Declare module with default export class fails to build

[firefish5000]

snowpack build seems to fail when a d.ts file contains a declare module with a default export class.

/* eslint-disable i18next/no-literal-string */
declare module '*.svx' {
  export default class Svx extends Svelte2TsxComponent<any,any,any> {}
}

works fine with tsc and snowpack dev. Fails on snowpack build with

[snowpack] ✘ /full/path/src/types/mdsvex.d.ts
  Error: Transform failed with 1 error:
/full/path/src/types/mdsvex.d.ts:3:9: error: Unexpected "default"
    at failureErrorWithLog (/full/path/node_modules/esbuild/lib/main.js:643:15)
    at /full/path/node_modules/esbuild/lib/main.js:543:33
    at handleIncomingPacket (/full/path/node_modules/esbuild/lib/main.js:489:9)
    at Socket.readFromStdout (/full/path/node_modules/esbuild/lib/main.js:432:7)
    at Socket.emit (events.js:315:20)
    at addChunk (_stream_readable.js:309:12)
    at readableAddChunk (_stream_readable.js:284:9)
    at Socket.Readable.push (_stream_readable.js:223:10)
    at Pipe.onStreamRead (internal/stream_base_commons.js:188:23)

For reference, here is the Svelte2TsxComponent definition. Should be unrelated to the issue

declare class Svelte2TsxComponent<
  Props extends Record<string ,unknown> = unknown
  ,Events extends Record<string ,unknown> = unknown
  ,Slots extends Record<string ,unknown> = unknown
> {
  $$prop_def: Props
  $$events_def: Events
  $$slot_def: Slots

  constructor(options: {
    props?: Props & Record<string ,unknown>
  });

  $on<K extends keyof Events>(
    event: K ,
    handler: (e: Events[K]) => void
  ): () => void;
  $set(props: Partial<Props> & Record<string ,unknown>): void;
}

Additional usage example, which will also trigger this issue

Adds typings to the untyped `svelte-awesome` package

/* eslint-disable import/no-default-export */
/* eslint-disable i18next/no-literal-string */
declare module 'svelte-awesome' {
  import type { IconDefinition } from '@fortawesome/free-regular-svg-icons'

  export default class Icon extends Svelte2TsxComponent<{
    data: IconDefinition
    scale?: number
    spin?: boolean
    inverse?: boolean
    pulse?: boolean
    flip?: 'horizontal'|'vertical'
    label?: string
    // self = null // I think this is used internally only
    style?: string
    class?: string
  }> {}
}

Might be an upstream issue. I know nothing of esbuild so I am posting this here hopeing someone in the know will see.

[FredKSchott]

Huh, there's a chance that Snowpack doesn't work with .d.ts files in source code in the final build. We're probably sending them to esbuild as if they are TS files, which they aren't.

We should add a fix to just ignore .d.ts files in the build step.