class.c, injected_constructor: prevent loop exits exiting

Using last, next etc would pop the context stack to above the
call_sv(), generally resulting in a crash or assertion failure.

The search the context to pop to stops at the top of the current
context stack, and PUSHSTACKi() switches to a new stack, preventing
the search from finding any loop outside the call_sv()

Similar to #16608

Author: tonycoz

class.c

@@ -175,6 +175,8 @@ XS(injected_constructor)
 
     SV *self = sv_2mortal(newRV_noinc(instance));
 
+    PUSHSTACKi(PERLSI_CONSTRUCTOR);
+
     assert(aux->xhv_class_initfields_cv);
     {
         ENTER;
@@ -221,6 +223,9 @@ XS(injected_constructor)
         }
     }
 
+    POPSTACK;
+    SPAGAIN;
+
     if(params && hv_iterinit(params) > 0) {
         /* TODO: consider sorting these into a canonical order, but that's awkward */
         HE *he = hv_iternext(params);

cop.h

@@ -1259,6 +1259,7 @@ struct context {
 #define PERLSI_MULTICALL       10
 #define PERLSI_REGCOMP         11
 #define PERLSI_SMARTMATCH      12
+#define PERLSI_CONSTRUCTOR     13
 
 struct stackinfo {
     AV *		si_stack;	/* stack for current runlevel */

deb.c

@@ -238,7 +238,8 @@ static const char * const si_names[] = {
     "REQUIRE",
     "MULTICALL",
     "REGCOMP",
-    "SMARTMATCH"
+    "SMARTMATCH",
+    "CONSTRUCTOR"
 };
 #endif
 

t/lib/croak/class

@@ -185,3 +185,31 @@ class XXX {
 }
 EXPECT
 Cannot apply a :writer attribute to a non-scalar field at - line 6.
+########
+use v5.36;
+use feature 'class';
+no warnings 'experimental::class';
+sub f { last }
+class X {
+    field $x = ::f();
+}
+# two warnings since we exit the initfields cv and f()
+X->new for 0;
+EXPECT
+Exiting subroutine via last at - line 4.
+Exiting subroutine via last at - line 4.
+Can't "last" outside a loop block at - line 4.
+########
+use v5.36;
+use feature 'class';
+no warnings 'experimental::class';
+class X {
+    field $x;
+    ADJUST {
+        last;
+    }
+}
+X->new for 0;
+EXPECT
+Exiting subroutine via last at - line 7.
+Can't "last" outside a loop block at - line 7.