Add minify debug env var to investigate minifier bugs

[timneutkens]

Adds support for NEXT_DEBUG_MINIFY=1 next build which will log out the bundled code before minification so that it can be investigated.
Since this will generally overflow the terminal history unless configured to keep everything it's recommended to pipe it to a log file:

NEXT_DEBUG_MINIFY=1 next build > log.txt

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have helpful link attached, see contributing.md

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes by running yarn lint

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
buildDuration	17.5s	17.4s	-130ms
buildDurationCached	3.5s	3.5s	-26ms
nodeModulesSize	335 MB	335 MB	⚠️ +668 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.875	2.817	-0.06
/ avg req/sec	869.67	887.35	+17.68
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.358	1.43	⚠️ +0.07
/error-in-render avg req/sec	1840.89	1748.11	⚠️ -92.78

Client Bundles (main, webpack, commons)

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	28.3 kB	28.3 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	72.2 kB	72.2 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
_app-HASH.js gzip	1.37 kB	1.37 kB	✓
_error-HASH.js gzip	194 B	194 B	✓
amp-HASH.js gzip	312 B	312 B	✓
css-HASH.js gzip	327 B	327 B	✓
dynamic-HASH.js gzip	2.38 kB	2.38 kB	✓
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	635 B	635 B	✓
image-HASH.js gzip	4.44 kB	4.44 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	1.87 kB	1.87 kB	✓
routerDirect..HASH.js gzip	321 B	321 B	✓
script-HASH.js gzip	383 B	383 B	✓
withRouter-HASH.js gzip	318 B	318 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	13.3 kB	13.3 kB	✓

Client Build Manifests

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
index.html gzip	524 B	524 B	✓
link.html gzip	536 B	536 B	✓
withRouter.html gzip	517 B	517 B	✓
Overall change	1.58 kB	1.58 kB	✓

---

Default Build with SWC (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
buildDuration	18.8s	18.8s	-34ms
buildDurationCached	3.5s	3.5s	-21ms
nodeModulesSize	335 MB	335 MB	⚠️ +668 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.904	2.838	-0.07
/ avg req/sec	860.77	880.76	+19.99
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.32	1.348	⚠️ +0.03
/error-in-render avg req/sec	1893.45	1854.13	⚠️ -39.32

Client Bundles (main, webpack, commons)

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	28.5 kB	28.5 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	72.5 kB	72.5 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
_app-HASH.js gzip	1.35 kB	1.35 kB	✓
_error-HASH.js gzip	180 B	180 B	✓
amp-HASH.js gzip	305 B	305 B	✓
css-HASH.js gzip	321 B	321 B	✓
dynamic-HASH.js gzip	2.38 kB	2.38 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	622 B	622 B	✓
image-HASH.js gzip	4.46 kB	4.46 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	1.91 kB	1.91 kB	✓
routerDirect..HASH.js gzip	314 B	314 B	✓
script-HASH.js gzip	375 B	375 B	✓
withRouter-HASH.js gzip	309 B	309 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	13.2 kB	13.2 kB	✓

Client Build Manifests

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	timneutkens/next.js add/minify-debug-flag	Change
index.html gzip	522 B	522 B	✓
link.html gzip	534 B	534 B	✓
withRouter.html gzip	515 B	515 B	✓
Overall change	1.57 kB	1.57 kB	✓

Commit: 6f81543