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

[Piotr Zegar via cfe-commits]

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@@ -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();
----------------
PiotrZSL wrote:

`enumerator_begin -> enumerators.begin()`, be consistent, even better do:
`auto Enumerators =  Node.enumerators()`

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