FontForge script to cleanly patch a font with a set of symbols fonts.

patch.ff

#!/usr/bin/env fontforge

# Usage: patch.ff <font_to_patch> <symbol_font_1> ... <symbol_font_n>

Open($1)


###
### PS NAMES
###

# the fontname is important to get right because the TTF Family and Subfamily are derived from it.
fontname_components = StrSplit($fontname, "-", 2)
fontname = fontname_components[0] + "Symbols"
if ( SizeOf(fontname_components) == 2 )
  # this is usually the case
  fontname = fontname + "-" + fontname_components[1]
endif
SetFontNames(fontname, $familyname + " Symbols", $fullname + " Symbols")


###
### TTF NAMES
###

# for IDs see: https://docs.microsoft.com/en-us/typography/opentype/spec/name#name-ids
ttf_lang = 0x409 # English (US)

ttf_family = GetTTFName(ttf_lang, 1)
if ( ttf_family!="" )
  # adjust the Family if it exists
  SetTTFName(ttf_lang, 1, ttf_family + " Symbols")
endif

ttf_prefered_family = GetTTFName(ttf_lang, 16)
if ( ttf_prefered_family!="" )
  # adjust the Preferred Family if it exists
  SetTTFName(ttf_lang, 16, ttf_prefered_family + " Symbols")
endif

ttf_uniqueid = GetTTFName(ttf_lang, 3)
if ( ttf_uniqueid!="" )
  # adjust the Unique ID if it exists
  SetTTFName(ttf_lang, 3, ttf_uniqueid + ";Symbols")
endif


###
### PATCHING
###

ascent = $ascent
descent = $descent

i=2
while ( i < $argc )
  Open($argv[i])
  Print("Patching with symbol font " + (i - 1) + "/" + ($argc - 2) + ": " + $filename:t)
  SelectAll()
  ScaleToEm(ascent, descent)
  /* RoundToInt() # should we use this? */
  scaled_filename = $filename:r + "-temp.sfd"
  Save(scaled_filename)
  Close()
  Open($1)
  MergeFonts(scaled_filename)
  i++
endloop


###
### SAVING
###

patched_filename = $filename:r + "-" + "Symbols." + $filename:e
Generate(patched_filename)
Print("Generated patched font at: " + patched_filename)
Close()

patch_all.sh

#!/usr/bin/env zsh
for FILE in "$@"
do
  ./patch.ff $FILE "$HOME/Library/Fonts/nonicons.ttf" "$HOME/Library/Fonts/Symbols-2048-em Nerd Font Complete.ttf"
done