Provide as much diagnostic information as possible in "panic: ..." messages.

The convention is that when the interpreter dies with an internal error, the
message starts "panic: ". Historically, many panic messages had been terse
fixed strings, which means that the out-of-range values that triggered the
panic are lost. Now we try to report these values, as such panics may not be
repeatable, and the original error message may be the only diagnostic we get
when we try to find the cause.

We can't report diagnostics when the panic message is generated by something
other than croak(), as we don't have *printf-style format strings. Don't
attempt to report values in panics related to *printf buffer overflows, as
attempting to format the values to strings may repeat or compound the
original error.

1 files changed, 9 insertions, 4 deletions

diff --git a/regcomp.c b/regcomp.c
index 6e7bb3e272..c8a6e96df0 100644
--- a/regcomp.c
+++ b/regcomp.c
@@ -5778,7 +5778,8 @@ S_reg_scan_name(pTHX_ RExC_state_t *pRExC_state, U32 flags)
             return sv_dat;
         }
         else {
-            Perl_croak(aTHX_ "panic: bad flag in reg_scan_name");
+            Perl_croak(aTHX_ "panic: bad flag %lx in reg_scan_name",
+		       (unsigned long) flags);
         }
         /* NOT REACHED */
     }
@@ -6093,7 +6094,9 @@ Perl__append_range_to_invlist(pTHX_ SV* const invlist, const UV start, const UV
 	if (array[final_element] > start
 	    || ELEMENT_RANGE_MATCHES_INVLIST(final_element))
 	{
-	    Perl_croak(aTHX_ "panic: attempting to append to an inversion list, but wasn't at the end of the list");
+	    Perl_croak(aTHX_ "panic: attempting to append to an inversion list, but wasn't at the end of the list, final=%"UVuf", start=%"UVuf", match=%c",
+		       array[final_element], start,
+		       ELEMENT_RANGE_MATCHES_INVLIST(final_element) ? 't' : 'f');
 	}
 
 	/* Here, it is a legal append.  If the new range begins with the first
@@ -11354,7 +11357,8 @@ S_reg_node(pTHX_ RExC_state_t *pRExC_state, U8 op)
 	return(ret);
     }
     if (RExC_emit >= RExC_emit_bound)
-        Perl_croak(aTHX_ "panic: reg_node overrun trying to emit %d", op);
+        Perl_croak(aTHX_ "panic: reg_node overrun trying to emit %d, %p>=%p",
+		   op, RExC_emit, RExC_emit_bound);
 
     NODE_ALIGN_FILL(ret);
     ptr = ret;
@@ -11409,7 +11413,8 @@ S_reganode(pTHX_ RExC_state_t *pRExC_state, U8 op, U32 arg)
 	return(ret);
     }
     if (RExC_emit >= RExC_emit_bound)
-        Perl_croak(aTHX_ "panic: reg_node overrun trying to emit %d", op);
+        Perl_croak(aTHX_ "panic: reg_node overrun trying to emit %d, %p>=%p",
+		   op, RExC_emit, RExC_emit_bound);
 
     NODE_ALIGN_FILL(ret);
     ptr = ret;