From af6b0fce736cc241172acb88a2767862c1fed3d3 Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Tue, 15 Jul 2025 17:05:24 +0100
Subject: [PATCH 01/15] Make CppInterOp llvm 21 compatible

---
 .github/workflows/emscripten.yml              | 59 ++++++++++++++++++-
 .github/workflows/main.yml                    | 46 +++++++++++++++
 CMakeLists.txt                                | 12 ++--
 lib/CppInterOp/Compatibility.h                | 11 ++++
 lib/CppInterOp/CppInterOp.cpp                 |  6 +-
 ...ws-emscripten-clang21-1-CrossCompile.patch | 20 +++++++
 ...1-2-shift-temporary-files-to-tmp-dir.patch | 15 +++++
 7 files changed, 159 insertions(+), 10 deletions(-)
 create mode 100644 patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
 create mode 100644 patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch

diff --git a/.github/workflows/emscripten.yml b/.github/workflows/emscripten.yml
index 98cc10ef3..3b0e60a42 100644
--- a/.github/workflows/emscripten.yml
+++ b/.github/workflows/emscripten.yml
@@ -77,6 +77,34 @@ jobs:
             llvm_enable_projects: "clang;lld"
             llvm_targets_to_build: "WebAssembly"
             emsdk_ver: "3.1.73"
+          - name: ubu24-arm-clang-repl-21-emscripten
+            os: ubuntu-24.04-arm
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang;lld"
+            llvm_targets_to_build: "WebAssembly"
+            emsdk_ver: "3.1.73"
+          - name: osx15-arm-clang-repl-21-emscripten
+            os: macos-15
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang;lld"
+            llvm_targets_to_build: "WebAssembly"
+            emsdk_ver: "3.1.73"
+          - name: ubu24-x86-clang-repl-21-emscripten
+            os: ubuntu-24.04
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang;lld"
+            llvm_targets_to_build: "WebAssembly"
+            emsdk_ver: "3.1.73"
+          - name: win2025-x86-clang-repl-21-emscripten
+            os: windows-2025
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang;lld"
+            llvm_targets_to_build: "WebAssembly"
+            emsdk_ver: "3.1.73"
 
     steps:
     - uses: actions/checkout@v4
@@ -199,7 +227,7 @@ jobs:
         else
           # Apply patches
           llvm_vers=$(echo "${{ matrix.clang-runtime }}" | tr '[:lower:]' '[:upper:]')
-          if [[ "${llvm_vers}" == "19" || "${llvm_vers}" == "20" ]]; then
+          if [[ "${llvm_vers}" == "19" || "${llvm_vers}" == "20" || "${llvm_vers}" == "21"  ]]; then
             git apply -v ../patches/llvm/emscripten-clang${{ matrix.clang-runtime }}-*.patch
             echo "Apply emscripten-clang${{ matrix.clang-runtime }}-*.patch patches:"
           fi
@@ -321,6 +349,11 @@ jobs:
             git apply -v emscripten-clang20-2-shift-temporary-files-to-tmp-dir.patch
             git apply -v emscripten-clang20-3-enable_exception_handling.patch
           }
+          elseif ( "${{ matrix.clang-runtime }}" -imatch "21" )
+          {
+            git apply -v Windows-emscripten-clang21-1-CrossCompile.patch
+            git apply -v emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch
+          }
           cd build
           echo "Apply clang${{ matrix.clang-runtime }}-*.patch patches:"
           emcmake cmake -DCMAKE_BUILD_TYPE=Release `
@@ -431,6 +464,30 @@ jobs:
             cling: Off
             micromamba_shell_init: powershell
             emsdk_ver: "3.1.73"
+          - name: ubu24-x86-clang-repl-21-emscripten_wasm
+            os: ubuntu-24.04
+            clang-runtime: '21'
+            cling: Off
+            micromamba_shell_init: bash
+            emsdk_ver: "3.1.73"
+          - name: osx15-arm-clang-repl-21-emscripten_wasm
+            os: macos-15
+            clang-runtime: '21'
+            cling: Off
+            micromamba_shell_init: bash
+            emsdk_ver: "3.1.73"
+          - name: ubu24-arm-clang-repl-21-emscripten_wasm
+            os: ubuntu-24.04-arm
+            clang-runtime: '21'
+            cling: Off
+            micromamba_shell_init: bash
+            emsdk_ver: "3.1.73"
+          - name: win2025-x86-clang-repl-21-emscripten
+            os: windows-2025
+            clang-runtime: '21'
+            cling: Off
+            micromamba_shell_init: powershell
+            emsdk_ver: "3.1.73"
 
     steps:
     - uses: actions/checkout@v4
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index bc40f0bea..605780436 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -23,6 +23,14 @@ jobs:
       matrix:
         include:
           # Ubuntu Arm Jobs
+          - name: ubu24-arm-gcc12-clang-repl-21
+            os: ubuntu-24.04-arm
+            compiler: gcc-12
+            clang-runtime: '21'
+            cling: Off
+            cppyy: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host;NVPTX"
           - name: ubu22-arm-gcc12-clang-repl-20-coverage
             os: ubuntu-22.04-arm
             compiler: gcc-12
@@ -66,6 +74,14 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # Ubuntu X86 Jobs
+          - name: ubu24-x86-gcc12-clang-repl-21
+            os: ubuntu-24.04
+            compiler: gcc-12
+            clang-runtime: '21'
+            cling: Off
+            cppyy: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host;NVPTX"
           - name: ubu24-x86-gcc12-clang-repl-20
             os: ubuntu-24.04
             compiler: gcc-12
@@ -100,6 +116,14 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # MacOS Arm Jobs
+          - name: osx15-arm-clang-clang-repl-21
+            os: macos-15
+            compiler: clang
+            clang-runtime: '21'
+            cling: Off
+            cppyy: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host"
           - name: osx15-arm-clang-clang-repl-20
             os: macos-15
             compiler: clang
@@ -134,6 +158,14 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # MacOS X86 Jobs
+          - name: osx13-x86-clang-clang-repl-21
+            os: macos-13
+            compiler: clang
+            clang-runtime: '21'
+            cling: Off
+            cppyy: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host"
           - name: osx13-x86-clang-clang-repl-20
             os: macos-13
             compiler: clang
@@ -168,6 +200,13 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # Windows Arm Jobs
+          - name: win11-msvc-clang-repl-21
+            os: windows-11-arm
+            compiler: msvc
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host;NVPTX"
           - name: win11-msvc-clang-repl-20
             os: windows-11-arm
             compiler: msvc
@@ -184,6 +223,13 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # Windows X86 Jobs
+          - name: win2025-msvc-clang-repl-21
+            os: windows-2025
+            compiler: msvc
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host;NVPTX"
           - name: win2025-msvc-clang-repl-20
             os: windows-2025
             compiler: msvc
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 981c57ced..cc8d38617 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -68,14 +68,14 @@ include(GNUInstallDirs)
   ## Define supported version of clang and llvm
 
