Undefined subroutine &%s called, close to label '%s'

pod/perldelta.pod

@@ -260,6 +260,18 @@ and L</New Warnings>
 
 =item *
 
+L<Undefined subroutine &%s called, close to label '%s'|perldiag/"Undefined subroutine &%s called, close to label '%s'">
+
+(F) The subroutine indicated hasn't been defined, or if it was, it has
+since been undefined. 
+
+This error could also indicate a mistyped package separator, when a 
+single colon was typed instead of two colons. For example, C<Foo:bar()> 
+would be parsed as the label C<Foo> followed by an unqualified function 
+name: C<foo: bar()>.
+
+=item *
+
 XXX L<message|perldiag/"message">
 
 =back

pod/perldiag.pod

@@ -6820,6 +6820,16 @@ Perhaps it's in a different package?  See L<perlfunc/sort>.
 (F) The subroutine indicated hasn't been defined, or if it was, it has
 since been undefined.
 
+=item Undefined subroutine &%s called, close to label '%s'
+
+(F) The subroutine indicated hasn't been defined, or if it was, it has
+since been undefined.
+
+This error could also indicate a mistyped package separator, when a
+single colon was typed instead of two colons. For example, C<Foo:bar()>
+would be parsed as the label C<Foo> followed by an unqualified function
+name: C<foo: bar()>.
+
 =item Undefined subroutine called
 
 (F) The anonymous subroutine you're trying to call hasn't been defined,

pp_hot.c

@@ -6212,6 +6212,33 @@ Perl_clear_defarray(pTHX_ AV* av, bool abandon)
     }
 }
 
+/* S_croak_undefined_subroutine is a helper function for pp_entersub.
+ * It takes assorted DIE() logic out of that hot function.
+ */
+static void
+S_croak_undefined_subroutine(pTHX_ CV const *cv, GV const *gv)
+{
+    if (cv) {
+        if (CvLEXICAL(cv) && CvHASGV(cv))
+            croak("Undefined subroutine &%" SVf " called",
+                       SVfARG(cv_name((CV*)cv, NULL, 0)));
+        else /* pp_entersub triggers when (CvANON(cv) || !CvHASGV(cv)) */
+            croak("Undefined subroutine called");
+    } else { /* pp_entersub triggers when (!cv) after `try_autoload` */
+        SV *sub_name = newSV_type_mortal(SVt_PV);
+        gv_efullname3(sub_name, gv, NULL);
+
+        /* Heuristic to spot BOOP:boop() typo, when the intention was
+         * to call BOOP::boop(). */
+        const char * label = CopLABEL(PL_curcop);
+        if (label) {
+            croak("Undefined subroutine &%" SVf " called, close to label '%s'",
+                SVfARG(sub_name), label);
+        }
+        croak("Undefined subroutine &%" SVf " called", SVfARG(sub_name));
+    }
+    NOT_REACHED; /* NOTREACHED */
+}
 
 PP(pp_entersub)
 {
@@ -6306,15 +6333,12 @@ PP(pp_entersub)
     assert((void*)&CvROOT(cv) == (void*)&CvXSUB(cv));
     while (UNLIKELY(!CvROOT(cv))) {
         GV* autogv;
-        SV* sub_name;
 
         /* anonymous or undef'd function leaves us no recourse */
         if (CvLEXICAL(cv) && CvHASGV(cv))
-            DIE(aTHX_ "Undefined subroutine &%" SVf " called",
-                       SVfARG(cv_name(cv, NULL, 0)));
-        if (CvANON(cv) || !CvHASGV(cv)) {
-            DIE(aTHX_ "Undefined subroutine called");
-        }
+            S_croak_undefined_subroutine(aTHX_ cv, NULL);
+        if (CvANON(cv) || !CvHASGV(cv))
+            S_croak_undefined_subroutine(aTHX_ cv, NULL);
 
         /* autoloaded stub? */
         if (cv != GvCV(gv = CvGV(cv))) {
@@ -6330,11 +6354,8 @@ PP(pp_entersub)
                                        : 0));
             cv = autogv ? GvCV(autogv) : NULL;
         }
-        if (!cv) {
-            sub_name = sv_newmortal();
-            gv_efullname3(sub_name, gv, NULL);
-            DIE(aTHX_ "Undefined subroutine &%" SVf " called", SVfARG(sub_name));
-        }
+        if (!cv)
+            S_croak_undefined_subroutine(aTHX_ NULL, gv);
     }
 
     /* unrolled "CvCLONE(cv) && ! CvCLONED(cv)" */

t/lib/croak/pp_hot

@@ -45,6 +45,15 @@ Undefined subroutine &main::foo called at - line 3.
    &$foosub;
 EXPECT
 Undefined subroutine &main::foo called at - line 2.
+########
+# NAME package separator typo, creating a label by accident
+   package BEEP;
+   sub boop;
+   package main;
+   BEEP:boop();
+EXPECT
+Undefined subroutine &main::boop called, close to label 'BEEP' at - line 4.
+
 ########
 # NAME calling undef scalar
    &{+undef};