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no-page-custom-font.js
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no-page-custom-font.js
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const NodeAttributes = require('../utils/node-attributes.js')
const { sep, posix } = require('path')
const url = 'https://nextjs.org/docs/messages/no-page-custom-font'
module.exports = {
meta: {
docs: {
description: 'Prevent page-only custom fonts.',
recommended: true,
url,
},
type: 'problem',
schema: [],
},
create: function (context) {
const paths = context.getFilename().split('pages')
const page = paths[paths.length - 1]
// outside of a file within `pages`, bail
if (!page) {
return {}
}
const is_Document =
page.startsWith(`${sep}_document`) ||
page.startsWith(`${posix.sep}_document`)
let documentImportName
let localDefaultExportId
let exportDeclarationType
return {
ImportDeclaration(node) {
if (node.source.value === 'next/document') {
const documentImport = node.specifiers.find(
({ type }) => type === 'ImportDefaultSpecifier'
)
if (documentImport && documentImport.local) {
documentImportName = documentImport.local.name
}
}
},
ExportDefaultDeclaration(node) {
exportDeclarationType = node.declaration.type
if (node.declaration.type === 'FunctionDeclaration') {
localDefaultExportId = node.declaration.id
return
}
if (
node.declaration.type === 'ClassDeclaration' &&
node.declaration.superClass &&
node.declaration.superClass.name === documentImportName
) {
localDefaultExportId = node.declaration.id
}
},
JSXOpeningElement(node) {
if (node.name.name !== 'link') {
return
}
const ancestors = context.getAncestors()
// if `export default <name>` is further down within the file after the
// currently traversed component, then `localDefaultExportName` will
// still be undefined
if (!localDefaultExportId) {
// find the top level of the module
const program = ancestors.find(
(ancestor) => ancestor.type === 'Program'
)
// go over each token to find the combination of `export default <name>`
for (let i = 0; i <= program.tokens.length - 1; i++) {
if (localDefaultExportId) {
break
}
const token = program.tokens[i]
if (token.type === 'Keyword' && token.value === 'export') {
const nextToken = program.tokens[i + 1]
if (
nextToken &&
nextToken.type === 'Keyword' &&
nextToken.value === 'default'
) {
const maybeIdentifier = program.tokens[i + 2]
if (maybeIdentifier && maybeIdentifier.type === 'Identifier') {
localDefaultExportId = { name: maybeIdentifier.value }
}
}
}
}
}
const parentComponent = ancestors.find((ancestor) => {
// export default class ... extends ...
if (exportDeclarationType === 'ClassDeclaration') {
return (
ancestor.type === exportDeclarationType &&
ancestor.superClass &&
ancestor.superClass.name === documentImportName
)
}
// export default function ...
if (exportDeclarationType === 'FunctionDeclaration') {
return (
ancestor.type === exportDeclarationType &&
isIdentifierMatch(ancestor.id, localDefaultExportId)
)
}
// function ...() {} export default ...
// class ... extends ...; export default ...
return isIdentifierMatch(ancestor.id, localDefaultExportId)
})
// file starts with _document and this <link /> is within the default export
if (is_Document && parentComponent) {
return
}
const attributes = new NodeAttributes(node)
if (!attributes.has('href') || !attributes.hasValue('href')) {
return
}
const hrefValue = attributes.value('href')
const isGoogleFont =
typeof hrefValue === 'string' &&
hrefValue.startsWith('https://fonts.googleapis.com/css')
if (isGoogleFont) {
const end = `This is discouraged. See: ${url}`
const message = is_Document
? `Using \`<link />\` outside of \`<Head>\` will disable automatic font optimization. ${end}`
: `Custom fonts not added in \`pages/_document.js\` will only load for a single page. ${end}`
context.report({
node,
message,
})
}
},
}
},
}
function isIdentifierMatch(id1, id2) {
return (id1 === null && id2 === null) || (id1 && id2 && id1.name === id2.name)
}