Prevent NEXT_PHASE env change in workers

[jbraithwaite]

process.env.NEXT_PHASE was moved in #20900 to be set during staticCheckSpan.traceAsyncFn. I believe this to be a mistake, the NEXT_PHASE should be set earlier in the code execution.

On a personal note, this impacts an application I am developing where we rely on the environment variable NEXT_PHASE to be set but is undefined when we check it.

[vattenapa]

I use NEXT_PHASE in a similar way too. Can a change like this can be considered for merging or not?

[ijjk]

Hi, relying on this env variable should be avoided if possible as it was initially added when we introduced requiring pages to check if they are eligible for the automatic static optimization to prevent loading un-necessary items but was not documented to be used in this way as it should not be needed.

To prevent a breaking change with older projects that did rely on this we can land this. Thanks for the PR!

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall decrease ✓

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	Change
buildDuration	18.3s	18.6s	⚠️ +243ms
buildDurationCached	3.6s	3.4s	-219ms
nodeModulesSize	350 MB	350 MB	-11 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.97	3.013	⚠️ +0.04
/ avg req/sec	841.81	829.75	⚠️ -12.06
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.372	1.381	⚠️ +0.01
/error-in-render avg req/sec	1822.42	1810.15	⚠️ -12.27

Client Bundles (main, webpack, commons)

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	30.2 kB	30.2 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	74 kB	74 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	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	326 B	326 B	✓
dynamic-HASH.js gzip	2.37 kB	2.37 kB	✓
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	919 B	919 B	✓
image-HASH.js gzip	4.73 kB	4.73 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	2.13 kB	2.13 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	14.1 kB	14.1 kB	✓

Client Build Manifests

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	Change
index.html gzip	532 B	532 B	✓
link.html gzip	546 B	546 B	✓
withRouter.html gzip	527 B	527 B	✓
Overall change	1.6 kB	1.6 kB	✓

---

Default Build with SWC (Decrease detected ✓)

General Overall decrease ✓

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	Change
buildDuration	19.9s	19.8s	-140ms
buildDurationCached	3.4s	3.5s	⚠️ +98ms
nodeModulesSize	350 MB	350 MB	-11 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.961	2.923	-0.04
/ avg req/sec	844.35	855.4	+11.05
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.342	1.363	⚠️ +0.02
/error-in-render avg req/sec	1862.26	1834.6	⚠️ -27.66

Client Bundles (main, webpack, commons)

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	30.3 kB	30.3 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	74.3 kB	74.3 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	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	2.36 kB	2.36 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	906 B	906 B	✓
image-HASH.js gzip	4.75 kB	4.75 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	2.19 kB	2.19 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	14.1 kB	14.1 kB	✓

Client Build Manifests

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	jbraithwaite/next.js jb/fix-next-phase	Change
index.html gzip	533 B	533 B	✓
link.html gzip	547 B	547 B	✓
withRouter.html gzip	527 B	527 B	✓
Overall change	1.61 kB	1.61 kB	✓

Commit: 02279fb