[perl #48332] Debugger corrupts symbol table munging

This reverts commit 92adfbd49af0758bcc9a198cf2df2bd78c4176b9, which
removed a necessary assignment for the sake of consting.

In doing so, it allows subroutine redefinition to work properly again
in the debugger.

5 files changed, 31 insertions, 4 deletions

diff --git a/MANIFEST b/MANIFEST
index 746e0c9bfa..63d04b2844 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -4413,6 +4413,7 @@ t/lib/cygwin.t			Builtin cygwin function tests
 t/lib/deprecate/Deprecated.pm	Deprecated module to test deprecate.pm
 t/lib/deprecate/Optionally.pm	Optionally deprecated module to test deprecate.pm
 t/lib/deprecate.t		Test deprecate.pm
+t/lib/Devel/switchd_empty.pm	Module for t/run/switchd.t
 t/lib/Devel/switchd.pm		Module for t/run/switchd.t
 t/lib/feature/bundle		Tests for feature bundles
 t/lib/feature/implicit		Tests for implicit loading of feature.pm
diff --git a/pod/perldelta.pod b/pod/perldelta.pod
index 4f5c5e2848..e3018dab98 100644
--- a/pod/perldelta.pod
+++ b/pod/perldelta.pod
@@ -645,6 +645,11 @@ This bug was introduced in version 5.13.5 and did not affect earlier
 versions
 L<[perl #78058]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=78058>.
 
+=item *
+
+Subroutine redefinition works once more in the debugger
+L<[perl #48332]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=48332>.
+
 =back
 
 =head1 Known Problems
diff --git a/t/lib/Devel/switchd_empty.pm b/t/lib/Devel/switchd_empty.pm
new file mode 100644
index 0000000000..bf9c1cde6e
--- /dev/null
+++ b/t/lib/Devel/switchd_empty.pm
@@ -0,0 +1,2 @@
+sub DB::DB {}
+1
diff --git a/t/run/switchd.t b/t/run/switchd.t
index f937093809..36cbb381bb 100644
--- a/t/run/switchd.t
+++ b/t/run/switchd.t
@@ -7,9 +7,9 @@ BEGIN {
 
 BEGIN { require "./test.pl"; }
 
-# This test depends on t/lib/Devel/switchd.pm.
+# This test depends on t/lib/Devel/switchd*.pm.
 
-plan(tests => 3);
+plan(tests => 4);
 
 my $r;
 
@@ -57,3 +57,18 @@ cmp_ok(
   0,
  'The debugger can see the lines of the main program under #!perl -d',
 );
+
+# [perl #48332]
+like(
+  runperl(
+   switches => [ '-Ilib', '-d:switchd_empty' ],
+   progs    => [
+    'sub foo { print qq _1\n_ }',
+    '*old_foo = \&foo;',
+    '*foo = sub { print qq _2\n_ };',
+    'old_foo(); foo();',
+   ],
+  ),
+  qr "1\r?\n2\r?\n",
+ 'Subroutine redefinition works in the debugger [perl #48332]',
+);
diff --git a/util.c b/util.c
index bed4c64629..75dbc1bf65 100644
--- a/util.c
+++ b/util.c
@@ -6526,13 +6526,17 @@ Perl_get_db_sub(pTHX_ SV **svp, CV *cv)
     PL_tainted = FALSE;
     save_item(dbsv);
     if (!PERLDB_SUB_NN) {
-	GV * const gv = CvGV(cv);
+	GV *gv = CvGV(cv);
 
 	if ( svp && ((CvFLAGS(cv) & (CVf_ANON | CVf_CLONED))
 	     || strEQ(GvNAME(gv), "END")
 	     || ((GvCV(gv) != cv) && /* Could be imported, and old sub redefined. */
 		 !( (SvTYPE(*svp) == SVt_PVGV)
-		    && (GvCV((const GV *)*svp) == cv) )))) {
+		    && (GvCV((const GV *)*svp) == cv)
+		    && (gv = (GV *)*svp) 
+		  )
+		)
+	)) {
 	    /* Use GV from the stack as a fallback. */
 	    /* GV is potentially non-unique, or contain different CV. */
 	    SV * const tmp = newRV(MUTABLE_SV(cv));