Hi klimek,

Change how error messages are constructed and stored in Diagnostics.
Separate the notion of 'context' when recursing down in the parser and actual 
errors.
This will simplify adding some new features, like argument overloading and 
error recovery.

http://llvm-reviews.chandlerc.com/D1168

Files:
  include/clang/ASTMatchers/Dynamic/Diagnostics.h
  lib/ASTMatchers/Dynamic/Diagnostics.cpp
  lib/ASTMatchers/Dynamic/Marshallers.h
  lib/ASTMatchers/Dynamic/Parser.cpp
  lib/ASTMatchers/Dynamic/Registry.cpp
Index: include/clang/ASTMatchers/Dynamic/Diagnostics.h
===================================================================
--- include/clang/ASTMatchers/Dynamic/Diagnostics.h
+++ include/clang/ASTMatchers/Dynamic/Diagnostics.h
@@ -49,7 +49,13 @@
 
 /// \brief Helper class to manage error messages.
 class Diagnostics {
- public:
+public:
+  /// \brief Parser context types.
+  enum ContextType {
+    CT_MatcherArg = 0,
+    CT_MatcherConstruct = 1
+  };
+
   /// \brief All errors from the system.
   enum ErrorType {
     ET_None = 0,
@@ -60,51 +66,95 @@
     ET_RegistryNotBindable = 4,
 
     ET_ParserStringError = 100,
-    ET_ParserMatcherArgFailure = 101,
-    ET_ParserMatcherFailure = 102,
-    ET_ParserNoOpenParen = 103,
-    ET_ParserNoCloseParen = 104,
-    ET_ParserNoComma = 105,
-    ET_ParserNoCode = 106,
-    ET_ParserNotAMatcher = 107,
-    ET_ParserInvalidToken = 108,
-    ET_ParserMalformedBindExpr = 109,
-    ET_ParserTrailingCode = 110,
-    ET_ParserUnsignedError = 111,
-    ET_ParserOverloadedType = 112
+    ET_ParserNoOpenParen = 101,
+    ET_ParserNoCloseParen = 102,
+    ET_ParserNoComma = 103,
+    ET_ParserNoCode = 104,
+    ET_ParserNotAMatcher = 105,
+    ET_ParserInvalidToken = 106,
+    ET_ParserMalformedBindExpr = 107,
+    ET_ParserTrailingCode = 108,
+    ET_ParserUnsignedError = 109,
+    ET_ParserOverloadedType = 110
   };
 
   /// \brief Helper stream class.
-  struct ArgStream {
+  class ArgStream {
+  public:
+    ArgStream(std::vector<std::string> *Out) : Out(Out) {}
     template <class T> ArgStream &operator<<(const T &Arg) {
       return operator<<(Twine(Arg));
     }
     ArgStream &operator<<(const Twine &Arg);
+
+  private:
     std::vector<std::string> *Out;
   };
 
-  /// \brief Push a frame to the beginning of the list
+  /// \brief Class defining a parser context.
+  ///
+  /// Used by the parser to specify (possibly recursive) contexts where the
+  /// parsing/construction can fail. Any error triggered within a context will
+  /// keep information about the context chain.
+  /// This class should be used as a RAII instance in the stack.
+  struct Context {
+  public:
+    /// \brief About to call the constructor for a matcher.
+    enum ConstructMatcherEnum { ConstructMatcher };
+    Context(ConstructMatcherEnum, Diagnostics *Error, StringRef MatcherName,
+            const SourceRange &MatcherRange);
+    /// \brief About to recurse into parsing one argument for a matcher.
+    enum MatcherArgEnum { MatcherArg };
+    Context(MatcherArgEnum, Diagnostics *Error, StringRef MatcherName,
+            const SourceRange &MatcherRange, unsigned ArgNumber);
+    ~Context();
+
+  private:
+    Diagnostics *const Error;
+  };
+
+  /// \brief Add an error to the diagnostics.
   ///
-  /// Returns a helper class to allow the caller to pass the arguments for the
+  /// All the context information will be kept on the error message.
+  /// \return a helper class to allow the caller to pass the arguments for the
   /// error message, using the << operator.
-  ArgStream pushErrorFrame(const SourceRange &Range, ErrorType Error);
+  ArgStream addError(const SourceRange &Range, ErrorType Error);
 
