YAML: Assign a value returned by the default constructor to the value in an optional mapping.

[arphaman]

Summary

This patch ensures that a value that's passed into YAML's IO mapOptional method is going to be assigned a value returned by the default constructor when the appropriate key is not present in the YAML mapping.

The current YAML documentation specifies that this should happen: http://llvm.org/docs/YamlIO.html#default-values

llvm/trunk/include/llvm/Support/YAMLTraits.h

private:
 
   template <typename T>
   void processKey(const char *Key, T &Val, bool Required) {
     void *SaveInfo;
     bool UseDefault;
     if ( this->preflightKey(Key, Required, false, UseDefault, SaveInfo) ) {
       yamlize(*this, Val, Required);
       this->postflightKey(SaveInfo);
+    } else if (UseDefault) {
+      Val = T();
     }
   }
 
 private:
   void  *Ctxt;
 };
 
 

llvm/trunk/unittests/Support/YAMLIOTest.cpp

namespace yaml {
   template <> struct MappingTraits<FooBarContainer> {
     static void mapping(IO &io, FooBarContainer &fb) {
       io.mapRequired("fbs", fb.fbs);
     }
   };
 }
 }
 
+struct FooBarOptional {
+  int Foo;
+  int Bar;
+};
+
+namespace llvm {
+namespace yaml {
+template <> struct MappingTraits<FooBarOptional> {
+  static void mapping(IO &YamlIO, FooBarOptional &Obj) {
+    YamlIO.mapRequired("foo", Obj.Foo);
+    YamlIO.mapOptional("bar", Obj.Bar);
+  }
+};
+}
+}
 
 //
 // Test the reading of a yaml mapping
 //
 TEST(YAMLIO, TestMapRead) {
   FooBar doc;
   {
     Input yin("---\nfoo:  3\nbar:  5\n...\n");
FooBar doc;
     yin >> doc;
 
     EXPECT_FALSE(yin.error());
     EXPECT_EQ(doc.foo, 3);
     EXPECT_EQ(doc.bar, 5);
   }
 }
 
+TEST(YAMLIO, TestMapReadOptional) {
+  FooBarOptional Doc;
+  Doc.Bar = 42;
+  {
+    Input In("---\nfoo:  3\n...\n");
+    In >> Doc;
+
+    EXPECT_FALSE(In.error());
+    EXPECT_EQ(Doc.Foo, 3);
+    EXPECT_EQ(Doc.Bar, 0);
+  }
+}
+
 TEST(YAMLIO, TestMalformedMapRead) {
   FooBar doc;
   Input yin("{foo: 3; bar: 5}", nullptr, suppressErrorMessages);
   yin >> doc;
   EXPECT_TRUE(!!yin.error());
 }
 
 //