trace-mapping.ts

import { encode, decode } from '@jridgewell/sourcemap-codec';

import resolve from './resolve';
import stripFilename from './strip-filename';
import maybeSort from './sort';
import buildBySources from './by-source';
import {
  memoizedState,
  memoizedBinarySearch,
  upperBound,
  lowerBound,
  found as bsFound,
} from './binary-search';
import {
  COLUMN,
  SOURCES_INDEX,
  SOURCE_LINE,
  SOURCE_COLUMN,
  NAMES_INDEX,
  REV_GENERATED_LINE,
  REV_GENERATED_COLUMN,
} from './sourcemap-segment';

import type { SourceMapSegment, ReverseSegment } from './sourcemap-segment';
import type {
  SourceMapV3,
  DecodedSourceMap,
  EncodedSourceMap,
  InvalidOriginalMapping,
  OriginalMapping,
  InvalidGeneratedMapping,
  GeneratedMapping,
  SourceMapInput,
  Needle,
  SourceNeedle,
  SourceMap,
  EachMapping,
  Bias,
} from './types';
import type { Source } from './by-source';
import type { MemoState } from './binary-search';

export type { SourceMapSegment } from './sourcemap-segment';
export type {
  SourceMap,
  DecodedSourceMap,
  EncodedSourceMap,
  Section,
  SectionedSourceMap,
  SourceMapV3,
  Bias,
  EachMapping,
  GeneratedMapping,
  InvalidGeneratedMapping,
  InvalidOriginalMapping,
  Needle,
  OriginalMapping,
  OriginalMapping as Mapping,
  SectionedSourceMapInput,
  SourceMapInput,
  SourceNeedle,
} from './types';

const LINE_GTR_ZERO = '`line` must be greater than 0 (lines start at line 1)';
const COL_GTR_EQ_ZERO = '`column` must be greater than or equal to 0 (columns start at column 0)';

export const LEAST_UPPER_BOUND = -1;
export const GREATEST_LOWER_BOUND = 1;

/**
 * Returns the encoded (VLQ string) form of the SourceMap's mappings field.
 */
export let encodedMappings: (map: TraceMap) => EncodedSourceMap['mappings'];

/**
 * Returns the decoded (array of lines of segments) form of the SourceMap's mappings field.
 */
export let decodedMappings: (map: TraceMap) => Readonly<DecodedSourceMap['mappings']>;

/**
 * A low-level API to find the segment associated with a generated line/column (think, from a
 * stack trace). Line and column here are 0-based, unlike `originalPositionFor`.
 */
export let traceSegment: (
  map: TraceMap,
  line: number,
  column: number,
) => Readonly<SourceMapSegment> | null;

/**
 * A higher-level API to find the source/line/column associated with a generated line/column
 * (think, from a stack trace). Line is 1-based, but column is 0-based, due to legacy behavior in
 * `source-map` library.
 */
export let originalPositionFor: (
  map: TraceMap,
  needle: Needle,
) => OriginalMapping | InvalidOriginalMapping;

/**
 * Finds the generated line/column position of the provided source/line/column source position.
 */
export let generatedPositionFor: (
  map: TraceMap,
  needle: SourceNeedle,
) => GeneratedMapping | InvalidGeneratedMapping;

/**
 * Finds all generated line/column positions of the provided source/line/column source position.
 */
export let allGeneratedPositionsFor: (map: TraceMap, needle: SourceNeedle) => GeneratedMapping[];

/**
 * Iterates each mapping in generated position order.
 */
export let eachMapping: (map: TraceMap, cb: (mapping: EachMapping) => void) => void;

/**
 * Retrieves the source content for a particular source, if its found. Returns null if not.
 */
export let sourceContentFor: (map: TraceMap, source: string) => string | null;

/**
 * A helper that skips sorting of the input map's mappings array, which can be expensive for larger
 * maps.
 */
export let presortedDecodedMap: (map: DecodedSourceMap, mapUrl?: string) => TraceMap;

/**
 * Returns a sourcemap object (with decoded mappings) suitable for passing to a library that expects
 * a sourcemap, or to JSON.stringify.
 */
export let decodedMap: (
  map: TraceMap,
) => Omit<DecodedSourceMap, 'mappings'> & { mappings: readonly SourceMapSegment[][] };

/**
 * Returns a sourcemap object (with encoded mappings) suitable for passing to a library that expects
 * a sourcemap, or to JSON.stringify.
 */
export let encodedMap: (map: TraceMap) => EncodedSourceMap;

export { AnyMap } from './any-map';

export class TraceMap implements SourceMap {
  declare version: SourceMapV3['version'];
  declare file: SourceMapV3['file'];
  declare names: SourceMapV3['names'];
  declare sourceRoot: SourceMapV3['sourceRoot'];
  declare sources: SourceMapV3['sources'];
  declare sourcesContent: SourceMapV3['sourcesContent'];

  declare resolvedSources: string[];
  private declare _encoded: string | undefined;

  private declare _decoded: SourceMapSegment[][] | undefined;
  private declare _decodedMemo: MemoState;

