[YAMLIO] Make line-wrapping configurable and test it.

[friss]

Summary

We would wrap flow mappings and sequences when they go over a hardcoded 70
characters limit. Make the wrapping column configurable (and default to 70
co the change should be NFC for current users). Passing 0 allows to completely
suppress the wrapping which makes it easier to handle in tools like FileCheck.

docs/YamlIO.rst

.. code-block:: c++
     struct MappingTraits<Stuff> {
       static void mapping(IO &io, Stuff &stuff) {
         ...
       }
 
       static const bool flow = true;
     }
 
+Flow mappings are subject to line wrapping according to the Output object configuration.
 
 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:
struct SequenceTraits<MyList> {
     // The existence of this member causes YAML I/O to use a flow sequence
     static const bool flow = true;
   };
 
 With the above, if you used MyList as the data type in your native data 
 structures, then when converted to YAML, a flow sequence of integers 
 will be used (e.g. [ 10, -3, 4 ]).
 
+Flow sequences are subject to line wrapping according to the Output object configuration.
 
 Utility Macros
 --------------
 Since a common source of sequences is std::vector<>, YAML I/O provides macros:
 LLVM_YAML_IS_SEQUENCE_VECTOR() and LLVM_YAML_IS_FLOW_SEQUENCE_VECTOR() which
 can be used to easily specify SequenceTraits<> on a std::vector type.  YAML 
 I/O does not partial specialize SequenceTraits on std::vector<> because that
 would force all vectors to be sequences.  An example use of the macros:

 traits use to shared context sensitive information.
 
 
 Output
 ======
 
 The llvm::yaml::Output class is used to generate a YAML document from your 
 in-memory data structures, using traits defined on your data types.  
-To instantiate an Output object you need an llvm::raw_ostream, and optionally 
-a context pointer:
+To instantiate an Output object you need an llvm::raw_ostream, an optional 
+context pointer and an optional wrapping column:
 
 .. code-block:: c++
 
       class Output : public IO {
       public:
-        Output(llvm::raw_ostream &, void *context=NULL);
+        Output(llvm::raw_ostream &, void *context = NULL, int WrapColumn = 70);
     
 Once you have an Output object, you can use the C++ stream operator on it
 to write your native data as YAML. One thing to recall is that a YAML file
 can contain multiple "documents".  If the top level data structure you are
 streaming as YAML is a mapping, scalar, or sequence, then Output assumes you
 are generating one document and wraps the mapping output 
 with  "``---``" and trailing "``...``".  
 
+The WrapColumn parameter will cause the flow mappings and sequences to
+line-wrap when they go over the supplied column. Pass 0 to completely
+suppress the wrapping.
+
 .. code-block:: c++
    
     using llvm::yaml::Output;
 
     void dumpMyMapDoc(const MyMapType &info) {
       Output yout(llvm::outs());
       yout << info;
     }

include/llvm/Support/YAMLTraits.h

 
 
 ///
 /// The Output class is used to generate a yaml document from in-memory structs
 /// and vectors.
 ///
 class Output : public IO {
 public:
-  Output(llvm::raw_ostream &, void *Ctxt=nullptr);
+  Output(llvm::raw_ostream &, void *Ctxt = nullptr, int WrapColumn = 70);
   ~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;
enum InState {
     inFlowSeq,
     inMapFirstKey,
     inMapOtherKey,
     inFlowMapFirstKey,
     inFlowMapOtherKey
   };
 
   llvm::raw_ostream       &Out;
+  int                      WrapColumn;
   SmallVector<InState, 8>  StateStack;
   int                      Column;
   int                      ColumnAtFlowStart;
   int                      ColumnAtMapFlowStart;
   bool                     NeedBitValueComma;
   bool                     NeedFlowSequenceComma;
   bool                     EnumerationMatchFound;
   bool                     NeedsNewLine;

lib/Support/YAMLTraits.cpp

 bool Input::canElideEmptySequence() {
   return false;
 }
 
 //===----------------------------------------------------------------------===//
 //  Output
 //===----------------------------------------------------------------------===//
 
-Output::Output(raw_ostream &yout, void *context)
+Output::Output(raw_ostream &yout, void *context, int WrapColumn)
     : IO(context),
       Out(yout),
+      WrapColumn(WrapColumn),
       Column(0),
       ColumnAtFlowStart(0),
       ColumnAtMapFlowStart(0),
       NeedBitValueComma(false),
       NeedFlowSequenceComma(false),
       EnumerationMatchFound(false),
       NeedsNewLine(false) {
 }

 void Output::endFlowSequence() {
   StateStack.pop_back();
   this->outputUpToEndOfLine(" ]");
 }
 
