Clang-tidy - Enum misuse check

[szepet]

Summary

The checker detects various cases when an enum is probably misused (as a bitmask).

For the heuristics suggestions and improvement ideas are welcome.

[hokein]

Please make sure the code align with LLVM code style (clang-format can help you to that).

clang-tidy/misc/EnumMisuseCheck.cpp

20

You can use std::distance(Enum->enumerator_begin(), Enum->enumerator_end()).

32

One variable declaration per line.

61

LLVM code style prefers to use preincrement (++I), the same below.

217

An unrelated comment.

clang-tidy/misc/EnumMisuseCheck.h

19

Fix FIXME.

24

Put it to private member.

28

As you defined a IsStrict option in the check, you need to override storeOptions method.

void EnumMisuseCheck::storeOptions(
    ClangTidyOptions::OptionMap &Opts) {
  Options.store(Opts, "IsStrict", IsStrict);
}

docs/clang-tidy/checks/misc-enum-misuse.rst

4

Could you add a few code examples here?

[Eugene.Zelenko]

Please mention this check in docs/ReleaseNotes.rst. See pre-4.0 branch versions as example.

clang-tidy/misc/EnumMisuseCheck.cpp

116

Please separate with empty line.

test/clang-tidy/misc-enum-misuse-weak.cpp

9

Please put closing }; on next line. Same in other places.

83

Please fix -Wextra-semi. Is next empty line excessive?

test/clang-tidy/misc-enum-misuse.cpp

42

Unnecessary empty line. Same at the end of function.

77

Please fix -Wextra-semi.

[etienneb]

drive-by, some comments.
Thanks for the check

clang-tidy/misc/EnumMisuseCheck.cpp

20

We tend to keep name meaningful and avoid abbreviation.
enumLen -> enumLength

35

nit: remove empty line

55

nit: static

81

nit: remove empty line

117

nit: const int x --> int x for all parameters

119

nit: line too long

127

A common pattern is:

if (const auto *DiffEnumOp = Result.Nodes.getNodeAs<BinaryOperator>("diffEnumOp")) {
   [...]
}

This way the scope is smaller and there is less chance to use it by mistake.

128

nit: no empty line

150

ditto for th "if (var = ...)" pattern

170

nit: remove the space after (s)

177

To be consistent with your comments, add newline here.

[szepet]

updating patch based on review comments

[aaron.ballman]

clang-tidy/misc/EnumMisuseCheck.cpp

31

I think this class can be replaced by std::minmax_element() over the EnumDec->enumerators() and then grabbing the actual values out of the resulting std::pair.

59

This function doesn't do what is described. It appears to be checking if the last value in the enumeration has all its bits set, not if the max value has all the bits set. e.g., it won't check:

enum E {
  MaxValue = 0xFFFFFFFF,
  First = 0,
  Second
};

clang-tidy/misc/EnumMisuseCheck.h

24

It is a private member already. I think this usage is fine.

[hokein]

Seems that you only uploaded the diff part, I only see the updated part of your patch now, and can't see the whole patch now (The review page says "Context not available"), could you upload the whole patch again?

docs/clang-tidy/checks/misc-enum-misuse.rst

31

Could you add some descriptions about what 1 stands for here? strict or non-strict? please leave a blank between "//" and comment words, the same below. Make sure the code here align with code style.

62

extra indentations.

[szepet]

full diff submitted

[etienneb]

some nits

docs/clang-tidy/checks/misc-enum-misuse.rst

38

nit: space after //
here and below.

38

nit: intervalls (typo)

test/clang-tidy/misc-enum-misuse-weak.cpp

49

you can remove "[misc-enum-misuse]" from the following line.
Only the first occurrence is enough.

[Prazek]

clang-tidy/misc/EnumMisuseCheck.cpp

20

s/\/\//\/\/\/

In other words, change to / (doxygen comment)

193

If the pointer returned from dyn_cast<EnumConstantDecl>(LhsDeclExpr->getDecl()) is assumed to be always not null, thn you can change it to cast<> (It will assert if null instead of returning nullptr)

docs/clang-tidy/checks/misc-enum-misuse.rst

30

I think all the code here needs to be indented by one or more to get into ..code:: block.

[szepet]

updates based on comments, counter and search functions replaced by std functions

[aaron.ballman]

clang-tidy/misc/EnumMisuseCheck.cpp

41

Doxygen comment here as well.

76

The wrapping for this comment is a bit strange, also should be using doxygen-style comments. Also, the grammar is a bit off for the comment. I would recommend:

Check if there are two or more enumerators that are not a power of 2 in the enum type, and that the enumeration contains enough elements to reasonably act as a bitmask. Exclude the case where the last enumerator is the sum of the lesser values or when it could contain consecutive values.

