There has been a regression where enabling rollup treeshaking causes errors during runtime because it will drop const access which will always evaluate to true or false. However, such `const` in `@angular/core` cannot be dropped because their value is changed when NGCC is run on `@angular/core`
VE
```
const SWITCH_IVY_ENABLED__POST_R3__ = true;
const SWITCH_IVY_ENABLED__PRE_R3__ = false;
const ivyEnabled = SWITCH_IVY_ENABLED__PRE_R3__;
```
Ivy (After NGCC)
```
const SWITCH_IVY_ENABLED__POST_R3__ = true;
const SWITCH_IVY_ENABLED__PRE_R3__ = false;
const ivyEnabled = SWITCH_IVY_ENABLED__POST_R3__;
```
FESM2015
```
load(path) {
/** @type {?} */
const legacyOfflineMode = this._compiler instanceof Compiler;
return legacyOfflineMode ? this.loadFactory(path) : this.loadAndCompile(path);
}
```
ESM2015
```
load(path) {
/** @type {?} */
const legacyOfflineMode = !ivyEnabled && this._compiler instanceof Compiler;
return legacyOfflineMode ? this.loadFactory(path) : this.loadAndCompile(path);
}
```
From the above we can see that `ivyEnabled ` is being treeshaken away when generating the FESM bundle which is causing runtime errors such as `Cannot find module './lazy/lazy.module.ngfactory'` since in Ivy we will always load the factories.
PR Close#32069
4f37487b1c