  private declare _bySources: Source[] | undefined;
  private declare _bySourceMemos: MemoState[] | undefined;

  constructor(map: SourceMapInput, mapUrl?: string | null) {
    const isString = typeof map === 'string';

    if (!isString && (map as unknown as { _decodedMemo: any })._decodedMemo) return map as TraceMap;

    const parsed = (isString ? JSON.parse(map) : map) as DecodedSourceMap | EncodedSourceMap;

    const { version, file, names, sourceRoot, sources, sourcesContent } = parsed;
    this.version = version;
    this.file = file;
    this.names = names || [];
    this.sourceRoot = sourceRoot;
    this.sources = sources;
    this.sourcesContent = sourcesContent;

    const from = resolve(sourceRoot || '', stripFilename(mapUrl));
    this.resolvedSources = sources.map((s) => resolve(s || '', from));

    const { mappings } = parsed;
    if (typeof mappings === 'string') {
      this._encoded = mappings;
      this._decoded = undefined;
    } else {
      this._encoded = undefined;
      this._decoded = maybeSort(mappings, isString);
    }

    this._decodedMemo = memoizedState();
    this._bySources = undefined;
    this._bySourceMemos = undefined;
  }

  static {
    encodedMappings = (map) => {
      return (map._encoded ??= encode(map._decoded!));
    };

    decodedMappings = (map) => {
      return (map._decoded ||= decode(map._encoded!));
    };

    traceSegment = (map, line, column) => {
      const decoded = decodedMappings(map);

      // It's common for parent source maps to have pointers to lines that have no
      // mapping (like a "//# sourceMappingURL=") at the end of the child file.
      if (line >= decoded.length) return null;

      const segments = decoded[line];
      const index = traceSegmentInternal(
        segments,
        map._decodedMemo,
        line,
        column,
        GREATEST_LOWER_BOUND,
      );

      return index === -1 ? null : segments[index];
    };

    originalPositionFor = (map, { line, column, bias }) => {
      line--;
      if (line < 0) throw new Error(LINE_GTR_ZERO);
      if (column < 0) throw new Error(COL_GTR_EQ_ZERO);

      const decoded = decodedMappings(map);

      // It's common for parent source maps to have pointers to lines that have no
      // mapping (like a "//# sourceMappingURL=") at the end of the child file.
      if (line >= decoded.length) return OMapping(null, null, null, null);

      const segments = decoded[line];
      const index = traceSegmentInternal(
        segments,
        map._decodedMemo,
        line,
        column,
        bias || GREATEST_LOWER_BOUND,
      );

      if (index === -1) return OMapping(null, null, null, null);

      const segment = segments[index];
      if (segment.length === 1) return OMapping(null, null, null, null);

      const { names, resolvedSources } = map;
      return OMapping(
        resolvedSources[segment[SOURCES_INDEX]],
        segment[SOURCE_LINE] + 1,
        segment[SOURCE_COLUMN],
        segment.length === 5 ? names[segment[NAMES_INDEX]] : null,
      );
    };

    allGeneratedPositionsFor = (map, { source, line, column, bias }) => {
      // SourceMapConsumer uses LEAST_UPPER_BOUND for some reason, so we follow suit.
      return generatedPosition(map, source, line, column, bias || LEAST_UPPER_BOUND, true);
    };

    generatedPositionFor = (map, { source, line, column, bias }) => {
      return generatedPosition(map, source, line, column, bias || GREATEST_LOWER_BOUND, false);
    };

    eachMapping = (map, cb) => {
      const decoded = decodedMappings(map);
      const { names, resolvedSources } = map;

      for (let i = 0; i < decoded.length; i++) {
        const line = decoded[i];
        for (let j = 0; j < line.length; j++) {
          const seg = line[j];

          const generatedLine = i + 1;
          const generatedColumn = seg[0];
          let source = null;
          let originalLine = null;
          let originalColumn = null;
          let name = null;
          if (seg.length !== 1) {
            source = resolvedSources[seg[1]];
            originalLine = seg[2] + 1;
            originalColumn = seg[3];
          }
          if (seg.length === 5) name = names[seg[4]];

          cb({
            generatedLine,
            generatedColumn,
            source,
            originalLine,
            originalColumn,
            name,
          } as EachMapping);
        }
      }
    };

    sourceContentFor = (map, source) => {
      const { sources, resolvedSources, sourcesContent } = map;
      if (sourcesContent == null) return null;

      let index = sources.indexOf(source);
      if (index === -1) index = resolvedSources.indexOf(source);

      return index === -1 ? null : sourcesContent[index];
    };

    presortedDecodedMap = (map, mapUrl) => {
      const tracer = new TraceMap(clone(map, []), mapUrl);
      tracer._decoded = map.mappings;
      return tracer;
    };

    decodedMap = (map) => {
      return clone(map, decodedMappings(map));
    };

    encodedMap = (map) => {
      return clone(map, encodedMappings(map));
    };