Also, I would call this isPossiblyBitMask instead of using "bit field" because a bit-field is a syntactic construct that is unrelated. Bitmask types are covered in the C++ standard under [bitmask.types] and are slightly different, but more closely related to what this check is looking for.

210

I think this diagnostic text is a bit confusing. The enum type shouldn't seem like a bit-field (but more like a bitmask), and I'm not certain what a misspelled number would be. I think the diagnostic is effectively saying that we guess this might be a bitmask, but some of the enumerator values don't make sense for that guess, and so this may be suspicious code -- but I really worry about the false positive rate for such a diagnostic. Have you run this check over a large body of work (like LLVM, Firefox, Chrome, etc)? If so, how do the diagnostics look?

Perhaps a different way to word the diagnostic is: "enum type used as a bitmask with an enumerator value that is not a power of 2" and place the diagnostic on the enumerator(s) that cause the problem rather than the enumeration as a whole.

213

s/bitmask/bitfield

215

Are these spurious parens around LhsConstant->getInitVal()?

220

Same comments here as above; if you can remove the duplicate code, that would be great, too.

clang-tidy/misc/EnumMisuseCheck.h

25

Can remove the private access specifier -- it's already private.

test/clang-tidy/misc-enum-misuse-weak.cpp

2

Please run clang-format over this file.

test/clang-tidy/misc-enum-misuse.cpp

2

Please run clang-format over this file.

[alexfh]

clang-tidy/misc/EnumMisuseCheck.cpp

29

I don't think the compound statement here is needed.

49

Please remove the outermost parentheses, they are superfluous.

57

nit: Please remove the empty line.

129

Please remove the empty line.

147

Formatting of the list seems rather uncommon for English text. Let's change to:

// Case 2:
//   a. ......
//   b. ......

(note the period after a and b, and Case N instead of 1. case).

165

No parentheses needed after !.

165

Braces should be used consistently in each if-else chain. Please add braces around the first if body.

173

No capitalization and trailing period needed.

225

Inner parentheses are not needed.

[alexfh]

clang-tidy/misc/EnumMisuseCheck.cpp

60

nit: The parameters are not iterators, so I'd change It1 and It2 to EnumConst1 and EnumConst2, E1 and E2, First and Second, Left and Right or something else not related to iterators. Same above in ValueRange and below in countNonPowOfTwoNum.

clang-tidy/misc/EnumMisuseCheck.h

26

I'd move the private section to the bottom of the class definition.

[szepet]

Changes based on comments.

clang-tidy/misc/EnumMisuseCheck.cpp

76

Thanks for the recommendations! As you can see my grammar and vocabulary is a "bit strange" so I really appreciated the correction!

210

Here you can see the results on LLVM. (weak options, less false positive)

error.txt2 KBDownload

Here I have to mention that the last 4 results could be combined into one, because it`s actually the usage of the same enum in different files. If you wish I could easily change it.

[alexfh]

clang-tidy/misc/EnumMisuseCheck.cpp

216

Diagnostic messages are not full sentences, so they shouldn't start with a capital letter and end with a period.

clang-tidy/misc/EnumMisuseCheck.h

27

1. Please move the constructor body to the .cpp file so that the code reading and storing options are together.
2. Let's use a global flag StrictMode (used by one more check currently: http://clang.llvm.org/extra/clang-tidy/checks/misc-argument-comment.html, clang-tidy/misc/ArgumentCommentCheck.cpp). It can still be configured separately for each check, but overall it improves consistency. Also, let's make it non-strict by default.
   
   Options.get(...)

should change to

StrictMode(Options.getLocalOrGlobal("StrictMode", 0) != 0)

docs/clang-tidy/checks/misc-enum-misuse.rst

22

Please enclose inline code snippets in backquotes (+=, |=, etc.). Many places in this file and in doxygen comments.

30

Should be .. code-block:: c++.

32

Code block should be indented. Please compile the doc and make sure the result seems reasonable.

32

Could you add some descriptions about what 1 stands for here? strict or non-strict? please leave a blank between "//" and comment words, the same below. Make sure the code here align with code style.

Still not addressed.

39

nit: space after //
here and below.

This is still not addressed.

test/clang-tidy/misc-enum-misuse-weak.cpp

3

The format still seems off.

67

Is the commented line needed?

test/clang-tidy/misc-enum-misuse.cpp

3

Doesn't seem to be done: the format is still off.

[szepet]

Changes based on comments, fix a cast to dyn_cast bug, description updated (hopefully it became more clear).

