[PATCH] Add new warning to -Wparentheses for mixing overloaded shift operators and comparison operators

[Richard Trieu]

On Tue, Apr 16, 2013 at 6:40 AM, David Blaikie <dblaikie at gmail.com> wrote:

>
> On Apr 10, 2013 10:04 AM, "Richard Trieu" <rtrieu at google.com> wrote:
> >
> > Streams commonly overload the << and >> operators for input and output.
>  However, these operators have higher precedence than comparison operators.
>  Code written like this:
> >
> > cout << 5 == 4;
> >
> > Is interpreted as:
> >
> > (cout << 5) == 4;
> >
> > Instead of:
> >
> > cout << (5 == 4);
>
> What sort of statistics on success rate do you have with this warning? I
> wonder if it would find many intentional uses when dealing with numeric
> user defined tyows,.
>
Prior to this patch, two reports of this type of bug were found and fixed.
 This warning has not triggered on any other code I've tested, true or
false positive.

> >
> > http://llvm-reviews.chandlerc.com/D650
> >
> > Files:
> >   lib/Sema/SemaExpr.cpp
> >   test/Sema/parentheses.cpp
> >   include/clang/Basic/DiagnosticSemaKinds.td
> >   include/clang/Basic/DiagnosticGroups.td
> >
> > Index: lib/Sema/SemaExpr.cpp
> > ===================================================================
> > --- lib/Sema/SemaExpr.cpp
> > +++ lib/Sema/SemaExpr.cpp
> > @@ -8819,6 +8819,27 @@
> >    }
> >  }
> >
> > +static void DiagnoseShiftCompare(Sema &S, SourceLocation OpLoc,
> > +                                 Expr *LHSExpr, Expr *RHSExpr) {
> > +  CXXOperatorCallExpr *OCE = dyn_cast<CXXOperatorCallExpr>(LHSExpr);
> > +  if (!OCE) return;
>
> These early returns seem a little hard to spot in a fairly dense/flat
> piece if code. Might benefit from putting the return on their own line
> and/or some comments (or perhaps this is easy enough to read with syntax
> highlighting)
>
> > +  FunctionDecl *FD = OCE->getDirectCallee();
> > +  if (!FD || !FD->isOverloadedOperator()) return;
> > +  OverloadedOperatorKind Kind = FD->getOverloadedOperator();
> > +  if (Kind != OO_LessLess && Kind != OO_GreaterGreater) return;
> > +  S.Diag(OpLoc, diag::warn_overloaded_shift_in_comparison)
> > +      << LHSExpr->getSourceRange() << RHSExpr->getSourceRange()
> > +      << (Kind == OO_LessLess);
> > +  SuggestParentheses(S, OpLoc,
> > +                     S.PDiag(diag::note_evaluate_comparison_first),
> > +                     SourceRange(OCE->getArg(1)->getLocStart(),
> > +                                 RHSExpr->getLocEnd()));
> > +  SuggestParentheses(S, OCE->getOperatorLoc(),
> > +                     S.PDiag(diag::note_precedence_silence)
> > +                         << (Kind == OO_LessLess ? "<<" : ">>"),
> > +                     OCE->getSourceRange());
> > +}
> > +
> >  /// DiagnoseBinOpPrecedence - Emit warnings for expressions with tricky
> >  /// precedence.
> >  static void DiagnoseBinOpPrecedence(Sema &Self, BinaryOperatorKind Opc,
> > @@ -8847,6 +8868,11 @@
> >      DiagnoseAdditionInShift(Self, OpLoc, LHSExpr, Shift);
> >      DiagnoseAdditionInShift(Self, OpLoc, RHSExpr, Shift);
> >    }
> > +
> > +  // Warn on overloaded shift operators and comparisons, such as:
> > +  // cout << 5 == 4;
> > +  if (BinaryOperator::isComparisonOp(Opc))
> > +    DiagnoseShiftCompare(Self, OpLoc, LHSExpr, RHSExpr);
> >  }
> >
> >  // Binary Operators.  'Tok' is the token for the operator.
> > Index: test/Sema/parentheses.cpp
> > ===================================================================
> > --- test/Sema/parentheses.cpp
> > +++ test/Sema/parentheses.cpp
> > @@ -29,6 +29,12 @@
> >    (void)(s << b ? "foo" : "bar"); // expected-warning {{operator '?:'
> has lower precedence than '<<'}} \
> >                                    // expected-note {{place parentheses
> around the '?:' expression to evaluate it first}} \
> >                                    // expected-note {{place parentheses
> around the '<<' expression to silence this warning}}
> > +  (void)(s << 5 == 1); // expected-warning {{overloaded operator << has
> lower precedence than comparison operator}} \
> > +                       // expected-note {{place parentheses around the
> '<<' expression to silence this warning}} \
> > +                       // expected-note {{place parentheses around
> comparison expression to evaluate it first}}
> > +  (void)(s >> 5 == 1); // expected-warning {{overloaded operator >> has
> lower precedence than comparison operator}} \
> > +                       // expected-note {{place parentheses around the
> '>>' expression to silence this warning}} \
> > +                       // expected-note {{place parentheses around
> comparison expression to evaluate it first}}
> >  }
> >
> >  struct S {
> > Index: include/clang/Basic/DiagnosticSemaKinds.td
> > ===================================================================
> > --- include/clang/Basic/DiagnosticSemaKinds.td
> > +++ include/clang/Basic/DiagnosticSemaKinds.td
> > @@ -4025,6 +4025,13 @@
> >  def warn_logical_and_in_logical_or : Warning<
> >    "'&&' within '||'">, InGroup<LogicalOpParentheses>;
> >
> > +def warn_overloaded_shift_in_comparison :Warning<
> > +  "overloaded operator %select{>>|<<}0 has lower precedence than "
> > +  "comparison operator">,
> > +  InGroup<OverloadedShiftOpParentheses>;
> > +def note_evaluate_comparison_first :Note<
> > +  "place parentheses around comparison expression to evaluate it
> first">;
> > +
> >  def warn_addition_in_bitshift : Warning<
> >    "operator '%0' has lower precedence than '%1'; "
> >    "'%1' will be evaluated first">, InGroup<ShiftOpParentheses>;
> > Index: include/clang/Basic/DiagnosticGroups.td
> > ===================================================================
> > --- include/clang/Basic/DiagnosticGroups.td
> > +++ include/clang/Basic/DiagnosticGroups.td
> > @@ -122,6 +122,7 @@
> >  def BitwiseOpParentheses: DiagGroup<"bitwise-op-parentheses">;
> >  def LogicalOpParentheses: DiagGroup<"logical-op-parentheses">;
> >  def ShiftOpParentheses: DiagGroup<"shift-op-parentheses">;
> > +def OverloadedShiftOpParentheses:
> DiagGroup<"overloaded-shift-op-parentheses">;
> >  def DanglingElse: DiagGroup<"dangling-else">;
> >  def DanglingField : DiagGroup<"dangling-field">;
> >  def DistributedObjectModifiers :
> DiagGroup<"distributed-object-modifiers">;
> > @@ -352,6 +353,7 @@
> >                              [LogicalOpParentheses,
> >                               BitwiseOpParentheses,
> >                               ShiftOpParentheses,
> > +                             OverloadedShiftOpParentheses,
> >                               ParenthesesOnEquality,
> >                               DanglingElse]>;
> >
> > _______________________________________________
> > cfe-commits mailing list
> > cfe-commits at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
> >
>
>
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