-  struct ErrorFrame {
+  /// \brief Information stored for one frame of the context.
+  struct ContextFrame {
+    ContextType Type;
+    SourceRange Range;
+    std::vector<std::string> Args;
+
+    std::string ToString() const;
+  };
+
+  /// \brief Inforation stored for each error found.
+  struct ErrorContent {
+    std::vector<ContextFrame> ContextStack;
     SourceRange Range;
     ErrorType Type;
     std::vector<std::string> Args;
 
     std::string ToString() const;
   };
-  ArrayRef<ErrorFrame> frames() const { return Frames; }
+  ArrayRef<ErrorContent> errors() const { return Errors; }
 
-  /// \brief Returns a string representation of the last frame.
+  /// \brief Returns a simple string representation of each error.
+  ///
+  /// Each error only show the error message without any context.
   std::string ToString() const;
-  /// \brief Returns a string representation of the whole frame stack.
+  /// \brief Returns the full string representation of each error.
+  ///
+  /// Each error message contains the full context.
   std::string ToStringFull() const;
 
- private:
-   std::vector<ErrorFrame> Frames;
+private:
+  /// \brief Helper function used by the constructors of ContextFrame.
+  ArgStream pushContextFrame(ContextType Type, SourceRange Range);
+
+  std::vector<ContextFrame> ContextStack;
+  std::vector<ErrorContent> Errors;
 };
 
 }  // namespace dynamic
Index: lib/ASTMatchers/Dynamic/Diagnostics.cpp
===================================================================
--- lib/ASTMatchers/Dynamic/Diagnostics.cpp
+++ lib/ASTMatchers/Dynamic/Diagnostics.cpp
@@ -13,20 +13,56 @@
 namespace ast_matchers {
 namespace dynamic {
 
-Diagnostics::ArgStream &
-Diagnostics::ArgStream::operator<<(const Twine &Arg) {
+Diagnostics::ArgStream Diagnostics::pushContextFrame(ContextType Type,
+                                                     SourceRange Range) {
+  ContextStack.push_back(ContextFrame());
+  ContextFrame& data = ContextStack.back();
+  data.Type = Type;
+  data.Range = Range;
+  return ArgStream(&data.Args);
+}
+
+Diagnostics::Context::Context(ConstructMatcherEnum, Diagnostics *Error,
+                              StringRef MatcherName,
+                              const SourceRange &MatcherRange)
+    : Error(Error) {
+  Error->pushContextFrame(CT_MatcherConstruct, MatcherRange) << MatcherName;
+}
+
+Diagnostics::Context::Context(MatcherArgEnum, Diagnostics *Error,
+                              StringRef MatcherName,
+                              const SourceRange &MatcherRange,
+                              unsigned ArgNumber)
+    : Error(Error) {
+  Error->pushContextFrame(CT_MatcherArg, MatcherRange) << ArgNumber
+                                                       << MatcherName;
+}
+
+Diagnostics::Context::~Context() { Error->ContextStack.pop_back(); }
+
+Diagnostics::ArgStream &Diagnostics::ArgStream::operator<<(const Twine &Arg) {
   Out->push_back(Arg.str());
   return *this;
 }
 
-Diagnostics::ArgStream Diagnostics::pushErrorFrame(const SourceRange &Range,
-                                                   ErrorType Error) {
-  Frames.insert(Frames.begin(), ErrorFrame());
-  ErrorFrame &Last = Frames.front();
+Diagnostics::ArgStream Diagnostics::addError(const SourceRange &Range,
+                                             ErrorType Error) {
+  Errors.push_back(ErrorContent());
+  ErrorContent &Last = Errors.back();
+  Last.ContextStack = ContextStack;
   Last.Range = Range;
   Last.Type = Error;
-  ArgStream Out = { &Last.Args };
-  return Out;
+  return ArgStream(&Last.Args);
+}
+
+StringRef ContextTypeToString(Diagnostics::ContextType Type) {
+  switch (Type) {
+    case Diagnostics::CT_MatcherConstruct:
+      return "Error building matcher $0.";
+    case Diagnostics::CT_MatcherArg:
+      return "Error parsing argument $0 for matcher $1.";
+  }
+  llvm_unreachable("Unknown ContextType value.");
 }
 
