@netlify/config/src/mutations/config_prop_name.js

Netlify config module

// Retrieve normalized property name
export const getPropName = function (keys) {
  return keys.reduce(normalizeDynamicProp, '')
}

// Some properties are user-defined, i.e. we need to replace them with a "*" token
// Check if a property name is dynamic, such as `functions.{functionName}`, or
// is an array index.
// In those cases, we replace it by "*".
const normalizeDynamicProp = function (propName, key) {
  const normalizedKey = Number.isInteger(key) || DYNAMIC_OBJECT_PROPS.has(propName) ? '*' : String(key)
  return propName === '' ? normalizedKey : `${propName}.${normalizedKey}`
}

// Properties with dynamic children
const DYNAMIC_OBJECT_PROPS = new Set(['build.services', 'build.environment', 'functions', 'functions.*'])