Add ability to easily add info to DEBUG output

This commit adds two macros that a user can define and recompile Perl to
get every active DEBUG statement to do some thing beyond what it would
normally do.

This allows someone to recompile Perl when they need to delve deeper
into fixing a bug without otherwise increasing memory use or slowing
execution.

1 files changed, 33 insertions, 2 deletions

diff --git a/perl.h b/perl.h
index 3235ee1254..17a21a1c42 100644
--- a/perl.h
+++ b/perl.h
@@ -4487,16 +4487,47 @@ Gid_t getegid (void);
                               }                                         \
     } STMT_END
 
+/* These allow you to customize your debugging output  for specialized,
+ * generally temporary ad-hoc purposes.  For example, if you need 'errno'
+ * preserved, you can add definitions to these macros (either in this file for
+ * the whole program, or before the #include "perl.h" in a particular .c file
+ * you're trying to debug) and recompile:
+ *
+ * #define DEBUG_PRE_STMTS   dSAVE_ERRNO;
+ * #define DEBUG_POST_STMTS  RESTORE_ERRNO;
+ *
+ * Other potential things include displaying timestamps, location information,
+ * which thread, etc.  Heres an example with both errno and location info:
+ *
+ * #define DEBUG_PRE_STMTS   dSAVE_ERRNO;  \
+ *              PerlIO_printf(Perl_debug_log, "%s:%d: ", __FILE__, __LINE__);
+ * #define DEBUG_POST  RESTORE_ERRNO;
+ *
+ * All DEBUG statements in the compiled scope will be have these extra
+ * statements compiled in; they will be executed only for the DEBUG statements
+ * whose flags are turned on.
+ */
+#ifndef DEBUG_PRE_STMTS
+#  define DEBUG_PRE_STMTS
+#endif
+#ifndef DEBUG_POST_STMTS
+#  define DEBUG_POST_STMTS
+#endif
+
 #  define DEBUG__(t, a)                                                 \
         STMT_START {                                                    \
-                if (t) STMT_START {a;} STMT_END;                        \
+            if (t) STMT_START {                                         \
+                DEBUG_PRE_STMTS a; DEBUG_POST_STMTS                     \
+            } STMT_END;                                                 \
         } STMT_END
 
 #  define DEBUG_f(a) DEBUG__(DEBUG_f_TEST, a)
 
 /* For re_comp.c, re_exec.c, assume -Dr has been specified */
 #  ifdef PERL_EXT_RE_BUILD
-#    define DEBUG_r(a) STMT_START {a;} STMT_END
+#    define DEBUG_r(a) STMT_START {                                     \
+                            DEBUG_PRE_STMTS a; DEBUG_POST_STMTS         \
+                       } STMT_END;
 #  else
 #    define DEBUG_r(a) DEBUG__(DEBUG_r_TEST, a)
 #  endif /* PERL_EXT_RE_BUILD */