - start.character : raw.generatedCharacter;
            const newGeneratedCharacter = rawGeneratedLine === 0 ? rawGeneratedCharacter + generatedCharacter : rawGeneratedCharacter;
            addMapping(newGeneratedLine, newGeneratedCharacter, newSourceIndex, newSourceLine, newSourceCharacter, newNameIndex);
        }
        exit();
    }

    function shouldCommitMapping() {
        return !hasLast
            || lastGeneratedLine !== pendingGeneratedLine
            || lastGeneratedCharacter !== pendingGeneratedCharacter
            || lastSourceIndex !== pendingSourceIndex
            || lastSourceLine !== pendingSourceLine
            || lastSourceCharacter !== pendingSourceCharacter
            || lastNameIndex !== pendingNameIndex;
    }

    function appendMappingCharCode(charCode: number) {
        mappingCharCodes.push(charCode);
        // String.fromCharCode accepts its arguments on the stack, so we have to chunk the input,
        // otherwise we can get stack overflows for large source maps
        if (mappingCharCodes.length >= 1024) {
            flushMappingBuffer();
        }
    }

    function commitPendingMapping() {
        if (!hasPending || !shouldCommitMapping()) {
            return;
        }

        enter();

        // Line/Comma delimiters
        if (lastGeneratedLine < pendingGeneratedLine) {
            // Emit line delimiters
            do {
                appendMappingCharCode(CharacterCodes.semicolon);
                lastGeneratedLine++;
            }
            while (lastGeneratedLine < pendingGeneratedLine);
            // Only need to set this once
            lastGeneratedCharacter = 0;
        }
        else {
            Debug.assertEqual(lastGeneratedLine, pendingGeneratedLine, "generatedLine cannot backtrack");
            // Emit comma to separate the entry
            if (hasLast) {
                appendMappingCharCode(CharacterCodes.comma);
            }
        }

        // 1. Relative generated character
        appendBase64VLQ(pendingGeneratedCharacter - lastGeneratedCharacter);
        lastGeneratedCharacter = pendingGeneratedCharacter;

        if (hasPendingSource) {
            // 2. Relative sourceIndex
            appendBase64VLQ(pendingSourceIndex - lastSourceIndex);
            lastSourceIndex = pendingSourceIndex;

            // 3. Relative source line
            appendBase64VLQ(pendingSourceLine - lastSourceLine);
            lastSourceLine = pendingSourceLine;

            // 4. Relative source character
            appendBase64VLQ(pendingSourceCharacter - lastSourceCharacter);
            lastSourceCharacter = pendingSourceCharacter;

            if (hasPendingName) {
                // 5. Relative nameIndex
                appendBase64VLQ(pendingNameIndex - lastNameIndex);
                lastNameIndex = pendingNameIndex;
            }
        }

        hasLast = true;
        exit();
    }

    function flushMappingBuffer(): void {
        if (mappingCharCodes.length > 0) {
            mappings += String.fromCharCode.apply(undefined, mappingCharCodes);
            mappingCharCodes.length = 0;
        }
    }

    function toJSON(): RawSourceMap {
        commitPendingMapping();
        flushMappingBuffer();
        return {
            version: 3,
            file,
            sourceRoot,
            sources,
            names,
            mappings,
            sourcesContent,
        };
    }

    function appendBase64VLQ(inValue: number): void {
        // Add a new least significant bit that has the sign of the value.
        // if negative number the least significant bit that gets added to the number has value 1
        // else least significant bit value that gets added is 0
        // eg. -1 changes to binary : 01 [1] => 3
        //     +1 changes to binary : 01 [0] => 2
        if (inValue < 0) {
            inValue = ((-inValue) << 1) + 1;
        }
        else {
            inValue = inValue << 1;
        }

        // Encode 5 bits at a time starting from least significant bits
        do {
            let currentDigit = inValue & 31; // 11111
            inValue = inValue >> 5;
            if (inValue > 0) {
                // There are still more digits to decode, set the msb (6th bit)
                currentDigit = currentDigit | 32;
            }
            appendMappingCharCode(base64FormatEncode(currentDigit));
        }
        while (inValue > 0);
    }
}

