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extract-const-value.ts
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extract-const-value.ts
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import type {
ArrayExpression,
BooleanLiteral,
ExportDeclaration,
Identifier,
KeyValueProperty,
Module,
Node,
NullLiteral,
NumericLiteral,
ObjectExpression,
RegExpLiteral,
StringLiteral,
TemplateLiteral,
VariableDeclaration,
} from '@swc/core'
export class NoSuchDeclarationError extends Error {}
function isExportDeclaration(node: Node): node is ExportDeclaration {
return node.type === 'ExportDeclaration'
}
function isVariableDeclaration(node: Node): node is VariableDeclaration {
return node.type === 'VariableDeclaration'
}
function isIdentifier(node: Node): node is Identifier {
return node.type === 'Identifier'
}
function isBooleanLiteral(node: Node): node is BooleanLiteral {
return node.type === 'BooleanLiteral'
}
function isNullLiteral(node: Node): node is NullLiteral {
return node.type === 'NullLiteral'
}
function isStringLiteral(node: Node): node is StringLiteral {
return node.type === 'StringLiteral'
}
function isNumericLiteral(node: Node): node is NumericLiteral {
return node.type === 'NumericLiteral'
}
function isArrayExpression(node: Node): node is ArrayExpression {
return node.type === 'ArrayExpression'
}
function isObjectExpression(node: Node): node is ObjectExpression {
return node.type === 'ObjectExpression'
}
function isKeyValueProperty(node: Node): node is KeyValueProperty {
return node.type === 'KeyValueProperty'
}
function isRegExpLiteral(node: Node): node is RegExpLiteral {
return node.type === 'RegExpLiteral'
}
function isTemplateLiteral(node: Node): node is TemplateLiteral {
return node.type === 'TemplateLiteral'
}
export class UnsupportedValueError extends Error {
/** @example `config.runtime[0].value` */
path?: string
constructor(message: string, paths?: string[]) {
super(message)
// Generating "path" that looks like "config.runtime[0].value"
let codePath: string | undefined
if (paths) {
codePath = ''
for (const path of paths) {
if (path[0] === '[') {
// "array" + "[0]"
codePath += path
} else {
if (codePath === '') {
codePath = path
} else {
// "object" + ".key"
codePath += `.${path}`
}
}
}
}
this.path = codePath
}
}
function extractValue(node: Node, path?: string[]): any {
if (isNullLiteral(node)) {
return null
} else if (isBooleanLiteral(node)) {
// e.g. true / false
return node.value
} else if (isStringLiteral(node)) {
// e.g. "abc"
return node.value
} else if (isNumericLiteral(node)) {
// e.g. 123
return node.value
} else if (isRegExpLiteral(node)) {
// e.g. /abc/i
return new RegExp(node.pattern, node.flags)
} else if (isIdentifier(node)) {
switch (node.value) {
case 'undefined':
return undefined
default:
throw new UnsupportedValueError(
`Unknown identifier "${node.value}"`,
path
)
}
} else if (isArrayExpression(node)) {
// e.g. [1, 2, 3]
const arr = []
for (let i = 0, len = node.elements.length; i < len; i++) {
const elem = node.elements[i]
if (elem) {
if (elem.spread) {
// e.g. [ ...a ]
throw new UnsupportedValueError(
'Unsupported spread operator in the Array Expression',
path
)
}
arr.push(extractValue(elem.expression, path && [...path, `[${i}]`]))
} else {
// e.g. [1, , 2]
// ^^
arr.push(undefined)
}
}
return arr
} else if (isObjectExpression(node)) {
// e.g. { a: 1, b: 2 }
const obj: any = {}
for (const prop of node.properties) {
if (!isKeyValueProperty(prop)) {
// e.g. { ...a }
throw new UnsupportedValueError(
'Unsupported spread operator in the Object Expression',
path
)
}
let key
if (isIdentifier(prop.key)) {
// e.g. { a: 1, b: 2 }
key = prop.key.value
} else if (isStringLiteral(prop.key)) {
// e.g. { "a": 1, "b": 2 }
key = prop.key.value
} else {
throw new UnsupportedValueError(
`Unsupported key type "${prop.key.type}" in the Object Expression`,
path
)
}
obj[key] = extractValue(prop.value, path && [...path, key])
}
return obj
} else if (isTemplateLiteral(node)) {
// e.g. `abc`
if (node.expressions.length !== 0) {
// TODO: should we add support for `${'e'}d${'g'}'e'`?
throw new UnsupportedValueError(
'Unsupported template literal with expressions',
path
)
}
// When TemplateLiteral has 0 expressions, the length of quasis is always 1.
// Because when parsing TemplateLiteral, the parser yields the first quasi,
// then the first expression, then the next quasi, then the next expression, etc.,
// until the last quasi.
// Thus if there is no expression, the parser ends at the frst and also last quasis
//
// A "cooked" interpretation where backslashes have special meaning, while a
// "raw" interpretation where backslashes do not have special meaning
// https://exploringjs.com/impatient-js/ch_template-literals.html#template-strings-cooked-vs-raw
const [{ cooked, raw }] = node.quasis
return cooked ?? raw
} else {
throw new UnsupportedValueError(
`Unsupported node type "${node.type}"`,
path
)
}
}
/**
* Extracts the value of an exported const variable named `exportedName`
* (e.g. "export const config = { runtime: 'experimental-edge' }") from swc's AST.
* The value must be one of (or throws UnsupportedValueError):
* - string
* - boolean
* - number
* - null
* - undefined
* - array containing values listed in this list
* - object containing values listed in this list
*
* Throws NoSuchDeclarationError if the declaration is not found.
*/
export function extractExportedConstValue(
module: Module,
exportedName: string
): any {
for (const moduleItem of module.body) {
if (!isExportDeclaration(moduleItem)) {
continue
}
const declaration = moduleItem.declaration
if (!isVariableDeclaration(declaration)) {
continue
}
if (declaration.kind !== 'const') {
continue
}
for (const decl of declaration.declarations) {
if (
isIdentifier(decl.id) &&
decl.id.value === exportedName &&
decl.init
) {
return extractValue(decl.init, [exportedName])
}
}
}
throw new NoSuchDeclarationError()
}