   set(CLANG_MIN_SUPPORTED 18.0)
-  set(CLANG_MAX_SUPPORTED "20.1.x")
-  set(CLANG_VERSION_UPPER_BOUND 21.0.0)
+  set(CLANG_MAX_SUPPORTED "21.1.x")
+  set(CLANG_VERSION_UPPER_BOUND 22.0.0)
   set(LLD_MIN_SUPPORTED 18.0)
-  set(LLD_MAX_SUPPORTED "20.1.x")
-  set(LLD_VERSION_UPPER_BOUND 21.0.0)
+  set(LLD_MAX_SUPPORTED "21.1.x")
+  set(LLD_VERSION_UPPER_BOUND 22.0.0)
   set(LLVM_MIN_SUPPORTED 18.0)
-  set(LLVM_MAX_SUPPORTED "20.1.x")
-  set(LLVM_VERSION_UPPER_BOUND 21.0.0)
+  set(LLVM_MAX_SUPPORTED "21.1.x")
+  set(LLVM_VERSION_UPPER_BOUND 22.0.0)
 
   ## Set Cmake packages search order
 
diff --git a/lib/CppInterOp/Compatibility.h b/lib/CppInterOp/Compatibility.h
index ddee92574..f82d67453 100644
--- a/lib/CppInterOp/Compatibility.h
+++ b/lib/CppInterOp/Compatibility.h
@@ -31,6 +31,17 @@ static inline char* GetEnv(const char* Var_Name) {
 #endif
 }
 
+#if CLANG_VERSION_MAJOR < 21
+#define clang_LookupResult_Found clang::LookupResult::Found
+#define clang_LookupResult_Not_Found clang::LookupResult::NotFound
+#define clang_LookupResult_Found_Overloaded clang::LookupResult::FoundOverloaded
+#else
+#define clang_LookupResult_Found clang::LookupResultKind::Found
+#define clang_LookupResult_Not_Found clang::LookupResultKind::NotFound
+#define clang_LookupResult_Found_Overloaded                                    \
+  clang::LookupResultKind::FoundOverloaded
+#endif
+
 #if CLANG_VERSION_MAJOR < 19
 #define Template_Deduction_Result Sema::TemplateDeductionResult
 #define Template_Deduction_Result_Success                                      \
diff --git a/lib/CppInterOp/CppInterOp.cpp b/lib/CppInterOp/CppInterOp.cpp
index 01a14ce03..b6e16323b 100755
--- a/lib/CppInterOp/CppInterOp.cpp
+++ b/lib/CppInterOp/CppInterOp.cpp
@@ -1135,16 +1135,16 @@ bool GetClassTemplatedMethods(const std::string& name, TCppScope_t parent,
   auto* DC = clang::Decl::castToDeclContext(D);
   Cpp_utils::Lookup::Named(&S, R, DC);
 
-  if (R.getResultKind() == clang::LookupResult::NotFound && funcs.empty())
+  if (R.getResultKind() == clang_LookupResult_Not_Found && funcs.empty())
     return false;
 
   // Distinct match, single Decl
-  else if (R.getResultKind() == clang::LookupResult::Found) {
+  else if (R.getResultKind() == clang_LookupResult_Found) {
     if (IsTemplatedFunction(R.getFoundDecl()))
       funcs.push_back(R.getFoundDecl());
   }
   // Loop over overload set
-  else if (R.getResultKind() == clang::LookupResult::FoundOverloaded) {
+  else if (R.getResultKind() == clang_LookupResult_Found_Overloaded) {
     for (auto* Found : R)
       if (IsTemplatedFunction(Found))
         funcs.push_back(Found);
diff --git a/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch b/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
new file mode 100644
index 000000000..a1ffeccc8
--- /dev/null
+++ b/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
@@ -0,0 +1,20 @@
+diff --git a/llvm/cmake/modules/CrossCompile.cmake b/llvm/cmake/modules/CrossCompile.cmake
+index 39b4abaa0..474ceddbb 100644
+--- a/llvm/cmake/modules/CrossCompile.cmake
++++ b/llvm/cmake/modules/CrossCompile.cmake
+@@ -74,10 +74,12 @@ function(llvm_create_cross_target project_name target_name toolchain buildtype)
+   endif()
+ 
+   add_custom_command(OUTPUT ${${project_name}_${target_name}_BUILD}/CMakeCache.txt
+-    COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}"
++    COMMAND ${CMAKE_COMMAND} -G Ninja
+         -DCMAKE_MAKE_PROGRAM="${CMAKE_MAKE_PROGRAM}"
+-        -DCMAKE_C_COMPILER_LAUNCHER="${CMAKE_C_COMPILER_LAUNCHER}"
+-        -DCMAKE_CXX_COMPILER_LAUNCHER="${CMAKE_CXX_COMPILER_LAUNCHER}"
++        -DCMAKE_C_COMPILER="clang-cl"
++        -DCMAKE_CXX_COMPILER="clang-cl"
++        -DCMAKE_ASM_MASM_COMPILER=llvm-ml
++        -DCMAKE_ASM_MASM_FLAGS="-m64"
+         ${CROSS_TOOLCHAIN_FLAGS_${target_name}} ${CMAKE_CURRENT_SOURCE_DIR}
+         ${CROSS_TOOLCHAIN_FLAGS_${project_name}_${target_name}}
+         -DLLVM_TARGET_IS_CROSSCOMPILE_HOST=TRUE
diff --git a/patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch b/patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch
new file mode 100644
index 000000000..32ac45c13
--- /dev/null
+++ b/patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch
@@ -0,0 +1,15 @@
+diff --git a/clang/lib/Interpreter/Wasm.cpp b/clang/lib/Interpreter/Wasm.cpp
+index aa10b160ccf8..184867e2b55f 100644
+--- a/clang/lib/Interpreter/Wasm.cpp
++++ b/clang/lib/Interpreter/Wasm.cpp
+@@ -76,8 +76,8 @@ llvm::Error WasmIncrementalExecutor::addModule(PartialTranslationUnit &PTU) {
+   llvm::TargetMachine *TargetMachine = Target->createTargetMachine(
+       PTU.TheModule->getTargetTriple(), "", "", TO, llvm::Reloc::Model::PIC_);
+   PTU.TheModule->setDataLayout(TargetMachine->createDataLayout());
+-  std::string ObjectFileName = PTU.TheModule->getName().str() + ".o";
+-  std::string BinaryFileName = PTU.TheModule->getName().str() + ".wasm";
++  std::string ObjectFileName = "/tmp/" + PTU.TheModule->getName().str() + ".o";
++  std::string BinaryFileName = "/tmp/" + PTU.TheModule->getName().str() + ".wasm";
+ 
+   std::error_code Error;
+   llvm::raw_fd_ostream ObjectFileOutput(llvm::StringRef(ObjectFileName), Error);

