TS8031

When it fires

A call cycle: a function that reaches itself, directly or through other functions. WGSL has no call stack, so Tint rejects the emitted module (cyclic dependency found: 'a' -> 'b' -> 'a'); before this the front end accepted it and emitted it with zero diagnostics.

Example

"use typeshade"

function fold(x: f32): f32 {
  if (x < 1.) {
    return x
  }
  return fold(x * 0.5)
}

@fragment
export function main(@location(0) uv: vec2): vec4 {
  return vec4(uv, fold(uv.x * 8.), 1.)
}

Compiled at build time against the pinned compiler, this program gets:

How to fix it

The same program, corrected. It compiles with no diagnostic.

"use typeshade"

function fold(x: f32): f32 {
  let y = x
  for (let i = 0; i < 8; i++) {
    if (y < 1.) {
      break
    }
    y = y * 0.5
  }
  return y
}

@fragment
export function main(@location(0) uv: vec2): vec4 {
  return vec4(uv, fold(uv.x * 8.), 1.)
}

The rules this enforces

Rule 8.4 Test

A function must not take part in a call cycle, directly or through other functions; the check reads the calls a body writes, and the calls a method call, an accessor and new lower to, before any optimisation, so a call in a branch the optimizer would drop is a cycle too.

Rule 8.18 Test

A function whose parameter has a function type, written out (f: (x: f32) => f32) or through a type alias of one, takes a function: a function declared at the top of the file or of a namespace, a method, a static method, a constructor, a field that holds a function (Rule 8.16) and a local function (Rule 8.17).

Rule 8.19 Test

A function that writes no return type returns what its body does, as TypeScript infers it: a function of the file or of a namespace, a local function (Rule 8.17), each instance of a generic function (Rule 8.9) and of a function that takes a function (Rule 8.18), a method, a getter and a field that holds a function (Rule 8.16) take the type of their first return with a value, the returns after it are typed against that type as against a written one, and one with no such return returns nothing.

Rule 12.6 Test

A requirement the front end can check must be checked at the front end, in the author’s words, and not left to Tint or a driver.

See also

• Functions
• Error codes

Source

Where the compiler raises this code at commit 26de7be8, one line per file:

• src/compiler/ts/lower/function.ts:559 (4 sites)
• src/compiler/ts/recursion.ts:202 (2 sites)