merge #190: terminal Nerd Font icon fallback (ShelbyTang)

2026-08-24 01:34:10 +08:00
parent 53f3a2c246 dd5a3dda07
commit abe9c4fc46
3 changed files with 321 additions and 8 deletions
@@ -9,8 +9,184 @@ import { clampTerminalFontSize, type SidebarPrefs } from '../prefs-shared.ts'
 /** The built-in fallback stack when neither the user nor the theme sets one. */
 export const DEFAULT_TERMINAL_FONT_FAMILY = '"SF Mono", Menlo, Consolas, "Liberation Mono", monospace'

+/**
+ * Icon fonts appended to whichever base stack wins, so shell prompts that
+ * draw glyphs from the Nerd Font Private Use Areas resolve to a real glyph
+ * instead of the missing-glyph box (aka tofu).
+ *
+ * Why this is needed even though the OS "should" fall back automatically:
+ * prompt frameworks (starship, powerlevel10k, oh-my-posh) take their icons
+ * from the PUA. Chromium's implicit system fallback reliably covers the
+ * *BMP* PUA (U+E000–U+F8FF — e.g. the U+E0B0 powerline separator) but NOT
+ * the *supplementary-plane* PUA-B (U+F0000+) where Nerd Fonts v3 relocated
+ * the Material Design icon set. Naming the families explicitly makes the
+ * browser consult them per character, which covers both planes.
+ *
+ * Deliberately NOT listed: color-emoji families. Chromium routes genuine
+ * emoji code points through a dedicated emoji fallback path (which is why
+ * emoji already render), so naming them buys nothing here — while placing a
+ * color font ahead of the generic family risks capturing BMP symbols the
+ * prompt expects in monospace (U+26A0 ⚠, U+2714 ✔ …) and rendering them as
+ * wide color glyphs that break the cell grid.
+ *
+ * Ordering rationale: the symbols-only patches ship glyphs without Latin,
+ * so they can never hijack ASCII metrics — the safest first hop. The
+ * fully-patched distributions follow for users who installed one of those
+ * instead. Both the `… Mono` and proportional family names are listed
+ * because the Nerd Fonts installers register them as distinct families.
+ *
+ * These are strictly *appended*, never prepended: xterm derives its cell
+ * metrics from the first entry, so the base font must stay in front or the
+ * whole grid would be re-measured against an icon font.
+ */
+export const ICON_FONT_FALLBACKS: readonly string[] = [
+  // Symbols-only patches (glyph coverage without Latin) — ideal fallbacks.
+  '"Symbols Nerd Font Mono"',
+  '"Symbols Nerd Font"',
+  // Common fully-patched Nerd Font distributions.
+  '"Hack Nerd Font Mono"',
+  '"Hack Nerd Font"',
+  '"JetBrainsMono Nerd Font Mono"',
+  '"JetBrainsMono Nerd Font"',
+  '"FiraCode Nerd Font Mono"',
+  '"FiraCode Nerd Font"',
+  '"CaskaydiaCove Nerd Font Mono"',
+  '"CaskaydiaCove Nerd Font"',
+  '"SauceCodePro Nerd Font Mono"',
+  '"UbuntuMono Nerd Font Mono"',
+  '"Iosevka Nerd Font Mono"',
+  '"MesloLGS Nerd Font Mono"',
+  '"MesloLGS NF"',
+]
+
+/**
+ * CSS generic font families. A generic is a catch-all that always resolves,
+ * so icon fonts must be spliced in *before* the first one to stay reachable.
+ */
+const GENERIC_FAMILIES = new Set([
+  'monospace', 'serif', 'sans-serif', 'cursive', 'fantasy',
+  'system-ui', 'ui-monospace', 'ui-serif', 'ui-sans-serif', 'ui-rounded',
+  'math', 'emoji', 'fangsong',
+])
+
+/**
+ * CSS-wide keywords. These are only valid as an *entire* declaration value,
+ * so a stack cannot be appended to one.
+ */
+const CSS_WIDE_KEYWORDS = new Set(['inherit', 'initial', 'unset', 'revert', 'revert-layer'])
+
+/** Normalize one family name for comparison: unquote, collapse runs of
+ *  whitespace, casefold. */
+function normalizeFamily(family: string): string {
+  return family
+    .trim()
+    .replace(/^["']|["']$/g, '')
+    .replace(/\s+/g, ' ')
+    .trim()
+    .toLowerCase()
+}
+
+/**
+ * Split a CSS font-family stack on its top-level commas.
+ *
+ * Naive `split(',')` would corrupt quoted family names containing a comma
+ * and function values such as `var(--x, monospace)`, so quotes (with
+ * backslash escapes) and parentheses are tracked.
+ *
+ * @param stack - a CSS font-family stack.
