[clang][diagnostics] added warning for possible enum compare typo #168445
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@llvm/pr-subscribers-clang Author: None (GrumpyPigSkin) ChangesAdded diagnosis and fixit comment for possible accidental comparison operator in an enum. Closes: #168146 Full diff: https://github.com/llvm/llvm-project/pull/168445.diff 3 Files Affected:
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 3e864475f22a1..b4da42584c78f 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/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.
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 086dd8ba1c670..ae3e6f2f49917 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/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())
diff --git a/clang/test/Sema/warn-enum-compare-typo.c b/clang/test/Sema/warn-enum-compare-typo.c
new file mode 100644
index 0000000000000..ee6ef0676b4b8
--- /dev/null
+++ b/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
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@AaronBallman Please could you advise on who is best to review :) |
🐧 Linux x64 Test Results
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ojhunt
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Nov 18, 2025
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ojhunt
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Conceptually a good idea, but I think it could be re-worked such that it is more accurate - avoiding both false-positives and negatives.
Also needs test coverage for other common idioms as we don't want a warning that fires all the time on valid/idiomatic code.
| 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 " |
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My inclination is for "may" rather than "likely", there also needs to be a way to suppress this warning locally - having to put pragmas around blocks is error prone, and using a global -Wno- flag loses the warning for all code.
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I would say "is potentially a typo for a shift operator '%1'"
As for the suppression, I think an explicit cast to bool would be a reasonable marker of "I meant to do that".
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Author
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I have gone with "is potentially a typo for a shift operator '%1'".
I used any explicit cast to suppress the warning, is that fine?
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✅ With the latest revision this PR passed the C/C++ code formatter. |
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Thanks! You should also add a release note to clang/docs/ReleaseNotes.rst so users know about the improved diagnostic.
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/166/builds/4081 Here is the relevant piece of the build log for the reference |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/27/builds/19207 Here is the relevant piece of the build log for the reference |
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Added diagnosis and fixit comment for possible accidental comparison operator in an enum.
Closes: #168146