Regression in 20.2 - New/incorrect build errors with 20.2 - Cannot use "||" with "??" without parentheses

[NateRadebaugh]

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

20.1.6

Description

This same code used to work but after updating to 20.2 latest I'm seeing the following errors in a handful of places:

X [ERROR] Cannot use "||" with "??" without parentheses
Expressions of the form "x ?? y || z" are not allowed in JavaScript. You must disambiguate between "(x ?? y) || z" and "x ?? (y || z)" by adding parentheses.

Couple of concerns:

1. Should this be a breaking change like this?
2. The error itself seems to come from the .html file but the error mentioned in the CLI appears to be a generated file/line numbers instead of my raw code.
3. I do have parenthesis in my HTML file, so not sure what recourse I could have to fix this in user-land

Minimal Reproduction

Stackblitz:
https://stackblitz.com/edit/stackblitz-starters-jsu7gzpr?file=src%2Fexample%2Fexample.component.ts

import { Component, signal } from '@angular/core';

@Component({
  standalone: true,
  selector: 'app-example',
  template: `
    <h1>Example!</h1>
    {{ (someSignal() ?? false)  || screenIsReadOnly() }}
  `,
})
export class ExampleComponent {
  someSignal = signal<boolean | undefined>(true);
  screenIsReadOnly = signal<boolean | undefined>(false);
}

Exception or Error

> X [ERROR] Cannot use "||" with "??" without parentheses
>   Expressions of the form "x ?? y || z" are not allowed in JavaScript. You must disambiguate between "(x ?? y) || z" and "x ?? (y || z)" by adding parentheses.

Your Environment

Angular CLI: 20.2.0
Node: 20.19.1
Package Manager: npm 10.8.2
OS: linux x64
    

Angular: 20.2.0
... animations, build, cli, common, compiler, compiler-cli, core
... forms, platform-browser, router

Package                      Version
------------------------------------
@angular-devkit/architect    0.2002.0
@angular-devkit/core         20.2.0
@angular-devkit/schematics   20.2.0
@schematics/angular          20.2.0
rxjs                         7.8.2
typescript                   5.9.2
zone.js                      0.15.1

Anything else relevant?

No response

[JeanMeche]

Confirmed, we have a regression on the compiler output between 20.1.8 and 20.2.0. Some parentheses are stripped.

[JeanMeche]

This is related to the update to TS 5.8 to TS 5.9. If you force TS 5.8 it'll work fine until fix the issue in the compiler.

Edit: TS Repro of what changed between TS 5.8 and 5.9: https://stackblitz.com/edit/vitejs-vite-a11yrnds?file=package.json,src%2Fmain.ts

[JeanMeche]

Root issue has been fixed microsoft/TypeScript/issues/62307