C++: Safe accessing of elements of TranslationUnit::_tokens

Until now std::vector::at() was used to access the elements. This is
handy for debugging since an exception is thrown for invalid indices,
but it does not stop Qt Creator from crashing because exceptions are not
caught.

This is especially a problem for the parser, which has to look ahead via
LA(n), which accesses TranslationUnit::_tokens.

With this patch, explicit bounds checking is done before accessing the
elements and thus calls to

  std::vector::at() // bounds checking, throwing out_of_range

were replaced by calls to

  std::vector::operator[]() // no bounds checking, not throwing out_of_range

Measuring the parse time for the Qt Creator project shows that there is
no slowdown. In both cases, with and without the patch, about 15s are
needed on the authors machine.

Task-number: QTCREATORBUG-10453

Change-Id: I32b12a526ff7199bcadfc21a3deb5354063a3e3b
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/libs/3rdparty/cplusplus/TranslationUnit.cpp

@@ -40,6 +40,8 @@
 
 using namespace CPlusPlus;
 
+const Token TranslationUnit::nullToken;
+
 TranslationUnit::TranslationUnit(Control *control, const StringLiteral *fileId)
     : _control(control),
       _fileId(fileId),
@@ -58,9 +60,7 @@ TranslationUnit::TranslationUnit(Control *control, const StringLiteral *fileId)
 TranslationUnit::~TranslationUnit()
 {
     (void) _control->switchTranslationUnit(_previousTranslationUnit);
-    delete _tokens;
-    delete _comments;
-    delete _pool;
+    release();
 }
 
 Control *TranslationUnit::control() const
@@ -95,7 +95,7 @@ const char *TranslationUnit::spell(unsigned index) const
     if (! index)
         return 0;
 
-    return _tokens->at(index).spell();
+    return tokenAt(index).spell();
 }
 
 unsigned TranslationUnit::commentCount() const
@@ -105,19 +105,19 @@ const Token &TranslationUnit::commentAt(unsigned index) const
 { return _comments->at(index); }
 
 const Identifier *TranslationUnit::identifier(unsigned index) const
-{ return _tokens->at(index).identifier; }
+{ return tokenAt(index).identifier; }
 
 const Literal *TranslationUnit::literal(unsigned index) const
-{ return _tokens->at(index).literal; }
+{ return tokenAt(index).literal; }
 
 const StringLiteral *TranslationUnit::stringLiteral(unsigned index) const
-{ return _tokens->at(index).string; }
+{ return tokenAt(index).string; }
 
 const NumericLiteral *TranslationUnit::numericLiteral(unsigned index) const
-{ return _tokens->at(index).number; }
+{ return tokenAt(index).number; }
 
 unsigned TranslationUnit::matchingBrace(unsigned index) const
-{ return _tokens->at(index).close_brace; }
+{ return tokenAt(index).close_brace; }
 
 MemoryPool *TranslationUnit::memoryPool() const
 { return _pool; }
@@ -143,7 +143,7 @@ void TranslationUnit::tokenize()
     lex.setScanCommentTokens(true);
 
     std::stack<unsigned> braces;
-    _tokens->push_back(Token()); // the first token needs to be invalid!
+    _tokens->push_back(nullToken); // the first token needs to be invalid!
 
     pushLineOffset(0);
     pushPreprocessorLine(0, 1, fileId());
@@ -250,7 +250,8 @@ void TranslationUnit::tokenize()
         } else if (tk.f.kind == T_RBRACE && ! braces.empty()) {
             const unsigned open_brace_index = braces.top();
             braces.pop();
-            (*_tokens)[open_brace_index].close_brace = unsigned(_tokens->size());
+            if (open_brace_index < tokenCount())
+                (*_tokens)[open_brace_index].close_brace = unsigned(_tokens->size());
         } else if (tk.isComment()) {
             _comments->push_back(tk);
             continue; // comments are not in the regular token stream
@@ -507,13 +508,15 @@ void TranslationUnit::fatal(unsigned index, const char *format, ...)
 
 unsigned TranslationUnit::findPreviousLineOffset(unsigned tokenIndex) const
 {
-    unsigned lineOffset = _lineOffsets[findLineNumber(_tokens->at(tokenIndex).offset)];
+    unsigned lineOffset = _lineOffsets[findLineNumber(tokenAt(tokenIndex).offset)];
     return lineOffset;
 }
 
 bool TranslationUnit::maybeSplitGreaterGreaterToken(unsigned tokenIndex)
 {
-    Token &tok = _tokens->at(tokenIndex);
+    if (tokenIndex >= tokenCount())
+        return false;
+    Token &tok = (*_tokens)[tokenIndex];
     if (tok.kind() != T_GREATER_GREATER)
         return false;
 
@@ -538,9 +541,17 @@ bool TranslationUnit::maybeSplitGreaterGreaterToken(unsigned tokenIndex)
     return true;
 }
 
+void TranslationUnit::releaseTokensAndComments()
+{
+    delete _tokens;
+    _tokens = 0;
+    delete _comments;
+    _comments = 0;
+}
+
 void TranslationUnit::showErrorLine(unsigned index, unsigned column, FILE *out)
 {
-    unsigned lineOffset = _lineOffsets[findLineNumber(_tokens->at(index).offset)];
+    unsigned lineOffset = _lineOffsets[findLineNumber(tokenAt(index).offset)];
     for (const char *cp = _firstSourceChar + lineOffset + 1; *cp && *cp != '\n'; ++cp) {
         fputc(*cp, out);
     }
@@ -567,10 +578,5 @@ void TranslationUnit::resetAST()
 void TranslationUnit::release()
 {
     resetAST();
-    delete _tokens;
-    _tokens = 0;
-    delete _comments;
-    _comments = 0;
+    releaseTokensAndComments();
 }
-
-

src/libs/3rdparty/cplusplus/TranslationUnit.h

@@ -63,9 +63,11 @@ public:
 
     void setSource(const char *source, unsigned size);
 
-    unsigned tokenCount() const { return unsigned(_tokens->size()); }
-    const Token &tokenAt(unsigned index) const { return _tokens->at(index); }
-    int tokenKind(unsigned index) const { return _tokens->at(index).f.kind; }
+    unsigned tokenCount() const { return _tokens ? unsigned(_tokens->size()) : unsigned(0); }
+    const Token &tokenAt(unsigned index) const
+    { return _tokens && index < tokenCount() ? (*_tokens)[index] : nullToken; }
+
+    int tokenKind(unsigned index) const { return tokenAt(index).f.kind; }
     const char *spell(unsigned index) const;
 
     unsigned commentCount() const;
@@ -167,11 +169,14 @@ private:
         { return offset < other.offset; }
     };
 
+    void releaseTokensAndComments();
     unsigned findLineNumber(unsigned offset) const;
     unsigned findColumnNumber(unsigned offset, unsigned lineNumber) const;
     PPLine findPreprocessorLine(unsigned offset) const;
     void showErrorLine(unsigned index, unsigned column, FILE *out);
 
+    static const Token nullToken;
+
     Control *_control;
     const StringLiteral *_fileId;
     const char *_firstSourceChar;