[parser] Hide expression classifiers in parser implementation

src/parsing/expression-classifier.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_PARSING_EXPRESSION_CLASSIFIER_H
 #define V8_PARSING_EXPRESSION_CLASSIFIER_H
 
 #include "src/messages.h"
 #include "src/parsing/scanner.h"
-#include "src/parsing/token.h"
 
 namespace v8 {
 namespace internal {
 
 class DuplicateFinder;
 
 #define ERROR_CODES(T)                       \
   T(ExpressionProduction, 0)                 \
   T(FormalParameterInitializerProduction, 1) \
   T(BindingPatternProduction, 2)             \
   T(AssignmentPatternProduction, 3)          \
   T(DistinctFormalParametersProduction, 4)   \
   T(StrictModeFormalParametersProduction, 5) \
   T(ArrowFormalParametersProduction, 6)      \
   T(LetPatternProduction, 7)                 \
   T(TailCallExpressionProduction, 8)         \
   T(AsyncArrowFormalParametersProduction, 9)
 
+// Expression classifiers serve two purposes:
+//
+// 1) They keep track of error messages that are pending (and other
+//    related information), waiting for the parser to decide whether
+//    the parsed expression is a pattern or not.
+// 2) They keep track of expressions that may need to be rewritten, if
+//    the parser decides that they are not patterns.  (A different
+//    mechanism implements the rewriting of patterns.)
+//
+// Expression classifiers are used by the parser in a stack fashion.
+// Each new classifier is pushed on top of the stack.  This happens
+// automatically by the class's constructor.  While on top of the
+// stack, the classifier records pending error messages and tracks the
+// pending non-patterns of the expression that is being parsed.
+//
+// At the end of its life, a classifier is either "accumulated" to the
+// one that is below it on the stack, or is "discarded".  The former
+// is achieved by calling the method Accumulate.  The latter is
+// achieved automatically by the destructor, but it can happen earlier
+// by calling the method Discard.  Both actions result in removing the
+// classifier from the parser's stack.
+
 template <typename Types>
 class ExpressionClassifier {
  public:
   enum ErrorKind : unsigned {
 #define DEFINE_ERROR_KIND(NAME, CODE) k##NAME = CODE,
     ERROR_CODES(DEFINE_ERROR_KIND)
 #undef DEFINE_ERROR_KIND
     kUnusedError = 15  // Larger than error codes; should fit in 4 bits
   };
 
@@ skipping 26 matching lines @@
 #define DEFINE_ALL_PRODUCTIONS(NAME, CODE) NAME |
     AllProductions = ERROR_CODES(DEFINE_ALL_PRODUCTIONS) /* | */ 0
 #undef DEFINE_ALL_PRODUCTIONS
   };
   // clang-format on
 
   enum FunctionProperties : unsigned {
     NonSimpleParameter = 1 << 0
   };
 
-  explicit ExpressionClassifier(const typename Types::Base* base,
+  explicit ExpressionClassifier(typename Types::Base* base,
                                 DuplicateFinder* duplicate_finder = nullptr)
-      : zone_(base->impl()->zone()),
+      : base_(base),
+        previous_(base->classifier_),
+        zone_(base->impl()->zone()),
         non_patterns_to_rewrite_(base->impl()->GetNonPatternList()),
         reported_errors_(base->impl()->GetReportedErrorList()),
         duplicate_finder_(duplicate_finder),
         invalid_productions_(0),
         function_properties_(0) {
+    base->classifier_ = this;
     reported_errors_begin_ = reported_errors_end_ = reported_errors_->length();
     non_pattern_begin_ = non_patterns_to_rewrite_->length();
   }

[nickie, 2016/08/30 09:30:15]

We probably should add, at the bottom of the class:

    DISALLOW_COPY_AND_ASSIGN(ExpressionClassifier);

[nickie, 2016/08/31 08:19:53]

Done.

 
-  ~ExpressionClassifier() { Discard(); }
+  V8_INLINE ~ExpressionClassifier() {
+    Discard();
+    if (base_->classifier_ == this) base_->classifier_ = previous_;
+  }
 
   V8_INLINE bool is_valid(unsigned productions) const {
     return (invalid_productions_ & productions) == 0;
   }
 
   V8_INLINE DuplicateFinder* duplicate_finder() const {
     return duplicate_finder_;
   }
 
   V8_INLINE bool is_valid_expression() const {
@@ skipping 252 matching lines @@
           reported_errors_->at(reported_errors_end_-1).kind =
               kArrowFormalParametersProduction;
         }
       }
     }
     reported_errors_->Rewind(reported_errors_end_);
     inner->reported_errors_begin_ = inner->reported_errors_end_ =
         reported_errors_end_;
   }
 
-  // Accumulate errors that can be arbitrarily deep in an expression.
-  // These correspond to the ECMAScript spec's 'Contains' operation
-  // on productions. This includes:
-  //
-  // - YieldExpression is disallowed in arrow parameters in a generator.
-  // - AwaitExpression is disallowed in arrow parameters in an async function.
-  // - AwaitExpression is disallowed in async arrow parameters.
-  //
-  V8_INLINE void AccumulateFormalParameterContainmentErrors(
-      ExpressionClassifier* inner) {
-    Accumulate(inner, FormalParameterInitializerProduction |
-                          AsyncArrowFormalParametersProduction);
-  }
-
   V8_INLINE int GetNonPatternBegin() const { return non_pattern_begin_; }
 
   V8_INLINE void Discard() {
     if (reported_errors_end_ == reported_errors_->length()) {
       reported_errors_->Rewind(reported_errors_begin_);
       reported_errors_end_ = reported_errors_begin_;
     }
     DCHECK_EQ(reported_errors_begin_, reported_errors_end_);
     DCHECK_LE(non_pattern_begin_, non_patterns_to_rewrite_->length());
     non_patterns_to_rewrite_->Rewind(non_pattern_begin_);
   }
 
+  ExpressionClassifier* previous() const { return previous_; }
+
  private:
   V8_INLINE const Error& reported_error(ErrorKind kind) const {
     if (invalid_productions_ & (1 << kind)) {
       for (int i = reported_errors_begin_; i < reported_errors_end_; i++) {
         if (reported_errors_->at(i).kind == kind)
           return reported_errors_->at(i);
       }
       UNREACHABLE();
     }
     // We should only be looking for an error when we know that one has
@@ skipping 16 matching lines @@
   // could be either after the existing errors of this classifier (i.e.,
   // in an inner classifier) or it could be an existing error (in case a
   // copy is needed).
   V8_INLINE void Copy(int i) {
     DCHECK_LT(i, reported_errors_->length());
     if (reported_errors_end_ != i)
       reported_errors_->at(reported_errors_end_) = reported_errors_->at(i);
     reported_errors_end_++;
   }
 
+  typename Types::Base* base_;
+  ExpressionClassifier* previous_;
   Zone* zone_;
   ZoneList<typename Types::Expression>* non_patterns_to_rewrite_;
   ZoneList<Error>* reported_errors_;
   DuplicateFinder* duplicate_finder_;
   // The uint16_t for non_pattern_begin_ will not be enough in the case,
   // e.g., of an array literal containing more than 64K inner array
   // literals with spreads, as in:
   // var N=65536; eval("var x=[];" + "[" + "[...x],".repeat(N) + "].length");
   // An implementation limit error in ParserBase::AddNonPatternForRewriting
   // will be triggered in this case.
@@ skipping 12 matching lines @@
 };
 
 
 #undef ERROR_CODES
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_EXPRESSION_CLASSIFIER_H