[NewErrors] 4.6.0-dev.20211205 vs 4.5.2

[typescript-bot]

The following errors were reported by 4.6.0-dev.20211205, but not by 4.5.2

microsoft/vscode

2 of 52 projects failed to build with the old tsc

src/tsconfig.json

• error TS2532: Object is possibly 'undefined'.
  • src/vs/workbench/services/workingCopy/common/storedFileWorkingCopy.ts#L357
  • src/vs/workbench/services/workingCopy/common/storedFileWorkingCopy.ts#L725
  • src/vs/workbench/services/workingCopy/common/storedFileWorkingCopy.ts#L825
  • src/vs/workbench/services/workingCopy/common/storedFileWorkingCopy.ts#L907
  • src/vs/workbench/services/workingCopy/common/untitledFileWorkingCopy.ts#L250

src/tsconfig.tsec.json

• error TS2532: Object is possibly 'undefined'.
  • src/vs/workbench/services/workingCopy/common/storedFileWorkingCopy.ts#L357
  • src/vs/workbench/services/workingCopy/common/storedFileWorkingCopy.ts#L725
  • src/vs/workbench/services/workingCopy/common/storedFileWorkingCopy.ts#L825
  • src/vs/workbench/services/workingCopy/common/storedFileWorkingCopy.ts#L907
  • src/vs/workbench/services/workingCopy/common/untitledFileWorkingCopy.ts#L250

lensapp/lens

4 of 5 projects failed to build with the old tsc

tsconfig.json

• error TS7023: 'steps' implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.
  • src/renderer/components/wizard/wizard.tsx#L55
• error TS7006: Parameter 'stepElem' implicitly has an 'any' type.
  • src/renderer/components/wizard/wizard.tsx#L105

[RyanCavanaugh]

VS Code break:

interface DatafulFoo<T> {
    data: T;
}

class Foo<T extends string> {
    data: T | undefined;

    bar() {
        if (this.hasData()) {
            this.data.toLocaleLowerCase();
        }
    }

    hasData(): this is DatafulFoo<T> {
        return true;
    }
}