Emit an error for enum increments and decrements in C++ mode.

Fixes PR16394.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187955 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/DiagnosticSemaKinds.td

@@ -4882,6 +4882,8 @@ def note_member_declared_here : Note<
 def err_decrement_bool : Error<"cannot decrement expression of type bool">;
 def warn_increment_bool : Warning<
   "incrementing expression of type bool is deprecated">, InGroup<Deprecated>;
+def err_increment_decrement_enum : Error<
+  "cannot %select{decrement|increment}0 expression of enum type %1">;
 def err_catch_incomplete_ptr : Error<
   "cannot catch pointer to incomplete type %0">;
 def err_catch_incomplete_ref : Error<

lib/Sema/SemaExpr.cpp

@@ -8377,6 +8377,10 @@ static QualType CheckIncrementDecrementOperand(Sema &S, Expr *Op,
     }
     // Increment of bool sets it to true, but is deprecated.
     S.Diag(OpLoc, diag::warn_increment_bool) << Op->getSourceRange();
+  } else if (S.getLangOpts().CPlusPlus && ResType->isEnumeralType()) {
+    // Error on enum increments and decrements in C++ mode
+    S.Diag(OpLoc, diag::err_increment_decrement_enum) << IsInc << ResType;
+    return QualType();
   } else if (ResType->isRealType()) {
     // OK!
   } else if (ResType->isPointerType()) {

test/Sema/enum-increment.c

@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -fsyntax-only %s -verify
+// expected-no-diagnostics
+enum A { A1, A2, A3 };
+typedef enum A A;
+void test() {
+  A a;
+  a++;
+  a--;
+  ++a;
+  --a;
+  a = a + 1;
+  a = a - 1;
+}

test/SemaCXX/enum-increment.cpp

@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -fsyntax-only %s -verify
+
+enum A { A1, A2, A3 };
+void test() {
+  A a;
+  a++;  // expected-error{{cannot increment expression of enum type 'A'}}
+  a--;  // expected-error{{cannot decrement expression of enum type 'A'}}
+  ++a;  // expected-error{{cannot increment expression of enum type 'A'}}
+  --a;  // expected-error{{cannot decrement expression of enum type 'A'}}
+}
+
+enum B {B1, B2};
+inline B &operator++ (B &b) { b = B((int)b+1); return b; }
+inline B operator++ (B &b, int) { B ret = b; ++b; return b; }
+
+void foo(enum B b) { ++b; b++; }