[szepet]

test/clang-tidy/misc-enum-misuse.cpp

4

Could you specify which part of the file seems off? I have run the clang format with the same options on testfiles as on the others.

[aaron.ballman]

test/clang-tidy/misc-enum-misuse.cpp

4

enum A { A = 1,
         B = 2,
         C = 4,
         D = 8,
         E = 16,
         F = 32,
         G = 63
};

should be:

enum A {
  A = 1,
  B = 2,
  C = 4,
  D = 8,
  E = 16,
  F = 32,
  G = 63
};

is what I was thinking was incorrect, but perhaps clang-format allows such constructs?

67

Do you intend to have the return 0; here?

[szepet]

cast to dyn-cast change in order to fix a bug, changes based on comments

[alexfh]

Close, but still a bunch of comments in the docs and a suggestion to fix a class of false positives.

clang-tidy/misc/EnumMisuseCheck.cpp

211

1. llvm/lib/MC/ELFObjectWriter.cpp:903 - the warning looks reasonable.
2. llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoderCommon.h:66 - the warning looks reasonable (ATTR_max doesn't seem to be useful for the bitmask enum).
3. llvm/tools/clang/lib/Basic/IdentifierTable.cpp:95 - two issues here:
   1. the "possibly contains misspelled number(s) " message could be more useful, if it specified which member corresponds to the possibly misspelled number
   2. I suppose, the check considers KEYALL = (0x1fffff & ~KEYNOMS18 & ~KEYNOOPENCL) to be incorrect. I think, it should exclude enum members initialized with a bit arithmetic expressions, since it's rather common to define aliases for a certain combination of flags.
4. llvm/tools/clang/lib/Frontend/Rewrite/RewriteModernObjC.cpp:5083 and friends - the warning looks reasonable, since it's hard to understand the motivation for the BLOCK_FIELD_IS_OBJECT = 3. If it's a combination of flags, it should be written as such, and the check should ignore enum members initialized with a bit arithmetic expression.

docs/clang-tidy/checks/misc-enum-misuse.rst

10

Too much indentation here.

39

1. Enum should not start with a capital letter, since it's a keyword.
2. Please indent the code block contents by 2 spaces (currently, it's indented by 1).
3. Please clang-format all code samples.

48

Commas should be used instead of semicolons.

55

Missing semicolon.

In general, please make sure code snippets are valid code. Otherwise, it creates unneeded obstacles in reading the code.

[szepet]

In order to decrease false positive rate, the bitmask specific checker part investigate only the enumconstans which was initilized by a literal. (If this is too strong it can be modified)

Renamed the checker to be more consistent with the checkers used for similar purpose.

Documentation code examples updated.

[alexfh]

Thank you for the updates!

Please re-run the check on LLVM to see what has changed.

clang-tidy/misc/SuspiciousEnumUsageCheck.cpp

53 ↗

(On Diff #71925)

nit: Add an empty line above.

61 ↗

(On Diff #71925)

nit: Add an empty line above.

67 ↗

(On Diff #71925)

nit: Please add braces, since the body doesn't fit on a line.

155 ↗

(On Diff #71925)

Why?

175 ↗

(On Diff #71925)

Use early return here.

208 ↗

(On Diff #71925)

One variable definition at a time, please.

216 ↗

(On Diff #71925)

Use early return here.

clang-tidy/misc/SuspiciousEnumUsageCheck.h

32–35 ↗

(On Diff #71925)

These can be just static constants in the .cpp file. Apart from that, const char X[] = ...; is a better way to define string constants, otherwise you would have to go with const char * const X = ...; to make the pointer const as well.

docs/clang-tidy/checks/misc-suspicious-enum-usage.rst

4 ↗

(On Diff #71925)

This line should be aligned with the line above.

9 ↗

(On Diff #71925)

Remove two spaces at the start of the line.

11 ↗

(On Diff #71925)

There's no "Weak" option, it's the "Strict" option set to false / 0.

12 ↗

(On Diff #71925)

Please use the :option: notation and add the option description (.. option:: ...). See, for example, modernize-use-emplace.rst.

31 ↗

(On Diff #71925)

This notation is used to make the previous line a heading. Doesn't seem to be the case here. See http://llvm.org/docs/SphinxQuickstartTemplate.html for some examples. Please also try to build your docs to check for obvious issues.

test/clang-tidy/misc-suspicious-enum-usage-strict.cpp

18 ↗

(On Diff #71925)

Add check lines for notes as well (I don't think you'll be able to use [[@LINE]] for most of them, but you can probably just skip the line.

