Add asGeneric() methods to generic readers, builders, and interfaces which casts…

Add asGeneric() methods to generic readers, builders, and interfaces which casts them to the same type but with different generic parameters.

c++/src/capnp/capability-test.c++

@@ -787,9 +787,16 @@ TEST(Capability, Generics) {
     List<uint32_t>::Reader qux = response.getQux();
     qux.size();
     checkTestMessage(response.getGen().getFoo());
-  }, [](kj::Exception&& e) {});
+  }, [](kj::Exception&& e) {
+    // Ignore exception (which we'll always get because we're calling a null capability).
+  });
 
   promise.wait(waitScope);
+
+  // Check that asGeneric<>() compiles.
+  test::TestGenerics<TestAllTypes>::Interface<>::Client castClient = client.asGeneric<>();
+  test::TestGenerics<TestAllTypes>::Interface<TestAllTypes>::Client castClient2 =
+      client.asGeneric<TestAllTypes>();
 }
 
 TEST(Capability, Generics2) {

c++/src/capnp/compiler/capnpc-c++.c++

@@ -576,7 +576,7 @@ private:
       return node.getIsGeneric();
     }
 
-    kj::StringTree decl(bool withDefaults) const {
+    kj::StringTree decl(bool withDefaults, kj::StringPtr suffix = nullptr) const {
       // "template <typename T, typename U>" for this type. Includes default assignments
       // ("= ::capnp::AnyPointer") if `withDefaults` is true. Returns empty string if this type
       // is not parameterized.
@@ -588,7 +588,7 @@ private:
       } else {
         return kj::strTree(
             "template <", kj::StringTree(KJ_MAP(p, params) {
-              return kj::strTree("typename ", p.getName(),
+              return kj::strTree("typename ", p.getName(), suffix,
                   withDefaults ? " = ::capnp::AnyPointer" : "");
             }, ", "), ">\n");
       }
@@ -608,7 +608,7 @@ private:
       }
     }
 
-    kj::StringTree args() const {
+    kj::StringTree args(kj::StringPtr suffix = nullptr) const {
       // "<T, U>" for this type.
       auto params = node.getParameters();
 
@@ -617,7 +617,7 @@ private:
       } else {
         return kj::strTree(
             "<", kj::StringTree(KJ_MAP(p, params) {
-              return kj::strTree(p.getName());
+              return kj::strTree(p.getName(), suffix);
             }, ", "), ">");
       }
     }
@@ -1741,6 +1741,13 @@ private:
         "  }\n"
         "#endif  // !CAPNP_LITE\n"
         "\n",
+        templateContext.isGeneric() ? kj::strTree(
+          "  ", templateContext.decl(true, "2"),
+          "  typename ", unqualifiedParentType, templateContext.args("2"), "::Reader asGeneric() {\n"
+          "    return typename ", unqualifiedParentType, templateContext.args("2"),
+                     "::Reader(_reader);\n"
+          "  }\n"
+          "\n") : kj::strTree(),
         isUnion ? kj::strTree("  inline Which which() const;\n") : kj::strTree(),
         kj::mv(methodDecls),
         "private:\n"
@@ -1778,6 +1785,13 @@ private:
         "  inline ::kj::StringTree toString() const { return asReader().toString(); }\n"
         "#endif  // !CAPNP_LITE\n"
         "\n",
+        templateContext.isGeneric() ? kj::strTree(
+          "  ", templateContext.decl(true, "2"),
+          "  typename ", unqualifiedParentType, templateContext.args("2"), "::Builder asGeneric() {\n"
+          "    return typename ", unqualifiedParentType, templateContext.args("2"),
+                       "::Builder(_builder);\n"
+          "  }\n"
+          "\n") : kj::strTree(),
         isUnion ? kj::strTree("  inline Which which();\n") : kj::strTree(),
         kj::mv(methodDecls),
         "private:\n"
@@ -2213,6 +2227,12 @@ private:
           "  Client& operator=(Client& other);\n"
           "  Client& operator=(Client&& other);\n"
           "\n",
+          templateContext.isGeneric() ? kj::strTree(
+            "  ", templateContext.decl(true, "2"),
+            "  typename ", name, templateContext.args("2"), "::Client asGeneric() {\n"
+            "    return castAs<", name, templateContext.args("2"), ">();\n"
+            "  }\n"
+            "\n") : kj::strTree(),
           KJ_MAP(m, methods) { return kj::mv(m.clientDecls); },
           "\n"
           "protected:\n"

c++/src/capnp/encoding-test.c++

@@ -1687,6 +1687,22 @@ TEST(Encoding, Generics) {
   initTestMessage(root.initBasic().initFoo());
   checkTestMessage(reader.getBasic().getFoo());
 
+  {
+    auto typed = root.getBasic();
+    test::TestGenerics<>::Reader generic = typed.asGeneric<>();
+    checkTestMessage(generic.getFoo().getAs<TestAllTypes>());
+    test::TestGenerics<TestAllTypes>::Reader halfGeneric = typed.asGeneric<TestAllTypes>();
+    checkTestMessage(halfGeneric.getFoo());
+  }
+
+  {
+    auto typed = root.getBasic().asReader();
+    test::TestGenerics<>::Reader generic = typed.asGeneric<>();
+    checkTestMessage(generic.getFoo().getAs<TestAllTypes>());
+    test::TestGenerics<TestAllTypes>::Reader halfGeneric = typed.asGeneric<TestAllTypes>();
+    checkTestMessage(halfGeneric.getFoo());
+  }
+
   initTestMessage(root.initInner().initFoo());
   checkTestMessage(reader.getInner().getFoo());
 

c++/src/capnp/persistent.capnp.h

@@ -178,6 +178,11 @@ public:
   Client& operator=(Client& other);
   Client& operator=(Client&& other);
 
