Fix infinite loop handling non-type template parameters

Fixes infinite loop due to () brackets in a non-type template
parameter containing an expression

Fixes #2418

Non-trivial expressions are still not qualified properly though.

CHANGES.current

@@ -50,3 +50,9 @@ Version 4.2.0 (in progress)
             shown into the user interface file will provide the appropriate fix and
             the warning will disappear. This is important to do as swig-4.2 will
             not be able to provide this helpful warning.
+
+2022-11-02: wsfulton
+            #2418 Fix infinite loop handling non-type template parameters.
+
+            Fixes infinite loop due to () brackets in a non-type template
+            parameter containing an expression.

Examples/test-suite/common.mk

@@ -639,6 +639,7 @@ CPP11_TEST_BROKEN = \
 # C++14 test cases.
 CPP14_TEST_CASES += \
 	cpp14_binary_integer_literals \
+	cpp14_enable_if_t \
 
 # Broken C++14 test cases.
 CPP14_TEST_BROKEN = \

Examples/test-suite/cpp14_enable_if_t.i

@@ -0,0 +1,34 @@
+%module cpp14_enable_if_t
+
+// test use of enable_if_t but without full %template instantiation, that is no enable_if_t definition is parsed
+
+%inline %{
+#include <type_traits>
+typedef int node_t;
+typedef int position_t;
+
+template <typename A, typename B, std::enable_if_t<std::is_integral_v<A>, bool> = true>
+  void enableif1(const A a, const B b) {}
+
+// tests non-type template parameters within () brackets - was causing an infinite loop, issue #2418
+template <typename A, typename B, std::enable_if_t<(std::is_integral_v<A>), bool> = true>
+  void enableif2(const A a, const B b) {}
+
+template <typename A, typename B, std::enable_if_t<(std::is_integral_v<A> || std::is_same_v<A, node_t>), bool> = true>
+  void enableif3(const A a, const B b) {}
+
+template <typename A, typename B, std::enable_if_t<(std::is_integral_v<A> or std::is_same_v<A, node_t>) and (std::is_integral_v<B> or std::is_same_v<B, position_t>), bool> = true>
+  void enableif4(const A a, const B b) {}
+
+template <typename A, typename B, std::enable_if_t<(std::is_integral_v<A> and std::is_integral_v<B>), bool> = true>
+  int enableif5(const A a, const B b) {
+    return a + b;
+  }
+
+void tester() {
+  enableif5<int, int>(10, 20);
+}
+%}
+
+// non-type template parameters working well in SWIG, below is a simple workaround as the 3rd parameter is defaulted for enable_if_t (which is just SFINAE to give a nice C++ compiler error)
+%template(enableif5) enableif5<int, int, true>; // workaround

Examples/test-suite/java/cpp14_enable_if_t_runme.java

@@ -0,0 +1,19 @@
+import cpp14_enable_if_t.*;
+
+public class cpp14_enable_if_t_runme {
+
+  static {
+    try {
+        System.loadLibrary("cpp14_enable_if_t");
+    } catch (UnsatisfiedLinkError e) {
+      System.err.println("Native code library failed to load. See the chapter on Dynamic Linking Problems in the SWIG Java documentation for help.\n" + e);
+      System.exit(1);
+    }
+  }
+
+  public static void main(String argv[])
+  {
+    if (cpp14_enable_if_t.enableif5(10, 20) != 30)
+      throw new RuntimeException("enableif5 not working");
+  }
+}

Source/Swig/symbol.c

@@ -1518,7 +1518,8 @@ Node *Swig_symbol_isoverloaded(Node *n) {
 static SwigType *symbol_template_qualify(const SwigType *e, Symtab *st) {
   String *tprefix, *tsuffix;
   SwigType *qprefix;
-  List *targs;
+  String *targs;
+  List *targslist;
   Node *tempn;
   Symtab *tscope;
   Iterator ti;
@@ -1541,12 +1542,15 @@ static SwigType *symbol_template_qualify(const SwigType *e, Symtab *st) {
   tprefix = SwigType_templateprefix(e);
   tsuffix = SwigType_templatesuffix(e);
   qprefix = Swig_symbol_type_qualify(tprefix, st);
-  targs = SwigType_parmlist(e);
+  targs = SwigType_templateargs(e);
+  targslist = SwigType_parmlist(targs);
   tempn = Swig_symbol_clookup_local(tprefix, st);
   tscope = tempn ? Getattr(tempn, "sym:symtab") : 0;
   Append(qprefix, "<(");
-  for (ti = First(targs); ti.item;) {
+  for (ti = First(targslist); ti.item;) {
     String *vparm;
+    /* TODO: the logic here should be synchronised with that in SwigType_typedef_qualified() */
+    /* TODO: ti.item might be a non-type parameter possibly within (), eg: (std::is_integral_v<(A)>||std::is_same_v<(A,node_t)>) */
     String *qparm = Swig_symbol_type_qualify(ti.item, st);
     if (tscope && (tscope != st)) {
       String *ty = Swig_symbol_type_qualify(qparm, tscope);
@@ -1568,6 +1572,7 @@ static SwigType *symbol_template_qualify(const SwigType *e, Symtab *st) {
   Delete(tprefix);
   Delete(tsuffix);
   Delete(targs);
+  Delete(targslist);
 #ifdef SWIG_DEBUG
   Printf(stderr, "symbol_temp_qual %s %s\n", e, qprefix);
 #endif

Source/Swig/typesys.c

@@ -1148,6 +1148,7 @@ SwigType *SwigType_typedef_qualified(const SwigType *t) {
 	Append(qprefix, "<(");
 	pi = First(parms);
 	while ((p = pi.item)) {
+	  /* TODO: the logic here should be synchronised with that in symbol_template_qualify() in symbol.c */
 	  String *qt = SwigType_typedef_qualified(p);
 	  if (Equal(qt, p)) {	/*  && (!Swig_scopename_check(qt))) */
 	    /* No change in value.  It is entirely possible that the parameter is an integer value.