[szepet]

Updates based on comments (the testfile note comments will be added in the next commit)

Some changes in the algorithm/design:
In non-strict mode the checker will only investigate the operations between different enum types.
In strict mode we check the suspicious bitmasks too.
(In the previous comments we always talked about only the strict mode heuristics and looked on the strict results. )

So strict mode results in this revision where we investigate only the literals:

results.txt4 KBDownload

[szepet]

clang-tidy/misc/SuspiciousEnumUsageCheck.cpp

155 ↗

(On Diff #71925)

Because the hasDisjointValueRange function could not decide the values properly. So in case of an empty Enum it would not make sense. Fortunately we know that the empty case should not be reported so used early return on this.

That is why this is needed if we want a deterministic check.

[szepet]

Note message checks added to testfiles.

[szepet]

What is your opinion about the new results? I hope the checker can make it into 4.0.

[alexfh]

LG with one nit. Feel free to ping earlier next time.

clang-tidy/misc/SuspiciousEnumUsageCheck.cpp

170–171 ↗

(On Diff #73439)

Looks like this is the same as in case 3 below, so you could just move this check out of the branch and remove the duplication below.

[alexfh]

clang-tidy/misc/SuspiciousEnumUsageCheck.cpp

155 ↗

(On Diff #71925)

BTW, this might make sense to be explained in the comment in the code itself (code review comments are bad means of documenting code).

[szepet]

Minor changes to improve the readability of the code according to comments.

[alexfh]

A few more notes, all fine for a follow up.

clang-tidy/misc/SuspiciousEnumUsageCheck.cpp

202 ↗

(On Diff #81848)

Looks like you're doing exactly same thing twice for lhs and rhs. Pull this out to a function. Fine for a follow up.

212–213 ↗

(On Diff #81848)

There's not much value in these variables.

215–219 ↗

(On Diff #81848)

This code doesn't need the lhs/rhs variable declared above it. Move it up.

220–227 ↗

(On Diff #81848)

This code can be pulled to a function / method to avoid repeating it twice (starting from the const auto *LhsExpr = Result.Nodes.getNodeAs<Expr>("lhsExpr"); part).

docs/clang-tidy/checks/misc-suspicious-enum-usage.rst

31 ↗

(On Diff #71925)

This is not done yet.

[aaron.ballman]

clang-tidy/misc/SuspiciousEnumUsageCheck.cpp

31 ↗

(On Diff #81848)

Please drop the (s) from the diagnostic. The phrase "but some literal are not" is incorrect. Alternatively, you could use the %plural diagnostic modifier (see note_constexpr_baa_value_insufficient_alignment in DiagnosticASTKinds.td for an example usage).

[szepet]

The requested changes have been made.
Some more refactor on the Case2 since it is the same as the LHS/RHS case. Moved more common statements out of the branch (Case2-3) for better readabilty. (And less code duplication.)

clang-tidy/misc/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS support)
 
 add_clang_library(clangTidyMiscModule
   ArgumentCommentCheck.cpp
   AssertSideEffectCheck.cpp
   MisplacedConstCheck.cpp
   UnconventionalAssignOperatorCheck.cpp
   BoolPointerImplicitConversionCheck.cpp
   DanglingHandleCheck.cpp
   DefinitionsInHeadersCheck.cpp
+  EnumMisuseCheck.cpp
   FoldInitTypeCheck.cpp
   ForwardDeclarationNamespaceCheck.cpp
   InaccurateEraseCheck.cpp
   IncorrectRoundings.cpp
   InefficientAlgorithmCheck.cpp
   MacroParenthesesCheck.cpp
   MacroRepeatedSideEffectsCheck.cpp
   MiscTidyModule.cpp

clang-tidy/misc/EnumMisuseCheck.h

+//===--- EnumMisuseCheck.h - clang-tidy--------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_ENUM_MISUSE_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_ENUM_MISUSE_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace misc {
+
+/// FIXME: Write a short description.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/misc-enum-misuse.html
+class EnumMisuseCheck : public ClangTidyCheck {
+    const bool IsStrict;
+
+  public:
+    EnumMisuseCheck(StringRef Name, ClangTidyContext *Context)
+        : ClangTidyCheck(Name, Context), IsStrict(Options.get("IsStrict", 1)) {}
+    void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+    void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace misc
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_ENUM_MISUSE_H

