[clang-tools-extra] [clang-tidy] add new check readability-enum-initial-value (PR #86129)

[Piotr Zegar via cfe-commits]

================
@@ -0,0 +1,193 @@
+//===--- EnumInitialValueCheck.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 "EnumInitialValueCheck.h"
+#include "../utils/LexerUtils.h"
+#include "clang/AST/Decl.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Basic/Diagnostic.h"
+#include "clang/Basic/SourceLocation.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallString.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::readability {
+
+EnumInitialValueCheck::EnumInitialValueCheck(StringRef Name,
+                                             ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      AllowExplicitZeroFirstInitialValue(
+          Options.get("AllowExplicitZeroFirstInitialValue", true)),
+      AllowExplicitLinearInitialValues(
+          Options.get("AllowExplicitLinearInitialValues", true)) {}
+
+void EnumInitialValueCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "AllowExplicitZeroFirstInitialValue",
+                AllowExplicitZeroFirstInitialValue);
+  Options.store(Opts, "AllowExplicitLinearInitialValues",
+                AllowExplicitLinearInitialValues);
+}
+
+namespace {
+
+bool isNoneEnumeratorsInitialized(const EnumDecl &Node) {
+  return llvm::all_of(Node.enumerators(), [](const EnumConstantDecl *ECD) {
+    return ECD->getInitExpr() == nullptr;
+  });
+}
+
+bool isOnlyFirstEnumeratorsInitialized(const EnumDecl &Node) {
+  bool IsFirst = true;
+  for (const EnumConstantDecl *ECD : Node.enumerators())
+    if (IsFirst) {
+      IsFirst = false;
+      if (ECD->getInitExpr() == nullptr)
+        return false;
+    } else {
+      if (ECD->getInitExpr() != nullptr)
+        return false;
+    }
+  return !IsFirst;
+}
+
+bool isAllEnumeratorsInitialized(const EnumDecl &Node) {
+  return llvm::all_of(Node.enumerators(), [](const EnumConstantDecl *ECD) {
+    return ECD->getInitExpr() != nullptr;
+  });
+}
+
+/// Check if \p Enumerator is initialized with a (potentially negated) \c
+/// IntegerLiteral.
+bool isInitializedByLiteral(const EnumConstantDecl *Enumerator) {
+  const Expr *const Init = Enumerator->getInitExpr();
+  if (!Init)
+    return false;
+  return Init->isIntegerConstantExpr(Enumerator->getASTContext());
+}
+
+AST_MATCHER(EnumDecl, hasConsistentInitialValues) {
+  return isNoneEnumeratorsInitialized(Node) ||
+         isOnlyFirstEnumeratorsInitialized(Node) ||
+         isAllEnumeratorsInitialized(Node);
+}
+
+AST_MATCHER(EnumDecl, hasZeroFirstInitialValue) {
+  if (Node.enumerators().empty())
+    return false;
+  const EnumConstantDecl *ECD = *Node.enumerators().begin();
+  return isOnlyFirstEnumeratorsInitialized(Node) &&
+         isInitializedByLiteral(ECD) && ECD->getInitVal().isZero();
+}
+
+/// Excludes bitfields because enumerators initialized with the result of a
+/// bitwise operator on enumeration values or any other expr that is not a
+/// potentially negative integer literal.
+/// Enumerations where it is not directly clear if they are used with
+/// bitmask, evident when enumerators are only initialized with (potentially
+/// negative) integer literals, are ignored. This is also the case when all
+/// enumerators are powers of two (e.g., 0, 1, 2).
+AST_MATCHER(EnumDecl, hasLinearInitialValues) {
+  if (Node.enumerators().empty())
+    return false;
+  const EnumConstantDecl *const FirstEnumerator = *Node.enumerator_begin();
+  llvm::APSInt PrevValue = FirstEnumerator->getInitVal();
+  if (!isInitializedByLiteral(FirstEnumerator))
+    return false;
+  bool AllEnumeratorsArePowersOfTwo = true;
+  for (const EnumConstantDecl *Enumerator :
+       llvm::drop_begin(Node.enumerators())) {
+    const llvm::APSInt NewValue = Enumerator->getInitVal();
+    if (NewValue != ++PrevValue)
+      return false;
+    if (!isInitializedByLiteral(Enumerator))
+      return false;
+    PrevValue = NewValue;
+    AllEnumeratorsArePowersOfTwo &= NewValue.isPowerOf2();
+  }
+  return !AllEnumeratorsArePowersOfTwo;
+}
+
+} // namespace
+
+void EnumInitialValueCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      enumDecl(unless(hasConsistentInitialValues())).bind("inconsistent"),
+      this);
+  if (!AllowExplicitZeroFirstInitialValue)
+    Finder->addMatcher(enumDecl(hasZeroFirstInitialValue()).bind("zero_first"),
+                       this);
+  if (!AllowExplicitLinearInitialValues)
+    Finder->addMatcher(enumDecl(hasLinearInitialValues()).bind("linear"), this);
+}
+
+static void cleanInitialValue(DiagnosticBuilder &Diag,
+                              const EnumConstantDecl *ECD,
+                              const SourceManager &SM,
+                              const LangOptions &LangOpts) {
+  std::optional<Token> EqualToken = utils::lexer::findNextTokenSkippingComments(
+      ECD->getLocation(), SM, LangOpts);
+  if (!EqualToken.has_value())
+    return;
+  SourceLocation EqualLoc{EqualToken->getLocation()};
+  if (EqualLoc.isInvalid() || EqualLoc.isMacroID())
+    return;
+  SourceRange InitExprRange = ECD->getInitExpr()->getSourceRange();
+  if (InitExprRange.isInvalid() || InitExprRange.getBegin().isMacroID() ||
+      InitExprRange.getEnd().isMacroID())
+    return;
+  Diag << FixItHint::CreateRemoval(EqualLoc)
+       << FixItHint::CreateRemoval(InitExprRange);
+  return;
+}
+
+void EnumInitialValueCheck::check(const MatchFinder::MatchResult &Result) {
+  if (const auto *Enum = Result.Nodes.getNodeAs<EnumDecl>("inconsistent")) {
+    SourceLocation Loc = Enum->getBeginLoc();
+    if (Loc.isInvalid() || Loc.isMacroID())
+      return;
+    DiagnosticBuilder Diag =
+        diag(Loc, "inital values in enum %0 are not consistent, consider "
+                  "explicit initialization first, all or none of enumerators")
+        << Enum;
+    for (const EnumConstantDecl *ECD : Enum->enumerators())
+      if (ECD->getInitExpr() == nullptr) {
+        std::optional<Token> Next = utils::lexer::findNextTokenSkippingComments(
+            ECD->getLocation(), *Result.SourceManager, getLangOpts());
+        if (!Next.has_value() || Next->getLocation().isMacroID())
+          continue;
+        llvm::SmallString<8> Str{" = "};
+        ECD->getInitVal().toString(Str);
+        Diag << FixItHint::CreateInsertion(Next->getLocation(), Str);
+      }
+    return;
+  }
+  if (const auto *Enum = Result.Nodes.getNodeAs<EnumDecl>("zero_first")) {
+    const EnumConstantDecl *ECD = *Enum->enumerators().begin();
+    SourceLocation Loc = ECD->getLocation();
+    if (Loc.isInvalid() || Loc.isMacroID())
+      return;
+    DiagnosticBuilder Diag =
+        diag(Loc, "zero fist initial value in %0 can be ignored") << Enum;
----------------
PiotrZSL wrote:

consider: `zero initial value for the first enumerator in %0 can be disregarded`

https://github.com/llvm/llvm-project/pull/86129