TypeError: this._validator is not a function

🐞 bug report

Affected Package

The issue is caused by package @angular/forms in combination with AOT compilation

Is this a regression?

Yes, the previous version in which this bug was not present was: Angular 8 without AOT.

Description

When binding dynamic validator values to an input via [maxlength]="maxLength" if AOT compilation is enabled the validation is attempted before the validator is created. An error is logged to the console: ERROR TypeError: this._validator is not a function.

🔬 Minimal Reproduction

https://github.com/nathanrobinson/angular_ivy_aot_validation_error

🔥 Exception or Error

ERROR TypeError: this._validator is not a function
    at MinLengthValidator.validate (VM1588 vendor.js:67057)
    at VM1588 vendor.js:60658
    at VM1588 vendor.js:60606
    at Array.map (<anonymous>)
    at _executeValidators (VM1588 vendor.js:60602)
    at VM1588 vendor.js:60547
    at VM1588 vendor.js:60606
    at Array.map (<anonymous>)
    at _executeValidators (VM1588 vendor.js:60602)
    at FormControl.validator (VM1588 vendor.js:60547)

🌍 Your Environment

Angular Version:

Angular CLI: 8.0.0                                             
Node: 10.14.2                                                  
OS: win32 x64                                                  
Angular: 8.0.0                                                 
... animations, cdk, cli, common, compiler, compiler-cli, core 
... forms, language-service, material, platform-browser        
... platform-browser-dynamic, router                           
                                                               
Package                           Version                      
-----------------------------------------------------------    
@angular-devkit/architect         0.800.0                      
@angular-devkit/build-angular     0.800.0                      
@angular-devkit/build-optimizer   0.800.0                      
@angular-devkit/build-webpack     0.800.0                      
@angular-devkit/core              8.0.0                        
@angular-devkit/schematics        8.0.0                        
@ngtools/webpack                  8.0.0                        
@schematics/angular               8.0.0                        
@schematics/update                0.800.0                      
rxjs                              6.4.0                        
typescript                        3.5.1                        
webpack                           4.30.0                       

Anything else relevant? The OnChange loop seems to call validate before setting the attributes, and then call it again after setting the attributes. There are three instances in https://github.com/angular/angular/blob/master/packages/forms/src/directives/validators.ts where this._validator is called without checking if it is null. This could be resolved for example by rewriting

validate(control: AbstractControl): ValidationErrors|null {
    return this.minlength == null ? null : this._validator(control);
  }

as

validate(control: AbstractControl): ValidationErrors|null {
    return this.minlength == null || !this._validator ? null : this._validator(control);
  }

[gurachan]

9.0.0-rc.1 still exist

[igorkemack]

I have same error, angular 9.0.0-next.8