clang-tidy/misc/EnumMisuseCheck.cpp

+//===--- EnumMisuseCheck.cpp - clang-tidy----------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "EnumMisuseCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace misc {
+
+// Return the number of EnumConstantDecls in an EnumDecl.
+static int enumLen(const EnumDecl *EnumDec) {
+  int Counter = 0;
+
+  for (auto E : EnumDec->enumerators()) {
+    (void)E;
+    Counter++;
+  }
+  return Counter;
+}
+
+// Stores a min and a max value which describe an interval.
+struct ValueRange {
+  llvm::APSInt MinVal, MaxVal;
+
+  ValueRange(const EnumDecl *EnumDec) {
+
+    llvm::APSInt BeginVal = EnumDec->enumerator_begin()->getInitVal();
+    MinVal = BeginVal;
+    MaxVal = BeginVal;
+    for (auto E : EnumDec->enumerators()) {
+      llvm::APSInt Val = E->getInitVal();
+      if (Val < MinVal)
+        MinVal = Val;
+      else if (Val > MaxVal)
+        MaxVal = Val;
+    }
+  }
+};
+
+static bool hasDisjointValueRange(const EnumDecl *Enum1,
+                                  const EnumDecl *Enum2) {
+  ValueRange Range1(Enum1), Range2(Enum2);
+  return ((Range1.MaxVal < Range2.MinVal) || (Range2.MaxVal < Range1.MinVal));
+}
+
+bool hasCommonBit(const llvm::APSInt &Val1, const llvm::APSInt &Val2) {
+  return (Val1 & Val2).getExtValue();
+}
+
+bool isMaxValAllBitSet(const EnumDecl *EnumDec) {
+  for (auto I = EnumDec->enumerator_begin(), E = EnumDec->enumerator_end();
+       I != E; I++) {
+    auto It = I;
+    if (++It == E)
+      return I->getInitVal().countTrailingOnes() ==
+             I->getInitVal().getActiveBits();
+  }
+  llvm_unreachable("enum failed max value");
+}
+
+static int countNonPowOfTwoNum(const EnumDecl *EnumDec) {
+  int Counter = 0;
+  for (auto E : EnumDec->enumerators()) {
+    const llvm::APSInt Val = E->getInitVal();
+    if (!Val.isPowerOf2() && Val.getExtValue())
+      Counter++;
+  }
+  return Counter;
+}
+
+void EnumMisuseCheck::registerMatchers(MatchFinder *Finder) {
+
+  const auto enumExpr = [](StringRef RefName, StringRef DeclName) {
+    return allOf(ignoringImpCasts(expr().bind(RefName)),
+                 ignoringImpCasts(hasType(enumDecl().bind(DeclName))));
+  };
+
+  Finder->addMatcher(
+      binaryOperator(hasOperatorName("|"), hasLHS(enumExpr("", "enumDecl")),
+                     hasRHS(allOf(enumExpr("", "otherEnumDecl"),
+                                  ignoringImpCasts(hasType(enumDecl(
+                                      unless(equalsBoundNode("enumDecl"))))))))
+          .bind("diffEnumOp"),
+      this);
+
+  Finder->addMatcher(
+      binaryOperator(anyOf(hasOperatorName("+"), hasOperatorName("|")),
+                     hasLHS(enumExpr("lhsExpr", "enumDecl")),
+                     hasRHS(allOf(enumExpr("rhsExpr", ""),
+                                  ignoringImpCasts(hasType(
+                                      enumDecl(equalsBoundNode("enumDecl")))))))
+          .bind("enumBinOp"),
+      this);
+
+  Finder->addMatcher(
+      binaryOperator(anyOf(hasOperatorName("+"), hasOperatorName("|")),
+                     hasEitherOperand(
+                         allOf(hasType(isInteger()), unless(enumExpr("", "")))),
+                     hasEitherOperand(enumExpr("enumExpr", "enumDecl"))),
+      this);
+
+  Finder->addMatcher(
+      binaryOperator(anyOf(hasOperatorName("|="), hasOperatorName("+=")),
+                     hasRHS(enumExpr("enumExpr", "enumDecl"))),
+      this);
+}
+// if there is only one not power-of-2 value in the enum unless it is
+static bool isPossiblyBitField(const int NonPowOfTwoCounter, const int EnumLen,
+                               const ValueRange &VR, const EnumDecl *EnumDec) {
+  return NonPowOfTwoCounter >= 1 && NonPowOfTwoCounter <= 2 && NonPowOfTwoCounter < enumLen(EnumDec) / 2 &&
+         (VR.MaxVal - VR.MinVal != EnumLen - 1) && !(NonPowOfTwoCounter == 1 && isMaxValAllBitSet(EnumDec));
+}
+
+void EnumMisuseCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *DiffEnumOp = Result.Nodes.getNodeAs<BinaryOperator>("diffEnumOp");
+
+  // 1. case: The two enum values come from different types.
+  if (DiffEnumOp) {
+
+    const auto *EnumDec = Result.Nodes.getNodeAs<EnumDecl>("enumDecl");
+    const auto *OtherEnumDec =
