Slightly better decltype() support for expressions

decltype now accepts C++ expressions instead of just an ID, such as:

  int i,j;
  ...  decltype(i+j) ...
  ...  decltype(&i) ...

These result in a warning for non-trivial expressions which SWIG cannot evaluate:

  Warning 344: Unable to deduce decltype for 'i+j'.

See 'Type Inference' in CPlusPlus.html for workarounds.

Issue #1589
Issue #1590

Examples/test-suite/common.mk

@@ -624,6 +624,7 @@ CPP11_TEST_CASES += \
 	cpp11_thread_local \
 	cpp11_template_double_brackets \
 	cpp11_template_explicit \
+	cpp11_template_parameters_decltype \
 	cpp11_template_typedefs \
 	cpp11_type_traits \
 	cpp11_type_aliasing \

Examples/test-suite/cpp11_decltype.i

@@ -9,11 +9,35 @@
     int i;
     decltype(i) j;
 
-    auto foo( decltype(i) a ) -> decltype(i) {
+    auto get_number(decltype(i) a) -> decltype(i) {
       if (a==5)
         return 10;
       else
         return 0;
     }
   };
-  %}
+%}
+
+
+// These are ignored as unable to deduce decltype for (i+j)
+%ignore B::k;
+%ignore B::get_number_sum;
+%ignore B::get_number_address;
+#pragma SWIG nowarn=SWIGWARN_CPP11_DECLTYPE
+
+%inline %{
+  class B {
+  public:
+    int i;
+    decltype(i) j;
+    decltype(i+j) k;
+
+    auto get_number_sum(decltype(i+j) a) -> decltype(i+j) {
+      return i+j;
+    }
+
+    auto get_number_address(decltype(&i) a) -> decltype(&i) {
+      return &i;
+    }
+  };
+%}

Examples/test-suite/python/cpp11_decltype_runme.py

@@ -9,10 +9,10 @@ a.j = 10
 if a.j != 10:
     raise RuntimeError("Assignment to a.j failed.")
 
-b = a.foo(5)
+b = a.get_int(5)
 if b != 10:
-    raise RuntimeError("foo(5) should return 10.")
+    raise RuntimeError("get_int(5) should return 10.")
 
-b = a.foo(6)
+b = a.get_int(6)
 if b != 0:
-    raise RuntimeError("foo(6) should return 0.")
+    raise RuntimeError("get_int(6) should return 0.")