evanw/esbuild · error · Error

Duplicate source ${JSON.stringify(source)} found in source m

Error message

Duplicate source ${JSON.stringify(source)} found in source map

What it means

Thrown at scripts/verify-source-map.js:877. After parsing the generated source map, the harness iterates `sources` and counts how many times each entry appears; if any source path appears more than once it raises this error. Duplicate source entries make originalPositionFor / sourceContentFor ambiguous, so the map is rejected before deeper checks run.

Source

Thrown at scripts/verify-source-map.js:877

        const positions = map.allGeneratedPositionsFor({ source, line: inLine, column: inColumn })
        recordCheck(positions.length > 0, `expected generated positions: 1, observed generated positions: ${positions.length}`)
        let found = false
        for (const { line, column } of positions) {
          if (line === outLine && column === outColumn) {
            found = true
            break
          }
        }
        const expectedPosition = JSON.stringify({ line: outLine, column: outColumn })
        const observedPositions = JSON.stringify(positions)
        recordCheck(found, `expected generated position: ${expectedPosition}, observed generated positions: ${observedPositions}`)
      }
    }

    const sources = JSON.parse(outCodeMap).sources
    for (let source of sources) {
      if (sources.filter(s => s === source).length > 1) {
        throw new Error(`Duplicate source ${JSON.stringify(source)} found in source map`)
      }
    }

    const outMap = await new SourceMapConsumer(outCodeMap)
    checkMap(outCode, outMap)

    // Check that every generated location has an associated original position.
    // This only works when not bundling because bundling includes runtime code.
    if (flags.indexOf('--bundle') < 0) {
      // The last line doesn't have a source map entry, but that should be ok.
      const outLines = outCode.trimRight().split('\n');

      for (let outLine = 0; outLine < outLines.length; outLine++) {
        if (outLines[outLine].startsWith('#!') || outLines[outLine].startsWith('//')) {
          // Ignore the hashbang line and the source map comment itself
          continue;
        }

View on GitHub (pinned to f6058f8364)

Solutions

1. Inspect the generated `.map` file's `sources` array and identify the duplicated path(s).
2. If esbuild produced the duplicate legitimately (same path twice), treat it as an esbuild bug to fix in source-map generation (deduplicate sources).
3. If a plugin or path-normalization config caused the collision, normalize the source paths so they are unique.

Example fix

// before (.map sources contains a duplicate)
{ "sources": ["src/a.js", "src/a.js", "src/b.js"] }

// after (esbuild deduplicates; map is unambiguous)
{ "sources": ["src/a.js", "src/b.js"] }

function hasUniqueSources(mapObj) {
  const seen = new Set();
  for (const s of mapObj.sources) {
    if (seen.has(s)) return s; // duplicate
    seen.add(s);
  }
  return null;
}

try { runSourceMapCheck(); }
catch (e) {
  if (/Duplicate source .* found in source map/.test(e.message)) console.error('esbuild emitted a duplicate entry in .sources:', e.message);
  throw e;
}

When it happens

Trigger: esbuild emits a source map whose `sources` array lists the same source path twice (or more). This can happen when bundling combines modules that share a resolved path, when path normalization produces colliding strings, or when a plugin returns duplicate source entries.

Common situations: A bundling or source-map chaining change causes two input modules to resolve to the same source path in the map; a regression in esbuild's source-map deduplication; or nested source-map merging duplicates an entry.

Related errors

• Failed to find "${id}" in output
• Got null for source content for "${source}"
• Failed to find "${id}" in input
• Duplicated test name "${name}" in ${file}
• The esbuild JavaScript API cannot be bundled. Please mark th

AI-assisted analysis of evanw/esbuild@f6058f8364 (2026-08-09). Data as JSON: /api/errors/31244a29c753b6ea. Report an issue: GitHub.