// Sometimes tools can see the following line as a source mapping url comment, so we mangle it a bit (the [M])
/** @internal */
export const sourceMapCommentRegExpDontCareLineStart: RegExp = /\/\/[@#] source[M]appingURL=(.+)\r?\n?$/; // eslint-disable-line regexp/no-useless-character-class
/** @internal */
export const sourceMapCommentRegExp: RegExp = /^\/\/[@#] source[M]appingURL=(.+)\r?\n?$/; // eslint-disable-line regexp/no-useless-character-class

/** @internal */
export const whitespaceOrMapCommentRegExp: RegExp = /^\s*(\/\/[@#] .*)?$/;

/** @internal */
export interface LineInfo {
    getLineCount(): number;
    getLineText(line: number): string;
}

/** @internal */
export function getLineInfo(text: string, lineStarts: readonly number[]): LineInfo {
    return {
        getLineCount: () => lineStarts.length,
        getLineText: line => text.substring(lineStarts[line], lineStarts[line + 1]),
    };
}

/**
 * Tries to find the sourceMappingURL comment at the end of a file.
 *
 * @internal
 */
export function tryGetSourceMappingURL(lineInfo: LineInfo): string | undefined {
    for (let index = lineInfo.getLineCount() - 1; index >= 0; index--) {
        const line = lineInfo.getLineText(index);
        const comment = sourceMapCommentRegExp.exec(line);
        if (comment) {
            return comment[1].trimEnd();
        }
        // If we see a non-whitespace/map comment-like line, break, to avoid scanning up the entire file
        else if (!line.match(whitespaceOrMapCommentRegExp)) {
            break;
        }
    }
}

/* eslint-disable no-restricted-syntax */
function isStringOrNull(x: any) {
    return typeof x === "string" || x === null;
}

function isRawSourceMap(x: any): x is RawSourceMap {
    return x !== null
        && typeof x === "object"
        && x.version === 3
        && typeof x.file === "string"
        && typeof x.mappings === "string"
        && isArray(x.sources) && every(x.sources, isString)
        && (x.sourceRoot === undefined || x.sourceRoot === null || typeof x.sourceRoot === "string")
        && (x.sourcesContent === undefined || x.sourcesContent === null || isArray(x.sourcesContent) && every(x.sourcesContent, isStringOrNull))
        && (x.names === undefined || x.names === null || isArray(x.names) && every(x.names, isString));
}
/* eslint-enable no-restricted-syntax */

/** @internal */
export function tryParseRawSourceMap(text: string): RawSourceMap | undefined {
    try {
        const parsed = JSON.parse(text);
        if (isRawSourceMap(parsed)) {
            return parsed;
        }
    }
    catch {
        // empty
    }

    return undefined;
}

/** @internal */
export interface MappingsDecoder extends IterableIterator<Mapping> {
    readonly pos: number;
    readonly error: string | undefined;
    readonly state: Required<Mapping>;
}

/** @internal */
export interface Mapping {
    generatedLine: number;
    generatedCharacter: number;
    sourceIndex?: number;
    sourceLine?: number;
    sourceCharacter?: number;
    nameIndex?: number;
}

/** @internal */
export interface SourceMapping extends Mapping {
    sourceIndex: number;
    sourceLine: number;
    sourceCharacter: number;
}

/** @internal */
export function decodeMappings(mappings: string): MappingsDecoder {
    let done = false;
    let pos = 0;
    let generatedLine = 0;
    let generatedCharacter = 0;
    let sourceIndex = 0;
    let sourceLine = 0;
    let sourceCharacter = 0;
    let nameIndex = 0;
    let error: string | undefined;