From 3d74a26394a8e27f7a9129a64d3bac284c076cac Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Tue, 15 Jul 2025 21:03:13 +0100
Subject: [PATCH 02/15] Update Windows-emscripten-clang21-1-CrossCompile.patch

---
 .../llvm/Windows-emscripten-clang21-1-CrossCompile.patch    | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch b/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
index a1ffeccc8..00e0aef6f 100644
--- a/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
+++ b/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
@@ -8,9 +8,9 @@ index 39b4abaa0..474ceddbb 100644
    add_custom_command(OUTPUT ${${project_name}_${target_name}_BUILD}/CMakeCache.txt
 -    COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}"
 +    COMMAND ${CMAKE_COMMAND} -G Ninja
-         -DCMAKE_MAKE_PROGRAM="${CMAKE_MAKE_PROGRAM}"
--        -DCMAKE_C_COMPILER_LAUNCHER="${CMAKE_C_COMPILER_LAUNCHER}"
--        -DCMAKE_CXX_COMPILER_LAUNCHER="${CMAKE_CXX_COMPILER_LAUNCHER}"
+         "-DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}"
+-        "-DCMAKE_C_COMPILER_LAUNCHER=${CMAKE_C_COMPILER_LAUNCHER}"
+-        "-DCMAKE_CXX_COMPILER_LAUNCHER=${CMAKE_CXX_COMPILER_LAUNCHER}"
 +        -DCMAKE_C_COMPILER="clang-cl"
 +        -DCMAKE_CXX_COMPILER="clang-cl"
 +        -DCMAKE_ASM_MASM_COMPILER=llvm-ml

From aef6370df2014afc6d60a07699f94883f664ac00 Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Wed, 16 Jul 2025 09:20:19 +0100
Subject: [PATCH 03/15] Update exports.ld

---
 lib/CppInterOp/exports.ld | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/CppInterOp/exports.ld b/lib/CppInterOp/exports.ld
index 49b7b0d83..c1c4e59e8 100644
--- a/lib/CppInterOp/exports.ld
+++ b/lib/CppInterOp/exports.ld
@@ -50,4 +50,5 @@
 -Wl,--export=_ZNK5clang4Type14isFloatingTypeEv
 -Wl,--export=_ZNK5clang12FunctionDecl12getNumParamsEv
 -Wl,--export=__clang_Interpreter_SetValueNoAlloc
--Wl,--export=__clang_Interpreter_SetValueWithAlloc
\ No newline at end of file
+-Wl,--export=__clang_Interpreter_SetValueWithAlloc
+-Wl,--export=_ZN5clang11Interpreter6createENSt3__210unique_ptrINS_16CompilerInstanceENS1_14default_deleteIS3_EEEENS2_IN4llvm3orc12LLJITBuilderENS4_IS9_EEEE 

From 2a280d1536a4c0c89fc159c8e0f68624aee61a10 Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Wed, 16 Jul 2025 10:59:46 +0100
Subject: [PATCH 04/15] Update exports.ld

---
 lib/CppInterOp/exports.ld | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/CppInterOp/exports.ld b/lib/CppInterOp/exports.ld
index c1c4e59e8..65c3b439b 100644
--- a/lib/CppInterOp/exports.ld
+++ b/lib/CppInterOp/exports.ld
@@ -51,4 +51,5 @@
 -Wl,--export=_ZNK5clang12FunctionDecl12getNumParamsEv
 -Wl,--export=__clang_Interpreter_SetValueNoAlloc
 -Wl,--export=__clang_Interpreter_SetValueWithAlloc
--Wl,--export=_ZN5clang11Interpreter6createENSt3__210unique_ptrINS_16CompilerInstanceENS1_14default_deleteIS3_EEEENS2_IN4llvm3orc12LLJITBuilderENS4_IS9_EEEE 
+-Wl,--export=_ZN5clang11Interpreter6createENSt3__210unique_ptrINS_16CompilerInstanceENS1_14default_deleteIS3_EEEENS2_IN4llvm3orc12LLJITBuilderENS4_IS9_EEEE
+-Wl,--export=_ZNK5clang13CXXRecordDecl19isInjectedClassNameEv

From bbd2a48422d759ba2bb72b6d315506790c947dae Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Tue, 9 Sep 2025 16:02:20 +0100
Subject: [PATCH 05/15] Define Print_Canonical_Types for llvm 21 compatibility

---
 lib/CppInterOp/Compatibility.h | 6 ++++++
 lib/CppInterOp/CppInterOp.cpp  | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/CppInterOp/Compatibility.h b/lib/CppInterOp/Compatibility.h
index fe8eed44c..b1dc2daa9 100644
--- a/lib/CppInterOp/Compatibility.h
+++ b/lib/CppInterOp/Compatibility.h
@@ -31,6 +31,12 @@ static inline char* GetEnv(const char* Var_Name) {
 #endif
 }
 
