Local font files adjust fallbacks (#41180)

When using `@next/font/local` we can't have pre calculated metrics for the font. This PR uses fontkit to read metadata about the imported local font in order to generate a fallback. Also removes some props from the api that's better done automatically in the future. ## Bug - [ ] Related issues linked using `fixes #number` - [ ] Integration tests added - [ ] Errors have a helpful link attached, see `contributing.md` ## Feature - [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR. - [ ] Related issues linked using `fixes #number` - [ ] Integration tests added - [ ] Documentation added - [ ] Telemetry added. In case of a feature if it's used or not. - [ ] Errors have a helpful link attached, see `contributing.md` ## Documentation / Examples - [ ] Make sure the linting passes by running `pnpm lint` - [ ] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)
vercel · Oct 10, 2022 · 05498a0 · 05498a0
1 parent 6e4f1e2
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diff --git a/packages/font/fontkit.js b/packages/font/fontkit.js
@@ -0,0 +1,3 @@
+// eslint-disable-next-line import/no-extraneous-dependencies
+import { create } from 'fontkit'
+export default create
diff --git a/packages/font/package.json b/packages/font/package.json
@@ -12,9 +12,15 @@
   ],
   "license": "MIT",
   "scripts": {
-    "build": "rm -rf dist && tsc -d -p tsconfig.json",
+    "build": "rm -rf dist && pnpm ncc-fontkit && tsc -d -p tsconfig.json",
     "prepublishOnly": "cd ../../ && turbo run build",
-    "dev": "tsc -d -w -p tsconfig.json",
-    "typescript": "tsec --noEmit -p tsconfig.json"
+    "dev": "pnpm ncc-fontkit && tsc -d -w -p tsconfig.json",
+    "typescript": "tsec --noEmit -p tsconfig.json",
+    "ncc-fontkit": "ncc build ./fontkit.js -o dist/fontkit"
+  },
+  "devDependencies": {
+    "@types/fontkit": "2.0.0",
+    "@vercel/ncc": "0.34.0",
+    "fontkit": "2.0.2"
   }
 }
diff --git a/packages/font/src/google/loader.ts b/packages/font/src/google/loader.ts
@@ -2,7 +2,7 @@ import type { AdjustFontFallback, FontLoader } from 'next/font'
 // @ts-ignore
 import fetch from 'next/dist/compiled/node-fetch'
 // @ts-ignore
-import { calculateOverrideValues } from 'next/dist/server/font-utils'
+import { calculateSizeAdjustValues } from 'next/dist/server/font-utils'
 import {
   fetchCSSFromGoogleFonts,
   getFontAxes,
@@ -101,16 +101,16 @@ const downloadGoogleFonts: FontLoader = async ({
   let adjustFontFallbackMetrics: AdjustFontFallback | undefined
   if (adjustFontFallback) {
     try {
-      const { ascent, descent, lineGap, fallbackFont } =
-        calculateOverrideValues(
-          fontFamily,
-          require('next/dist/server/google-font-metrics.json')
+      const { ascent, descent, lineGap, fallbackFont, sizeAdjust } =
+        calculateSizeAdjustValues(
+          require('next/dist/server/google-font-metrics.json')[fontFamily]
         )
       adjustFontFallbackMetrics = {
         fallbackFont,
-        ascentOverride: ascent,
-        descentOverride: descent,
-        lineGapOverride: lineGap,
+        ascentOverride: `${ascent}%`,
+        descentOverride: `${descent}%`,
+        lineGapOverride: `${lineGap}%`,
+        sizeAdjust: `${sizeAdjust}%`,
       }
     } catch {
       console.error(

diff --git a/packages/font/src/local/index.ts b/packages/font/src/local/index.ts
@@ -1,9 +1,9 @@
 /* eslint-disable @typescript-eslint/no-unused-vars */
-import type { AdjustFontFallback, FontModule } from 'next/font'
+import type { FontModule } from 'next/font'
 type Display = 'auto' | 'block' | 'swap' | 'fallback' | 'optional'
 type CssVariable = `--${string}`
 type LocalFont = {
-  src: string | Array<{ file: string; unicodeRange: string }>
+  src: string
   display?: Display
   weight?: number
   style?: string
@@ -20,7 +20,7 @@ type LocalFont = {
   lineGapOverride?: string
   sizeAdjust?: string
 