+        Result.Nodes.getNodeAs<EnumDecl>("otherEnumDecl");
+
+    if (EnumDec->enumerator_begin() == EnumDec->enumerator_end() ||
+        OtherEnumDec->enumerator_begin() == OtherEnumDec->enumerator_end())
+      return;
+
+    if (!hasDisjointValueRange(EnumDec, OtherEnumDec))
+      diag(DiffEnumOp->getOperatorLoc(),
+           "enum values are from different enum types");
+
+    return;
+  }
+
+  // 2. case:
+  //   a, Investigating the right hand side of += or |= operator.
+  //   b, When the operator is | or + but only one of them is an
+  //      EnumExpr
+  const auto *EnumExpr = Result.Nodes.getNodeAs<Expr>("enumExpr");
+
+  if (EnumExpr) {
+    if (!IsStrict)
+      return;
+    const auto *EnumDec = Result.Nodes.getNodeAs<EnumDecl>("enumDecl");
+    ValueRange VR(EnumDec);
+    int EnumLen = enumLen(EnumDec);
+    int NonPowOfTwoCounter = countNonPowOfTwoNum(EnumDec);
+    if (isPossiblyBitField(NonPowOfTwoCounter, EnumLen, VR, EnumDec)) {
+      const auto *EnumDecExpr = dyn_cast<DeclRefExpr>(EnumExpr);
+      const auto *EnumConstDecl =
+          EnumDecExpr ? dyn_cast<EnumConstantDecl>(EnumDecExpr->getDecl())
+                      : nullptr;
+
+      if (EnumConstDecl && !(EnumConstDecl->getInitVal().isPowerOf2()))
+        diag(EnumExpr->getExprLoc(), "enum value is not power-of-2 unlike "
+                                     "most of the other values in the enum "
+                                     "type");
+      else if (!EnumConstDecl) {
+        diag(EnumDec->getInnerLocStart(), "enum type seems like a bitfield but "
+                                          "possibly contains misspelled "
+                                          "number(s) ");
+        diag(EnumExpr->getExprLoc(), "Used here as a bitfield.",
+             DiagnosticIDs::Note);
+      }
+    }
+    return;
+  }
+  // 3. case
+  // | or + operator where both argument comes from the same enum type
+
+  const auto *EnumBinOp = Result.Nodes.getNodeAs<BinaryOperator>("enumBinOp");
+
+  const auto *EnumDec = Result.Nodes.getNodeAs<EnumDecl>("enumDecl");
+
+  const auto *LhsExpr = Result.Nodes.getNodeAs<Expr>("lhsExpr");
+  const auto *RhsExpr = Result.Nodes.getNodeAs<Expr>("rhsExpr");
+
+  const auto *LhsDecExpr = dyn_cast<DeclRefExpr>(LhsExpr);
+  const auto *RhsDecExpr = dyn_cast<DeclRefExpr>(RhsExpr);
+
+  const auto *LhsConstant =
+      LhsDecExpr ? dyn_cast<EnumConstantDecl>(LhsDecExpr->getDecl()) : nullptr;
+  const auto *RhsConstant =
+      RhsDecExpr ? dyn_cast<EnumConstantDecl>(RhsDecExpr->getDecl()) : nullptr;
+  bool LhsVar = !LhsConstant, RhsVar = !RhsConstant;
+
+  if (!IsStrict && (LhsVar || RhsVar))
+    return;
+
+  int NonPowOfTwoCounter = countNonPowOfTwoNum(EnumDec);
+  ValueRange VR(EnumDec);
+  int EnumLen = enumLen(EnumDec);
+  if (isPossiblyBitField(NonPowOfTwoCounter, EnumLen, VR, EnumDec) &&
+      (IsStrict ||
+       (EnumBinOp->isBitwiseOp() && RhsConstant && LhsConstant &&
+        hasCommonBit(LhsConstant->getInitVal(), RhsConstant->getInitVal())))) {
+    if (LhsVar) {
+      diag(EnumDec->getInnerLocStart(), "enum type seems like a bitfield but "
+                                        "possibly contains misspelled "
+                                        "number(s)");
+      diag(EnumExpr->getExprLoc(), "Used here as a bitfield.",
+           DiagnosticIDs::Note);
+    } else if (!(LhsConstant->getInitVal()).isPowerOf2())
+      diag(LhsExpr->getExprLoc(), "left hand side value is not power-of-2 "
+                                  "unlike most other values in the enum type");
+
+    if (RhsVar) {
+      // if (LhsVar)
+      //   return;
+      diag(EnumDec->getInnerLocStart(), "enum type seems like a bitfield but "
+                                        "possibly contains misspelled "
+                                        "number(s)");
+      diag(EnumExpr->getExprLoc(), "Used here as a bitfield.",
+           DiagnosticIDs::Note);
+    } else if (!(RhsConstant->getInitVal()).isPowerOf2())
+      diag(RhsExpr->getExprLoc(), "right hand side value is not power-of-2 "
+                                  "unlike most other values in the enum type");
+  }
+}
+
+} // namespace misc
+} // namespace tidy
+} // namespace clang

