Fix set/unset state for short integer (typeset -si) (#211)

This commit fixes at least three bugs:
1. When issuing 'typeset -p' for unset variables typeset as short
   integer, a value of 0 was incorrectly diplayed.
2. ${x=y} and ${x:=y} were still broken for short integer types
   (re: 9f2389ed). ${x+set} and ${x:+nonempty} were also broken.
3. A memory fault could occur if typeset -l followed a -s option
   with integers. Additonally, now the last -s/-l wins out as the
   option to utilize instead of it always being short.

src/cmd/ksh93/include/name.h:
- Fix the nv_isnull() macro by removing the direct exclusion of
  short integers from this set/unset test. This breaks few things
  (only ${.sh.subshell} and ${.sh.level}, as far as we can tell)
  while potentially correcting many aspects of short integer use
  (at least bugs 1 and 2 above), as this macro is widely used.
- union Value: add new pid_t *pidp pointer member for PID values
  (see further below).

src/cmd/ksh93/bltins/typeset.c: b_typeset():
- To fix bug 3 above, unset the 'shortint' flag and NV_SHORT
  attribute bit upon encountering the -l optiobn.

*** To fix ${.sh.subshell} to work with the new nv_isnull():

src/cmd/ksh93/sh/defs.h:
- Add new 'realsubshell' member to the shgd (aka shp->gd) struct
  which will be the integer value for ${.sh.subshell}.

src/cmd/ksh93/sh/init.c,
src/cmd/ksh93/data/variables.c:
- Initialize SH_SUBSHELLNOD as a pointer to shgd->realsubshell
  instead of using a short value (.s) directly. Using a pointer
  allows nv_isnull() to return a positive for ${.sh.subshell} as
  a non-null pointer is what it checks for.
- While we're at it, initialize PPIDNOD ($PPID) and SH_PIDNOD
  (${.sh.pid}) using the new pdip union member, which is more
  correct as they are values of type pid_t.

src/cmd/ksh93/sh/subshell.c,
src/cmd/ksh93/sh/xec.c:
- Update the ${.sh.subshell} increases/decreases to refer to
  shgd->realsubshell (a.k.a. shp->gd->realsubshell).

*** To fix ${.sh.level} after changing nv_isnull():

src/cmd/ksh93/sh/macro.c: varsub():
- Add a specific exception for SH_LEVLNOD to the nv_isnull() test,
  so that ${.sh.level} is always considered to be set. Its handling
  throughout the code is too complex/special for a simple fix, so
  we have to special-case it, at least for now.

*** Regression test additions:

src/cmd/ksh93/tests/attributes.sh:
- Add in missing short integer tests and correct the one that
  existed. The -si test now yields 'typeset -x -r -s -i foo'
  instead of 'typeset -x -r -s -i foo=0' which brings it in line
  with all the others.
- Add in some other -l attribute tests for floats. Note, -lX test
  was not added as the size of long double is platform dependent.

src/cmd/ksh93/tests/variables.sh:
- Add tests for ${x=y} and ${x:=y} used on short int variables.

Co-authored-by: Martijn Dekker <martijn@inlv.org>

src/cmd/ksh93/tests/attributes.sh

@@ -513,11 +513,18 @@ typeset -A expect=(
 	[b]='typeset -x -r -b foo'
 	[i]='typeset -x -r -i foo'
 	[i37]='typeset -x -r -i 37 foo'
+	[ils]='typeset -x -r -s -i foo'
+	[isl]='typeset -x -r -l -i foo'
 	[l]='typeset -x -r -l foo'
+	[lF]='typeset -x -r -l -F foo'
+	[lE]='typeset -x -r -l -E foo'
 	[n]='typeset -n -r foo'
 	[s]='typeset -x -r foo'
-	[si]='typeset -x -r -s -i foo=0'
+	[si]='typeset -x -r -s -i foo'
 	[u]='typeset -x -r -u foo'
+	[ui]='typeset -x -r -u -i foo'
+	[usi]='typeset -x -r -s -u -i foo'
+	[uli]='typeset -x -r -l -u -i foo'
 	[A]='typeset -x -r -A foo=()'
 	[C]='typeset -x -r foo=()'
 	[E]='typeset -x -r -E foo'
@@ -532,6 +539,7 @@ typeset -A expect=(
 	[R]='typeset -x -r -R 0 foo'
 	[R17]='typeset -x -r -R 17 foo'
 	[X17]='typeset -x -r -X 17 foo'
+	[lX17]='typeset -x -r -l -X 17 foo'
 	[S]='typeset -x -r foo'
 	[T]='typeset -x -r foo'
 	[Z]='typeset -x -r -Z 0 -R 0 foo'

src/cmd/ksh93/tests/variables.sh

@@ -1201,6 +1201,7 @@ got=$(some_func() { :; }; trap some_func DEBUG; trap - DEBUG; print -r "${.sh.fu
 # =====
 # Before 2021-03-06, ${foo=bar} and ${foo:=bar} did not work if `foo` had a numeric type
 # https://github.com/ksh93/ksh/issues/157
+# https://github.com/ksh93/ksh/pull/211#issuecomment-792336825
 
 unset a b
 typeset -i a
@@ -1209,6 +1210,13 @@ got=${a=b}
 [[ $got == 42 ]] || err_exit "\${a=b}: expansion not working for integer type (expected '42', got '$got')"
 [[ $a == 42 ]] || err_exit "\${a=b}: a was not assigned the correct integer value (expected '42', got '$a')"
 
+unset a b
+typeset -si a
+b=3+39
+got=${a=b}
+[[ $got == 42 ]] || err_exit "\${a=b}: expansion not working for short integer type (expected '42', got '$got')"
+[[ $a == 42 ]] || err_exit "\${a=b}: a was not assigned the correct short integer value (expected '42', got '$a')"
+
 unset a b
 typeset -F a
 b=3.75+38.25
@@ -1224,6 +1232,13 @@ got=${a:=b}
 [[ $got == 42 ]] || err_exit "\${a:=b}: expansion not working for integer type (expected '42', got '$got')"
 [[ $a == 42 ]] || err_exit "\${a:=b}: a was not assigned the correct integer value (expected '42', got '$a')"
 
+unset a b
+typeset -si a
+b=3+39
+got=${a:=b}
+[[ $got == 42 ]] || err_exit "\${a:=b}: expansion not working for short integer type (expected '42', got '$got')"
+[[ $a == 42 ]] || err_exit "\${a:=b}: a was not assigned the correct short integer value (expected '42', got '$a')"
+
 unset a b
 typeset -F a
 b=3.75+38.25