-  adjustFontFallback?: AdjustFontFallback
+  adjustFontFallback?: 'Arial' | 'Times New Roman' | false
 }
 
 export default function localFont(options: LocalFont): FontModule {

diff --git a/packages/font/src/local/loader.ts b/packages/font/src/local/loader.ts
@@ -1,4 +1,9 @@
-import type { FontLoader } from 'next/font'
+// @ts-ignore
+import { calculateSizeAdjustValues } from 'next/dist/server/font-utils'
+// @ts-ignore
+// eslint-disable-next-line import/no-extraneous-dependencies
+import fontFromBuffer from '@next/font/dist/fontkit'
+import type { AdjustFontFallback, FontLoader } from 'next/font'
 
 import { promisify } from 'util'
 import { validateData } from './utils'
@@ -12,7 +17,9 @@ const fetchFonts: FontLoader = async ({
 }) => {
   const {
     family,
-    files,
+    src,
+    ext,
+    format,
     display,
     weight,
     style,
@@ -28,45 +35,73 @@ const fetchFonts: FontLoader = async ({
     adjustFontFallback,
   } = validateData(functionName, data)
 
-  const fontFaces = await Promise.all(
-    files.map(async ({ file, ext, format, unicodeRange }) => {
-      const resolved = await resolve(file)
-      const fileBuffer = await promisify(fs.readFile)(resolved)
+  const resolved = await resolve(src)
+  const fileBuffer = await promisify(fs.readFile)(resolved)
+  const fontUrl = emitFontFile(fileBuffer, ext, preload)
 
-      const fontUrl = emitFontFile(fileBuffer, ext, preload)
+  let fontMetadata: any
+  try {
+    fontMetadata = fontFromBuffer(fileBuffer)
+  } catch (e) {
+    console.error(`Failed to load font file: ${resolved}\n${e}`)
+  }
+
+  // Add fallback font
+  let adjustFontFallbackMetrics: AdjustFontFallback | undefined
+  if (fontMetadata && adjustFontFallback !== false) {
+    const {
+      ascent,
+      descent,
+      lineGap,
+      fallbackFont,
+      sizeAdjust: fallbackSizeAdjust,
+    } = calculateSizeAdjustValues({
+      category:
+        adjustFontFallback === 'Times New Roman' ? 'serif' : 'sans-serif',
+      ascent: fontMetadata.ascent,
+      descent: fontMetadata.descent,
+      lineGap: fontMetadata.lineGap,
+      unitsPerEm: fontMetadata.unitsPerEm,
+      xAvgCharWidth: (fontMetadata as any)['OS/2']?.xAvgCharWidth,
+    })
+    adjustFontFallbackMetrics = {
+      fallbackFont,
+      ascentOverride: `${ascent}%`,
+      descentOverride: `${descent}%`,
+      lineGapOverride: `${lineGap}%`,
+      sizeAdjust: `${fallbackSizeAdjust}%`,
+    }
+  }
 
-      const fontFaceProperties = [
-        ['font-family', `'${family}'`],
-        ['src', `url(${fontUrl}) format('${format}')`],
-        ['font-display', display],
-        ...(weight ? [['font-weight', weight]] : []),
-        ...(style ? [['font-style', style]] : []),
-        ...(ascentOverride ? [['ascent-override', ascentOverride]] : []),
-        ...(descentOverride ? [['descent-override', descentOverride]] : []),
-        ...(lineGapOverride ? [['line-gap-override', lineGapOverride]] : []),
-        ...(fontStretch ? [['font-stretch', fontStretch]] : []),
-        ...(fontFeatureSettings
-          ? [['font-feature-settings', fontFeatureSettings]]
-          : []),
-        ...(sizeAdjust ? [['size-adjust', sizeAdjust]] : []),
-        ...(unicodeRange ? [['unicode-range', unicodeRange]] : ''),
-      ]
+  const fontFaceProperties = [
+    ['font-family', `'${fontMetadata?.familyName ?? family}'`],
+    ['src', `url(${fontUrl}) format('${format}')`],
+    ['font-display', display],
+    ...(weight ? [['font-weight', weight]] : []),
+    ...(style ? [['font-style', style]] : []),
+    ...(ascentOverride ? [['ascent-override', ascentOverride]] : []),
+    ...(descentOverride ? [['descent-override', descentOverride]] : []),
+    ...(lineGapOverride ? [['line-gap-override', lineGapOverride]] : []),
+    ...(fontStretch ? [['font-stretch', fontStretch]] : []),
+    ...(fontFeatureSettings
+      ? [['font-feature-settings', fontFeatureSettings]]
+      : []),
+    ...(sizeAdjust ? [['size-adjust', sizeAdjust]] : []),
+  ]
 
-      return `@font-face {
+  const css = `@font-face {
 ${fontFaceProperties
   .map(([property, value]) => `${property}: ${value};`)
   .join('\n')}
 }`
-    })
-  )
 
   return {
-    css: fontFaces.join('\n'),
+    css,
     fallbackFonts: fallback,
     weight,
     style,
     variable,
-    adjustFontFallback,
+    adjustFontFallback: adjustFontFallbackMetrics,
   }
 }
 

diff --git a/packages/font/src/local/utils.ts b/packages/font/src/local/utils.ts
@@ -1,5 +1,3 @@
-import { AdjustFontFallback } from 'next/font'
-
 const allowedDisplayValues = ['auto', 'block', 'swap', 'fallback', 'optional']
 