    function generatedPosition(
      map: TraceMap,
      source: string,
      line: number,
      column: number,
      bias: Bias,
      all: false,
    ): GeneratedMapping | InvalidGeneratedMapping;
    function generatedPosition(
      map: TraceMap,
      source: string,
      line: number,
      column: number,
      bias: Bias,
      all: true,
    ): GeneratedMapping[];
    function generatedPosition(
      map: TraceMap,
      source: string,
      line: number,
      column: number,
      bias: Bias,
      all: boolean,
    ): GeneratedMapping | InvalidGeneratedMapping | GeneratedMapping[] {
      line--;
      if (line < 0) throw new Error(LINE_GTR_ZERO);
      if (column < 0) throw new Error(COL_GTR_EQ_ZERO);

      const { sources, resolvedSources } = map;
      let sourceIndex = sources.indexOf(source);
      if (sourceIndex === -1) sourceIndex = resolvedSources.indexOf(source);
      if (sourceIndex === -1) return all ? [] : GMapping(null, null);

      const generated = (map._bySources ||= buildBySources(
        decodedMappings(map),
        (map._bySourceMemos = sources.map(memoizedState)),
      ));

      const segments = generated[sourceIndex][line];
      if (segments == null) return all ? [] : GMapping(null, null);

      const memo = map._bySourceMemos![sourceIndex];

      if (all) return sliceGeneratedPositions(segments, memo, line, column, bias);

      const index = traceSegmentInternal(segments, memo, line, column, bias);
      if (index === -1) return GMapping(null, null);

      const segment = segments[index];
      return GMapping(segment[REV_GENERATED_LINE] + 1, segment[REV_GENERATED_COLUMN]);
    }
  }
}

function clone<T extends string | readonly SourceMapSegment[][]>(
  map: TraceMap | DecodedSourceMap | EncodedSourceMap,
  mappings: T,
): T extends string ? EncodedSourceMap : DecodedSourceMap {
  return {
    version: map.version,
    file: map.file,
    names: map.names,
    sourceRoot: map.sourceRoot,
    sources: map.sources,
    sourcesContent: map.sourcesContent,
    mappings,
  } as any;
}

function OMapping(source: null, line: null, column: null, name: null): InvalidOriginalMapping;
function OMapping(
  source: string,
  line: number,
  column: number,
  name: string | null,
): OriginalMapping;
function OMapping(
  source: string | null,
  line: number | null,
  column: number | null,
  name: string | null,
): OriginalMapping | InvalidOriginalMapping {
  return { source, line, column, name } as any;
}

function GMapping(line: null, column: null): InvalidGeneratedMapping;
function GMapping(line: number, column: number): GeneratedMapping;
function GMapping(
  line: number | null,
  column: number | null,
): GeneratedMapping | InvalidGeneratedMapping {
  return { line, column } as any;
}

function traceSegmentInternal(
  segments: SourceMapSegment[],
  memo: MemoState,
  line: number,
  column: number,
  bias: Bias,
): number;
function traceSegmentInternal(
  segments: ReverseSegment[],
  memo: MemoState,
  line: number,
  column: number,
  bias: Bias,
): number;
function traceSegmentInternal(
  segments: SourceMapSegment[] | ReverseSegment[],
  memo: MemoState,
  line: number,
  column: number,
  bias: Bias,
): number {
  let index = memoizedBinarySearch(segments, column, memo, line);
  if (bsFound) {
    index = (bias === LEAST_UPPER_BOUND ? upperBound : lowerBound)(segments, column, index);
  } else if (bias === LEAST_UPPER_BOUND) index++;

  if (index === -1 || index === segments.length) return -1;
  return index;
}

function sliceGeneratedPositions(
  segments: ReverseSegment[],
  memo: MemoState,
  line: number,
  column: number,
  bias: Bias,
): GeneratedMapping[] {
  let min = traceSegmentInternal(segments, memo, line, column, GREATEST_LOWER_BOUND);

  // We ignored the bias when tracing the segment so that we're guarnateed to find the first (in
  // insertion order) segment that matched. Even if we did respect the bias when tracing, we would
  // still need to call `lowerBound()` to find the first segment, which is slower than just looking
  // for the GREATEST_LOWER_BOUND to begin with. The only difference that matters for us is when the
  // binary search didn't match, in which case GREATEST_LOWER_BOUND just needs to increment to
  // match LEAST_UPPER_BOUND.
  if (!bsFound && bias === LEAST_UPPER_BOUND) min++;

  if (min === -1 || min === segments.length) return [];

  // We may have found the segment that started at an earlier column. If this is the case, then we
  // need to slice all generated segments that match _that_ column, because all such segments span
  // to our desired column.
  const matchedColumn = bsFound ? column : segments[min][COLUMN];

  // The binary search is not guaranteed to find the lower bound when a match wasn't found.
  if (!bsFound) min = lowerBound(segments, matchedColumn, min);
  const max = upperBound(segments, matchedColumn, min);

  const result = [];
  for (; min <= max; min++) {
    const segment = segments[min];
    result.push(GMapping(segment[REV_GENERATED_LINE] + 1, segment[REV_GENERATED_COLUMN]));
  }
  return result;
}