YAML: Add an optional 'flow' field to the mapping trait to allow flow mapping output.

[arphaman]

Summary

This patch adds an optional flow field to the MappingTrait class that enables yaml IO to output flow mappings.
I have a patch that updates the documentation as well, I will post it later.

[arphaman]

I've updated the patch to include the documentation changes.

[arphaman]

Refactoring: I've extracted the output of the flow mapping key into a separate method as suggested by Justin.

llvm/trunk/docs/YamlIO.rst

struct MappingTraits<Stuff> {
       static StringRef validate(IO &io, Stuff &stuff) {
         // Look at all fields in 'stuff' and if there
         // are any bad values return a string describing
         // the error.  Otherwise return an empty string.
         return StringRef();
       }
     };
 
+Flow Mapping
+------------
+A YAML "flow mapping" is a mapping that uses the inline notation
+(e.g { x: 1, y: 0 } ) when written to YAML. To specify that a type should be
+written in YAML using flow mapping, your MappingTraits specialization should
+add "static const bool flow = true;". For instance:
+
+.. code-block:: c++
+
+    using llvm::yaml::MappingTraits;
+    using llvm::yaml::IO;
+
+    struct Stuff {
+      ...
+    };
+
+    template <>
+    struct MappingTraits<Stuff> {
+      static void mapping(IO &io, Stuff &stuff) {
+        ...
+      }
+
+      static const bool flow = true;
+    }
+
 
 Sequence
 ========
 
 To be translated to or from a YAML sequence for your type T you must specialize
 llvm::yaml::SequenceTraits on T and implement two methods:
 ``size_t size(IO &io, T&)`` and
 ``T::value_type& element(IO &io, T&, size_t indx)``.  For example:

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

 ///       }
 ///     };
 template<class T>
 struct MappingTraits {
   // Must provide:
   // static void mapping(IO &io, T &fields);
   // Optionally may provide:
   // static StringRef validate(IO &io, T &fields);
+  //
+  // The optional flow flag will cause generated YAML to use a flow mapping
+  // (e.g. { a: 0, b: 1 }):
+  // static const bool flow = true;
 };
 
 
 /// This class should be specialized by any integral type that converts
 /// to/from a YAML scalar where there is a one-to-one mapping between
 /// in-memory values and a string in YAML.  For example:
 ///
 ///     struct ScalarEnumerationTraits<Colors> {
public:
   virtual void endFlowSequence() = 0;
 
   virtual bool mapTag(StringRef Tag, bool Default=false) = 0;
   virtual void beginMapping() = 0;
   virtual void endMapping() = 0;
   virtual bool preflightKey(const char*, bool, bool, bool &, void *&) = 0;
   virtual void postflightKey(void*) = 0;
 
+  virtual void beginFlowMapping() = 0;
+  virtual void endFlowMapping() = 0;
+
   virtual void beginEnumScalar() = 0;
   virtual bool matchEnumScalar(const char*, bool) = 0;
   virtual bool matchEnumFallback() = 0;
   virtual void endEnumScalar() = 0;
 
   virtual bool beginBitSetScalar(bool &) = 0;
   virtual bool bitSetMatch(const char*, bool) = 0;
   virtual void endBitSetScalar() = 0;
else {
     }
   }
 }
 
 
 template<typename T>
 typename std::enable_if<validatedMappingTraits<T>::value, void>::type
 yamlize(IO &io, T &Val, bool) {
+  if (has_FlowTraits<MappingTraits<T>>::value)
+    io.beginFlowMapping();
+  else
     io.beginMapping();
   if (io.outputting()) {
     StringRef Err = MappingTraits<T>::validate(io, Val);
     if (!Err.empty()) {
       llvm::errs() << Err << "\n";
       assert(Err.empty() && "invalid struct trying to be written as yaml");
     }
   }
   MappingTraits<T>::mapping(io, Val);
   if (!io.outputting()) {
     StringRef Err = MappingTraits<T>::validate(io, Val);
     if (!Err.empty())
       io.setError(Err);
   }
+  if (has_FlowTraits<MappingTraits<T>>::value)
+    io.endFlowMapping();
+  else
     io.endMapping();
 }
 
