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fix(build): inject createRequire banner to support CJS deps in ESM bundles #166

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Merged
derekmisler merged 2 commits into from
May 4, 2026
+12 −0
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fix(build): inject createRequire banner to support CJS deps in ESM bundles #166

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105606a
fix(build): inject createRequire banner to support CJS deps in ESM bu…
docker-agent May 4, 2026
843c614
fix(build): use var for require banner and add ESM-only comment
docker-agent May 4, 2026
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12 changes: 12 additions & 0 deletions tsup.config.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -34,4 +34,16 @@ export default defineConfig({
// runtime, so every npm dependency (AWS SDK, @actions/core, @octokit/…) must
// be bundled in. Node.js built-ins stay external automatically (platform:'node').
noExternal: [/.*/],
// CJS packages bundled into ESM (e.g. tunnel@0.0.6 via @actions/http-client)
// call require('net') / require('tls') at runtime. esbuild's __require shim
// checks `typeof require !== "undefined"` — which is false in pure ESM — and
// throws "Dynamic require of 'net' is not supported". Injecting createRequire
// as a top-level banner supplies a real require() before the shim runs,
// so those CJS modules can load Node.js built-ins normally.
// NOTE: this banner uses import/import.meta.url — only valid in ESM output.
// If format is ever extended to include 'cjs', this must be conditioned or
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@docker-agent docker-agent May 4, 2026

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[LOW] Module-scoped require in security-sensitive bundle — acknowledged

const require = createRequire(import.meta.url) introduces a working require() into the module scope of every output bundle. In pure ESM without this banner, no require exists at all.

A few things are worth being aware of (not blockers):

  • The require is module-scoped, not global — globalThis.require stays undefined, so only code already executing inside the bundle can call it.
  • All CJS require() calls in bundled deps route through esbuild's __require shim (which delegates to this require), so the exposure is bounded to the bundle's existing dependency graph.
  • None of the current dependencies (tunnel, @actions/core, AWS SDK) are known to pass user-controlled input to require() — but the action handles API keys and signed commits, so it's worth keeping in mind if new CJS dependencies are added.

Empirically confirmed to not cause issues in any current code path. ✅

// moved to a format-specific banner ({ esm: '...' }) to avoid a parse error.
banner: {
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@docker-agent docker-agent Bot May 4, 2026

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[LOW] Banner uses ESM-only syntax — will silently break if 'cjs' is ever added to format

The injected banner contains an import statement and import.meta.url, both of which are syntax errors in CommonJS output. The current config only emits ESM (format: ['esm']), so this is harmless today.

If a future maintainer extends format to ['esm', 'cjs'] (a common tsup pattern), the banner will be emitted verbatim into .cjs files and cause a parse failure. A short comment on the banner block noting the ESM-only constraint would guard against this:

// NOTE: this banner uses import/import.meta.url — only valid in ESM.
// If format is ever extended to include 'cjs', this must be conditioned
// or moved to a format-specific banner (banner: { esm: '...' }).
banner: {
  js: "import { createRequire } from 'node:module'; const require = createRequire(import.meta.url);",
},

Not a current bug; just a maintenance note.

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@docker-agent docker-agent May 4, 2026

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Done — the three-line ESM-only warning comment has been added directly above the banner: block in commit 843c614. It calls out explicitly that the import/import.meta.url syntax is only valid in ESM output and what action to take if 'cjs' is ever added to format.

js: "import { createRequire } from 'node:module'; var require = createRequire(import.meta.url);",
},
});
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