Add a test for perl_clone with CLONEf_COPY_STACKS to XS-APItest.

CLONEf_COPY_STACKS is only used by the windows pseudo-fork.
This test allows testing/debugging of CLONEf_COPY_STACK without needing threads or Windows.

3 files changed, 109 insertions, 0 deletions

diff --git a/MANIFEST b/MANIFEST
index 48a3987acc..0725658f0d 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -3657,6 +3657,7 @@ ext/XS-APItest/t/call_checker.t	test call checker plugin API
 ext/XS-APItest/t/caller.t	XS::APItest: tests for caller_cx
 ext/XS-APItest/t/call.t		XS::APItest extension
 ext/XS-APItest/t/cleanup.t	test stack behaviour on unwinding
+ext/XS-APItest/t/clone-with-stack.t	test clone with CLONEf_COPY_STACKS works
 ext/XS-APItest/t/cophh.t	test COPHH API
 ext/XS-APItest/t/copyhints.t	test hv_copy_hints_hv() API
 ext/XS-APItest/t/customop.t	XS::APItest: tests for custom ops
diff --git a/ext/XS-APItest/APItest.xs b/ext/XS-APItest/APItest.xs
index 21f417d25c..acd1b5e42f 100644
--- a/ext/XS-APItest/APItest.xs
+++ b/ext/XS-APItest/APItest.xs
@@ -2682,6 +2682,61 @@ CODE:
     XSRETURN_UNDEF;
 }
 
+#ifdef USE_ITHREADS
+
+void
+clone_with_stack()
+CODE:
+{
+    PerlInterpreter *interp = aTHX; /* The original interpreter */
+    PerlInterpreter *interp_dup;    /* The duplicate interpreter */
+    int oldscope = 1; /* We are responsible for all scopes */
+
+    interp_dup = perl_clone(interp, CLONEf_COPY_STACKS | CLONEf_CLONE_HOST );
+
+    /* destroy old perl */
+    PERL_SET_CONTEXT(interp);
+
+    POPSTACK_TO(PL_mainstack);
+    dounwind(-1);
+    LEAVE_SCOPE(0);
+
+    while (interp->Iscopestack_ix > 1)
+        LEAVE;
+    FREETMPS;
+
+    perl_destruct(interp);
+    perl_free(interp);
+
+    /* switch to new perl */
+    PERL_SET_CONTEXT(interp_dup);
+
+    /* continue after 'clone_with_stack' */
+    interp_dup->Iop = interp_dup->Iop->op_next;
+
+    /* run with new perl */
+    Perl_runops_standard(interp_dup);
+
+    /* We may have additional unclosed scopes if fork() was called
+     * from within a BEGIN block.  See perlfork.pod for more details.
+     * We cannot clean up these other scopes because they belong to a
+     * different interpreter, but we also cannot leave PL_scopestack_ix
+     * dangling because that can trigger an assertion in perl_destruct().
+     */
+    if (PL_scopestack_ix > oldscope) {
+        PL_scopestack[oldscope-1] = PL_scopestack[PL_scopestack_ix-1];
+        PL_scopestack_ix = oldscope;
+    }
+
+    perl_destruct(interp_dup);
+    perl_free(interp_dup);
+
+    /* call the real 'exit' not PerlProc_exit */
+#undef exit
+    exit(0);
+}
+
+#endif /* USE_ITHREDS */
 
 SV*
 take_svref(SVREF sv)
diff --git a/ext/XS-APItest/t/clone-with-stack.t b/ext/XS-APItest/t/clone-with-stack.t
new file mode 100644
index 0000000000..943a123427
--- /dev/null
+++ b/ext/XS-APItest/t/clone-with-stack.t
@@ -0,0 +1,53 @@
+#!perl
+
+use strict;
+use warnings;
+
+require "../../t/test.pl";
+
+use XS::APItest;
+
+# clone_with_stack creates a clone of the perl interpreter including
+# the stack, then destroys the original interpreter and runs the
+# remaining code using the new one.
+# This is like doing a psuedo-fork and exiting the parent.
+
+use Config;
+if (not $Config{'useithreads'}) {
+    skip_all("clone_with_stack requires threads");
+}
+
+plan(3);
+
+fresh_perl_is( <<'----', <<'====', undef, "minimal clone_with_stack" );
+use XS::APItest;
+clone_with_stack();
+print "ok\n";
+----
+ok
+====
+
+fresh_perl_is( <<'----', <<'====', undef, "inside a subroutine" );
+use XS::APItest;
+sub f {
+    clone_with_stack();
+}
+f();
+print "ok\n";
+----
+ok
+====
+
+{
+    local our $TODO = "clone_with_stack inside a begin block";
+    fresh_perl_is( <<'----', <<'====', undef, "inside a BEGIN block" );
+use XS::APItest;
+BEGIN {
+    clone_with_stack();
+}
+print "ok\n";
+----
+ok
+====
+
+}