[clang-tools-extra] [clang-tidy] detect redundant uses of LLVM's cast, dyn_cast (PR #189274)

[Victor Chernyakin via cfe-commits]

================
@@ -0,0 +1,131 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "RedundantCastingCheck.h"
+#include "clang/AST/Expr.h"
+#include "clang/AST/ExprCXX.h"
+#include "clang/AST/TemplateBase.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Lex/Lexer.h"
+#include "llvm/ADT/STLExtras.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::llvm_check {
+
+namespace {
+AST_MATCHER(Expr, isMacroID) { return Node.getExprLoc().isMacroID(); }
+AST_MATCHER_P(OverloadExpr, hasAnyUnresolvedName, ArrayRef<StringRef>, Names) {
+  auto DeclName = Node.getName();
+  if (!DeclName.isIdentifier())
+    return false;
+  const IdentifierInfo *II = DeclName.getAsIdentifierInfo();
+  return llvm::any_of(Names, [II](StringRef Name) { return II->isStr(Name); });
+}
+} // namespace
+
+static StringRef FunctionNames[] = {
+    "cast",     "cast_or_null",     "cast_if_present",
+    "dyn_cast", "dyn_cast_or_null", "dyn_cast_if_present"};
+
+void RedundantCastingCheck::registerMatchers(MatchFinder *Finder) {
+  auto AnyCalleeName = [](ArrayRef<StringRef> CalleeName) {
+    return allOf(unless(isMacroID()), unless(cxxMemberCallExpr()),
+                 callee(expr(ignoringImpCasts(
+                     declRefExpr(to(namedDecl(hasAnyName(CalleeName))),
+                                 hasAnyTemplateArgumentLoc(anything()))
+                         .bind("callee")))));
+  };
+  auto AnyCalleeNameInUninstantiatedTemplate =
+      [](ArrayRef<StringRef> CalleeName) {
+        return allOf(unless(isMacroID()), unless(cxxMemberCallExpr()),
+                     callee(expr(ignoringImpCasts(
+                         unresolvedLookupExpr(hasAnyUnresolvedName(CalleeName))
+                             .bind("callee")))));
+      };
+  Finder->addMatcher(
+      callExpr(
+          AnyCalleeName(FunctionNames),
+          hasAncestor(functionDecl().bind("context")))
+          .bind("call"),
+      this);
+  Finder->addMatcher(
+      callExpr(AnyCalleeNameInUninstantiatedTemplate(FunctionNames))
+          .bind("call"),
+      this);
+}
+
+static QualType stripPointerOrReference(QualType Ty) {
+  QualType Pointee = Ty->getPointeeType();
+  if (Pointee.isNull())
+    return Ty;
+  return Pointee;
+}
+
+void RedundantCastingCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto &Nodes = Result.Nodes;
+  const auto *Call = Nodes.getNodeAs<CallExpr>("call");
+  if (Call->getNumArgs() != 1)
+    return;
+
+  CanQualType RetTy;
+  std::string FuncName;
+  if (const auto *ResolvedCallee = Nodes.getNodeAs<DeclRefExpr>("callee")) {
+    const auto *F = dyn_cast<FunctionDecl>(ResolvedCallee->getDecl());
+    const auto *SurroundingFunc = Nodes.getNodeAs<FunctionDecl>("context");
+    // Casts can be redundant for some instantiations but not others.
+    // Only emit warnings in templates in the uninstantated versions.
+    if (SurroundingFunc->isTemplateInstantiation())
+      return;
+
+    RetTy = stripPointerOrReference(F->getReturnType())
+                ->getCanonicalTypeUnqualified();
+    FuncName = F->getName();
+  } else if (const auto *UnresolvedCallee =
+                 Nodes.getNodeAs<UnresolvedLookupExpr>("callee")) {
+    if (UnresolvedCallee->getNumTemplateArgs() != 1)
+      return;
+    auto TArg = UnresolvedCallee->template_arguments()[0].getArgument();
+    if (TArg.getKind() != TemplateArgument::Type)
+      return;
+
+    RetTy = TArg.getAsType()->getCanonicalTypeUnqualified();
+    FuncName = UnresolvedCallee->getName().getAsString();
+  } else {
+    return;
+  }
+
+  const auto *Arg = Call->getArg(0);
+  const CanQualType FromTy =
+      stripPointerOrReference(Arg->getType())->getCanonicalTypeUnqualified();
+  const auto *FromDecl = FromTy->getAsCXXRecordDecl();
+  const auto *RetDecl = RetTy->getAsCXXRecordDecl();
+  const bool IsDerived = FromDecl && RetDecl && FromDecl->isDerivedFrom(RetDecl);
+  if (FromTy != RetTy && !IsDerived)
+    return;
+
+  auto GetText = [&](SourceRange R) {
+    return Lexer::getSourceText(CharSourceRange::getTokenRange(R),
+                                *Result.SourceManager, getLangOpts());
+  };
+  StringRef ArgText = GetText(Arg->getSourceRange());
+  diag(Call->getExprLoc(), "redundant use of '%0'")
+      << FuncName
+      << FixItHint::CreateReplacement(Call->getSourceRange(), ArgText);
+  diag(Arg->getExprLoc(), "source expression %0 has type %1",
+       DiagnosticIDs::Note)
+      << Arg << Arg->IgnoreParenImpCasts()->getType();
----------------
localspook wrote:

The source expression is potentially quite big, so putting it all into the warning message may be a bit spammy. I think though you can pipe its source range into the diagnostic, that way it'll be underlined:
```suggestion
  diag(Arg->getExprLoc(), "source expression has type %1",
       DiagnosticIDs::Note)
      << Arg->getSourceRange() << Arg->IgnoreParenImpCasts()->getType();
```

https://github.com/llvm/llvm-project/pull/189274