    // TODO(jakebailey): can we implement this without writing next ourselves?
    return {
        get pos() {
            return pos;
        },
        get error() {
            return error;
        },
        get state() {
            return captureMapping(/*hasSource*/ true, /*hasName*/ true);
        },
        next() {
            while (!done && pos < mappings.length) {
                const ch = mappings.charCodeAt(pos);
                if (ch === CharacterCodes.semicolon) {
                    // new line
                    generatedLine++;
                    generatedCharacter = 0;
                    pos++;
                    continue;
                }

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

                let hasSource = false;
                let hasName = false;

                generatedCharacter += base64VLQFormatDecode();
                if (hasReportedError()) return stopIterating();
                if (generatedCharacter < 0) return setErrorAndStopIterating("Invalid generatedCharacter found");

                if (!isSourceMappingSegmentEnd()) {
                    hasSource = true;

                    sourceIndex += base64VLQFormatDecode();
                    if (hasReportedError()) return stopIterating();
                    if (sourceIndex < 0) return setErrorAndStopIterating("Invalid sourceIndex found");
                    if (isSourceMappingSegmentEnd()) return setErrorAndStopIterating("Unsupported Format: No entries after sourceIndex");

                    sourceLine += base64VLQFormatDecode();
                    if (hasReportedError()) return stopIterating();
                    if (sourceLine < 0) return setErrorAndStopIterating("Invalid sourceLine found");
                    if (isSourceMappingSegmentEnd()) return setErrorAndStopIterating("Unsupported Format: No entries after sourceLine");

                    sourceCharacter += base64VLQFormatDecode();
                    if (hasReportedError()) return stopIterating();
                    if (sourceCharacter < 0) return setErrorAndStopIterating("Invalid sourceCharacter found");

                    if (!isSourceMappingSegmentEnd()) {
                        hasName = true;
                        nameIndex += base64VLQFormatDecode();
                        if (hasReportedError()) return stopIterating();
                        if (nameIndex < 0) return setErrorAndStopIterating("Invalid nameIndex found");

                        if (!isSourceMappingSegmentEnd()) return setErrorAndStopIterating("Unsupported Error Format: Entries after nameIndex");
                    }
                }

                return { value: captureMapping(hasSource, hasName), done };
            }

            return stopIterating();
        },
        [Symbol.iterator]() {
            return this;
        },
    };

    function captureMapping(hasSource: true, hasName: true): Required<Mapping>;
    function captureMapping(hasSource: boolean, hasName: boolean): Mapping;
    function captureMapping(hasSource: boolean, hasName: boolean): Mapping {
        return {
            generatedLine,
            generatedCharacter,
            sourceIndex: hasSource ? sourceIndex : undefined,
            sourceLine: hasSource ? sourceLine : undefined,
            sourceCharacter: hasSource ? sourceCharacter : undefined,
            nameIndex: hasName ? nameIndex : undefined,
        };
    }

    function stopIterating(): { value: never; done: true; } {
        done = true;
        return { value: undefined!, done: true };
    }

    function setError(message: string) {
        if (error === undefined) {
            error = message;
        }
    }

    function setErrorAndStopIterating(message: string) {
        setError(message);
        return stopIterating();
    }

    function hasReportedError() {
        return error !== undefined;
    }

    function isSourceMappingSegmentEnd() {
        return (pos === mappings.length ||
            mappings.charCodeAt(pos) === CharacterCodes.comma ||
            mappings.charCodeAt(pos) === CharacterCodes.semicolon);
    }

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

        for (; moreDigits; pos++) {
            if (pos >= mappings.length) return setError("Error in decoding base64VLQFormatDecode, past the mapping string"), -1;

            // 6 digit number
            const currentByte = base64FormatDecode(mappings.charCodeAt(pos));
            if (currentByte === -1) return setError("Invalid character in VLQ"), -1;

            // 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;
    }
}

/** @internal */
export function sameMapping<T extends Mapping>(left: T, right: T): boolean {
    return left === right
        || left.generatedLine === right.generatedLine
            && left.generatedCharacter === right.generatedCharacter
            && left.sourceIndex === right.sourceIndex
            && left.sourceLine === right.sourceLine
            && left.sourceCharacter === right.sourceCharacter
            && left.nameIndex === right.nameIndex;
}

