Fix seg fault using %template

Fix seg fault when instantiating templates with parameters that are function
parameters containing templates, such as:

              %template(MyC) C<int(std::vector<int>)>;

Closes #983

CHANGES.current

@@ -7,6 +7,12 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.2.0 (in progress)
 ===========================
 
+2023-01-03: wsfulton
+            #983 Fix seg fault when instantiating templates with parameters that are function
+            parameters containing templates, such as:
+
+              %template(MyC) C<int(std::vector<int>)>;
+
 2023-01-03: wsfulton
             Complete support for C++11 variadic function templates. Support was previously limited
             to just one template parameter. Now zero or more template parameters are supported

Examples/test-suite/java/template_function_parm_runme.java

@@ -0,0 +1,25 @@
+import template_function_parm.*;
+
+public class template_function_parm_runme {
+
+  static {
+    try {
+      System.loadLibrary("template_function_parm");
+    } 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[]) {
+    VectorInt vi = new VectorInt();
+    vi.add(10);
+    vi.add(20);
+    vi.add(30);
+
+    MyC myc = new MyC();
+    int sum = myc.take_function(template_function_parmConstants.accumulate_integers, vi);
+    if (sum != 60)
+      throw new RuntimeException("Expected sum of 60, got " + sum);
+  }
+}

Examples/test-suite/template_function_parm.i

@@ -0,0 +1,28 @@
+%module template_function_parm
+
+%include <std_vector.i>
+
+%{
+#include <numeric>
+static int accumulate_integers(std::vector<int> vi) {
+  int sum = std::accumulate(vi.begin(), vi.end(), 0);
+  return sum;
+}
+%}
+
+%inline %{
+template<typename A>
+struct C {
+  int take_function(int fp(std::vector<int>), std::vector<int> v) {
+    return fp(v);
+  }
+};
+%}
+
+%constant int accumulate_integers(std::vector<int>);
+
+%template(VectorInt) std::vector<int>;
+
+// seg fault #983
+%template(MyC) C<int(std::vector<int>)>;
+

Source/Swig/symbol.c

@@ -1746,7 +1746,7 @@ SwigType *Swig_symbol_typedef_reduce(const SwigType *ty, Symtab *tab) {
 
   n = Swig_symbol_clookup(base, tab);
   if (!n) {
-    if (SwigType_istemplate(ty)) {
+    if (SwigType_istemplate(base)) {
       SwigType *qt = Swig_symbol_template_reduce(base, tab);
       Append(prefix, qt);
       Delete(qt);