first prototype of tracing checks

when run is_stable_method(m,trace_scfg), you get a text file
checks/$m.name with types that were tried when checking type stability

src/StabilityCheck.jl

@@ -21,7 +21,7 @@ export @stable, @stable!, @stable!_nop,
     SkippedUnionAlls, UnboundedUnionAlls, SkipMandatory,
     Stb, Uns,
     UConstr, UConstrExist, AnyParam, VarargParam, TcFail, OutOfFuel, GenericMethod,
-    SearchCfg, build_typesdb_scfg, default_scfg,
+    SearchCfg, build_typesdb_scfg, default_scfg, trace_scfg,
 
     # Utils
     split_method # mostly for testing
@@ -124,6 +124,12 @@ is_stable_method(m::Method, scfg :: SearchCfg = default_scfg) :: StCheck = begin
     @debug "is_stable_method: $m"
     global stepCount = 0
 
+    # trace TS checks and store to a file
+    if scfg.trace_checks
+        mkpath("checks")
+        fchecks = open("checks/$(m.name)", "w")
+    end
+
     # preemptively load types DB if available: we may need to sample
     # unbounded exists any minute
     if scfg.typesDBcfg.use_types_db
@@ -143,10 +149,16 @@ is_stable_method(m::Method, scfg :: SearchCfg = default_scfg) :: StCheck = begin
     #          and party if we're concrete
     @debug "is_stable_method: check against signature (2a)"
     try
+        scfg.trace_checks &&
+            println(fchecks, sig_types)
         if is_stable_call(func, sig_types)
+            scfg.trace_checks &&
+                close(fchecks)
             return Stb(1)
         end
     catch e
+        scfg.trace_checks &&
+            close(fchecks)
         return TcFail(sig_types, e)
     end
 
@@ -187,17 +199,23 @@ is_stable_method(m::Method, scfg :: SearchCfg = default_scfg) :: StCheck = begin
 
         # the actual stability check
         try
+            scfg.trace_checks &&
+                println(fchecks, ts)
             if ! is_stable_call(func, ts)
                 push!(unst, ts)
                 if scfg.failfast
                     break
                 end
             end
         catch e
+            scfg.trace_checks &&
+                close(fchecks)
             return TcFail(ts, e)
         end
     end
 
+    scfg.trace_checks &&
+        close(fchecks)
     result isa OutOfFuel &&
         return result
     return if isempty(unst)

src/types.jl

@@ -122,6 +122,9 @@ Base.@kwdef struct SearchCfg
 
     typesDBcfg :: TypesDBCfg = TypesDBCfg()
 #   ^--- Parameters of the types DB.
+
+    trace_checks :: Bool = false
+#   ^-- create a file recording all type stability checks of a method
 end
 
 #
@@ -131,6 +134,8 @@ default_scfg = SearchCfg()
 
 fast_scfg = SearchCfg(fuel=30)
 
+trace_scfg = SearchCfg(trace_checks=true)
+
 build_typesdb_scfg(inFile = intypesCsvFileDefault; sample_count :: Int = 100000) = begin
     tdbFull = typesDB(inFile)
     sampleCountActual = min(length(tdbFull),sample_count)