 StringRef ErrorTypeToString(Diagnostics::ErrorType Type) {
@@ -42,10 +78,6 @@
 
   case Diagnostics::ET_ParserStringError:
     return "Error parsing string token: <$0>";
-  case Diagnostics::ET_ParserMatcherArgFailure:
-    return "Error parsing argument $0 for matcher $1.";
-  case Diagnostics::ET_ParserMatcherFailure:
-    return "Error building matcher $0.";
   case Diagnostics::ET_ParserNoOpenParen:
     return "Error parsing matcher. Found token <$0> while looking for '('.";
   case Diagnostics::ET_ParserNoCloseParen:
@@ -95,25 +127,41 @@
   return Out;
 }
 
-std::string Diagnostics::ErrorFrame::ToString() const {
-  StringRef FormatString = ErrorTypeToString(Type);
-  std::string ErrorOut = FormatErrorString(FormatString, Args);
+static std::string MaybeAddLineCol(Twine Input, const SourceRange& Range) {
   if (Range.Start.Line > 0 && Range.Start.Column > 0)
     return (Twine(Range.Start.Line) + ":" + Twine(Range.Start.Column) + ": " +
-            ErrorOut).str();
-  return ErrorOut;
+            Input).str();
+  return Input.str();
+}
+
+std::string Diagnostics::ContextFrame::ToString() const {
+  return MaybeAddLineCol(FormatErrorString(ContextTypeToString(Type), Args),
+                         Range);
+}
+
+std::string Diagnostics::ErrorContent::ToString() const {
+  return MaybeAddLineCol(FormatErrorString(ErrorTypeToString(Type), Args),
+                         Range);
 }
 
 std::string Diagnostics::ToString() const {
-  if (Frames.empty()) return "";
-  return Frames[Frames.size() - 1].ToString();
+  std::string Result;
+  for (size_t i = 0, e = Errors.size(); i != e; ++i) {
+    if (i != 0) Result += "\n";
+    Result += Errors[i].ToString();
+  }
+  return Result;
 }
 
 std::string Diagnostics::ToStringFull() const {
   std::string Result;
-  for (size_t i = 0, end = Frames.size(); i != end; ++i) {
-    if (i > 0) Result += "\n";
-    Result += Frames[i].ToString();
+  for (size_t i = 0, e = Errors.size(); i != e; ++i) {
+    if (i != 0) Result += "\n";
+    const ErrorContent &Error = Errors[i];
+    for (size_t i = 0, e = Error.ContextStack.size(); i != e; ++i) {
+      Result += Error.ContextStack[i].ToString() + "\n";
+    }
+    Result += Error.ToString();
   }
   return Result;
 }
Index: lib/ASTMatchers/Dynamic/Marshallers.h
===================================================================
--- lib/ASTMatchers/Dynamic/Marshallers.h
+++ lib/ASTMatchers/Dynamic/Marshallers.h
@@ -152,14 +152,14 @@
 /// \brief Helper macros to check the arguments on all marshaller functions.
 #define CHECK_ARG_COUNT(count)                                                 \
   if (Args.size() != count) {                                                  \
-    Error->pushErrorFrame(NameRange, Error->ET_RegistryWrongArgCount)          \
+    Error->addError(NameRange, Error->ET_RegistryWrongArgCount)                \
         << count << Args.size();                                               \
     return MatcherList();                                                      \
   }
 
