Merge changes I6358a393,I2d9f276b,Idd096dc9 into main

* changes:
  clang-tidy: write a lint for charptr_cast
  tree-wide: automated migration to charptr_cast
  clang-tidy: enforce the new rules

12 files changed, 115 insertions, 14 deletions

diff --git a/.clang-tidy b/.clang-tidy
index 0cc1f2520..87f6d0404 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -16,6 +16,20 @@ Checks:
   - -bugprone-unchecked-optional-access
     # many warnings, seems like a questionable lint
   - -bugprone-branch-clone
+    # all thrown exceptions must derive from std::exception
+  - hicpp-exception-baseclass
+    # capturing async lambdas are dangerous
+  - cppcoreguidelines-avoid-capturing-lambda-coroutines
+    # crimes must be appropriately declared as crimes
+  - cppcoreguidelines-pro-type-cstyle-cast
+  - lix-*
+    # This can not yet be applied to Lix itself since we need to do source
+    # reorganization so that lix/ include paths work.
+  - -lix-fixincludes
+    # This lint is included as an example, but the lib function it replaces is
+    # already gone.
+  - -lix-hasprefixsuffix
+
 
 CheckOptions:
   bugprone-reserved-identifier.AllowedIdentifiers: '__asan_default_options'
diff --git a/src/libstore/build/worker.cc b/src/libstore/build/worker.cc
index aaa4e8907..a27cb0076 100644
--- a/src/libstore/build/worker.cc
+++ b/src/libstore/build/worker.cc
@@ -1,3 +1,4 @@
+#include "charptr-cast.hh"
 #include "machines.hh"
 #include "worker.hh"
 #include "substitution-goal.hh"
@@ -539,7 +540,7 @@ void Worker::waitForInput()
                 } else {
                     printMsg(lvlVomit, "%1%: read %2% bytes",
                         goal->getName(), rd);
-                    std::string_view data(reinterpret_cast<char *>(buffer.data()), rd);
+                    std::string_view data(charptr_cast<char *>(buffer.data()), rd);
                     j->lastOutput = after;
                     handleWorkResult(goal, goal->handleChildOutput(k, data));
                 }
diff --git a/src/libstore/crypto.cc b/src/libstore/crypto.cc
index e8ab15537..6f4a36735 100644
--- a/src/libstore/crypto.cc
+++ b/src/libstore/crypto.cc
@@ -1,3 +1,4 @@
+#include "charptr-cast.hh"
 #include "crypto.hh"
 #include "file-system.hh"
 #include "globals.hh"
@@ -44,15 +45,15 @@ std::string SecretKey::signDetached(std::string_view data) const
 {
     unsigned char sig[crypto_sign_BYTES];
     unsigned long long sigLen;
-    crypto_sign_detached(sig, &sigLen, reinterpret_cast<const unsigned char *>(data.data()), data.size(),
-        reinterpret_cast<const unsigned char *>(key.data()));
+    crypto_sign_detached(sig, &sigLen, charptr_cast<const unsigned char *>(data.data()), data.size(),
+        charptr_cast<const unsigned char *>(key.data()));
     return name + ":" + base64Encode(std::string(reinterpret_cast<char *>(sig), sigLen));
 }
 
 PublicKey SecretKey::toPublicKey() const
 {
     unsigned char pk[crypto_sign_PUBLICKEYBYTES];
-    crypto_sign_ed25519_sk_to_pk(pk, reinterpret_cast<const unsigned char *>(key.data()));
+    crypto_sign_ed25519_sk_to_pk(pk, charptr_cast<const unsigned char *>(key.data()));
     return PublicKey(name, std::string(reinterpret_cast<char *>(pk), crypto_sign_PUBLICKEYBYTES));
 }
 
@@ -85,9 +86,9 @@ bool verifyDetached(const std::string & data, const std::string & sig,
     if (sig2.size() != crypto_sign_BYTES)
         throw Error("signature is not valid");
 
