[clang-tools-extra] [clang-tidy] Add new check bugprone-tagged-union-member-count (PR #89925)

[Kristóf Umann via cfe-commits]

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@@ -0,0 +1,182 @@
+//===--- TaggedUnionMemberCountCheck.cpp - clang-tidy ---------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "TaggedUnionMemberCountCheck.h"
+#include "../utils/OptionsUtils.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallSet.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::bugprone {
+
+TaggedUnionMemberCountCheck::TaggedUnionMemberCountCheck(
+    StringRef Name, ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      StrictModeIsEnabled(Options.get(StrictModeIsEnabledOptionName, true)),
+      CountingEnumHeuristicIsEnabled(
+          Options.get(CountingEnumHeuristicIsEnabledOptionName, true)),
+      RawCountingEnumPrefixes(Options.get(CountingEnumPrefixesOptionName, "")),
+      RawCountingEnumSuffixes(
+          Options.get(CountingEnumSuffixesOptionName, "count")),
+      ParsedCountingEnumPrefixes(
+          utils::options::parseStringList(RawCountingEnumPrefixes)),
+      ParsedCountingEnumSuffixes(
+          utils::options::parseStringList(RawCountingEnumSuffixes)) {}
+
+void TaggedUnionMemberCountCheck::storeOptions(
+    ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, StrictModeIsEnabledOptionName, StrictModeIsEnabled);
+  Options.store(Opts, CountingEnumHeuristicIsEnabledOptionName,
+                CountingEnumHeuristicIsEnabled);
+  Options.store(Opts, CountingEnumPrefixesOptionName, RawCountingEnumPrefixes);
+  Options.store(Opts, CountingEnumSuffixesOptionName, RawCountingEnumSuffixes);
+}
+
+void TaggedUnionMemberCountCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      recordDecl(
+          allOf(anyOf(isStruct(), isClass()),
+                has(fieldDecl(hasType(qualType(hasCanonicalType(recordType()))))
+                        .bind("union")),
+                has(fieldDecl(hasType(qualType(hasCanonicalType(enumType()))))
+                        .bind("tags"))))
+          .bind("root"),
+      this);
+}
+
+static bool isUnion(const FieldDecl *R) {
+  return R->getType().getCanonicalType().getTypePtr()->isUnionType();
+}
+
+static bool isEnum(const FieldDecl *R) {
+  return R->getType().getCanonicalType().getTypePtr()->isEnumeralType();
+}
+
+static bool hasMultipleUnionsOrEnums(const RecordDecl *Rec) {
+  return llvm::count_if(Rec->fields(), isUnion) > 1 ||
+         llvm::count_if(Rec->fields(), isEnum) > 1;
+}
+
+static bool signEquals(const llvm::APSInt &A, const llvm::APSInt &B) {
+  return (A.isNegative() && B.isNegative()) ||
+         (A.isStrictlyPositive() && B.isStrictlyPositive()) ||
+         (A.isZero() && B.isZero());
+}
+
+static bool greaterBySign(const llvm::APSInt &A, const llvm::APSInt &B) {
+  return (A.isNonNegative() && B.isNegative()) ||
+         (A.isStrictlyPositive() && B.isNonPositive());
+}
+
+bool TaggedUnionMemberCountCheck::isCountingEnumLikeName(
+    StringRef Name) const noexcept {
+  if (llvm::any_of(ParsedCountingEnumPrefixes,
+                   [&Name](const StringRef &prefix) -> bool {
+                     return Name.starts_with_insensitive(prefix);
+                   }))
+    return true;
+  if (llvm::any_of(ParsedCountingEnumSuffixes,
+                   [&Name](const StringRef &suffix) -> bool {
+                     return Name.ends_with_insensitive(suffix);
+                   }))
+    return true;
+  return false;
+}
+
+size_t TaggedUnionMemberCountCheck::getNumberOfValidEnumValues(
+    const EnumDecl *Ed) const noexcept {
+  bool FoundMax = false;
+  llvm::APSInt MaxTagValue;
+  llvm::SmallSet<llvm::APSInt, 32> EnumValues;
+
+  // Heuristic for counter enum constants.
+  //
+  //   enum tag_with_counter {
+  //     tag1,
+  //     tag2,
+  //     tag_count, <-- Searching for these enum constants
+  //   };
+  //
+  // The final tag count is decreased by 1 if and only if:
+  // 1. There is only one counting enum constant,
+  // 2. The counting enum constant is the last enum constant that is defined,
+  // 3. The value of the counting enum constant is the largest out of every enum
+  //    constant.
+  // The 'ce' prefix is a shorthand for 'counting enum'.
+  size_t CeCount = 0;
+  bool IsLast = false;
+  llvm::APSInt CeValue = llvm::APSInt::get(0);
+
+  for (const auto &&[index, enumerator] : llvm::enumerate(Ed->enumerators())) {
+    const llvm::APSInt Val = enumerator->getInitVal();
+    EnumValues.insert(Val);
+    if (FoundMax) {
+      if (greaterBySign(Val, MaxTagValue) ||
+          (signEquals(Val, MaxTagValue) && Val > MaxTagValue)) {
+        MaxTagValue = Val;
+      }
+    } else {
+      MaxTagValue = Val;
+      FoundMax = true;
+    }
+
+    if (CountingEnumHeuristicIsEnabled) {
+      if (isCountingEnumLikeName(enumerator->getName())) {
+        IsLast = true;
+        CeValue = Val;
+        CeCount += 1;
+      } else {
+        IsLast = false;
+      }
+    }
+  }
+
+  size_t ValidValuesCount = EnumValues.size();
+  if (CeCount == 1 && IsLast && CeValue == MaxTagValue) {
+    ValidValuesCount -= 1;
+  }
+
+  return ValidValuesCount;
+}
+
+void TaggedUnionMemberCountCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const auto *Root = Result.Nodes.getNodeAs<RecordDecl>("root");
+  const auto *UnionField = Result.Nodes.getNodeAs<FieldDecl>("union");
+  const auto *TagField = Result.Nodes.getNodeAs<FieldDecl>("tags");
+
+  // The matcher can only narrow down the type to recordType()
+  if (!isUnion(UnionField))
+    return;
+
+  if (hasMultipleUnionsOrEnums(Root))
+    return;
----------------
Szelethus wrote:

I'm not sure how can they be of benefit. We already have `isUnion` for TagDecls.

https://github.com/llvm/llvm-project/pull/89925