+#if CLANG_VERSION_MAJOR < 21
+#define Print_Canonical_Types PrintCanonicalTypes
+#else
+#define Print_Canonical_Types PrintAsCanonical
+#endif
+
 #if CLANG_VERSION_MAJOR < 21
 #define clang_LookupResult_Found clang::LookupResult::Found
 #define clang_LookupResult_Not_Found clang::LookupResult::NotFound
diff --git a/lib/CppInterOp/CppInterOp.cpp b/lib/CppInterOp/CppInterOp.cpp
index 819ec72c1..6613e2546 100755
--- a/lib/CppInterOp/CppInterOp.cpp
+++ b/lib/CppInterOp/CppInterOp.cpp
@@ -1954,7 +1954,7 @@ static void GetDeclName(const clang::Decl* D, ASTContext& Context,
   PrintingPolicy Policy(Context.getPrintingPolicy());
   Policy.SuppressTagKeyword = true;
   Policy.SuppressUnwrittenScope = true;
-  Policy.PrintCanonicalTypes = true;
+  Policy.Print_Canonical_Types = true;
   if (const TypeDecl* TD = dyn_cast<TypeDecl>(D)) {
     // This is a class, struct, or union member.
     QualType QT;

From 68a3695b9701bb4be192dc22143409d88bb59741 Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Tue, 15 Jul 2025 17:05:24 +0100
Subject: [PATCH 06/15] Make CppInterOp llvm 21 compatible

---
 .github/workflows/emscripten.yml              | 59 ++++++++++++++++++-
 .github/workflows/main.yml                    | 46 +++++++++++++++
 CMakeLists.txt                                | 12 ++--
 lib/CppInterOp/Compatibility.h                | 11 ++++
 lib/CppInterOp/CppInterOp.cpp                 |  6 +-
 ...ws-emscripten-clang21-1-CrossCompile.patch | 20 +++++++
 ...1-2-shift-temporary-files-to-tmp-dir.patch | 15 +++++
 7 files changed, 159 insertions(+), 10 deletions(-)
 create mode 100644 patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
 create mode 100644 patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch

diff --git a/.github/workflows/emscripten.yml b/.github/workflows/emscripten.yml
index daa4d8152..3c27a20b1 100644
--- a/.github/workflows/emscripten.yml
+++ b/.github/workflows/emscripten.yml
@@ -77,6 +77,34 @@ jobs:
             llvm_enable_projects: "clang;lld"
             llvm_targets_to_build: "WebAssembly"
             emsdk_ver: "3.1.73"
+          - name: ubu24-arm-clang-repl-21-emscripten
+            os: ubuntu-24.04-arm
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang;lld"
+            llvm_targets_to_build: "WebAssembly"
+            emsdk_ver: "3.1.73"
+          - name: osx15-arm-clang-repl-21-emscripten
+            os: macos-15
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang;lld"
+            llvm_targets_to_build: "WebAssembly"
+            emsdk_ver: "3.1.73"
+          - name: ubu24-x86-clang-repl-21-emscripten
+            os: ubuntu-24.04
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang;lld"
+            llvm_targets_to_build: "WebAssembly"
+            emsdk_ver: "3.1.73"
+          - name: win2025-x86-clang-repl-21-emscripten
+            os: windows-2025
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang;lld"
+            llvm_targets_to_build: "WebAssembly"
+            emsdk_ver: "3.1.73"
 
     steps:
     - uses: actions/checkout@v5
@@ -201,7 +229,7 @@ jobs:
         else
           # Apply patches
           llvm_vers=$(echo "${{ matrix.clang-runtime }}" | tr '[:lower:]' '[:upper:]')
-          if [[ "${llvm_vers}" == "19" || "${llvm_vers}" == "20" ]]; then
+          if [[ "${llvm_vers}" == "19" || "${llvm_vers}" == "20" || "${llvm_vers}" == "21"  ]]; then
             git apply -v ../patches/llvm/emscripten-clang${{ matrix.clang-runtime }}-*.patch
             echo "Apply emscripten-clang${{ matrix.clang-runtime }}-*.patch patches:"
           fi
@@ -327,6 +355,11 @@ jobs:
             git apply -v emscripten-clang20-2-shift-temporary-files-to-tmp-dir.patch
             git apply -v emscripten-clang20-3-enable_exception_handling.patch
           }
+          elseif ( "${{ matrix.clang-runtime }}" -imatch "21" )
+          {
+            git apply -v Windows-emscripten-clang21-1-CrossCompile.patch
+            git apply -v emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch
+          }
           cd build
           echo "Apply clang${{ matrix.clang-runtime }}-*.patch patches:"
           emcmake cmake -DCMAKE_BUILD_TYPE=Release `
@@ -439,6 +472,30 @@ jobs:
             cling: Off
             micromamba_shell_init: powershell
             emsdk_ver: "3.1.73"
+          - name: ubu24-x86-clang-repl-21-emscripten_wasm
+            os: ubuntu-24.04
+            clang-runtime: '21'
+            cling: Off
+            micromamba_shell_init: bash
+            emsdk_ver: "3.1.73"
+          - name: osx15-arm-clang-repl-21-emscripten_wasm
+            os: macos-15
+            clang-runtime: '21'
+            cling: Off
+            micromamba_shell_init: bash
+            emsdk_ver: "3.1.73"
+          - name: ubu24-arm-clang-repl-21-emscripten_wasm
+            os: ubuntu-24.04-arm
+            clang-runtime: '21'
+            cling: Off
+            micromamba_shell_init: bash
+            emsdk_ver: "3.1.73"
+          - name: win2025-x86-clang-repl-21-emscripten
+            os: windows-2025
+            clang-runtime: '21'
+            cling: Off
+            micromamba_shell_init: powershell
+            emsdk_ver: "3.1.73"
 