-    return crypto_sign_verify_detached(reinterpret_cast<unsigned char *>(sig2.data()),
-        reinterpret_cast<const unsigned char *>(data.data()), data.size(),
-        reinterpret_cast<const unsigned char *>(key->second.key.data())) == 0;
+    return crypto_sign_verify_detached(charptr_cast<unsigned char *>(sig2.data()),
+        charptr_cast<const unsigned char *>(data.data()), data.size(),
+        charptr_cast<const unsigned char *>(key->second.key.data())) == 0;
 }
 
 PublicKeys getDefaultPublicKeys()
diff --git a/src/libstore/sqlite.cc b/src/libstore/sqlite.cc
index 3114aad48..8d0bfcb11 100644
--- a/src/libstore/sqlite.cc
+++ b/src/libstore/sqlite.cc
@@ -1,3 +1,4 @@
+#include "charptr-cast.hh"
 #include "sqlite.hh"
 #include "globals.hh"
 #include "logging.hh"
@@ -201,7 +202,7 @@ bool SQLiteStmt::Use::next()
 
 std::optional<std::string> SQLiteStmt::Use::getStrNullable(int col)
 {
-    auto s = reinterpret_cast<const char *>(sqlite3_column_text(stmt, col));
+    auto s = charptr_cast<const char *>(sqlite3_column_text(stmt, col));
     return s != nullptr ? std::make_optional<std::string>((s)) : std::nullopt;
 }
 
diff --git a/src/libutil/charptr-cast.hh b/src/libutil/charptr-cast.hh
index 990f2ec55..ec53d8924 100644
--- a/src/libutil/charptr-cast.hh
+++ b/src/libutil/charptr-cast.hh
@@ -134,6 +134,7 @@ template<typename To, typename From>
     requires charptr_cast_detail::IsCharCastable<From, To>
 inline To charptr_cast(From p)
 {
+    // NOLINTNEXTLINE(lix-charptrcast): stop the linter ever getting too clever and causing funny recursion
     return reinterpret_cast<To>(p);
 }
 
diff --git a/src/libutil/compression.cc b/src/libutil/compression.cc
index 6b0fa9d15..5152a2146 100644
--- a/src/libutil/compression.cc
+++ b/src/libutil/compression.cc
@@ -1,3 +1,4 @@
+#include "charptr-cast.hh"
 #include "compression.hh"
 #include "tarfile.hh"
 #include "signals.hh"
@@ -160,7 +161,7 @@ struct BrotliDecompressionSource : Source
 
     size_t read(char * data, size_t len) override
     {
-        uint8_t * out = reinterpret_cast<uint8_t *>(data);
+        uint8_t * out = charptr_cast<uint8_t *>(data);
         const auto * begin = out;
 
         while (len && !BrotliDecoderIsFinished(state.get())) {
@@ -172,7 +173,7 @@ struct BrotliDecompressionSource : Source
                 } catch (EndOfFile &) {
                     break;
                 }
-                next_in = reinterpret_cast<const uint8_t *>(buf.get());
+                next_in = charptr_cast<const uint8_t *>(buf.get());
             }
 
             if (!BrotliDecoderDecompressStream(
@@ -238,7 +239,7 @@ struct BrotliCompressionSink : ChunkedCompressionSink
 
     void writeInternal(std::string_view data) override
     {
-        auto next_in = reinterpret_cast<const uint8_t *>(data.data());
+        auto next_in = charptr_cast<const uint8_t *>(data.data());
         size_t avail_in = data.size();
         uint8_t * next_out = outbuf;
         size_t avail_out = sizeof(outbuf);
diff --git a/src/libutil/file-descriptor.cc b/src/libutil/file-descriptor.cc
index 7c82988b3..be9f8c889 100644
--- a/src/libutil/file-descriptor.cc
+++ b/src/libutil/file-descriptor.cc
@@ -1,3 +1,4 @@
+#include "charptr-cast.hh"
 #include "file-system.hh"
 #include "finally.hh"
 #include "logging.hh"
@@ -115,7 +116,7 @@ Generator<Bytes> drainFDSource(int fd, bool block)
                 throw SysError("reading from file");
         }
         else if (rd == 0) break;
-        else co_yield std::span{reinterpret_cast<char *>(buf.data()), (size_t) rd};
+        else co_yield std::span{charptr_cast<char *>(buf.data()), (size_t) rd};
     }
 }
 
diff --git a/src/libutil/tarfile.cc b/src/libutil/tarfile.cc
index f024149ec..316751533 100644
--- a/src/libutil/tarfile.cc
+++ b/src/libutil/tarfile.cc
@@ -1,6 +1,7 @@
 #include <archive.h>
 #include <archive_entry.h>
 