 template<typename T>
 typename std::enable_if<unvalidatedMappingTraits<T>::value, void>::type
 yamlize(IO &io, T &Val, bool) {
+  if (has_FlowTraits<MappingTraits<T>>::value) {
+    io.beginFlowMapping();
+    MappingTraits<T>::mapping(io, Val);
+    io.endFlowMapping();
+  } else {
     io.beginMapping();
     MappingTraits<T>::mapping(io, Val);
     io.endMapping();
   }
+}
 
 template<typename T>
 typename std::enable_if<missingTraits<T>::value, void>::type
 yamlize(IO &io, T &Val, bool) {
   char missing_yaml_trait_for_type[sizeof(MissingTrait<T>)];
 }
 
 template<typename T>

 
 private:
   bool outputting() override;
   bool mapTag(StringRef, bool) override;
   void beginMapping() override;
   void endMapping() override;
   bool preflightKey(const char *, bool, bool, bool &, void *&) override;
   void postflightKey(void *) override;
+  void beginFlowMapping() override;
+  void endFlowMapping() override;
   unsigned beginSequence() override;
   void endSequence() override;
   bool preflightElement(unsigned index, void *&) override;
   void postflightElement(void *) override;
   unsigned beginFlowSequence() override;
   bool preflightFlowElement(unsigned , void *&) override;
   void postflightFlowElement(void *) override;
   void endFlowSequence() override;
public:
   ~Output() override;
 
   bool outputting() override;
   bool mapTag(StringRef, bool) override;
   void beginMapping() override;
   void endMapping() override;
   bool preflightKey(const char *key, bool, bool, bool &, void *&) override;
   void postflightKey(void *) override;
+  void beginFlowMapping() override;
+  void endFlowMapping() override;
   unsigned beginSequence() override;
   void endSequence() override;
   bool preflightElement(unsigned, void *&) override;
   void postflightElement(void *) override;
   unsigned beginFlowSequence() override;
   bool preflightFlowElement(unsigned, void *&) override;
   void postflightFlowElement(void *) override;
   void endFlowSequence() override;
public:
   void endDocuments();
 
 private:
   void output(StringRef s);
   void outputUpToEndOfLine(StringRef s);
   void newLineCheck();
   void outputNewLine();
   void paddedKey(StringRef key);
+  void flowKey(StringRef Key);
 
-  enum InState { inSeq, inFlowSeq, inMapFirstKey, inMapOtherKey };
+  enum InState {
+    inSeq,
+    inFlowSeq,
+    inMapFirstKey,
+    inMapOtherKey,
+    inFlowMapFirstKey,
+    inFlowMapOtherKey
+  };
 
   llvm::raw_ostream       &Out;
   SmallVector<InState, 8>  StateStack;
   int                      Column;
   int                      ColumnAtFlowStart;
+  int                      ColumnAtMapFlowStart;
   bool                     NeedBitValueComma;
   bool                     NeedFlowSequenceComma;
   bool                     EnumerationMatchFound;
   bool                     NeedsNewLine;
 };
 
 
 

llvm/trunk/lib/Support/YAMLTraits.cpp

void Input::endMapping() {
   for (const auto &NN : MN->Mapping) {
     if (!MN->isValidKey(NN.first())) {
       setError(NN.second.get(), Twine("unknown key '") + NN.first() + "'");
       break;
     }
   }
 }
 
+void Input::beginFlowMapping() { beginMapping(); }
+
+void Input::endFlowMapping() { endMapping(); }
+
 unsigned Input::beginSequence() {
   if (SequenceHNode *SQ = dyn_cast<SequenceHNode>(CurrentNode))
     return SQ->Entries.size();
   if (isa<EmptyHNode>(CurrentNode))
     return 0;
   // Treat case where there's a scalar "null" value as an empty sequence.
   if (ScalarHNode *SN = dyn_cast<ScalarHNode>(CurrentNode)) {
     if (isNull(SN->value()))

 //  Output
 //===----------------------------------------------------------------------===//
 