clang-tidy/misc/MiscTidyModule.cpp

 #include "../ClangTidyModuleRegistry.h"
 #include "ArgumentCommentCheck.h"
 #include "AssertSideEffectCheck.h"
 #include "MisplacedConstCheck.h"
 #include "UnconventionalAssignOperatorCheck.h"
 #include "BoolPointerImplicitConversionCheck.h"
 #include "DanglingHandleCheck.h"
 #include "DefinitionsInHeadersCheck.h"
+#include "EnumMisuseCheck.h"
 #include "FoldInitTypeCheck.h"
 #include "ForwardDeclarationNamespaceCheck.h"
 #include "InaccurateEraseCheck.h"
 #include "IncorrectRoundings.h"
 #include "InefficientAlgorithmCheck.h"
 #include "MacroParenthesesCheck.h"
 #include "MacroRepeatedSideEffectsCheck.h"
 #include "MisplacedWideningCastCheck.h"
void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
     CheckFactories.registerCheck<UnconventionalAssignOperatorCheck>(
         "misc-unconventional-assign-operator");
     CheckFactories.registerCheck<BoolPointerImplicitConversionCheck>(
         "misc-bool-pointer-implicit-conversion");
     CheckFactories.registerCheck<DanglingHandleCheck>(
         "misc-dangling-handle");
     CheckFactories.registerCheck<DefinitionsInHeadersCheck>(
         "misc-definitions-in-headers");
+    CheckFactories.registerCheck<EnumMisuseCheck>(
+        "misc-enum-misuse");
     CheckFactories.registerCheck<FoldInitTypeCheck>(
         "misc-fold-init-type");
     CheckFactories.registerCheck<ForwardDeclarationNamespaceCheck>(
         "misc-forward-declaration-namespace");
     CheckFactories.registerCheck<InaccurateEraseCheck>(
         "misc-inaccurate-erase");
     CheckFactories.registerCheck<IncorrectRoundings>(
         "misc-incorrect-roundings");

docs/clang-tidy/checks/list.rst

.. toctree::
    llvm-include-order
    llvm-namespace-comment
    llvm-twine-local
    misc-argument-comment
    misc-assert-side-effect
    misc-bool-pointer-implicit-conversion
    misc-dangling-handle
    misc-definitions-in-headers
+   misc-enum-misuse
    misc-fold-init-type
    misc-forward-declaration-namespace
    misc-inaccurate-erase
    misc-incorrect-roundings
    misc-inefficient-algorithm
    misc-macro-parentheses
    misc-macro-repeated-side-effects
    misc-misplaced-const

docs/clang-tidy/checks/misc-enum-misuse.rst

+.. title:: clang-tidy - misc-enum-misuse
+
+misc-enum-misuse
+================
+
+The checker detects various cases when an enum is probably misused (as a bitfield).
+  1. When "add" or "bitwise or" is used between two enum which come from different
+     types and these types valuerange's are not disjoint.
+
+  In the following cases you can choose either "Strict" or "Weak" option.
+  In "Strict" mode we check if the used EnumConstantDecl type contains almost
+  only pow-of-2 numbers and the non pow-of-2 numbers at most the third of the
+  enum type. (At the same time maximum 2 can be different and we assume that in
+  this case one of them can be the ALL options so the other is misspelled.) So
+  whenever it is used we diagnose a misuse and give a warning.
+
+  In the "Weak" case we only say it is misused if on the both side of the |
+  operator the EnumConstantDecls have common bit so we could lose information
+  (and all the "Strict" conditions).
+
+  2. Investigating the right hand side of += or |= operator. (only in "Strict")
+  3. Check only the enum value side of a | or + operator if one of them is not
+     enum val. (only in "Strict")
+  4. Check both side of | or + operator where the enum values are from the same
+     enum type.