+  template <typename SturdyRef2 = ::capnp::AnyPointer, typename Owner2 = ::capnp::AnyPointer>
+  typename Persistent<SturdyRef2, Owner2>::Client asGeneric() {
+    return castAs<Persistent<SturdyRef2, Owner2>>();
+  }
+
   ::capnp::Request<typename  ::capnp::Persistent<SturdyRef, Owner>::SaveParams, typename  ::capnp::Persistent<SturdyRef, Owner>::SaveResults> saveRequest(
       ::kj::Maybe< ::capnp::MessageSize> sizeHint = nullptr);
 
@@ -222,6 +227,10 @@ public:
   }
 #endif  // !CAPNP_LITE
 
+    typename SaveParams::Reader asGeneric() {
+    return typename SaveParams::Reader(_reader);
+  }
+
   inline bool hasSealFor() const;
   inline  ::capnp::ReaderFor<Owner> getSealFor() const;
 
@@ -254,6 +263,10 @@ public:
   inline ::kj::StringTree toString() const { return asReader().toString(); }
 #endif  // !CAPNP_LITE
 
+    typename SaveParams::Builder asGeneric() {
+    return typename SaveParams::Builder(_builder);
+  }
+
   inline bool hasSealFor();
   inline  ::capnp::BuilderFor<Owner> getSealFor();
   inline void setSealFor( ::capnp::ReaderFor<Owner> value);
@@ -308,6 +321,10 @@ public:
   }
 #endif  // !CAPNP_LITE
 
+    typename SaveResults::Reader asGeneric() {
+    return typename SaveResults::Reader(_reader);
+  }
+
   inline bool hasSturdyRef() const;
   inline  ::capnp::ReaderFor<SturdyRef> getSturdyRef() const;
 
@@ -340,6 +357,10 @@ public:
   inline ::kj::StringTree toString() const { return asReader().toString(); }
 #endif  // !CAPNP_LITE
 
+    typename SaveResults::Builder asGeneric() {
+    return typename SaveResults::Builder(_builder);
+  }
+
   inline bool hasSturdyRef();
   inline  ::capnp::BuilderFor<SturdyRef> getSturdyRef();
   inline void setSturdyRef( ::capnp::ReaderFor<SturdyRef> value);
@@ -396,6 +417,11 @@ public:
   Client& operator=(Client& other);
   Client& operator=(Client&& other);
 
+  template <typename InternalRef2 = ::capnp::AnyPointer, typename ExternalRef2 = ::capnp::AnyPointer, typename InternalOwner2 = ::capnp::AnyPointer, typename ExternalOwner2 = ::capnp::AnyPointer>
+  typename RealmGateway<InternalRef2, ExternalRef2, InternalOwner2, ExternalOwner2>::Client asGeneric() {
+    return castAs<RealmGateway<InternalRef2, ExternalRef2, InternalOwner2, ExternalOwner2>>();
+  }
+
   ::capnp::Request<typename  ::capnp::RealmGateway<InternalRef, ExternalRef, InternalOwner, ExternalOwner>::ImportParams, typename  ::capnp::Persistent<InternalRef, InternalOwner>::SaveResults> importRequest(
       ::kj::Maybe< ::capnp::MessageSize> sizeHint = nullptr);
   ::capnp::Request<typename  ::capnp::RealmGateway<InternalRef, ExternalRef, InternalOwner, ExternalOwner>::ExportParams, typename  ::capnp::Persistent<ExternalRef, ExternalOwner>::SaveResults> exportRequest(
@@ -446,6 +472,10 @@ public:
   }
 #endif  // !CAPNP_LITE
 
+    typename ImportParams::Reader asGeneric() {
+    return typename ImportParams::Reader(_reader);
+  }
+
   inline bool hasCap() const;
 #if !CAPNP_LITE
   inline typename  ::capnp::Persistent<ExternalRef, ExternalOwner>::Client getCap() const;
@@ -483,6 +513,10 @@ public:
   inline ::kj::StringTree toString() const { return asReader().toString(); }
 #endif  // !CAPNP_LITE
 
+    typename ImportParams::Builder asGeneric() {
+    return typename ImportParams::Builder(_builder);
+  }
+
   inline bool hasCap();
 #if !CAPNP_LITE
   inline typename  ::capnp::Persistent<ExternalRef, ExternalOwner>::Client getCap();
@@ -546,6 +580,10 @@ public:
   }
 #endif  // !CAPNP_LITE
 
+    typename ExportParams::Reader asGeneric() {
+    return typename ExportParams::Reader(_reader);
+  }
+
   inline bool hasCap() const;
 #if !CAPNP_LITE
   inline typename  ::capnp::Persistent<InternalRef, InternalOwner>::Client getCap() const;
@@ -583,6 +621,10 @@ public:
   inline ::kj::StringTree toString() const { return asReader().toString(); }
 #endif  // !CAPNP_LITE
 
+    typename ExportParams::Builder asGeneric() {
+    return typename ExportParams::Builder(_builder);
+  }
+
   inline bool hasCap();
 #if !CAPNP_LITE
   inline typename  ::capnp::Persistent<InternalRef, InternalOwner>::Client getCap();