Cross-module dead code elimination of constant doesn't work with defines

[vlovich]

Hmm.... I think I must be doing something wrong. I'm trying to take advantage of #1981 in 0.14.19. have a constants.ts file like this:

declare global {
  const __IS_PRODUCTION_BUILD__: boolean
}
export const isProductionBuild = __IS_PRODUCTION_BUILD__

In build.mjs I have:

...
define: {
  __IS_PRODUCTION_BUILD__: process.env.NODE_ENV === 'production'
}
...

I've used isProductionBuild in my code like so:

// Workaround for https://github.com/cloudflare/miniflare/issues/191
import { isProductionBuild } from './constants'

function isDateInstance(value: any): value is Date {
  if (!isProductionBuild) {
    return value instanceof Date || (typeof value === 'object' && value.constructor.name === 'Date')
  }
  return value instanceof Date
}

function someFunction(value: any) {
   if (isDateInstance(value)) {
     ...
   }
}

I would expect that the conditional if (isDateInstance(value)) gets minified to if(value instanceof Date) in a production build. Instead I see:

function KA(e){return!0?e instanceof Date:e instanceof Date||e instanceof Object&&e.constructor.name==="Date"}

and later

if(KA(t))

[evanw]

General function inlining like this is not an optimization that esbuild does. This is documented here: https://esbuild.github.io/api/#minify-considerations. You are welcome to use another tool instead if you need this optimization.

[vlovich]

Fine, but it's still not inlining the constant as intended right?.

function isWorkaroundDateInstance(value: any): value is Date {
   return value instanceof Date || (typeof value === 'object' && value.constructor.name === 'Date')
}

if (value instanceof Date || (!isProductionBuild && isWorkaroundDateInstance(value) {
}

becomes

if(t instanceof Date||!!0&&KA(t))

rather than

if(t instanceof Date)

It's failing to recognize that !!0&&anything can be stripped because it will never evaluate to true.

[vlovich]

FWIW this behaves as intended:

if (value instanceof Date || (!__IS_PRODUCTION_BUILD__ && isWorkaroundDateInstance(value) {
}

so this does seem to be a constant inlining problem.

[evanw]

This is also in the documentation. What you are referring to is the "Cross-statement constant propagation" bullet point. You can read more about why this limitation exists here: #2006 (comment).

[evanw]

This is a known design limitation. The best way to do this is to avoid indirection through another variable, as described above. Closing as "won't fix."