     steps:
     - uses: actions/checkout@v5
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 20232cca1..ace7a1ead 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -23,6 +23,14 @@ jobs:
       matrix:
         include:
           # Ubuntu Arm Jobs
+          - name: ubu24-arm-gcc12-clang-repl-21
+            os: ubuntu-24.04-arm
+            compiler: gcc-12
+            clang-runtime: '21'
+            cling: Off
+            cppyy: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host;NVPTX"
           - name: ubu22-arm-gcc12-clang-repl-20-coverage
             os: ubuntu-22.04-arm
             compiler: gcc-12
@@ -66,6 +74,14 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # Ubuntu X86 Jobs
+          - name: ubu24-x86-gcc12-clang-repl-21
+            os: ubuntu-24.04
+            compiler: gcc-12
+            clang-runtime: '21'
+            cling: Off
+            cppyy: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host;NVPTX"
           - name: ubu24-x86-gcc12-clang-repl-20
             os: ubuntu-24.04
             compiler: gcc-12
@@ -100,6 +116,14 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # MacOS Arm Jobs
+          - name: osx15-arm-clang-clang-repl-21
+            os: macos-15
+            compiler: clang
+            clang-runtime: '21'
+            cling: Off
+            cppyy: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host"
           - name: osx15-arm-clang-clang-repl-20
             os: macos-15
             compiler: clang
@@ -134,6 +158,14 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # MacOS X86 Jobs
+          - name: osx13-x86-clang-clang-repl-21
+            os: macos-13
+            compiler: clang
+            clang-runtime: '21'
+            cling: Off
+            cppyy: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host"
           - name: osx13-x86-clang-clang-repl-20
             os: macos-13
             compiler: clang
@@ -168,6 +200,13 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # Windows Arm Jobs
+          - name: win11-msvc-clang-repl-21
+            os: windows-11-arm
+            compiler: msvc
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host;NVPTX"
           - name: win11-msvc-clang-repl-20
             os: windows-11-arm
             compiler: msvc
@@ -184,6 +223,13 @@ jobs:
             llvm_enable_projects: "clang"
             llvm_targets_to_build: "host;NVPTX"
           # Windows X86 Jobs
+          - name: win2025-msvc-clang-repl-21
+            os: windows-2025
+            compiler: msvc
+            clang-runtime: '21'
+            cling: Off
+            llvm_enable_projects: "clang"
+            llvm_targets_to_build: "host;NVPTX"
           - name: win2025-msvc-clang-repl-20
             os: windows-2025
             compiler: msvc
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5d1aa034d..1850ddcc4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -68,14 +68,14 @@ include(GNUInstallDirs)
   ## Define supported version of clang and llvm
 
   set(CLANG_MIN_SUPPORTED 18.0)
-  set(CLANG_MAX_SUPPORTED "20.1.x")
-  set(CLANG_VERSION_UPPER_BOUND 21.0.0)
+  set(CLANG_MAX_SUPPORTED "21.1.x")
+  set(CLANG_VERSION_UPPER_BOUND 22.0.0)
   set(LLD_MIN_SUPPORTED 18.0)
-  set(LLD_MAX_SUPPORTED "20.1.x")
-  set(LLD_VERSION_UPPER_BOUND 21.0.0)
+  set(LLD_MAX_SUPPORTED "21.1.x")
+  set(LLD_VERSION_UPPER_BOUND 22.0.0)
   set(LLVM_MIN_SUPPORTED 18.0)
-  set(LLVM_MAX_SUPPORTED "20.1.x")
-  set(LLVM_VERSION_UPPER_BOUND 21.0.0)
+  set(LLVM_MAX_SUPPORTED "21.1.x")
+  set(LLVM_VERSION_UPPER_BOUND 22.0.0)
 
   ## Set Cmake packages search order
 
diff --git a/lib/CppInterOp/Compatibility.h b/lib/CppInterOp/Compatibility.h
index 24c822dec..fe8eed44c 100644
--- a/lib/CppInterOp/Compatibility.h
+++ b/lib/CppInterOp/Compatibility.h
@@ -31,6 +31,17 @@ static inline char* GetEnv(const char* Var_Name) {
 #endif
 }
 
+#if CLANG_VERSION_MAJOR < 21
+#define clang_LookupResult_Found clang::LookupResult::Found
+#define clang_LookupResult_Not_Found clang::LookupResult::NotFound
+#define clang_LookupResult_Found_Overloaded clang::LookupResult::FoundOverloaded
+#else
+#define clang_LookupResult_Found clang::LookupResultKind::Found
+#define clang_LookupResult_Not_Found clang::LookupResultKind::NotFound
+#define clang_LookupResult_Found_Overloaded                                    \
+  clang::LookupResultKind::FoundOverloaded
+#endif
+
 #if CLANG_VERSION_MAJOR < 19
 #define Template_Deduction_Result Sema::TemplateDeductionResult
 #define Template_Deduction_Result_Success                                      \
diff --git a/lib/CppInterOp/CppInterOp.cpp b/lib/CppInterOp/CppInterOp.cpp
index f1527b4a8..896a20e32 100755
--- a/lib/CppInterOp/CppInterOp.cpp
+++ b/lib/CppInterOp/CppInterOp.cpp
@@ -1307,16 +1307,16 @@ bool GetClassTemplatedMethods(const std::string& name, TCppScope_t parent,
   auto* DC = clang::Decl::castToDeclContext(D);
   Cpp_utils::Lookup::Named(&S, R, DC);
 
-  if (R.getResultKind() == clang::LookupResult::NotFound && funcs.empty())
+  if (R.getResultKind() == clang_LookupResult_Not_Found && funcs.empty())
     return false;
 
