On my systems there is a path in the fonts list that looks like
/nix/store/<hash>-<font>.ttf. The previous code assumed that every font path
contains at least one more slash which isn't the case here.
The code matched on the / after the $out path of the derivation:
/nix/store/<hash>-<name>/share/X11/fonts/...
^
That slash only exists if the font lives in a subdirectory, which
isn't strictly required. In my case I've a few font files that are
located at /nix/store/<hash>-<name>.ttf and are assembled into a
folder as symlinks. (See example below)
Any attempt at calling realpath(3) on them (potentially recursively)
will result in the single file entry in the store being returned.
Whenever that font is being loaded flatpak segfaulted like so:
```
(gdb) bt
#0 0x00005583b3673763 in get_nix_closure ()
#1 0x00005583b3673711 in get_nix_closure ()
#2 0x00005583b36737dc in add_nix_store_symlink_targets ()
#3 0x00005583b36749a8 in add_font_path_args ()
#4 0x00005583b367b3f4 in flatpak_run_app ()
#5 0x00005583b35e4f08 in flatpak_builtin_run ()
#6 0x00005583b35a5970 in main ()
(gdb) x/5i $rip
=> 0x5583b3673763 <get_nix_closure+307>: movb $0x0,(%rax)
0x5583b3673766 <get_nix_closure+310>: call 0x5583b35a46a0 <g_hash_table_add@plt>
0x5583b367376b <get_nix_closure+315>: jmp 0x5583b3673699 <get_nix_closure+105>
0x5583b3673770 <get_nix_closure+320>: xor %edi,%edi
0x5583b3673772 <get_nix_closure+322>: lea 0x30475(%rip),%rsi # 0x5583b36a3bee
(gdb) x/s $rsi
0x5583e92d2180: "/nix/store/<hash>-A.ttf"
(gdb) print $rax
$1 = 0
```
RAX pointing to 0 here corresponds to the pointer `p` in the source
code. So the code attempted to dereference a null pointer as no further
slash (the return value of strchr(3)) could be found.
The modification in this commit ensures that we check for `p != 0` so
we don't run into this situation again.
Adding the path to the closure will still be done, even if no further
slash can be found, as that still points to a valid store path.
----
Nix code for custom fonts:
```nix
let
files = [
./A.ttf
./B.ttf
];
in
runCommandNoCC "custom-fonts" {} ''
mkdir -p $out/share/fonts/truetype
cd $out/share/fonts/truetype
${ lib.concatStringsSep "\n" (map (file: "ln -s ${file} ${baseNameOf file}") files)}
''
```
this creates some eval errors that will be fixed in the next commit
done with the following script:
```fish
\#!/usr/bin/env fish
set packagesjson (nix eval --impure --json --expr '
let
lib = import ./lib;
in
import pkgs/servers/x11/xorg/default.nix (lib.mapAttrs (
name: _:
if name == "lib" then
lib
else if name == "config" then
{ allowAliases = false; }
else
name
) (__functionArgs (import pkgs/servers/x11/xorg/default.nix))) { }
' | jq)
set one (grep '^ [A-Za-z0-9_-]*$' pkgs/servers/x11/xorg/default.nix | string trim | string replace -r '$' Z | sort | string sub -e -1)
set two (grep '^ [A-Za-z0-9_-]* = [A-Za-z0-9_-]*;$' pkgs/servers/x11/xorg/default.nix | cut -d= -f1 | string trim | string replace -r '$' Z | sort | string sub -e -1)
for arg in $one $two
set oname $arg
set nname (echo $packagesjson | jq -r .$oname)
if test $nname = null
echo (set_color red)warn:(set_color normal) unknown package xorg.$oname >&2
continue
end
echo $oname "->" $nname
# replace basic xorg.$name references
for file in (rg -F "xorg.$oname" --files-with-matches pkgs)
# special cases
sd -F "$oname = xorg.$oname;" "$nname = $nname;" $file
# replace
sd -F "xorg.$oname" "$nname" $file
# fixup function arguments
# prevent duplicate function args
if grep -E " ($oname|$nname),\$" $file >/dev/null
continue
end
if grep 'xorg\..' $file >/dev/null # case1: there is more so we can't just remove the function arg
if grep ' xorg,$' $file >/dev/null
sd ' xorg,$' " xorg,
$nname," $file
else if grep ' xorg ? .*,$' $file >/dev/null
sd 'xorg( ? .*),$' "xorg\$1,
$nname," $file
else
sd -F 'xorg,' "$nname,
xorg," $file
end
else # case there is no more xorg..* so we can just replace the function arg
sd 'xorg(| ? .*),.*$' "$nname," $file
end
end
end
nix fmt
```
Otherwise, flatpak looks for configuration files inside the Nix store:
$ flatpak list --installation=test -v
F: No installations directory in /nix/store/gb76s3h00k2r95snjdxs3840sn3ab22f-flatpak-1.16.1/etc/flatpak/installations.d. Skipping
error: Could not find installation test
This was previously fixed in 01189fb832 ("flatpak: fix config
location") but lost in the conversion to Meson in
ae96b31920 ("flatpak: 1.14.10 -> 1.16.0").
The 1.14.8 -> 1.14.10 update broke cross compilation, because the upstream
build script now invokes runtime dependencies for feature detection.
<5a2503f1e8/configure.ac (L178)>
It seems the package will be more robust against changes if we simply
emulate these checks rather than attempt to patch them out individually.