 bool Output::preflightFlowElement(unsigned, void *&) {
   if (NeedFlowSequenceComma)
     output(", ");
-  if (Column > 70) {
+  if (WrapColumn && Column > WrapColumn) {
     output("\n");
     for (int i = 0; i < ColumnAtFlowStart; ++i)
       output(" ");
     Column = ColumnAtFlowStart;
     output("  ");
   }
   return true;
 }
if (key.size() < strlen(spaces))
     output(&spaces[key.size()]);
   else
     output(" ");
 }
 
 void Output::flowKey(StringRef Key) {
   if (StateStack.back() == inFlowMapOtherKey)
     output(", ");
-  if (Column > 70) {
+  if (WrapColumn && Column > WrapColumn) {
     output("\n");
     for (int I = 0; I < ColumnAtMapFlowStart; ++I)
       output(" ");
     Column = ColumnAtMapFlowStart;
     output("  ");
   }
   output(Key);
   output(": ");

unittests/Support/YAMLIOTest.cpp

 TEST(YAMLIO, TestEmptyStringSucceedsForSequence) {
   std::vector<uint8_t> seq;
   Input yin("", /*Ctxt=*/nullptr, suppressErrorMessages);
   yin >> seq;
 
   EXPECT_FALSE(yin.error());
   EXPECT_TRUE(seq.empty());
 }
+
+struct FlowMap {
+  llvm::StringRef str1, str2, str3;
+  FlowMap(llvm::StringRef str1, llvm::StringRef str2, llvm::StringRef str3)
+    : str1(str1), str2(str2), str3(str3) {}
+};
+
+namespace llvm {
+namespace yaml {
+  template <>
+  struct MappingTraits<FlowMap> {
+    static void mapping(IO &io, FlowMap &fm) {
+      io.mapRequired("str1", fm.str1);
+      io.mapRequired("str2", fm.str2);
+      io.mapRequired("str3", fm.str3);
+    }
+
+    static const bool flow = true;
+  };
+}
+}
+
+struct FlowSeq {
+  llvm::StringRef str;
+  FlowSeq(llvm::StringRef S) : str(S) {}
+  FlowSeq() = default;
+};
+
+template <>
+struct ScalarTraits<FlowSeq> {
+  static void output(const FlowSeq &value, void*, llvm::raw_ostream &out) {
+    out << value.str;
+  }
+  static StringRef input(StringRef scalar, void*, FlowSeq &value) {
+    value.str = scalar;
+    return "";
+  }
+
+  static bool mustQuote(StringRef S) { return false; }
+};
+
+LLVM_YAML_IS_FLOW_SEQUENCE_VECTOR(FlowSeq)
+
+TEST(YAMLIO, TestWrapFlow) {
+  std::string out;
+  llvm::raw_string_ostream ostr(out);
+  FlowMap Map("This is str1", "This is str2", "This is str3");
+  std::vector<FlowSeq> Seq;
+  Seq.emplace_back("This is str1");
+  Seq.emplace_back("This is str2");
+  Seq.emplace_back("This is str3");
+
+  {
+    // 20 is just bellow the total length of the first mapping field.
+    // We should wreap at every element.
+    Output yout(ostr, nullptr, 15);
+
+    yout << Map;
+    ostr.flush();
+    EXPECT_EQ(out,
+              "---\n"
+              "{ str1: This is str1, \n"
+              "  str2: This is str2, \n"
+              "  str3: This is str3 }\n"
+              "...\n");
+    out.clear();
+
+    yout << Seq;
+    ostr.flush();
+    EXPECT_EQ(out,
+              "---\n"
+              "[ This is str1, \n"
+              "  This is str2, \n"
+              "  This is str3 ]\n"
+              "...\n");
+    out.clear();
+  }
+  {
+    // 25 will allow the second field to be output on the first line.
+    Output yout(ostr, nullptr, 25);
+
+    yout << Map;
+    ostr.flush();
+    EXPECT_EQ(out,
+              "---\n"
+              "{ str1: This is str1, str2: This is str2, \n"
+              "  str3: This is str3 }\n"
+              "...\n");
+    out.clear();
+
+    yout << Seq;
+    ostr.flush();
+    EXPECT_EQ(out,
+              "---\n"
+              "[ This is str1, This is str2, \n"
+              "  This is str3 ]\n"
+              "...\n");
+    out.clear();
+  }
+  {
+    // 0 means no wrapping.
+    Output yout(ostr, nullptr, 0);
+
+    yout << Map;
+    ostr.flush();
+    EXPECT_EQ(out,
+              "---\n"
+              "{ str1: This is str1, str2: This is str2, str3: This is str3 }\n"
+              "...\n");
+    out.clear();
+
+    yout << Seq;
+    ostr.flush();
+    EXPECT_EQ(out,
+              "---\n"
+              "[ This is str1, This is str2, This is str3 ]\n"
+              "...\n");
+    out.clear();
+  }
+}