dbJLink: Restore the jlink::debug flag, add debug and trace link types

src/ioc/db/dbJLink.h

@@ -39,6 +39,7 @@ typedef struct jlink {
     struct jlif *pif;       /* Link methods */
     struct jlink *parent;   /* NULL for top-level links */
     int parseDepth;         /* Used by parser, unused afterwards */
+    unsigned debug:1;       /* Set to request debug output to console */
     /* Link types extend or embed this structure for private storage */
 } jlink;
 

src/std/link/Makefile

@@ -14,5 +14,6 @@ DBD += links.dbd
 dbRecStd_SRCS += lnkConst.c
 dbRecStd_SRCS += lnkCalc.c
 dbRecStd_SRCS += lnkState.c
+dbRecStd_SRCS += lnkDebug.c
 
 HTMLS += links.html

src/std/link/links.dbd.pod

@@ -15,6 +15,10 @@ The following additional link types are available in this release:
 
 =item * L<dbState|/"dbState Link state">
 
+=item * L<Debug|/"Debug Link debug">
+
+=item * L<Trace|/"Trace Link trace">
+
 =back
 
 =head2 Using JSON Links
@@ -200,3 +204,35 @@ link is initialized if it doesn't already exist.
  {state:"!simEnable"}
 
 =cut
+
+
+link(debug, lnkDebugIf)
+variable(lnkDebug_debug, int)
+
+=head3 Debug Link C<"debug">
+
+The debug link type exists to enable debugging of other link types; it provides
+no functionality itself other than to turn on the debug flag for the child link
+that is its only parameter and pass all link operations down to that link.
+
+=head4 Example
+
+ {debug:{state:"redBeam"}}
+
+=cut
+
+
+link(trace, lnkTraceIf)
+
+=head3 Trace Link C<"trace">
+
+The trace link type is a relative of the debug link type that also traces the
+operation of its child link. At creation it turns on the debug flag of its child
+link, then it prints the method arguments and return values of all link
+operations before / after passing control down to the child link.
+
+=head4 Example
+
+ {trace:{state:"redBeam"}}
+
+=cut