Fix crash dumping subtype that cannot be represented in FST

Issue #840

NEWS.md

@@ -8,8 +8,7 @@
   correctly in VHDL-2008 mode (#826).
 - Fixed a memory corruption bug when evaluating certain aggregates that
   contain a range association (#827).
-- Fixed a crash when using the `'subtype` attribute with a constrained
-  port declaration (#837).
+- Resolved several other minor issues (#837, #839, #840).
 
 ## Version 1.11.2 - 2024-01-04
 - Fixed an incorrect length check in the equivalent process for

src/rt/wave.c

@@ -270,7 +270,11 @@ static fst_type_t *fst_type_for(type_t type, const loc_t *loc)
    switch (type_kind(type)) {
    case T_SUBTYPE:
       {
-         *ft = *fst_type_for(type_base(type), loc);
+         fst_type_t *baseft = fst_type_for(type_base(type), loc);
+         if (baseft == NULL)
+            goto poison;
+
+         *ft = *baseft;
 
          switch (is_well_known(type_ident(type))) {
          case W_STD_NATURAL:  ft->sdt = FST_SDT_VHDL_NATURAL; break;

test/regress/gold/issue840.dump

@@ -0,0 +1,2 @@
+#0 issue840.t 00000000000000000000000000000001
+#1000000 issue840.t 00000000000000000000000000000010

test/regress/issue840.vhd

@@ -0,0 +1,23 @@
+entity issue840 is
+end entity;
+
+architecture test of issue840 is
+    type t_array2d is array (natural range <>, natural range <>) of bit;
+    subtype t_sub is t_array2d(1 to 3, 1 to 3);
+
+    signal s : t_sub;
+    signal t : integer;
+begin
+
+    process is
+    begin
+        s <= ("101", "110", "111");
+        t <= 1;
+        wait for 1 ns;
+        s <= ("110", "000", "101");
+        t <= 2;
+        wait for 1 ns;
+        wait;
+    end process;
+
+end architecture;

test/regress/testlist.txt

@@ -918,3 +918,4 @@ issue825        normal
 issue826        normal,2008
 issue827        normal,2008
 issue839        normal
+issue840        wave