+ * @returns the trimmed, non-empty family entries in source order.
+ */
+function splitFamilies(stack: string): string[] {
+  const entries: string[] = []
+  let buffer = ''
+  let quote: string | null = null
+  let depth = 0
+  for (let i = 0; i < stack.length; i += 1) {
+    const char = stack[i] as string
+    if (quote !== null) {
+      // Escapes are copied verbatim so `\"` does not close the quote.
+      if (char === '\\' && i + 1 < stack.length) {
+        buffer += char + (stack[i + 1] as string)
+        i += 1
+        continue
+      }
+      buffer += char
+      if (char === quote) quote = null
+      continue
+    }
+    if (char === '"' || char === "'") {
+      quote = char
+      buffer += char
+      continue
+    }
+    if (char === '(') depth += 1
+    else if (char === ')') depth = Math.max(0, depth - 1)
+    else if (char === ',' && depth === 0) {
+      entries.push(buffer)
+      buffer = ''
+      continue
+    }
+    buffer += char
+  }
+  entries.push(buffer)
+  return entries.map(entry => entry.trim()).filter(entry => entry !== '')
+}
+
+/**
+ * Append {@link ICON_FONT_FALLBACKS} to a CSS font-family stack, keeping
+ * the caller's own entries and order intact.
+ *
+ * - Families already named in `stack` are not duplicated (quote-, case- and
+ *   whitespace-insensitive), so a user who already lists their Nerd Font
+ *   keeps their exact priority.
+ * - The icon fonts are spliced in ahead of the *first* generic family
+ *   (`monospace` etc.), because a generic always resolves: anything after it
+ *   would never be consulted.
+ * - Idempotent — re-applying to an already-topped-up stack is a no-op, which
+ *   matters because `TerminalView` diffs the resolved value against the live
+ *   `term.options.fontFamily` before reflowing.
+ *
+ * @param stack - a CSS font-family stack (base font first).
+ * @returns the stack with icon fallbacks merged in.
+ */
+export function withIconFontFallbacks(stack: string): string {
+  const entries = splitFamilies(stack)
+  if (entries.length === 0) return ICON_FONT_FALLBACKS.join(', ')
+
+  const present = new Set(entries.map(normalizeFamily))
+  const additions = ICON_FONT_FALLBACKS.filter(family => !present.has(normalizeFamily(family)))
+  if (additions.length === 0) return entries.join(', ')
+
+  const firstGeneric = entries.findIndex(entry => GENERIC_FAMILIES.has(normalizeFamily(entry)))
+  const cut = firstGeneric === -1 ? entries.length : firstGeneric
+  return [...entries.slice(0, cut), ...additions, ...entries.slice(cut)].join(', ')
+}
+
+/**
+ * Reduce one link of the base-family chain to a usable stack, or `''` when
+ * it cannot carry appended fallbacks so the next link should win.
+ *
+ * Rejecting CSS-wide keywords matters because the theme font arrives as a
+ * raw token value (`tokenValue('--ds-font-family-code')`); skins do set
+ * tokens to `initial`/`inherit`/`unset` (see `effectiveTokenValue` in
+ * `theme.ts`, which guards the color tokens for the same reason). Appending
+ * to such a value yields an invalid `font-family`, which the CSSOM discards
+ * silently — the terminal would lose the theme font *and* the icon fonts.
+ */
+function usableBase(value: string | undefined): string {
+  const trimmed = (value ?? '').trim()
+  if (trimmed === '') return ''
+  if (CSS_WIDE_KEYWORDS.has(trimmed.toLowerCase())) return ''
+  return trimmed
+}
+
 /**
 * Resolve the xterm font options for the given prefs.
+ *
+ * The base family keeps its existing precedence — user pref > theme code
+ * font > built-in stack — and then {@link withIconFontFallbacks} tops it up
+ * so prompt icons resolve regardless of which base won.
+ *
 * @param prefs - the current side card preferences.
 * @param themeFontFamily - the app's theme code font (`--ds-font-family-code`
 *   token value, read live by the caller); undefined when the token is absent.
@@ -20,9 +196,11 @@ export function resolveTerminalFont(
  prefs: SidebarPrefs,
  themeFontFamily: string | undefined,
 ): { fontFamily: string; fontSize: number } {
-  const custom = prefs.terminalFontFamily.trim()
+  const base = usableBase(prefs.terminalFontFamily)
+    || usableBase(themeFontFamily)
+    || DEFAULT_TERMINAL_FONT_FAMILY
  return {
-    fontFamily: custom !== '' ? custom : (themeFontFamily || DEFAULT_TERMINAL_FONT_FAMILY),
+    fontFamily: withIconFontFallbacks(base),
    fontSize: clampTerminalFontSize(prefs.terminalFontSize),
  }
 }