Template literal expression is not assignable to matching template literal type · Issue #43243 · microsoft/TypeScript (original) (raw)

Bug Report

🔎 Search Terms

template literal types, template literal assignability

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about template literal types.

⏯ Playground Link

Playground link with relevant code

💻 Code

type Templated = ${string} ${string};

const value1: string = "abc"; const templated1: Templated = ${value1} abc as const; // Type '${string} abc' is not assignable to type '${string} ${string}'.

const value2 = "abc"; const templated2: Templated = ${value2} abc as const;

Note in the second case, where value2 is a literal string, the assignment works okay.

🙁 Actual behavior

Type '`${string} abc`' is not assignable to type '`${string} ${string}`'.

🙂 Expected behavior

I would expect this value to be assignable, since the statically known value type matches the template pattern.

It is also odd that the two cases above behave differently.