ngcc - recover from being stopped mid-build

🐞 bug report

Affected Package

The issue is caused by package @angular/compiler

Is this a regression?

Yes, the previous version in which this bug was not present was: 9.0.2

Description

It was working fine in 9.0.2. Can someone explain me this error ?

🔬 Minimal Reproduction

https://stackblitz.com/...

🔥 Exception or Error

Compiling @ng-bootstrap/ng-bootstrap : module as esm5
Error: Tried to write D:/test/student/node_modules/@ng-bootstrap/ng-bootstrap/accordion/accordion-config.d.ts.__ivy_ngcc_bak with an ngcc back up file but it already exists so not writing, nor backing up, D:/test/student/node_modules/@ng-bootstrap/ng-bootstrap/accordion/accordion-config.d.ts.
This error may be because two or more entry-points overlap and ngcc has been asked to process some files more than once.
You should check other entry-points in this package and set up a config to ignore any that you are not using.
Error: Tried to write D:/test/student/node_modules/@ng-bootstrap/ng-bootstrap/accordion/accordion.d.ts.__ivy_ngcc_bak with an ngcc back up file but it already exists so not writing, nor backing up, D:/test/student/node_modules/@ng-bootstrap/ng-bootstrap/accordion/accordion.d.ts.
This error may be because two or more entry-points overlap and ngcc has been asked to process some files more than once.
You should check other entry-points in this package and set up a config to ignore any that you are not using.
Error: Tried to write D:/test/student/node_modules/@ng-bootstrap/ng-bootstrap/accordion/accordion.module.d.ts.__ivy_ngcc_bak with an ngcc back up file but it already exists so not writing, nor backing up, D:/test/student/node_modules/@ng-bootstrap/ng-bootstrap/accordion/accordion.module.d.ts.
This error may be because two or more entry-points overlap and ngcc has been asked to process some files more than once.
You should check other entry-points in this package and set up a config to ignore any that you are not using.
Error: Tried to write D:/test/student/node_modules/@ng-bootstrap/ng-bootstrap/alert/alert-config.d.ts.__ivy_ngcc_bak with an ngcc back up file but it already exists so not writing, nor backing up, D:/test/student/node_modules/@ng-bootstrap/ng-bootstrap/alert/alert-config.d.ts.
This error may be because two or more entry-points overlap and ngcc has been asked to process some files more than once.
You should check other entry-points in this package and set up a config to ignore any that you are not using.
Error: Tried to write D:/test/student/node_modules/@ng-bootstrap/ng-bootstrap/alert/alert.d.ts.__ivy_ngcc_bak with an ngcc back up file but it already exists so not writing, nor backing up, D:/test/student/node_modules/@ng-bootstrap/ng-bootstrap/alert/alert.d.ts.

🌍 Your Environment

Angular Version:

ng --version

     _                      _                 ____ _     ___
    / \   _ __   __ _ _   _| | __ _ _ __     / ___| |   |_ _|
   / △ \ | '_ \ / _` | | | | |/ _` | '__|   | |   | |    | |
  / ___ \| | | | (_| | |_| | | (_| | |      | |___| |___ | |
 /_/   \_\_| |_|\__, |\__,_|_|\__,_|_|       \____|_____|___|
                |___/


Angular CLI: 9.1.0
Node: 10.16.3
OS: win32 x64

Angular: 9.1.0
... animations, cli, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router
Ivy Workspace: Yes

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.901.0
@angular-devkit/build-angular     0.901.0
@angular-devkit/build-optimizer   0.901.0
@angular-devkit/build-webpack     0.901.0
@angular-devkit/core              9.1.0
@angular-devkit/schematics        9.1.0
@ngtools/webpack                  9.1.0
@schematics/angular               9.1.0
@schematics/update                0.901.0
rxjs                              6.5.4
typescript                        3.8.3
webpack                           4.42.0

Anything else relevant?

[gkalpak]

Glad you got it working.

Generally, ngcc is able to resume when interrupted, unless it happens to be interrupted after starting writing files for a specific entry-point (and before completing writing them). This is a relatively small part of the whole ngcc processing, so the chances of this happening are small.

Unfortunetely, it is currently not possible to safely recover when interrupted during file writing. Maybe we could improve the error message to explain that it might be a result of a previous instance exiting unexpectedly (e.g. being stopped by the user before completing). We could even add a marker in the exntry-point’s package.json when starting processing it, so it is easier to detect this situation.

[petebacondarwin]

We don’t have enough capacity to implement a solution to make ngcc resilient to being killed in this way right now. Instead we will update the error message to indicate that this error might be caused by killing ngcc and may be resolved by removing and reinstalling the node_modules.