[clang][diagnostics] added warning for possible enum compare typo

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -13707,4 +13707,14 @@ def err_amdgcn_load_lds_size_invalid_value : Error<"invalid size value">;
 def note_amdgcn_load_lds_size_valid_value : Note<"size must be %select{1, 2, or 4|1, 2, 4, 12 or 16}0">;
 
 def err_amdgcn_coop_atomic_invalid_as : Error<"cooperative atomic requires a global or generic pointer">;
+
+def warn_comparison_in_enum_initializer
+    : Warning<"comparison operator '%0' in enumerator constant is likely a "
+              "typo for "
+              "the shift operator '%1'">,
+      InGroup<DiagGroup<"enum-compare-typo">>;
+
+def note_enum_compare_typo_suggest
+    : Note<"use '%0' to perform a bitwise shift">;
+
 } // end of sema component.

clang/lib/Sema/SemaDecl.cpp

@@ -20129,6 +20129,30 @@ EnumConstantDecl *Sema::CheckEnumConstant(EnumDecl *Enum,
   if (Val)
     Val = DefaultLvalueConversion(Val).get();
 
+  if (Val) {
+    if (const BinaryOperator *BinOp =
+            dyn_cast<BinaryOperator>(Val->IgnoreParenImpCasts())) {
+      if (BinOp->getOpcode() == BO_LT || BinOp->getOpcode() == BO_GT) {
+        const Expr *LHS = BinOp->getLHS()->IgnoreParenImpCasts();
+        if (const auto *IntLiteral = dyn_cast<IntegerLiteral>(LHS)) {
+          if (IntLiteral->getValue() == 1) {
+            auto suggestedOp = (BinOp->getOpcode() == BO_LT)
+                                   ? BinaryOperator::getOpcodeStr(BO_Shl)
+                                   : BinaryOperator::getOpcodeStr(BO_Shr);
+            SourceLocation OperatorLoc = BinOp->getOperatorLoc();
+
+            Diag(OperatorLoc, diag::warn_comparison_in_enum_initializer)
+                << BinOp->getOpcodeStr() << suggestedOp;
+
+            Diag(OperatorLoc, diag::note_enum_compare_typo_suggest)
+                << suggestedOp
+                << FixItHint::CreateReplacement(OperatorLoc, suggestedOp);
+          }
+        }
+      }
+    }
+  }
+
   if (Val) {
     if (Enum->isDependentType() || Val->isTypeDependent() ||
         Val->containsErrors())

clang/test/Sema/warn-enum-compare-typo.c

@@ -0,0 +1,38 @@
+// RUN: %clang_cc1 -fsyntax-only -Wenum-compare-typo -verify %s 
+// RUN: %clang_cc1 -fsyntax-only -Wenum-compare-typo -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
+
+enum E {
+  kOptionGood1 = 1ull << 0,
+  kOptionGood2 = 1ull >> 0,
+  // expected-warning@+3 {{comparison operator '<' in enumerator constant is likely a typo for the shift operator '<<'}} 
+  // expected-note@+2 {{use '<<' to perform a bitwise shift}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE+1]]:22-[[@LINE+1]]:23}:"<<"
+  kOptionBad1 = 1ull < 1,
+  // expected-warning@+3 {{comparison operator '>' in enumerator constant is likely a typo for the shift operator '>>'}}
+  // expected-note@+2 {{use '>>' to perform a bitwise shift}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE+1]]:19-[[@LINE+1]]:20}:">>"
+  kOptionBad2 = 1 > 3,
+  // expected-warning@+3 {{comparison operator '>' in enumerator constant is likely a typo for the shift operator '>>'}} 
+  // expected-note@+2 {{use '>>' to perform a bitwise shift}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE+1]]:20-[[@LINE+1]]:21}:">>"
+  kOptionBad3 = (1 > 2)
+};
+
+// Ensure the warning does not fire on valid code
+enum F {
+  kSomeValue = 10,
+  kComparison = kSomeValue > 5, // No warning
+  kMaxEnum = 255,
+  kIsValid = kMaxEnum > 0, // No warning
+  kSum = 10 + 20,          // No warning
+  kShift = 2 << 5          // No warning
+};
+
+// Ensure the diagnostic group works
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wenum-compare-typo"
+enum G {
+  kIgnored = 1 < 10 // No warning
+};
+#pragma clang diagnostic pop