   // Distinct match, single Decl
-  else if (R.getResultKind() == clang::LookupResult::Found) {
+  else if (R.getResultKind() == clang_LookupResult_Found) {
     if (IsTemplatedFunction(R.getFoundDecl()))
       funcs.push_back(R.getFoundDecl());
   }
   // Loop over overload set
-  else if (R.getResultKind() == clang::LookupResult::FoundOverloaded) {
+  else if (R.getResultKind() == clang_LookupResult_Found_Overloaded) {
     for (auto* Found : R)
       if (IsTemplatedFunction(Found))
         funcs.push_back(Found);
diff --git a/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch b/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
new file mode 100644
index 000000000..a1ffeccc8
--- /dev/null
+++ b/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
@@ -0,0 +1,20 @@
+diff --git a/llvm/cmake/modules/CrossCompile.cmake b/llvm/cmake/modules/CrossCompile.cmake
+index 39b4abaa0..474ceddbb 100644
+--- a/llvm/cmake/modules/CrossCompile.cmake
++++ b/llvm/cmake/modules/CrossCompile.cmake
+@@ -74,10 +74,12 @@ function(llvm_create_cross_target project_name target_name toolchain buildtype)
+   endif()
+ 
+   add_custom_command(OUTPUT ${${project_name}_${target_name}_BUILD}/CMakeCache.txt
+-    COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}"
++    COMMAND ${CMAKE_COMMAND} -G Ninja
+         -DCMAKE_MAKE_PROGRAM="${CMAKE_MAKE_PROGRAM}"
+-        -DCMAKE_C_COMPILER_LAUNCHER="${CMAKE_C_COMPILER_LAUNCHER}"
+-        -DCMAKE_CXX_COMPILER_LAUNCHER="${CMAKE_CXX_COMPILER_LAUNCHER}"
++        -DCMAKE_C_COMPILER="clang-cl"
++        -DCMAKE_CXX_COMPILER="clang-cl"
++        -DCMAKE_ASM_MASM_COMPILER=llvm-ml
++        -DCMAKE_ASM_MASM_FLAGS="-m64"
+         ${CROSS_TOOLCHAIN_FLAGS_${target_name}} ${CMAKE_CURRENT_SOURCE_DIR}
+         ${CROSS_TOOLCHAIN_FLAGS_${project_name}_${target_name}}
+         -DLLVM_TARGET_IS_CROSSCOMPILE_HOST=TRUE
diff --git a/patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch b/patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch
new file mode 100644
index 000000000..32ac45c13
--- /dev/null
+++ b/patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch
@@ -0,0 +1,15 @@
+diff --git a/clang/lib/Interpreter/Wasm.cpp b/clang/lib/Interpreter/Wasm.cpp
+index aa10b160ccf8..184867e2b55f 100644
+--- a/clang/lib/Interpreter/Wasm.cpp
++++ b/clang/lib/Interpreter/Wasm.cpp
+@@ -76,8 +76,8 @@ llvm::Error WasmIncrementalExecutor::addModule(PartialTranslationUnit &PTU) {
+   llvm::TargetMachine *TargetMachine = Target->createTargetMachine(
+       PTU.TheModule->getTargetTriple(), "", "", TO, llvm::Reloc::Model::PIC_);
+   PTU.TheModule->setDataLayout(TargetMachine->createDataLayout());
+-  std::string ObjectFileName = PTU.TheModule->getName().str() + ".o";
+-  std::string BinaryFileName = PTU.TheModule->getName().str() + ".wasm";
++  std::string ObjectFileName = "/tmp/" + PTU.TheModule->getName().str() + ".o";
++  std::string BinaryFileName = "/tmp/" + PTU.TheModule->getName().str() + ".wasm";
+ 
+   std::error_code Error;
+   llvm::raw_fd_ostream ObjectFileOutput(llvm::StringRef(ObjectFileName), Error);

From a6919e748214d03f324c847af2936e0fe89f3a6f Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Tue, 15 Jul 2025 21:03:13 +0100
Subject: [PATCH 07/15] Update Windows-emscripten-clang21-1-CrossCompile.patch

---
 .../llvm/Windows-emscripten-clang21-1-CrossCompile.patch    | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch b/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
index a1ffeccc8..00e0aef6f 100644
--- a/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
+++ b/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
@@ -8,9 +8,9 @@ index 39b4abaa0..474ceddbb 100644
    add_custom_command(OUTPUT ${${project_name}_${target_name}_BUILD}/CMakeCache.txt
 -    COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}"
 +    COMMAND ${CMAKE_COMMAND} -G Ninja
-         -DCMAKE_MAKE_PROGRAM="${CMAKE_MAKE_PROGRAM}"
--        -DCMAKE_C_COMPILER_LAUNCHER="${CMAKE_C_COMPILER_LAUNCHER}"
--        -DCMAKE_CXX_COMPILER_LAUNCHER="${CMAKE_CXX_COMPILER_LAUNCHER}"
+         "-DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}"
+-        "-DCMAKE_C_COMPILER_LAUNCHER=${CMAKE_C_COMPILER_LAUNCHER}"
+-        "-DCMAKE_CXX_COMPILER_LAUNCHER=${CMAKE_CXX_COMPILER_LAUNCHER}"
 +        -DCMAKE_C_COMPILER="clang-cl"
 +        -DCMAKE_CXX_COMPILER="clang-cl"
 +        -DCMAKE_ASM_MASM_COMPILER=llvm-ml

From a4801b4edf14f974a293fc7d77181e5077e7419c Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Wed, 16 Jul 2025 09:20:19 +0100
Subject: [PATCH 08/15] Update exports.ld

---
 lib/CppInterOp/exports.ld | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/CppInterOp/exports.ld b/lib/CppInterOp/exports.ld
index e22490f2a..dbe06bb32 100644
--- a/lib/CppInterOp/exports.ld
+++ b/lib/CppInterOp/exports.ld
@@ -51,4 +51,6 @@
 -Wl,--export=_ZNK5clang12FunctionDecl12getNumParamsEv
 -Wl,--export=__clang_Interpreter_SetValueNoAlloc
 -Wl,--export=__clang_Interpreter_SetValueWithAlloc
+-Wl,--export=_ZN5clang11Interpreter6createENSt3__210unique_ptrINS_16CompilerInstanceENS1_14default_deleteIS3_EEEENS2_IN4llvm3orc12LLJITBuilderENS4_IS9_EEEE 
+
 -Wl,--export=_ZN4llvm15SmallVectorBaseIjE8set_sizeEm
\ No newline at end of file

From 113b7a6732e21225d648f13868dd9759cf73f530 Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Wed, 16 Jul 2025 10:59:46 +0100
Subject: [PATCH 09/15] Update exports.ld

---
 lib/CppInterOp/exports.ld | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/CppInterOp/exports.ld b/lib/CppInterOp/exports.ld
index dbe06bb32..918c6fd34 100644
--- a/lib/CppInterOp/exports.ld
+++ b/lib/CppInterOp/exports.ld
@@ -51,6 +51,7 @@
 -Wl,--export=_ZNK5clang12FunctionDecl12getNumParamsEv
 -Wl,--export=__clang_Interpreter_SetValueNoAlloc
 -Wl,--export=__clang_Interpreter_SetValueWithAlloc
--Wl,--export=_ZN5clang11Interpreter6createENSt3__210unique_ptrINS_16CompilerInstanceENS1_14default_deleteIS3_EEEENS2_IN4llvm3orc12LLJITBuilderENS4_IS9_EEEE 
+-Wl,--export=_ZN5clang11Interpreter6createENSt3__210unique_ptrINS_16CompilerInstanceENS1_14default_deleteIS3_EEEENS2_IN4llvm3orc12LLJITBuilderENS4_IS9_EEEE
+-Wl,--export=_ZNK5clang13CXXRecordDecl19isInjectedClassNameEv
 
 -Wl,--export=_ZN4llvm15SmallVectorBaseIjE8set_sizeEm
\ No newline at end of file

From ed5b80c2bf99fc964136965d4304955ef503d7cd Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Tue, 9 Sep 2025 16:02:20 +0100
Subject: [PATCH 10/15] Define Print_Canonical_Types for llvm 21 compatibility

