clang-tidy: write a lint for charptr_cast

This lets us ensure that nobody is putting in new reinterpret_cast
instances where they could safely use charptr_cast instead.

Change-Id: I6358a3934c8133c7150042635843bdbb6b9218d4

1 files changed, 45 insertions, 0 deletions

diff --git a/subprojects/lix-clang-tidy/CharPtrCast.cc b/subprojects/lix-clang-tidy/CharPtrCast.cc
new file mode 100644
index 000000000..e76797f5d
--- /dev/null
+++ b/subprojects/lix-clang-tidy/CharPtrCast.cc
@@ -0,0 +1,45 @@
+#include "CharPtrCast.hh"
+#include <clang/AST/ExprCXX.h>
+#include <clang/Basic/Diagnostic.h>
+#include <clang/Tooling/Transformer/SourceCode.h>
+
+namespace nix::clang_tidy {
+using namespace clang::ast_matchers;
+using namespace clang;
+
+void CharPtrCastCheck::registerMatchers(ast_matchers::MatchFinder *Finder) {
+  Finder->addMatcher(
+      traverse(clang::TK_IgnoreUnlessSpelledInSource,
+               cxxReinterpretCastExpr(allOf(
+                   hasDestinationType(qualType(pointsTo(isAnyCharacter()))),
+                   has(expr(hasType(qualType(pointsTo(isAnyCharacter()))))))))
+          .bind("reinterpret-cast-expr"),
+      this);
+}
+
+void CharPtrCastCheck::check(
+    const ast_matchers::MatchFinder::MatchResult &Result) {
+  const auto ReinterpretCastExpr =
+      Result.Nodes.getNodeAs<CXXReinterpretCastExpr>("reinterpret-cast-expr");
+  const auto ToTypeSpan = ReinterpretCastExpr->getAngleBrackets();
+  const auto & SM = Result.Context->getSourceManager();
+
+  auto Diag =
+      diag(ReinterpretCastExpr->getExprLoc(),
+           "reinterpret_cast used for trivially safe character pointer cast");
+  Diag << ReinterpretCastExpr->getSourceRange();
+
+  auto Inside = tooling::getText(*ReinterpretCastExpr->getSubExprAsWritten(),
+                                 *Result.Context);
+
+  Diag << Inserter.createIncludeInsertion(SM.getFileID(ReinterpretCastExpr->getExprLoc()), "charptr-cast.hh");
+
+  llvm::Twine Replacement =
+      "charptr_cast" +
+      tooling::getText(CharSourceRange(ToTypeSpan, true), *Result.Context) +
+      "(" + Inside + ")";
+  Diag << FixItHint::CreateReplacement(ReinterpretCastExpr->getSourceRange(),
+                                       Replacement.str());
+}
+
+} // namespace nix::clang_tidy