Add warning group -Woverloaded-shift-op-parentheses to -Wparentheses. This

will fire on code such as:

  cout << x == 0;

which the compiler will intrepret as

  (cout << x) == 0;

This warning comes with two fixits attached to notes, one for parentheses to
silence the warning, and another to evaluate the comparison first.

llvm-svn: 179662

4 files changed, 47 insertions, 0 deletions

diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index a12a4f974ef..a7ef2185df2 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -122,6 +122,7 @@ def GlobalConstructors : DiagGroup<"global-constructors">;
 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 @@ def Parentheses : DiagGroup<"parentheses",
                             [LogicalOpParentheses,
                              BitwiseOpParentheses,
                              ShiftOpParentheses,
+                             OverloadedShiftOpParentheses,
                              ParenthesesOnEquality,
                              DanglingElse]>;
 
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index fd9ea51df5b..1330ad68b6d 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -4041,6 +4041,13 @@ def warn_bitwise_and_in_bitwise_or : Warning<
 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>;
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index cdfdc09e06e..ce60f9171fd 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -8877,6 +8877,33 @@ static void DiagnoseAdditionInShift(Sema &S, SourceLocation OpLoc,
   }
 }
 
+static void DiagnoseShiftCompare(Sema &S, SourceLocation OpLoc,
+                                 Expr *LHSExpr, Expr *RHSExpr) {
+  CXXOperatorCallExpr *OCE = dyn_cast<CXXOperatorCallExpr>(LHSExpr);
+  if (!OCE)
+    return;
+
+  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,
@@ -8905,6 +8932,11 @@ static void DiagnoseBinOpPrecedence(Sema &Self, BinaryOperatorKind Opc,
     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.
diff --git a/clang/test/Sema/parentheses.cpp b/clang/test/Sema/parentheses.cpp
index 145414a53ac..58edc0ba294 100644
--- a/clang/test/Sema/parentheses.cpp
+++ b/clang/test/Sema/parentheses.cpp
@@ -29,6 +29,12 @@ void f(Stream& s, bool b) {
   (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 {