No emit error in return value, when function type declaration not "inline"

[spat-ne-hochu]

Environment
version
"typescript": "3.0.1",

tsconfig
json { "compilerOptions": { "target": "es6", "moduleResolution": "node", "noResolve": false, "sourceMap": true, "skipLibCheck": true, "strict": true, "noImplicitReturns": true, "emitDecoratorMetadata": true, "experimentalDecorators": true, "lib": [ "es5", "es6", "es7", "es2015", "es2015.reflect", "es2015.symbol", "es2015.promise", "es2016", "es2016.array.include", "es2017", "dom", "dom.iterable" ], "jsx" : "react", "types": [ "jasmine" ] }, "exclude": [ "node_modules" ] }

Code

type A = () => { b: number; c: number; } 
const a: A  = () => {
  return {
    b: 3,
    c: 4,
    d: 9, // no emit error, but must emit error
  };
};

const a2: () => { b: number; c: number; } = () => {
  return {
    b: 3,
    c: 4,
    d: 9, // no emit error, but must emit error
  };
};

const a3 = () : { b: number, c: number } => {
  return {
    b: 3,
    c: 4,
    d: 9, // emit error, ok!
  };
};

Expected behavior:
All three functions must emit error, because "d" field not exists in return type

Actual behavior:
Only last function emit error
Type '{ b: number; c: number; d: number; }' is not assignable to type '{ b: number; c: number; }'.
Object literal may only specify known properties, and 'd' does not exist in type '{ b: number; c: number; }'.

Playground Link: https://www.typescriptlang.org/play/#src=type%20A%20%3D%20()%20%3D%3E%20%7B%20b%3A%20number%3B%20c%3A%20number%3B%20%7D%20%0D%0Aconst%20a%3A%20A%20%20%3D%20()%20%3D%3E%20%7B%0D%0A%20%20return%20%7B%0D%0A%20%20%20%20b%3A%203%2C%0D%0A%20%20%20%20c%3A%204%2C%0D%0A%20%20%20%20d%3A%209%2C%0D%0A%20%20%7D%3B%0D%0A%7D%3B%0D%0A%0D%0Aconst%20a2%3A%20()%20%3D%3E%20%7B%20b%3A%20number%3B%20c%3A%20number%3B%20%7D%20%3D%20()%20%3D%3E%20%7B%0D%0A%20%20return%20%7B%0D%0A%20%20%20%20b%3A%203%2C%0D%0A%20%20%20%20c%3A%204%2C%0D%0A%20%20%20%20d%3A%209%2C%0D%0A%20%20%7D%3B%0D%0A%7D%3B%0D%0A%0D%0Aconst%20a3%20%3D%20()%20%3A%20%7B%20b%3A%20number%2C%20c%3A%20number%20%7D%20%3D%3E%20%7B%0D%0A%20%20return%20%7B%0D%0A%20%20%20%20b%3A%203%2C%0D%0A%20%20%20%20c%3A%204%2C%0D%0A%20%20%20%20d%3A%209%2C%0D%0A%20%20%7D%3B%0D%0A%7D%3B

[RyanCavanaugh]

Duplicate of #12632

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.