 Output::Output(raw_ostream &yout, void *context)
     : IO(context),
       Out(yout),
       Column(0),
       ColumnAtFlowStart(0),
+      ColumnAtMapFlowStart(0),
       NeedBitValueComma(false),
       NeedFlowSequenceComma(false),
       EnumerationMatchFound(false),
       NeedsNewLine(false) {
 }
 
 Output::~Output() {
 }

 void Output::endMapping() {
   StateStack.pop_back();
 }
 
 bool Output::preflightKey(const char *Key, bool Required, bool SameAsDefault,
                           bool &UseDefault, void *&) {
   UseDefault = false;
   if (Required || !SameAsDefault) {
+    auto State = StateStack.back();
+    if (State == inFlowMapFirstKey || State == inFlowMapOtherKey) {
+      flowKey(Key);
+    } else {
       this->newLineCheck();
       this->paddedKey(Key);
+    }
     return true;
   }
   return false;
 }
 
 void Output::postflightKey(void *) {
   if (StateStack.back() == inMapFirstKey) {
     StateStack.pop_back();
     StateStack.push_back(inMapOtherKey);
+  } else if (StateStack.back() == inFlowMapFirstKey) {
+    StateStack.pop_back();
+    StateStack.push_back(inFlowMapOtherKey);
   }
 }
 
+void Output::beginFlowMapping() {
+  StateStack.push_back(inFlowMapFirstKey);
+  this->newLineCheck();
+  ColumnAtMapFlowStart = Column;
+  output("{ ");
+}
+
+void Output::endFlowMapping() {
+  StateStack.pop_back();
+  this->outputUpToEndOfLine(" }");
+}
+
 void Output::beginDocuments() {
   this->outputUpToEndOfLine("---");
 }
 
 bool Output::preflightDocument(unsigned index) {
   if (index > 0)
     this->outputUpToEndOfLine("\n---");
   return true;

 
 void Output::output(StringRef s) {
   Column += s.size();
   Out << s;
 }
 
 void Output::outputUpToEndOfLine(StringRef s) {
   this->output(s);
-  if (StateStack.empty() || StateStack.back() != inFlowSeq)
+  if (StateStack.empty() || (StateStack.back() != inFlowSeq &&
+                             StateStack.back() != inFlowMapFirstKey &&
+                             StateStack.back() != inFlowMapOtherKey))
     NeedsNewLine = true;
 }
 
 void Output::outputNewLine() {
   Out << "\n";
   Column = 0;
 }
 
void Output::newLineCheck() {
 
   assert(StateStack.size() > 0);
   unsigned Indent = StateStack.size() - 1;
   bool OutputDash = false;
 
   if (StateStack.back() == inSeq) {
     OutputDash = true;
   } else if ((StateStack.size() > 1) && ((StateStack.back() == inMapFirstKey) ||
-             (StateStack.back() == inFlowSeq)) &&
+             (StateStack.back() == inFlowSeq) ||
+             (StateStack.back() == inFlowMapFirstKey)) &&
              (StateStack[StateStack.size() - 2] == inSeq)) {
     --Indent;
     OutputDash = true;
   }
 
   for (unsigned i = 0; i < Indent; ++i) {
     output("  ");
   }
   if (OutputDash) {
     output("- ");
   }
 
 }
 
 void Output::paddedKey(StringRef key) {
   output(key);
   output(":");
   const char *spaces = "                ";
   if (key.size() < strlen(spaces))
     output(&spaces[key.size()]);
   else
     output(" ");
 }
 
