From 8f26c5e65f6c34fd8fa3aa80705b507904d77b09 Mon Sep 17 00:00:00 2001
From: Robert Schulze <robert@clickhouse.com>
Date: Tue, 28 Mar 2023 21:34:35 +0000
Subject: [PATCH] Fix compilation with libcxx 16

After upgrading our (ClickHouse's) libcxx from 15 to 16, the compiler
started to complain about usage of an incomplete type "RoseInstruction"
in this (header) function:

  void RoseProgram::replace(Iter it, std::unique_ptr<RoseInstruction> ri) {
    ...

The reason is that libcxx 16 is the first version which implements C++23
constexpr std::unique_ptr (P2273R3, see (*)). RoseProgram::replace()
happens to be be const-evaluatable and the compiler tries to run
std::unique_ptr's ctor + dtor. This fails because at this point
RoseInstruction isn't defined yet.

There are two ways of fixing this:
1. Include rose_build_instruction.h (which contains RoseInstruction)
   into rose_build_program.h. Disadvantage: The new include will
   propagate transitively into all callers.
2. Move the function implementation into the source file which sees
   RoseInstruction's definition already. Disadvantage: Template
   instantiation is no longer automatic, instead there must be either a)
   explicit template instantiation (e.g. in rose_build_program.cpp) or
   b) all callers which instantiate the function must live in the same
   source file and do the instantiations by themselves. Fortunately, the
   latter is the case here, but potential future code outside
   rose_build_program.cpp will require ugly explicit instantiation.

(*) https://en.cppreference.com/w/cpp/23
---
 src/rose/rose_build_program.cpp | 9 +++++++++
 src/rose/rose_build_program.h   | 8 +-------
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/src/rose/rose_build_program.cpp b/src/rose/rose_build_program.cpp
index 3ddf2fcd..8e179e36 100644
--- a/src/rose/rose_build_program.cpp
+++ b/src/rose/rose_build_program.cpp
@@ -204,6 +204,15 @@ void RoseProgram::add_block(RoseProgram &&block) {
                 make_move_iterator(block.prog.end()));
 }
 
+template<class Iter>
+void RoseProgram::replace(Iter it, std::unique_ptr<RoseInstruction> ri) {
+    assert(!prog.empty());
+
+    const RoseInstruction *old_ptr = it->get();
+    *it = move(ri);
+    update_targets(prog.begin(), prog.end(), old_ptr, it->get());
+}
+
 bytecode_ptr<char> writeProgram(RoseEngineBlob &blob,
                                 const RoseProgram &program) {
     u32 total_len = 0;
diff --git a/src/rose/rose_build_program.h b/src/rose/rose_build_program.h
index 6ad5529c..1882279d 100644
--- a/src/rose/rose_build_program.h
+++ b/src/rose/rose_build_program.h
@@ -124,13 +124,7 @@ public:
      * \brief Replace the instruction pointed to by the given iterator.
      */
     template<class Iter>
-    void replace(Iter it, std::unique_ptr<RoseInstruction> ri) {
-        assert(!prog.empty());
-
-        const RoseInstruction *old_ptr = it->get();
-        *it = move(ri);
-        update_targets(prog.begin(), prog.end(), old_ptr, it->get());
-    }
+    void replace(Iter it, std::unique_ptr<RoseInstruction> ri);
 };
 
 bytecode_ptr<char> writeProgram(RoseEngineBlob &blob,