Dramatic increase in build time for @angular-devkit/build-angular >= 20.2.x

[kris-vista]

Command

build

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

@angular-devkit/build-angular 20.1.6

Description

We run an nx monorepo with around 20+ Angular applications, some of these applications are quite large and are made up of 50+ child libraries
Most developers run Windows

Our apps currently do not use esbuild, they are still using @angular-devkit/build-angular:browser

After updating from Angular 20.1.x to 20.2.x (We have also tried 20.3.x) the build process has dramatically slowed down, to give an example, when running serve on one of our larger apps, making a change to an html file would take around 10 - 30 seconds to do a rebuild, now it takes around 5 minutes.

I have narrowed this down to @angular-devkit/build-angular by reducing versions of libraries, running builds and seeing how long it takes, I can run the application with all angular versions at 20.2.x but @angular-devkit/build-angular at 20.1.6 and the build speeds return to normal

Minimal Reproduction

I'm not sure how to give instructions to rerpoduce this issue as it requires a large app but if you have a large app on the latest version of angular, useing @angular-devkit/build-angular:browser for the builder

• Run serve, note how long it takes
• Change a file, note how long a rebuild takes

then downgrade @angular-devkit/build-angular to 20.1.6, re run serve and note the new times

I'm happy to run some debug tasks but I'm not sure what to run at this point.

Exception or Error

Your Environment

Angular CLI: 20.2.2
Node: 22.20.0
Package Manager: npm 10.9.3
OS: win32 x64


Angular: 20.2.4
... animations, common, compiler, compiler-cli, core, elements
... forms, language-service, localize, platform-browser
... platform-browser-dynamic, router, service-worker

Package                         Version
---------------------------------------
@angular-devkit/architect       0.2002.2
@angular-devkit/build-angular   20.2.2
@angular-devkit/core            20.2.2
@angular-devkit/schematics      20.2.2
@angular/cdk                    20.2.3
@angular/cli                    20.2.2
@angular/youtube-player         19.1.2
@schematics/angular             20.2.2
ng-packagr                      20.2.0
rxjs                            7.8.1
typescript                      5.9.2
zone.js                         0.15.0


I am also running NX 21.5.2

Anything else relevant?

Updating to es build makes things better but i have also noticed running tests is slower than usual too

[clydin]

Other than dependency version updates, few changes have been made to the browser builder within those version ranges.
One potential item to look at is if there is a postcss.config.json or .postcssrc.json in the project or workspace root. Support was added to load those and use them when processing both global and component stylesheets.

If performance is a prime concern, please consider switching to the application build system. It has provided up to a 70% reduction in build times for some projects.

[kris-vista]

Other than dependency version updates, few changes have been made to the browser builder within those version ranges. One potential item to look at is if there is a postcss.config.json or .postcssrc.json in the project or workspace root. Support was added to load those and use them when processing both global and component stylesheets.

If performance is a prime concern, please consider switching to the application build system. It has provided up to a 70% reduction in build times for some projects.

I don't have postcss.config.json or .postcssrc.json anywhere in the monorepo

I am slowly switching to esbuild but this takes time in a largeish monorepo and it was such a dramatic change in build speeds I presume I'm not the only one suffering from it and that it should be reported

[clydin]

We have not had any other reports regarding this currently.
If you have some time, you can attempt to narrow down the root cause with your projects by trying 20.2.0 followed by each prerelease version (20.2.0-rc.1, 20.2.0-rc.0, 20.2.0-next.3, etc.). Hopefully, that should help to isolate the specific commit.

[kris-vista]

I tried all the way back to "@angular-devkit/build-angular": "20.2.0-next.0" and its still slow there too unfortunately, so whatever is happening was introduced between 20.1.6 and 20.2.0-next.0

Using @angular-devkit/build-angular:application does make application builds much faster but I am still having massive slow down on testing libraries, they now take forever to complete, and again, downgrading just @angular-devkit/build-angular to 20.1.6 makes everything speed right up again

One very important thing I have noticed, this appears to be a Windows specific issue, our build pipeline which is using Ubuntu works fine, but all our developers using Windows have this issue

Is there any sort of trace I can run against my build to see where things are hanging?