/** @internal */
export function isSourceMapping(mapping: Mapping): mapping is SourceMapping {
    return mapping.sourceIndex !== undefined
        && mapping.sourceLine !== undefined
        && mapping.sourceCharacter !== undefined;
}

function base64FormatEncode(value: number) {
    return value >= 0 && value < 26 ? CharacterCodes.A + value :
        value >= 26 && value < 52 ? CharacterCodes.a + value - 26 :
        value >= 52 && value < 62 ? CharacterCodes._0 + value - 52 :
        value === 62 ? CharacterCodes.plus :
        value === 63 ? CharacterCodes.slash :
        Debug.fail(`${value}: not a base64 value`);
}

function base64FormatDecode(ch: number) {
    return ch >= CharacterCodes.A && ch <= CharacterCodes.Z ? ch - CharacterCodes.A :
        ch >= CharacterCodes.a && ch <= CharacterCodes.z ? ch - CharacterCodes.a + 26 :
        ch >= CharacterCodes._0 && ch <= CharacterCodes._9 ? ch - CharacterCodes._0 + 52 :
        ch === CharacterCodes.plus ? 62 :
        ch === CharacterCodes.slash ? 63 :
        -1;
}

interface MappedPosition {
    generatedPosition: number;
    source: string | undefined;
    sourceIndex: number | undefined;
    sourcePosition: number | undefined;
    nameIndex: number | undefined;
}

interface SourceMappedPosition extends MappedPosition {
    source: string;
    sourceIndex: number;
    sourcePosition: number;
}

function isSourceMappedPosition(value: MappedPosition): value is SourceMappedPosition {
    return value.sourceIndex !== undefined
        && value.sourcePosition !== undefined;
}

function sameMappedPosition(left: MappedPosition, right: MappedPosition) {
    return left.generatedPosition === right.generatedPosition
        && left.sourceIndex === right.sourceIndex
        && left.sourcePosition === right.sourcePosition;
}

function compareSourcePositions(left: SourceMappedPosition, right: SourceMappedPosition) {
    // Compares sourcePosition without comparing sourceIndex
    // since the mappings are grouped by sourceIndex
    Debug.assert(left.sourceIndex === right.sourceIndex);
    return compareValues(left.sourcePosition, right.sourcePosition);
}

function compareGeneratedPositions(left: MappedPosition, right: MappedPosition) {
    return compareValues(left.generatedPosition, right.generatedPosition);
}

function getSourcePositionOfMapping(value: SourceMappedPosition) {
    return value.sourcePosition;
}

function getGeneratedPositionOfMapping(value: MappedPosition) {
    return value.generatedPosition;
}

/** @internal */
export function createDocumentPositionMapper(host: DocumentPositionMapperHost, map: RawSourceMap, mapPath: string): DocumentPositionMapper {
    const mapDirectory = getDirectoryPath(mapPath);
    const sourceRoot = map.sourceRoot ? getNormalizedAbsolutePath(map.sourceRoot, mapDirectory) : mapDirectory;
    const generatedAbsoluteFilePath = getNormalizedAbsolutePath(map.file, mapDirectory);
    const generatedFile = host.getSourceFileLike(generatedAbsoluteFilePath);
    const sourceFileAbsolutePaths = map.sources.map(source => getNormalizedAbsolutePath(source, sourceRoot));
    const sourceToSourceIndexMap = new Map(sourceFileAbsolutePaths.map((source, i) => [host.getCanonicalFileName(source), i]));
    let decodedMappings: readonly MappedPosition[] | undefined;
    let generatedMappings: SortedReadonlyArray<MappedPosition> | undefined;
    let sourceMappings: readonly SortedReadonlyArray<SourceMappedPosition>[] | undefined;

    return {
        getSourcePosition,
        getGeneratedPosition,
    };

