Drop empty link sources; make install refuse them

Five directories swept in held no files — matplotlib, three gtk dirs and
one mpv. Git cannot represent an empty directory, so they existed on
mainframe where they were created but vanished on clone, and system76's
install failed with "Nonexistent target".

install now checks every link source exists before running dotbot, so this
surfaces on the machine that introduced it rather than the next one to
pull.

install

@@ -20,6 +20,15 @@ if [[ ! -f "${HOSTCONF}" ]]; then
   exit 1
 fi
 
+# Git cannot represent an empty directory, so a link whose source contains no
+# files disappears on clone and dotbot fails with "Nonexistent target". Catch
+# it here rather than on someone else's machine.
+missing=0
+while read -r src; do
+  [[ -e "${src}" ]] || { echo "install: link source missing from the repo: ${src}" >&2; missing=1; }
+done < <(grep -hoE '^\s+~[^:]*:\s+\S+' meta/base.conf.yaml "${HOSTCONF}" | awk '{print $NF}')
+(( missing )) && { echo "install: refusing to run with missing sources." >&2; exit 1; }
+
 git submodule update --init --recursive "${DOTBOT_DIR}"
 
 echo "==> base"

meta/base.conf.yaml

@@ -28,4 +28,3 @@
     ~/.config/lazygit:               common/lazygit
     ~/.config/ncmpcpp:               common/ncmpcpp
     ~/.config/neofetch:              common/neofetch
-    ~/.config/matplotlib:            common/matplotlib

meta/hosts/mainframe.conf.yaml

@@ -11,7 +11,6 @@
 
 - link:
     ~/.config/bob:                   hosts/mainframe/config/bob
-    ~/.config/gtk-3.0:               hosts/mainframe/config/gtk-3.0
     ~/.config/inbox-tidy:            hosts/mainframe/config/inbox-tidy
     ~/.config/llmfit:                hosts/mainframe/config/llmfit
     ~/.config/mimeapps.list:         hosts/mainframe/config/mimeapps.list

meta/hosts/sctfw004.conf.yaml

@@ -15,9 +15,7 @@
     ~/.config/gh:                    hosts/sctfw004/config/gh
     ~/.config/gtk-2.0:               hosts/sctfw004/config/gtk-2.0
     ~/.config/gtk-3.0:               hosts/sctfw004/config/gtk-3.0
-    ~/.config/gtk-4.0:               hosts/sctfw004/config/gtk-4.0
     ~/.config/mimeapps.list:         hosts/sctfw004/config/mimeapps.list
-    ~/.config/mpv:                   hosts/sctfw004/config/mpv
     ~/.config/pavucontrol.ini:       hosts/sctfw004/config/pavucontrol.ini
     ~/.config/swayimg:               hosts/sctfw004/config/swayimg
     ~/.config/swaync:                hosts/sctfw004/config/swaync

meta/hosts/system76.conf.yaml

@@ -15,7 +15,6 @@
     ~/.config/glow:                  hosts/system76/config/glow
     ~/.config/gtk-2.0:               hosts/system76/config/gtk-2.0
     ~/.config/gtk-3.0:               hosts/system76/config/gtk-3.0
-    ~/.config/gtk-4.0:               hosts/system76/config/gtk-4.0
     ~/.config/mimeapps.list:         hosts/system76/config/mimeapps.list
     ~/.config/mpd:                   hosts/system76/config/mpd
     ~/.config/mpv:                   hosts/system76/config/mpv