test/clang-tidy/misc-enum-misuse-weak.cpp

+// RUN: %check_clang_tidy %s misc-enum-misuse %t -- -config="{CheckOptions: [{key: misc-enum-misuse.IsStrict, value: 1}]}" --
+
+enum A { A = 1,
+         B = 2,
+         C = 4,
+         D = 8,
+         E = 16,
+         F = 32,
+         G = 63 };
+
+enum X { X = 8,
+         Y = 16,
+         Z = 4 };
+// CHECK-MESSAGES: :[[@LINE+1]]:1: warning: enum type seems like a bitfield but possibly contains misspelled number(s) [misc-enum-misuse]
+enum PP { P = 2,
+          Q = 3,
+          R = 4,
+          S = 8,
+          T = 16,
+          U = 31};
+
+enum { H,
+       I,
+       J,
+       K,
+       L };
+
+enum Days { Monday,
+            Tuesday,
+            Wednesday,
+            Thursday,
+            Friday,
+            Saturday,
+            Sunday };
+
+Days bestDay() {
+  return Friday;
+}
+
+int trigger() {
+  if (bestDay() | A)
+    return 1;
+  // CHECK-MESSAGES: :[[@LINE-2]]:17: warning: enum values are from different enum types [misc-enum-misuse]
+  if (I | Y)
+    return 1;
+  // CHECK-MESSAGES: :[[@LINE-2]]:9: warning: enum values are from different enum types [misc-enum-misuse]
+  if (P + Q == R)
+    return 1;
+  // CHECK-MESSAGES: :[[@LINE-2]]:11: warning: right hand side value is not power-of-2 unlike most other values in the enum type [misc-enum-misuse]
+  else if ((Q | R) == T)
+    return 1;
+  // CHECK-MESSAGES: :[[@LINE-2]]:13: warning: left hand side value is not power-of-2 unlike most other values in the enum type [misc-enum-misuse]
+  else
+    int k = T | Q;
+  // CHECK-MESSAGES: :[[@LINE-1]]:17: warning: right hand side value is not power-of-2 unlike most other values in the enum type [misc-enum-misuse]
+  unsigned p = R;
+  PP pp = Q;
+  p |= pp;
+  // Line 60 triggers the LINE:18 warning
+  p = A | G;
+  //p = G | X;
+    return 0;
+}
+
+int dont_trigger() {
+  int a = 1, b = 5;
+  int c = a + b;
+  int d = c | H, e = b * a;
+  a = B | C;
+  b = X | Z;
+ 
+  unsigned bitflag;
+  enum A aa = B;
+  bitflag = aa | C;
+
+  if (Tuesday != Monday + 1 ||
+      Friday - Thursday != 1 ||
+      Sunday + Wednesday == (Sunday | Wednesday))
+    return 1;
+  if (H + I + L == 42)
+    return 1;
+  return 42;
+};
+

test/clang-tidy/misc-enum-misuse.cpp

+// RUN: %check_clang_tidy %s misc-enum-misuse %t -- -config="{CheckOptions: [{key: misc-enum-misuse.IsStrict, value: 0}]}" --
+
+enum Empty {};
+
+enum A { A = 1,
+         B = 2,
+         C = 4,
+         D = 8,
+         E = 16,
+         F = 32,
+         G = 63 };
+
+enum X { X = 8,
+         Y = 16,
+         Z = 4 };
+
+enum {P = 2,
+         Q = 3,
+         R = 4,
+         S = 8,
+         T = 16 };
+
+enum { H,
+       I,
+       J,
+       K,
+       L };
+
+enum Days { Monday,
+            Tuesday,
+            Wednesday,
+            Thursday,
+            Friday,
+            Saturday,
+            Sunday };
+
+Days bestDay() {
+  return Friday;
+}
+
+int trigger() {
+
+  if (bestDay() | A)
+    return 1;
+  // CHECK-MESSAGES: :[[@LINE-2]]:17: warning: enum values are from different enum types [misc-enum-misuse]
+  if (I | Y)
+    return 1;
+  // CHECK-MESSAGES: :[[@LINE-2]]:9: warning: enum values are from different enum types [misc-enum-misuse]
+  unsigned p;
+  p = Q | P; 
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: left hand side value is not power-of-2 unlike most other values in the enum type [misc-enum-misuse]
+
+}
+
+int dont_trigger() {
+  if (A + G == E)
+    return 1;
+  else if ((Q | R) == T)
+    return 1;
+  else
+    int k = T | Q;
+  return 0;
+  Empty EmptyVal;
+  int emptytest = EmptyVal | B;
+  int a = 1, b = 5;
+  int c = a + b;
+  int d = c | H, e = b * a;
+  a = B | C;
+  b = X | Z;
+  if (Tuesday != Monday + 1 ||
+      Friday - Thursday != 1 ||
+      Sunday + Wednesday == (Sunday | Wednesday))
+    return 1;
+  if (H + I + L == 42)
+    return 1;
+  return 42;
+};