 const formatValues = (values: string[]) =>
@@ -15,12 +13,9 @@ const extToFormat = {
 
 type FontOptions = {
   family: string
-  files: Array<{
-    file: string
-    ext: string
-    format: string
-    unicodeRange?: string
-  }>
+  src: string
+  ext: string
+  format: string
   display: string
   weight?: number
   style?: string
@@ -35,7 +30,7 @@ type FontOptions = {
   fontVariationSettings?: string
   lineGapOverride?: string
   sizeAdjust?: string
-  adjustFontFallback?: AdjustFontFallback
+  adjustFontFallback?: string | false
 }
 export function validateData(functionName: string, data: any): FontOptions {
   if (functionName) {
@@ -68,39 +63,22 @@ export function validateData(functionName: string, data: any): FontOptions {
     )
   }
 
-  const srcArray = Array.isArray(src) ? src : [{ file: src }]
-
-  if (srcArray.length === 0) {
-    throw new Error('Src must contain one or more files')
+  if (!src) {
+    throw new Error('Missing required `src` property')
   }
 
-  const files = srcArray.map(({ file, unicodeRange }) => {
-    if (!file) {
-      throw new Error('Src array objects must have a `file` property')
-    }
-    if (srcArray.length > 1 && !unicodeRange) {
-      throw new Error(
-        "Files must have a unicode-range if there's more than one"
-      )
-    }
-
-    const ext = /\.(woff|woff2|eot|ttf|otf)$/.exec(file)?.[1]
-    if (!ext) {
-      throw new Error(`Unexpected file \`${file}\``)
-    }
-    return {
-      file,
-      unicodeRange,
-      ext,
-      format: extToFormat[ext as 'woff' | 'woff2' | 'eot' | 'ttf' | 'otf'],
-    }
-  })
+  const ext = /\.(woff|woff2|eot|ttf|otf)$/.exec(src)?.[1]
+  if (!ext) {
+    throw new Error(`Unexpected file \`${src}\``)
+  }
 
-  const family = /.+\/(.+?)\./.exec(files[0].file)![1]
+  const family = /.+\/(.+?)\./.exec(src)![1]
 
   return {
     family,
-    files,
+    src,
+    ext,
+    format: extToFormat[ext as 'woff' | 'woff2' | 'eot' | 'ttf' | 'otf'],
     display,
     weight,
     style,

diff --git a/packages/next/server/font-utils.ts b/packages/next/server/font-utils.ts
@@ -102,9 +102,8 @@ function formatOverrideValue(val: number) {
   return Math.abs(val * 100).toFixed(2)
 }
 
-export function calculateOverrideValues(font: string, fontMetrics: any) {
-  const fontKey = font.trim()
-  let { category, ascent, descent, lineGap, unitsPerEm } = fontMetrics[fontKey]
+export function calculateOverrideValues(fontMetrics: any) {
+  let { category, ascent, descent, lineGap, unitsPerEm } = fontMetrics
   const fallbackFont =
     category === 'serif' ? DEFAULT_SERIF_FONT : DEFAULT_SANS_SERIF_FONT
   ascent = formatOverrideValue(ascent / unitsPerEm)
@@ -119,14 +118,15 @@ export function calculateOverrideValues(font: string, fontMetrics: any) {
   }
 }
 
-export function calculateSizeAdjustValues(font: string, fontMetrics: any) {
-  const fontKey = font.trim()
+export function calculateSizeAdjustValues(fontMetrics: any) {
   let { category, ascent, descent, lineGap, unitsPerEm, xAvgCharWidth } =
-    fontMetrics[fontKey]
+    fontMetrics
   const fallbackFont =
     category === 'serif' ? DEFAULT_SERIF_FONT : DEFAULT_SANS_SERIF_FONT
 
-  let sizeAdjust = xAvgCharWidth / fallbackFont.xAvgCharWidth
+  let sizeAdjust = xAvgCharWidth
+    ? xAvgCharWidth / fallbackFont.xAvgCharWidth
+    : 1
 
   ascent = formatOverrideValue(ascent / (unitsPerEm * sizeAdjust))
   descent = formatOverrideValue(descent / (unitsPerEm * sizeAdjust))
@@ -145,8 +145,7 @@ function calculateOverrideCSS(font: string, fontMetrics: any) {
   const fontName = font.trim()
 
   const { ascent, descent, lineGap, fallbackFont } = calculateOverrideValues(
-    font,
-    fontMetrics
+    fontMetrics[fontName]
   )
 
   return `
@@ -164,7 +163,7 @@ function calculateSizeAdjustCSS(font: string, fontMetrics: any) {
   const fontName = font.trim()
 
   const { ascent, descent, lineGap, fallbackFont, sizeAdjust } =
-    calculateSizeAdjustValues(font, fontMetrics)
+    calculateSizeAdjustValues(fontMetrics[fontName])
 
   return `
     @font-face {