---
 lib/CppInterOp/Compatibility.h | 6 ++++++
 lib/CppInterOp/CppInterOp.cpp  | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/CppInterOp/Compatibility.h b/lib/CppInterOp/Compatibility.h
index fe8eed44c..b1dc2daa9 100644
--- a/lib/CppInterOp/Compatibility.h
+++ b/lib/CppInterOp/Compatibility.h
@@ -31,6 +31,12 @@ static inline char* GetEnv(const char* Var_Name) {
 #endif
 }
 
+#if CLANG_VERSION_MAJOR < 21
+#define Print_Canonical_Types PrintCanonicalTypes
+#else
+#define Print_Canonical_Types PrintAsCanonical
+#endif
+
 #if CLANG_VERSION_MAJOR < 21
 #define clang_LookupResult_Found clang::LookupResult::Found
 #define clang_LookupResult_Not_Found clang::LookupResult::NotFound
diff --git a/lib/CppInterOp/CppInterOp.cpp b/lib/CppInterOp/CppInterOp.cpp
index 896a20e32..0290dbe01 100755
--- a/lib/CppInterOp/CppInterOp.cpp
+++ b/lib/CppInterOp/CppInterOp.cpp
@@ -2108,7 +2108,7 @@ static void GetDeclName(const clang::Decl* D, ASTContext& Context,
   PrintingPolicy Policy(Context.getPrintingPolicy());
   Policy.SuppressTagKeyword = true;
   Policy.SuppressUnwrittenScope = true;
-  Policy.PrintCanonicalTypes = true;
+  Policy.Print_Canonical_Types = true;
   if (const TypeDecl* TD = dyn_cast<TypeDecl>(D)) {
     // This is a class, struct, or union member.
     QualType QT;

From 19e195177773c1dc599a417b6d152372d89b5a0f Mon Sep 17 00:00:00 2001
From: Vipul Cariappa <vipulcariappa@gmail.com>
Date: Mon, 15 Sep 2025 10:21:26 +0200
Subject: [PATCH 11/15] fix instantiation of templated class

instantiate templated classes to TSK_ExplicitInstantiationDefinition
---
 lib/CppInterOp/Compatibility.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/CppInterOp/Compatibility.h b/lib/CppInterOp/Compatibility.h
index b1dc2daa9..c6ab5cc70 100644
--- a/lib/CppInterOp/Compatibility.h
+++ b/lib/CppInterOp/Compatibility.h
@@ -429,11 +429,11 @@ inline void InstantiateClassTemplateSpecialization(
 #if CLANG_VERSION_MAJOR < 20
   interp.getSema().InstantiateClassTemplateSpecialization(
       clang::SourceLocation::getFromRawEncoding(1), CTSD,
-      clang::TemplateSpecializationKind::TSK_Undeclared, /*Complain=*/true);
+      clang::TemplateSpecializationKind::TSK_ExplicitInstantiationDefinition, /*Complain=*/true);
 #else
   interp.getSema().InstantiateClassTemplateSpecialization(
       clang::SourceLocation::getFromRawEncoding(1), CTSD,
-      clang::TemplateSpecializationKind::TSK_Undeclared, /*Complain=*/true,
+      clang::TemplateSpecializationKind::TSK_ExplicitInstantiationDefinition, /*Complain=*/true,
       /*PrimaryHasMatchedPackOnParmToNonPackOnArg=*/false);
 #endif
 }

From eaf352c49e2feded890c916f69ad5749a4a1ab76 Mon Sep 17 00:00:00 2001
From: Vipul Cariappa <vipulcariappa@gmail.com>
Date: Mon, 15 Sep 2025 10:26:26 +0200
Subject: [PATCH 12/15] fix instantiation of templated class

instantiate templated classes to TSK_ExplicitInstantiationDefinition
---
 lib/CppInterOp/Compatibility.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/CppInterOp/Compatibility.h b/lib/CppInterOp/Compatibility.h
index b1dc2daa9..42463c0b9 100644
--- a/lib/CppInterOp/Compatibility.h
+++ b/lib/CppInterOp/Compatibility.h
@@ -429,11 +429,13 @@ inline void InstantiateClassTemplateSpecialization(
 #if CLANG_VERSION_MAJOR < 20
   interp.getSema().InstantiateClassTemplateSpecialization(
       clang::SourceLocation::getFromRawEncoding(1), CTSD,
-      clang::TemplateSpecializationKind::TSK_Undeclared, /*Complain=*/true);
+      clang::TemplateSpecializationKind::TSK_ExplicitInstantiationDefinition,
+      /*Complain=*/true);
 #else
   interp.getSema().InstantiateClassTemplateSpecialization(
       clang::SourceLocation::getFromRawEncoding(1), CTSD,
-      clang::TemplateSpecializationKind::TSK_Undeclared, /*Complain=*/true,
+      clang::TemplateSpecializationKind::TSK_ExplicitInstantiationDefinition,
+      /*Complain=*/true,
       /*PrimaryHasMatchedPackOnParmToNonPackOnArg=*/false);
 #endif
 }

From bbbf6d0210107995bfc1057d72b0a2354b36dba7 Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Mon, 15 Sep 2025 21:56:11 +0100
Subject: [PATCH 13/15] Apply some PR comments

---
 .github/workflows/emscripten.yml              |  4 ++--
 Emscripten-build-instructions.md              | 14 ++++++-------
 README.md                                     |  8 ++++----
 ...ws-emscripten-clang21-1-CrossCompile.patch | 20 -------------------
 ...-1-shift-temporary-files-to-tmp-dir.patch} |  0
 5 files changed, 13 insertions(+), 33 deletions(-)
 delete mode 100644 patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
 rename patches/llvm/{emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch => emscripten-clang21-1-shift-temporary-files-to-tmp-dir.patch} (100%)