+#include "charptr-cast.hh"
 #include "file-system.hh"
 #include "logging.hh"
 #include "serialise.hh"
@@ -19,7 +20,7 @@ static ssize_t callback_read(struct archive * archive, void * _self, const void
     *buffer = self->buffer.data();
 
     try {
-        return self->source->read(reinterpret_cast<char *>(self->buffer.data()), self->buffer.size());
+        return self->source->read(charptr_cast<char *>(self->buffer.data()), self->buffer.size());
     } catch (EndOfFile &) {
         return 0;
     } catch (std::exception & err) {
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
diff --git a/subprojects/lix-clang-tidy/CharPtrCast.hh b/subprojects/lix-clang-tidy/CharPtrCast.hh
new file mode 100644
index 000000000..66883d055
--- /dev/null
+++ b/subprojects/lix-clang-tidy/CharPtrCast.hh
@@ -0,0 +1,32 @@
+#pragma once
+///@file
+
+#include <clang-tidy/ClangTidyCheck.h>
+#include <clang-tidy/utils/IncludeInserter.h>
+#include <clang/ASTMatchers/ASTMatchFinder.h>
+#include <llvm/ADT/StringRef.h>
+
+namespace nix::clang_tidy {
+
+using namespace clang;
+using namespace clang::tidy;
+
+class CharPtrCastCheck : public ClangTidyCheck {
+  tidy::utils::IncludeInserter Inserter{
+      Options.getLocalOrGlobal("IncludeStyle",
+                               tidy::utils::IncludeSorter::IS_Google),
+      false};
+
+public:
+  CharPtrCastCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+
+  void registerPPCallbacks(const SourceManager &, Preprocessor *PP,
+                           Preprocessor *) override {
+    Inserter.registerPreprocessor(PP);
+  }
+
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+} // namespace nix::clang_tidy
diff --git a/subprojects/lix-clang-tidy/LixClangTidyChecks.cc b/subprojects/lix-clang-tidy/LixClangTidyChecks.cc
index b3503dd3a..283e0e7c8 100644
--- a/subprojects/lix-clang-tidy/LixClangTidyChecks.cc
+++ b/subprojects/lix-clang-tidy/LixClangTidyChecks.cc
@@ -2,6 +2,7 @@
 #include <clang-tidy/ClangTidyModuleRegistry.h>
 #include "FixIncludes.hh"
 #include "HasPrefixSuffix.hh"
+#include "CharPtrCast.hh"
 
 namespace nix::clang_tidy {
 using namespace clang;
@@ -12,6 +13,7 @@ class NixClangTidyChecks : public ClangTidyModule {
         void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
             CheckFactories.registerCheck<HasPrefixSuffixCheck>("lix-hasprefixsuffix");
             CheckFactories.registerCheck<FixIncludesCheck>("lix-fixincludes");
+            CheckFactories.registerCheck<CharPtrCastCheck>("lix-charptrcast");
         }
 };
 
diff --git a/subprojects/lix-clang-tidy/meson.build b/subprojects/lix-clang-tidy/meson.build
index ef0226420..43648a1c8 100644
--- a/subprojects/lix-clang-tidy/meson.build
+++ b/subprojects/lix-clang-tidy/meson.build
@@ -5,9 +5,10 @@ project('lix-clang-tidy', ['cpp', 'c'],
 
 llvm = dependency('Clang', version: '>= 17', modules: ['libclang'])
 sources = files(
+  'CharPtrCast.cc',
+  'FixIncludes.cc',
   'HasPrefixSuffix.cc',
   'LixClangTidyChecks.cc',
-  'FixIncludes.cc',
 )
 
 lix_clang_tidy = shared_module('lix-clang-tidy', sources,