 #define CHECK_ARG_TYPE(index, type)                                            \
   if (!ArgTypeTraits<type>::is(Args[index].Value)) {                           \
-    Error->pushErrorFrame(Args[index].Range, Error->ET_RegistryWrongArgType)   \
+    Error->addError(Args[index].Range, Error->ET_RegistryWrongArgType)         \
         << (index + 1) << ArgTypeTraits<type>::asString()                      \
         << Args[index].Value.getTypeAsString();                                \
     return MatcherList();                                                      \
@@ -254,7 +254,7 @@
     const ParserValue &Arg = Args[i];
     const VariantValue &Value = Arg.Value;
     if (!ArgTraits::is(Value)) {
-      Error->pushErrorFrame(Arg.Range, Error->ET_RegistryWrongArgType)
+      Error->addError(Arg.Range, Error->ET_RegistryWrongArgType)
           << (i + 1) << ArgTraits::asString() << Value.getTypeAsString();
       HasError = true;
       break;
Index: lib/ASTMatchers/Dynamic/Parser.cpp
===================================================================
--- lib/ASTMatchers/Dynamic/Parser.cpp
+++ lib/ASTMatchers/Dynamic/Parser.cpp
@@ -162,8 +162,7 @@
       SourceRange Range;
       Range.Start = Result->Range.Start;
       Range.End = currentLocation();
-      Error->pushErrorFrame(Range, Error->ET_ParserUnsignedError)
-          << Result->Text;
+      Error->addError(Range, Error->ET_ParserUnsignedError) << Result->Text;
       Result->Kind = TokenInfo::TK_Error;
     }
   }
@@ -198,8 +197,7 @@
     SourceRange Range;
     Range.Start = Result->Range.Start;
     Range.End = currentLocation();
-    Error->pushErrorFrame(Range, Error->ET_ParserStringError)
-        << ErrorText;
+    Error->addError(Range, Error->ET_ParserStringError) << ErrorText;
     Result->Kind = TokenInfo::TK_Error;
   }
 
@@ -239,7 +237,7 @@
   assert(NameToken.Kind == TokenInfo::TK_Ident);
   const TokenInfo OpenToken = Tokenizer->consumeNextToken();
   if (OpenToken.Kind != TokenInfo::TK_OpenParen) {
-    Error->pushErrorFrame(OpenToken.Range, Error->ET_ParserNoOpenParen)
+    Error->addError(OpenToken.Range, Error->ET_ParserNoOpenParen)
         << OpenToken.Text;
     return false;
   }
@@ -256,27 +254,24 @@
       // We must find a , token to continue.
       const TokenInfo CommaToken = Tokenizer->consumeNextToken();
       if (CommaToken.Kind != TokenInfo::TK_Comma) {
-        Error->pushErrorFrame(CommaToken.Range, Error->ET_ParserNoComma)
+        Error->addError(CommaToken.Range, Error->ET_ParserNoComma)
             << CommaToken.Text;
         return false;
       }
     }
 
+    Diagnostics::Context Ctx(Diagnostics::Context::MatcherArg, Error,
+                             NameToken.Text, NameToken.Range, Args.size() + 1);
     ParserValue ArgValue;
     ArgValue.Text = Tokenizer->peekNextToken().Text;
     ArgValue.Range = Tokenizer->peekNextToken().Range;
-    if (!parseExpressionImpl(&ArgValue.Value)) {
-      Error->pushErrorFrame(NameToken.Range,
-                            Error->ET_ParserMatcherArgFailure)
-          << (Args.size() + 1) << NameToken.Text;
-      return false;
-    }
+    if (!parseExpressionImpl(&ArgValue.Value)) return false;
 
     Args.push_back(ArgValue);
   }
 
   if (EndToken.Kind == TokenInfo::TK_Eof) {
-    Error->pushErrorFrame(OpenToken.Range, Error->ET_ParserNoCloseParen);
+    Error->addError(OpenToken.Range, Error->ET_ParserNoCloseParen);
     return false;
   }
 
@@ -293,35 +288,32 @@
     //       explicit about the syntax error.
     if (BindToken.Kind != TokenInfo::TK_Ident ||
         BindToken.Text != TokenInfo::ID_Bind) {
-      Error->pushErrorFrame(BindToken.Range, Error->ET_ParserMalformedBindExpr);
+      Error->addError(BindToken.Range, Error->ET_ParserMalformedBindExpr);
       return false;
     }
     if (OpenToken.Kind != TokenInfo::TK_OpenParen) {
-      Error->pushErrorFrame(OpenToken.Range, Error->ET_ParserMalformedBindExpr);
+      Error->addError(OpenToken.Range, Error->ET_ParserMalformedBindExpr);
       return false;
     }
     if (IDToken.Kind != TokenInfo::TK_Literal || !IDToken.Value.isString()) {
-      Error->pushErrorFrame(IDToken.Range, Error->ET_ParserMalformedBindExpr);
+      Error->addError(IDToken.Range, Error->ET_ParserMalformedBindExpr);
       return false;
     }
     if (CloseToken.Kind != TokenInfo::TK_CloseParen) {
-      Error->pushErrorFrame(CloseToken.Range,
-                            Error->ET_ParserMalformedBindExpr);
+      Error->addError(CloseToken.Range, Error->ET_ParserMalformedBindExpr);
       return false;
     }
     BindID = IDToken.Value.getString();
   }
 
