Crash during elaboration when accessing elements of nested generic packages

[ALVAROPING1]

Found a crash during elaboration when using nested generic packages and trying to access their fields

OS: Ubuntu 22.04
NVC version: latest stable release (1.20.0)

Minimal code to reproduce it (test.vhdl):

package pkg1 is
    generic (a: natural);
end package;

package pkg1_inst is new work.pkg1 generic map (a => 2);

package pkg2 is
    generic (
        package pkg1_inst_sub is new work.pkg1 generic map (<>);
        -- If this is removed, nvc appears to get stuck and never exit
        -- (killed it after >1 min of no output)
        constant b: natural
    );
end package;

package pkg2_inst is new work.pkg2 generic map (
    pkg1_inst_sub => work.pkg1_inst,
    b => 0
);

entity Sub is
    generic (
        package pkg2_inst_sub is new work.pkg2 generic map (<>)
    );
end;

architecture rtl of Sub is
    package foo is new work.pkg1 generic map (
        a => pkg2_inst_sub.pkg1_inst_sub.a
    );
begin
end;

entity Top is
end;

architecture rtl of Top is
begin
    sub: entity work.Sub generic map (work.pkg2_inst);
end;

Running nvc -a test.vhdl -e top-rtl produces the following output:

Name       WORK.TOP.SUB.FOO
Kind       package
Context    WORK.TOP.SUB
Blocks     1
Registers  1
Types      2
Stamps     1
Variables  1
  A                                     // -2^31..2^31-1 => 0..2^31-1, constant
Begin
   0: r0 := package init STD.STANDARD   // P<STD.STANDARD>

** Fatal: (init): missing variable for generic A in WORK.TOP-RTL.elab
    > test.vhdl:39
    |
 39 |     sub: entity work.Sub generic map (work.pkg2_inst);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ while elaborating instance SUB
    |
    = Note: generic PKG2_INST_SUB => WORK.PKG2_INST
[0x55c47131a1e2] 
[0x55c471329b79] 
[0x55c4713ec54d] 
[0x55c4713ec930] 
[0x55c4713dc89d] 
[0x55c4713e9a94] 
[0x55c47141fd78] 
[0x55c471438171] 
[0x55c4714396e4] 
[0x55c47144311e] 
[0x55c47141f535] 
[0x55c4714d7955] 
[0x55c47146d690] 
[0x55c47139cbdb] 
[0x55c4713a5c18] 
[0x55c4713a4c3f] 
[0x55c4713a5c24] 
[0x55c47134530c] 
[0x55c471342157] 
[0x55c471344063] 
[0x55c471339cc3] 
[0x76a45f029d8f] (/usr/lib/x86_64-linux-gnu/libc.so.6) ../sysdeps/nptl/libc_start_call_main.h:58 __libc_start_call_main
[0x76a45f029e3f] (/usr/lib/x86_64-linux-gnu/libc.so.6) ../csu/libc-start.c:392 __libc_start_main@@GLIBC_2.34
[0x55c47133b1d4] 

nvc 1.20.0 (258d1f2) (Using LLVM 14.0.0) [x86_64-pc-linux-gnu]

Please report this bug at https://github.com/nickg/nvc/issues