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Type inference lost when destructuring #37638

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@jordyvandomselaar

Description

@jordyvandomselaar

TypeScript Version: Nightly

Search Terms:

  • Type inference wrong
  • Type destructuring

Expected behavior:

Type inference gets that my field is currently of dropdown type

Actual behavior:

It doesn't

Related Issues:

Code

export type DynamicFieldType = {
  visibleTo: "EVERYONE" | "EMPLOYEE" | "EMPLOYER";
  shouldBeVisibleTo: "EVERYONE" | "EMPLOYEE" | "EMPLOYER";
  name: string;
  isRequired: boolean;
  value: string;
  defaultValue: string;
  labels: {
    NL: string;
    EN: string;
  };
  onChange: (name: string, value: string) => void;
};

export type DropdownType = DynamicFieldType & {
  type: "dropdown";
  options: string[];
};

export type UploadType = DynamicFieldType & {
  type: "upload";
};

export type CheckboxType = DynamicFieldType & {
  type: "checkbox";
};

export type RadioType = DynamicFieldType & {
  type: "radio";
  options: string[];
};

export type TextType = DynamicFieldType & {
  type: "text";
};

export interface DynamicFieldProps {
  field: DropdownType | UploadType | CheckboxType | RadioType | TextType;
  intl: any; // TODO: update react-intl for types
}

const handleField = ({ field }: DynamicFieldProps): void => {
  switch (field.type) {
    case "dropdown":
      const foo = field.options;

      console.log("Success!");
  }
};

const failingHandleField = ({ field }: DynamicFieldProps): void => {
  const { type } = field;

  switch (type) {
    case "dropdown":
      const foo = field.options;

      console.log("It suddenly doesn't get it.");
  }
};
Output
const handleField = ({ field }) => {
    switch (field.type) {
        case "dropdown":
            const foo = field.options;
            console.log("Success!");
    }
};
const failingHandleField = ({ field }) => {
    const { type } = field;
    switch (type) {
        case "dropdown":
            const foo = field.options;
            console.log("It suddenly doesn't get it.");
    }
};
Compiler Options
{
  "compilerOptions": {
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "useDefineForClassFields": false,
    "alwaysStrict": true,
    "allowUnreachableCode": false,
    "allowUnusedLabels": false,
    "downlevelIteration": false,
    "noEmitHelpers": false,
    "noLib": false,
    "noStrictGenericChecks": false,
    "noUnusedLocals": false,
    "noUnusedParameters": false,
    "esModuleInterop": true,
    "preserveConstEnums": false,
    "removeComments": false,
    "skipLibCheck": false,
    "checkJs": false,
    "allowJs": false,
    "declaration": true,
    "experimentalDecorators": false,
    "emitDecoratorMetadata": false,
    "target": "ES2017",
    "module": "ESNext"
  }
}

Playground Link: Provided

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