    function processMapping(mapping: Mapping): MappedPosition {
        const generatedPosition = generatedFile !== undefined
            ? getPositionOfLineAndCharacter(generatedFile, mapping.generatedLine, mapping.generatedCharacter, /*allowEdits*/ true)
            : -1;
        let source: string | undefined;
        let sourcePosition: number | undefined;
        if (isSourceMapping(mapping)) {
            const sourceFile = host.getSourceFileLike(sourceFileAbsolutePaths[mapping.sourceIndex]);
            source = map.sources[mapping.sourceIndex];
            sourcePosition = sourceFile !== undefined
                ? getPositionOfLineAndCharacter(sourceFile, mapping.sourceLine, mapping.sourceCharacter, /*allowEdits*/ true)
                : -1;
        }
        return {
            generatedPosition,
            source,
            sourceIndex: mapping.sourceIndex,
            sourcePosition,
            nameIndex: mapping.nameIndex,
        };
    }

    function getDecodedMappings() {
        if (decodedMappings === undefined) {
            const decoder = decodeMappings(map.mappings);
            const mappings = arrayFrom(decoder, processMapping);
            if (decoder.error !== undefined) {
                if (host.log) {
                    host.log(`Encountered error while decoding sourcemap: ${decoder.error}`);
                }
                decodedMappings = emptyArray;
            }
            else {
                decodedMappings = mappings;
            }
        }
        return decodedMappings;
    }

    function getSourceMappings(sourceIndex: number) {
        if (sourceMappings === undefined) {
            const lists: SourceMappedPosition[][] = [];
            for (const mapping of getDecodedMappings()) {
                if (!isSourceMappedPosition(mapping)) continue;
                let list = lists[mapping.sourceIndex];
                if (!list) lists[mapping.sourceIndex] = list = [];
                list.push(mapping);
            }
            sourceMappings = lists.map(list => sortAndDeduplicate<SourceMappedPosition>(list, compareSourcePositions, sameMappedPosition));
        }
        return sourceMappings[sourceIndex];
    }

    function getGeneratedMappings() {
        if (generatedMappings === undefined) {
            const list: MappedPosition[] = [];
            for (const mapping of getDecodedMappings()) {
                list.push(mapping);
            }
            generatedMappings = sortAndDeduplicate(list, compareGeneratedPositions, sameMappedPosition);
        }
        return generatedMappings;
    }

    function getGeneratedPosition(loc: DocumentPosition): DocumentPosition {
        const sourceIndex = sourceToSourceIndexMap.get(host.getCanonicalFileName(loc.fileName));
        if (sourceIndex === undefined) return loc;

        const sourceMappings = getSourceMappings(sourceIndex);
        if (!some(sourceMappings)) return loc;

        let targetIndex = binarySearchKey(sourceMappings, loc.pos, getSourcePositionOfMapping, compareValues);
        if (targetIndex < 0) {
            // if no exact match, closest is 2's complement of result
            targetIndex = ~targetIndex;
        }

        const mapping = sourceMappings[targetIndex];
        if (mapping === undefined || mapping.sourceIndex !== sourceIndex) {
            return loc;
        }

        return { fileName: generatedAbsoluteFilePath, pos: mapping.generatedPosition }; // Closest pos
    }

    function getSourcePosition(loc: DocumentPosition): DocumentPosition {
        const generatedMappings = getGeneratedMappings();
        if (!some(generatedMappings)) return loc;

        let targetIndex = binarySearchKey(generatedMappings, loc.pos, getGeneratedPositionOfMapping, compareValues);
        if (targetIndex < 0) {
            // if no exact match, closest is 2's complement of result
            targetIndex = ~targetIndex;
        }

        const mapping = generatedMappings[targetIndex];
        if (mapping === undefined || !isSourceMappedPosition(mapping)) {
            return loc;
        }

        return { fileName: sourceFileAbsolutePaths[mapping.sourceIndex], pos: mapping.sourcePosition }; // Closest pos
    }
}

/** @internal */
export const identitySourceMapConsumer: DocumentPositionMapper = {
    getSourcePosition: identity,
    getGeneratedPosition: identity,
};