Recursion fix to correctly reset RecursionDepth whenever a longjmp occurs

doc/ref/debug.xml

@@ -876,20 +876,35 @@ brk> return;
 gap> 
 ]]></Log>
 <P/>
-This behaviour can be controlled using the following procedure.
+
+This behaviour can be controlled using the following procedures.
 
 <ManSection>
 <Func Name="SetRecursionTrapInterval" Arg='interval'/>
+<Func Name="GetRecursionDepth" Arg=''/>
 
 <Description>
-<A>interval</A> must be a non-negative small integer (between 0 and
-<M>2^{28}</M>). An <A>interval</A> of 0 suppresses the monitoring of recursion
+<Ref Func="GetRecursionDepth"/> returns the nesting level of the GAP
+interpreter. This is reset to 0 every time the break loop is entered.
+<Ref Func="SetRecursionTrapInterval"/> sets the depth of the stack at which
+GAP will enter the Break loop. <A>interval</A> must be a non-negative small
+integer (between 0 and <M>2^{28}</M>).
+An <A>interval</A> of 0 suppresses the monitoring of recursion
 altogether. In this case excessive recursion may cause &GAP; to crash.
 <P/>
 <Log><![CDATA[
-gap> dive:= function(depth) if depth>1 then dive(depth-1); fi; return; end;
-function( depth ) ... end
+gap> GetRecursionDepth();
+0
+gap> dive := function(depth)
+> if depth>1 then
+> dive(depth-1);
+> else
+> Print("Depth ", GetRecursionDepth());
+> fi;
+> end;;
 gap> SetRecursionTrapInterval(1000);
+gap> dive(100);
+Depth 100
 gap> dive(2500);
 recursion depth trap (1000)
  at
@@ -910,6 +925,8 @@ dive( depth - 1 ); called from
 Entering break read-eval-print loop ...
 you can 'quit;' to quit to outer loop, or
 you may 'return;' to continue
+brk> GetRecursionDepth();
+0
 brk> return;
 gap> SetRecursionTrapInterval(-1);
 SetRecursionTrapInterval( <interval> ): <interval> must be a non-negative smal\
@@ -918,19 +935,15 @@ not in any function
 Entering break read-eval-print loop ...
 you can 'quit;' to quit to outer loop, or
 you can replace <interval> via 'return <interval>;' to continue
-brk> return ();
-SetRecursionTrapInterval( <interval> ): <interval> must be a non-negative smal\
-l integer
-not in any function
-Entering break read-eval-print loop ...
-you can 'quit;' to quit to outer loop, or
-you can replace <interval> via 'return <interval>;' to continue
 brk> return 0;
 gap> dive(20000);
+Depth 20000
 gap> dive(2000000);
 Segmentation fault
 ]]></Log>
 </Description>
+
+
 </ManSection>
 
 </Section>

src/funcs.c

@@ -1718,6 +1718,10 @@ Obj FuncSetRecursionTrapInterval( Obj self, Obj interval )
  return 0;
 }
 
+Obj FuncGetRecursionDepth( Obj self )
+{
+ return INTOBJ_INT(STATE(RecursionDepth));
+}
 
 /****************************************************************************
 **
@@ -1731,8 +1735,10 @@ Obj FuncSetRecursionTrapInterval( Obj self, Obj interval )
 static StructGVarFunc GVarFuncs [] = {
 
  GVAR_FUNC(SetRecursionTrapInterval, 1, "interval"),
+ GVAR_FUNC(GetRecursionDepth, 0, ""),
  { 0, 0, 0, 0, 0 }
 
+
 };
 
 /****************************************************************************

src/read.h

@@ -46,7 +46,9 @@
 
 #define TRY_READ \
  if (!STATE(NrError)) { \
+ volatile Int recursionDepth = STATE(RecursionDepth); \
  if (sySetjmp(STATE(ReadJmpError))) { \
+ STATE(RecursionDepth) = recursionDepth; \
  STATE(NrError)++; \
  }\
  }\

tst/testinstall/depth.tst

@@ -0,0 +1,32 @@
+gap> START_TEST("depth.tst");
+
+# We don't know what the recursion depth will be when the test starts,
+# so do relative comparisons.
+gap> curdepth := GetRecursionDepth();;
+gap> GetRecursionDepth() - curdepth;
+0
+gap> dive := function(depth)
+> if depth>1 then
+> dive(depth-1);
+> else
+> Print("Depth ", GetRecursionDepth() - curdepth, "\n");
+> fi;
+> end;;
+gap> dive(10);
+Depth 10
+gap> dive(80);
+Depth 80
+gap> SetRecursionTrapInterval(50);
+gap> dive(80);
+Error, recursion depth trap (50)
+gap> SetRecursionTrapInterval(5000);
+gap> dive(80);
+Depth 80
+
+# Just want an error to occur to check the depth is reset correctly
+gap> IsAbelian(2);
+Error, no method found! For debugging hints type ?Recovery from NoMethodFound
+Error, no 1st choice method found for `IsCommutative' on 1 arguments
+gap> dive(80);
+Depth 80
+gap> STOP_TEST( "depth.tst", 1);