+void Output::flowKey(StringRef Key) {
+  if (StateStack.back() == inFlowMapOtherKey)
+    output(", ");
+  if (Column > 70) {
+    output("\n");
+    for (int I = 0; I < ColumnAtMapFlowStart; ++I)
+      output(" ");
+    Column = ColumnAtMapFlowStart;
+    output("  ");
+  }
+  output(Key);
+  output(": ");
+}
+
 //===----------------------------------------------------------------------===//
 //  traits for built-in types
 //===----------------------------------------------------------------------===//
 
 void ScalarTraits<bool>::output(const bool &Val, void *, raw_ostream &Out) {
   Out << (Val ? "true" : "false");
 }
 

llvm/trunk/unittests/Support/YAMLIOTest.cpp

TEST(YAMLIO, TestValidatingInput) {
   std::vector<MyValidation> docList;
   Input yin("--- \nvalue:  3.0\n"
             "--- \nvalue:  -1.0\n...\n",
             nullptr, suppressErrorMessages);
   yin >> docList;
   EXPECT_TRUE(!!yin.error());
 }
 
+//===----------------------------------------------------------------------===//
+//  Test flow mapping
+//===----------------------------------------------------------------------===//
+
+struct FlowFooBar {
+  int foo;
+  int bar;
+
+  FlowFooBar() : foo(0), bar(0) {}
+  FlowFooBar(int foo, int bar) : foo(foo), bar(bar) {}
+};
+
+typedef std::vector<FlowFooBar> FlowFooBarSequence;
+
+LLVM_YAML_IS_SEQUENCE_VECTOR(FlowFooBar)
+
+struct FlowFooBarDoc {
+  FlowFooBar attribute;
+  FlowFooBarSequence seq;
+};
+
+namespace llvm {
+namespace yaml {
+  template <>
+  struct MappingTraits<FlowFooBar> {
+    static void mapping(IO &io, FlowFooBar &fb) {
+      io.mapRequired("foo", fb.foo);
+      io.mapRequired("bar", fb.bar);
+    }
+
+    static const bool flow = true;
+  };
+
+  template <>
+  struct MappingTraits<FlowFooBarDoc> {
+    static void mapping(IO &io, FlowFooBarDoc &fb) {
+      io.mapRequired("attribute", fb.attribute);
+      io.mapRequired("seq", fb.seq);
+    }
+  };
+}
+}
+
+//
+// Test writing then reading back custom mappings
+//
+TEST(YAMLIO, TestReadWriteMyFlowMapping) {
+  std::string intermediate;
+  {
+    FlowFooBarDoc doc;
+    doc.attribute = FlowFooBar(42, 907);
+    doc.seq.push_back(FlowFooBar(1, 2));
+    doc.seq.push_back(FlowFooBar(0, 0));
+    doc.seq.push_back(FlowFooBar(-1, 1024));
+
+    llvm::raw_string_ostream ostr(intermediate);
+    Output yout(ostr);
+    yout << doc;
+
+    // Verify that mappings were written in flow style
+    ostr.flush();
+    llvm::StringRef flowOut(intermediate);
+    EXPECT_NE(llvm::StringRef::npos, flowOut.find("{ foo: 42, bar: 907 }"));
+    EXPECT_NE(llvm::StringRef::npos, flowOut.find("- { foo: 1, bar: 2 }"));
+    EXPECT_NE(llvm::StringRef::npos, flowOut.find("- { foo: 0, bar: 0 }"));
+    EXPECT_NE(llvm::StringRef::npos, flowOut.find("- { foo: -1, bar: 1024 }"));
+  }
+
+  {
+    Input yin(intermediate);
+    FlowFooBarDoc doc2;
+    yin >> doc2;
+
+    EXPECT_FALSE(yin.error());
+    EXPECT_EQ(doc2.attribute.foo, 42);
+    EXPECT_EQ(doc2.attribute.bar, 907);
+    EXPECT_EQ(doc2.seq.size(), 3UL);
+    EXPECT_EQ(doc2.seq[0].foo, 1);
+    EXPECT_EQ(doc2.seq[0].bar, 2);
+    EXPECT_EQ(doc2.seq[1].foo, 0);
+    EXPECT_EQ(doc2.seq[1].bar, 0);
+    EXPECT_EQ(doc2.seq[2].foo, -1);
+    EXPECT_EQ(doc2.seq[2].bar, 1024);
+  }
+}
 
 //===----------------------------------------------------------------------===//
 //  Test error handling
 //===----------------------------------------------------------------------===//
 
 //
 // Test error handling of unknown enumerated scalar
 //