[watson]

Summary

DEBUG-6327: list the instrumented functions a build ships, with their repository path and original line range, so Live Debugger can upload them as symbols. The upload is #593; for now the only consumer is an opt-in debug dump. Without DD_LIVE_DEBUGGER_SYMBOL_TABLE_PATH, the plugin adds no hooks and no build time.

buildReport                     # one-off builds only, not watch mode or dev servers
  for each emitted JS chunk
    scanChunk                   # pair $dd_probes('<id>') … $dd_throw( like brackets; nesting = parent
    readChunkDebugId            # from the runtime bootstrap
    locateFunctions             # start: $dd_probes in the final source map
                                # end: last mapped token up to $dd_throw, because minifiers and
                                #   expression-body arrows leave the marker itself unmapped
  buildSymbolTable              # path from the ID: strip ?query, resolve Yarn virtual paths + symlinks,
                                #   relative to the git root; dedupe on (ID, file, range)
  serializeSymbolTable          # SymDB scopes: MODULE per file, nested FUNCTION scopes, language "browser"
  writeSymbolTable              # never inside the output directory

No output parsing and no transform-hook collection, so it works with persistent bundler caches and only lists functions that survive tree-shaking. Never fails the build: problems are logged as warnings.

Also: core's outputJson now resolves once the file is written, not when the data has been read. The new tests exposed the race.

Evidence

• Before: nothing records which functions a build ships or where they are.
  After: symbolTable.integration.test.ts builds a fixture with esbuild, Rollup, Rspack, Vite and webpack, plus a minified Rspack production build: build rooted in a repo subdirectory, symlinked workspace package, Yarn PnP virtual path, loader query string on webpack and Rspack, multi-line arrow function with an expression body. E.g. for app/src/math.js:

  {
    "scope_type": "MODULE",
    "name": "app/src/math.js",
    "source_file": "app/src/math.js",
    "language_specifics": { "chunk_debug_ids": ["…"] },
    "scopes": [
      {
        "scope_type": "FUNCTION",
        "name": "add",
        "source_file": "app/src/math.js",
        "start_line": 1,
        "end_line": 6,
        "language_specifics": { "function_id": "src/math.js;add" },
        "scopes": [
          {
            "scope_type": "FUNCTION",
            "name": "double",
            "source_file": "app/src/math.js",
            "start_line": 2,
            "end_line": 4,
            "language_specifics": { "function_id": "src/math.js;double" }
          }
        ]
      }
    ]
  }

• Before: collecting in the transform hook would miss every module restored from webpack's filesystem cache.
  After: a warm-cache webpack build (transform didn't run) produces the same table as the cold build.

• web-ui (spa-rspack, production build with source maps, Live Debugger + RUM privacy, local plugin linked):

  Functions / files	605,487 / 94,051
  With a line range	99% (the rest are mostly compiler-injected helpers like _define_property)
  Yarn virtual-path functions	8,182, all with repository-relative sourceFile
  Table size	233 MB JSON, 12.9 MB gzipped
  Generation time	62–76 s on a ~37 min build (~3%); the build with the dump took 55 s longer wall-clock

  The first web-ui run had 45% of functions without a line range: minified expression-body arrows. The fallback lookups in locateFunctions fixed that; the integration test now covers it.

• Live Debugger suite: 437/437. yarn typecheck:all and yarn cli integrity pass.

Merge Danger

Door: two-way

Nothing new runs unless DD_LIVE_DEBUGGER_SYMBOL_TABLE_PATH is set.

Blast Radius: minimal

• Published packages gain a direct dependency on @jridgewell/trace-mapping 0.3.31, already installed through @jridgewell/remapping.
• outputJson resolves slightly later for its other caller, the output plugin.
• The transform now uses a constant for $dd_throw; generated code is unchanged.

🤖 Generated with Claude Code

[github-actions]

Live Debugger Runtime Benchmark

Benchmark results were not produced. Check the workflow logs for details.