[Question / bug] Accessing .warnings and .errors from JS w/ plugins

[zaydek]

(Similar to #665)

I’m having trouble accessing the .warnings and .errors values when plugins is active, for the JS API. When plugins is inactive, this works as expected. But once I enable plugins: [envPlugin], for example, I get undefined; undefined.

I assume this is because esbuild is exiting early, but I’m not sure how to capture the output still. I’ve been reading the JS source but I haven’t been able to figure this out for myself.

// https://esbuild.github.io/plugins/#using-plugins
const envPlugin = {
	names: "env",
	setup(build) {
		// Intercept import paths called "env" so esbuild doesn't attempt
		// to map them to a file system location. Tag them with the "env-ns"
		// namespace to reserve them for this plugin.
		build.onResolve({ filter: /^env$/ }, args => ({
			path: args.path,
			namespace: "env-ns",
		}))
		// Load paths tagged with the "env-ns" namespace and behave as if
		// they point to a JSON file containing the environment variables.
		build.onLoad({ filter: /.*/, namespace: "env-ns" }, () => ({
			contents: JSON.stringify(process.env),
			loader: "json",
		}))
	},
}

require("esbuild")
	.build({
		bundle: true,
		entryPoints: ["app.js"],
		logLevel: "silent",
		outfile: "out.js",
		// plugins: [envPlugin], // <- Uncomment here
	})
	.catch(err => {
		console.log(err.errors)
		console.log(err.warnings)
	})

Expected output:

[
  {
    detail: undefined,
    location: {
      column: 7,
      file: 'app.js',
      length: 1,
      line: 1,
      lineText: 'imports{ PATH } from "env"'
    },
    text: 'Expected ";" but found "{"'
  }
]
[]

Actual output (when plugins are enabled):

undefined
undefined

[evanw]

What does the text of the error say? Is it perhaps not one of esbuild's errors? It's possible that a non-esbuild error was thrown and was captured by the promise.

[zaydek]

Well when I uncomment there is no error, at least esbuild returns undefined and therefore there are no .errors or .warnings attached to the result. silent prevents the error from being logged to stderr but what I wanted is to interact with errors and warnings as a data structure.

I assume the plugin causes an internal error that isn’t passed back to the user.

[evanw]

If this code:

	.catch(err => {
		console.log(err.errors)
		console.log(err.warnings)
	})

results in this output:

undefined
undefined

then presumably an error is being thrown somewhere and err is an object without the errors or warnings properties. It would be helpful for me to know what the error is to get a better idea of where it's coming from. Then I should be in a better position to do something about this problem.

[zaydek]

Sorry that wasn’t more useful. I created a minimum repro here https://github.com/zaydek/esbuild-plugin-behavior.

The specific answer to your question; I get this error when plugins are enabled:

Error: Plugin at index 0 is missing a name
	at handlePlugins (/Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:642:15)
	at Object.buildOrServe (/Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:872:26)
	at /Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:1344:17
	at new Promise (<anonymous>)
	at Object.build (/Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:1343:14)
	at Object.build (/Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:1204:26)
	at /Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:1252:67
	at processTicksAndRejections (node:internal/process/task_queues:93:5)

In the repro, esbuild.js:

// Command: node esbuild.js

// https://esbuild.github.io/plugins/#using-plugins
const envPlugin = {
	// Intentionally uses names instead of name to break esbuild; the intent is to
	// make sure esbuild emits errors whether or not plugins are being used.
	names: "env",
	setup(build) {
		build.onResolve({ filter: /^env$/ }, args => ({
			path: args.path,
			namespace: "env-ns",
		}))
		build.onLoad({ filter: /.*/, namespace: "env-ns" }, () => ({
			contents: JSON.stringify(process.env),
			loader: "json",
		}))
	},
}

require("esbuild")
	.build({
		bundle: true,
		entryPoints: ["in/app.js"],
		logLevel: "silent",
		outfile: "out/out.js",
		// plugins: [envPlugin],
	})
	.catch(err => {
		console.log({ err })
	})

// I get expected output when plugins are disabled (commented out). This is
// what I expect; the error is an object that has properties .errors and
// .warnings which I can use.
//
// {
//   err: Error: Build failed with 1 error:
//   in/app.js:1:7: error: Expected ";" but found "{"
//       at failureErrorWithLog (/Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:1124:15)
//       at buildResponseToResult (/Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:879:32)
//       at /Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:974:20
//       at /Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:541:9
//       at handleIncomingPacket (/Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:624:9)
//       at Socket.readFromStdout (/Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:508:7)
//       at Socket.emit (node:events:329:20)
//       at addChunk (node:internal/streams/readable:304:12)
//       at readableAddChunk (node:internal/streams/readable:279:9)
//       at Socket.Readable.push (node:internal/streams/readable:218:10) {
//     errors: [ [Object] ],
//     warnings: []
//   }
// }
//
// I get unexpected output when plugins are enabled. This is undesirable because
// I want to be able to introspect on .errors and .warnings.
//
// {
//   err: Error: Plugin at index 0 is missing a name
//       at handlePlugins (/Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:642:15)
//       at Object.buildOrServe (/Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:872:26)
//       at /Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:1344:17
//       at new Promise (<anonymous>)
//       at Object.build (/Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:1343:14)
//       at Object.build (/Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:1204:26)
//       at /Users/zaydek/github/retro-plugin-arch/node_modules/esbuild/lib/main.js:1252:67
//       at processTicksAndRejections (node:internal/process/task_queues:93:5)
// }

Tested on 0.8.40.

[evanw]

Thanks for the detail. That makes it much more clear what's happening. At one point I was trying to funnel all validation errors through esbuild's general error function, but clearly that's not happening here. This is something to fix.

[zaydek]

Thank you Evan. I’m glad we’re synced up now. I’ll tag related issues for organizational purposes:

#665
#688

[zaydek]

Thank you!