   // Merge the start and end infos.
+  Diagnostics::Context Ctx(Diagnostics::Context::ConstructMatcher, Error,
+                           NameToken.Text, NameToken.Range);
   SourceRange MatcherRange = NameToken.Range;
   MatcherRange.End = EndToken.Range.End;
   MatcherList Result = S->actOnMatcherExpression(
       NameToken.Text, MatcherRange, BindID, Args, Error);
-  if (Result.empty()) {
-    Error->pushErrorFrame(NameToken.Range, Error->ET_ParserMatcherFailure)
-        << NameToken.Text;
-    return false;
-  }
+  if (Result.empty()) return false;
 
   *Value = Result;
   return true;
@@ -338,8 +330,8 @@
     return parseMatcherExpressionImpl(Value);
 
   case TokenInfo::TK_Eof:
-    Error->pushErrorFrame(Tokenizer->consumeNextToken().Range,
-                          Error->ET_ParserNoCode);
+    Error->addError(Tokenizer->consumeNextToken().Range,
+                    Error->ET_ParserNoCode);
     return false;
 
   case TokenInfo::TK_Error:
@@ -352,8 +344,7 @@
   case TokenInfo::TK_Period:
   case TokenInfo::TK_InvalidChar:
     const TokenInfo Token = Tokenizer->consumeNextToken();
-    Error->pushErrorFrame(Token.Range, Error->ET_ParserInvalidToken)
-        << Token.Text;
+    Error->addError(Token.Range, Error->ET_ParserInvalidToken) << Token.Text;
     return false;
   }
 
@@ -392,8 +383,8 @@
   CodeTokenizer Tokenizer(Code, Error);
   if (!Parser(&Tokenizer, S, Error).parseExpressionImpl(Value)) return false;
   if (Tokenizer.peekNextToken().Kind != TokenInfo::TK_Eof) {
-    Error->pushErrorFrame(Tokenizer.peekNextToken().Range,
-                          Error->ET_ParserTrailingCode);
+    Error->addError(Tokenizer.peekNextToken().Range,
+                    Error->ET_ParserTrailingCode);
     return false;
   }
   return true;
@@ -412,11 +403,11 @@
   if (!parseExpression(Code, S, &Value, Error))
     return NULL;
   if (!Value.isMatchers()) {
-    Error->pushErrorFrame(SourceRange(), Error->ET_ParserNotAMatcher);
+    Error->addError(SourceRange(), Error->ET_ParserNotAMatcher);
     return NULL;
   }
   if (Value.getMatchers().matchers().size() != 1) {
-    Error->pushErrorFrame(SourceRange(), Error->ET_ParserOverloadedType)
+    Error->addError(SourceRange(), Error->ET_ParserOverloadedType)
         << Value.getTypeAsString();
     return NULL;
   }
Index: lib/ASTMatchers/Dynamic/Registry.cpp
===================================================================
--- lib/ASTMatchers/Dynamic/Registry.cpp
+++ lib/ASTMatchers/Dynamic/Registry.cpp
@@ -298,8 +298,7 @@
   ConstructorMap::const_iterator it =
       RegistryData->constructors().find(MatcherName);
   if (it == RegistryData->constructors().end()) {
-    Error->pushErrorFrame(NameRange, Error->ET_RegistryNotFound)
-        << MatcherName;
+    Error->addError(NameRange, Error->ET_RegistryNotFound) << MatcherName;
     return MatcherList();
   }
 
@@ -322,7 +321,7 @@
       return *Bound;
     }
   }
-  Error->pushErrorFrame(NameRange, Error->ET_RegistryNotBindable);
+  Error->addError(NameRange, Error->ET_RegistryNotBindable);
   return MatcherList();
 }
 
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