@angular/material/index.d.ts' is not a module

Question

With Angular 8, While building the app, we encounter the following error:

app/modules/admin-module/pages/editor/editor.component.ts:6:27 - error TS2306: 
File ...node_modules/@angular/material/index.d.ts' is not a module.

Answer 1

After upgrading to Angular 9 (released today), I ran into this issue as well and found that they made the breaking change mentioned in the answer. I can't find a reason for why they made this change.

I have a material.module.ts file that I import / export all the material components (not the most efficient, but useful for quick development). I went through and updated all my imports to the individual material folders, although an index.ts barrel might be better. Again, not sure why they made this change, but I'm guessing it has to do with tree-shaking efficiencies.

Including my material.module.ts below in case it helps anyone, it's inspired off other material modules I've found:

NOTE: As other blog posts have mentioned and from my personal experience, be careful when using a shared module like below. I have 5~ different feature modules (lazy loaded) in my app that I imported my material module into. Out of curiosity, I stopped using the shared module and instead only imported the individual material components each feature module needed. This reduced my bundle size quite a bit, almost a 200kb reduction. I assumed that the build optimization process would properly drop any component not used by my modules, but it doesn't seem to be the case...

// material.module.ts
import { ModuleWithProviders, NgModule} from "@angular/core";
import { MAT_LABEL_GLOBAL_OPTIONS, MatNativeDateModule, MAT_DATE_LOCALE } from '@angular/material/core';
import { MatIconRegistry } from '@angular/material/icon';
import { MatAutocompleteModule } from '@angular/material/autocomplete';
import { MatBadgeModule } from '@angular/material/badge';
import { MatButtonModule } from '@angular/material/button';
import { MatButtonToggleModule } from '@angular/material/button-toggle';
import { MatCardModule } from '@angular/material/card';
import { MatCheckboxModule } from '@angular/material/checkbox';
import { MatChipsModule } from '@angular/material/chips';
import { MatStepperModule } from '@angular/material/stepper';
import { MatDatepickerModule } from '@angular/material/datepicker';
import { MatDialogModule } from '@angular/material/dialog';
import { MatExpansionModule } from '@angular/material/expansion';
import { MatFormFieldModule } from '@angular/material/form-field';
import { MatGridListModule } from '@angular/material/grid-list';
import { MatIconModule } from '@angular/material/icon';
import { MatInputModule } from '@angular/material/input';
import { MatListModule } from '@angular/material/list';
import { MatMenuModule } from '@angular/material/menu';
import { MatPaginatorModule } from '@angular/material/paginator';
import { MatProgressBarModule } from '@angular/material/progress-bar';
import { MatProgressSpinnerModule } from '@angular/material/progress-spinner';
import { MatRadioModule } from '@angular/material/radio';
import { MatRippleModule } from '@angular/material/core';
import { MatSelectModule } from '@angular/material/select';
import { MatSidenavModule } from '@angular/material/sidenav';
import { MatSliderModule } from '@angular/material/slider';
import { MatSlideToggleModule } from '@angular/material/slide-toggle';
import { MatSnackBarModule } from '@angular/material/snack-bar';
import { MatSortModule } from '@angular/material/sort';
import { MatTableModule } from '@angular/material/table';
import { MatTabsModule } from '@angular/material/tabs';
import { MatToolbarModule } from '@angular/material/toolbar';
import { MatTooltipModule } from '@angular/material/tooltip';
import { MatTreeModule } from '@angular/material/tree';

@NgModule({
    imports: [
        MatAutocompleteModule,
        MatBadgeModule,
        MatButtonModule,
        MatButtonToggleModule,
        MatCardModule,
        MatCheckboxModule,
        MatChipsModule,
        MatStepperModule,
        MatDatepickerModule,
        MatDialogModule,
        MatExpansionModule,
        MatFormFieldModule,
        MatGridListModule,
        MatIconModule,
        MatInputModule,
        MatListModule,
        MatMenuModule,
        MatPaginatorModule,
        MatProgressBarModule,
        MatProgressSpinnerModule,
        MatRadioModule,
        MatRippleModule,
        MatSelectModule,
        MatSidenavModule,
        MatSliderModule,
        MatSlideToggleModule,
        MatSnackBarModule,
        MatSortModule,
        MatTableModule,
        MatTabsModule,
        MatToolbarModule,
        MatTooltipModule,
        MatTreeModule,
        MatNativeDateModule
    ],
    exports: [
        MatAutocompleteModule,
        MatBadgeModule,
        MatButtonModule,
        MatButtonToggleModule,
        MatCardModule,
        MatCheckboxModule,
        MatChipsModule,
        MatStepperModule,
        MatDatepickerModule,
        MatDialogModule,
        MatExpansionModule,
        MatFormFieldModule,
        MatGridListModule,
        MatIconModule,
        MatInputModule,
        MatListModule,
        MatMenuModule,
        MatPaginatorModule,
        MatProgressBarModule,
        MatProgressSpinnerModule,
        MatRadioModule,
        MatRippleModule,
        MatSelectModule,
        MatSidenavModule,
        MatSliderModule,
        MatSlideToggleModule,
        MatSnackBarModule,
        MatSortModule,
        MatTableModule,
        MatTabsModule,
        MatToolbarModule,
        MatTooltipModule,
        MatTreeModule,
        MatNativeDateModule
    ],
    providers: [     
    ]
})
export class MaterialModule {
    constructor(public matIconRegistry: MatIconRegistry) {
        // matIconRegistry.registerFontClassAlias('fontawesome', 'fa');
    }

    static forRoot(): ModuleWithProviders<MaterialModule> {
        return {
            ngModule: MaterialModule,
            providers: [MatIconRegistry]
        };
    }
}

Answer 2

update: please check the answer of Jeff Gilliland below for updated solution

Seems like as this thread says a breaking change was issued:

Components can no longer be imported through "@angular/material". Use the individual secondary entry-points, such as @angular/material/button.

Update: can confirm, this was the issue. After downgrading @angular/[email protected]... to @angular/[email protected] we could solve this temporarily. Guess we need to update the project for a long term solution.