[clang-tools-extra] [clang-tidy] Detect std::rot[lr] pattern within modernize.use-std-bit (PR #186324)

[Baranov Victor via cfe-commits]

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@@ -141,6 +154,48 @@ void UseStdBitCheck::check(const MatchFinder::MatchResult &Result) {
            << IncludeInserter.createIncludeInsertion(
                   Source.getFileID(MatchedExpr->getBeginLoc()), "<bit>");
     }
+  } else if (const auto *MatchedExpr =
+                 Result.Nodes.getNodeAs<BinaryOperator>("rotate_expr")) {
+    const auto *MatchedVarDecl = Result.Nodes.getNodeAs<VarDecl>("v");
+    const auto ShiftLeftAmount =
+        Result.Nodes.getNodeAs<IntegerLiteral>("shift_left_amount")->getValue();
+    const auto ShiftRightAmount =
+        Result.Nodes.getNodeAs<IntegerLiteral>("shift_right_amount")
+            ->getValue();
+    const uint64_t MatchedVarSize =
+        Context.getTypeSize(MatchedVarDecl->getType());
+
+    // Overflowing shifts
+    if (ShiftLeftAmount.sge(MatchedVarSize))
+      return;
+    if (ShiftRightAmount.sge(MatchedVarSize))
+      return;
+    // Not a rotation.
+    if (MatchedVarSize != (ShiftLeftAmount + ShiftRightAmount))
+      return;
+
+    const bool NeedsIntCast =
+        MatchedExpr->getType() != MatchedVarDecl->getType();
+    const bool IsRotl = ShiftRightAmount.sge(ShiftLeftAmount);
+
+    const StringRef ReplacementFuncName = IsRotl ? "rotl" : "rotr";
+    const uint64_t ReplacementShiftAmount =
+        (IsRotl ? ShiftLeftAmount : ShiftRightAmount).getZExtValue();
+    auto Diag = diag(MatchedExpr->getBeginLoc(), "use 'std::%0' instead")
+                << ReplacementFuncName;
+    if (auto R = MatchedExpr->getSourceRange();
+        !R.getBegin().isMacroID() && !R.getEnd().isMacroID()) {
+      Diag << FixItHint::CreateReplacement(
+                  MatchedExpr->getSourceRange(),
+                  llvm::formatv("{3}std::{0}({1}, {2})", ReplacementFuncName,
+                                MatchedVarDecl->getName(),
+                                ReplacementShiftAmount,
+                                NeedsIntCast ? "(int)" : "")
----------------
vbvictor wrote:

I think we should avoid suggesting C-casts in C++. For example, clang suggest `static_cast` as fixes: https://godbolt.org/z/r4qeo4hrq  

But the best way is to handle this is a bool option to provide `static_cast<int>()` or not for fixes. (With off by default imho)

https://github.com/llvm/llvm-project/pull/186324