diff --git a/.github/workflows/emscripten.yml b/.github/workflows/emscripten.yml
index e4b2d8825..1f8648015 100644
--- a/.github/workflows/emscripten.yml
+++ b/.github/workflows/emscripten.yml
@@ -355,8 +355,8 @@ jobs:
           }
           elseif ( "${{ matrix.clang-runtime }}" -imatch "21" )
           {
-            git apply -v Windows-emscripten-clang21-1-CrossCompile.patch
-            git apply -v emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch
+            git apply -v emscripten-clang21-1-shift-temporary-files-to-tmp-dir.patch
+            git apply -v emscripten-clang21-2-enable_exception_handling.patch
           }
           cd build
           echo "Apply clang${{ matrix.clang-runtime }}-*.patch patches:"
diff --git a/Emscripten-build-instructions.md b/Emscripten-build-instructions.md
index 0854fed2d..f7c40673b 100644
--- a/Emscripten-build-instructions.md
+++ b/Emscripten-build-instructions.md
@@ -42,11 +42,11 @@ $env:PWD_DIR= $PWD.Path
 $env:SYSROOT_PATH="$env:EMSDK/upstream/emscripten/cache/sysroot"
 ```
 
-Now clone the 20.x release of the LLVM project repository and CppInterOp (the building of the emscripten version of llvm can be
+Now clone the 21.x release of the LLVM project repository and CppInterOp (the building of the emscripten version of llvm can be
 avoided by executing micromamba install llvm -c <https://repo.mamba.pm/emscripten-forge> and setting the LLVM_BUILD_DIR/$env:LLVM_BUILD_DIR appropriately)
 
 ```bash
-git clone --depth=1 --branch release/20.x https://github.com/llvm/llvm-project.git
+git clone --depth=1 --branch release/21.x https://github.com/llvm/llvm-project.git
 git clone --depth=1 https://github.com/compiler-research/CppInterOp.git
 ```
 
@@ -55,16 +55,16 @@ executing
 
 ```bash
 cd ./llvm-project/
-git apply -v ../CppInterOp/patches/llvm/emscripten-clang20-*.patch
+git apply -v ../CppInterOp/patches/llvm/emscripten-clang21-*.patch
 ```
 
 On Windows execute the following
 
 ```powershell
 cd .\llvm-project\
-cp -r ..\patches\llvm\emscripten-clang20*
-git apply -v emscripten-clang20-2-shift-temporary-files-to-tmp-dir.patch
-git apply -v emscripten-clang20-3-enable_exception_handling.patch
+cp -r ..\patches\llvm\emscripten-clang21*
+git apply -v emscripten-clang21-1-shift-temporary-files-to-tmp-dir.patch
+git apply -v emscripten-clang21-2-enable_exception_handling.patch
 ```
 
 We are now in a position to build an emscripten build of llvm by executing the following on Linux
@@ -343,7 +343,7 @@ of llvm you are building against)
 ```bash
 cd ../..
 git clone --depth=1 https://github.com/compiler-research/xeus-cpp.git
-export LLVM_VERSION=20
+export LLVM_VERSION=21
 cd ./xeus-cpp
 mkdir build
 cd build
diff --git a/README.md b/README.md
index e14a94d94..bd93923eb 100644
--- a/README.md
+++ b/README.md
@@ -104,10 +104,10 @@ git clone --depth=1 https://github.com/compiler-research/cppyy-backend.git
 
 #### Setup Clang-REPL
 
-Clone the 20.x release of the LLVM project repository.
+Clone the 1.x release of the LLVM project repository.
 
 ```bash
-git clone --depth=1 --branch release/20.x https://github.com/llvm/llvm-project.git
+git clone --depth=1 --branch release/21.x https://github.com/llvm/llvm-project.git
 cd llvm-project
 ```
 
@@ -406,10 +406,10 @@ git clone --depth=1 https://github.com/compiler-research/cppyy-backend.git
 
 #### Setup Clang-REPL
 
-Clone the 20.x release of the LLVM project repository.
+Clone the 21.x release of the LLVM project repository.
 
 ```bash
-git clone --depth=1 --branch release/20.x https://github.com/llvm/llvm-project.git
+git clone --depth=1 --branch release/21.x https://github.com/llvm/llvm-project.git
 cd llvm-project
 ```
 
diff --git a/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch b/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
deleted file mode 100644
index 00e0aef6f..000000000
--- a/patches/llvm/Windows-emscripten-clang21-1-CrossCompile.patch
+++ /dev/null
@@ -1,20 +0,0 @@
-diff --git a/llvm/cmake/modules/CrossCompile.cmake b/llvm/cmake/modules/CrossCompile.cmake
-index 39b4abaa0..474ceddbb 100644
---- a/llvm/cmake/modules/CrossCompile.cmake
-+++ b/llvm/cmake/modules/CrossCompile.cmake
-@@ -74,10 +74,12 @@ function(llvm_create_cross_target project_name target_name toolchain buildtype)
-   endif()
- 
-   add_custom_command(OUTPUT ${${project_name}_${target_name}_BUILD}/CMakeCache.txt
--    COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}"
-+    COMMAND ${CMAKE_COMMAND} -G Ninja
-         "-DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}"
--        "-DCMAKE_C_COMPILER_LAUNCHER=${CMAKE_C_COMPILER_LAUNCHER}"
--        "-DCMAKE_CXX_COMPILER_LAUNCHER=${CMAKE_CXX_COMPILER_LAUNCHER}"
-+        -DCMAKE_C_COMPILER="clang-cl"
-+        -DCMAKE_CXX_COMPILER="clang-cl"
-+        -DCMAKE_ASM_MASM_COMPILER=llvm-ml
-+        -DCMAKE_ASM_MASM_FLAGS="-m64"
-         ${CROSS_TOOLCHAIN_FLAGS_${target_name}} ${CMAKE_CURRENT_SOURCE_DIR}
-         ${CROSS_TOOLCHAIN_FLAGS_${project_name}_${target_name}}
-         -DLLVM_TARGET_IS_CROSSCOMPILE_HOST=TRUE
diff --git a/patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch b/patches/llvm/emscripten-clang21-1-shift-temporary-files-to-tmp-dir.patch
similarity index 100%
rename from patches/llvm/emscripten-clang21-2-shift-temporary-files-to-tmp-dir.patch
rename to patches/llvm/emscripten-clang21-1-shift-temporary-files-to-tmp-dir.patch

From c97eb37d47b8a326032f9a00123083afedca44f0 Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Mon, 15 Sep 2025 22:01:56 +0100
Subject: [PATCH 14/15] Updat 1.x to 21.x readme.md

---
 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/README.md b/README.md
index bd93923eb..6976c9b1e 100644
--- a/README.md
+++ b/README.md
@@ -104,7 +104,7 @@ git clone --depth=1 https://github.com/compiler-research/cppyy-backend.git
 
 #### Setup Clang-REPL
 
-Clone the 1.x release of the LLVM project repository.
+Clone the 21.x release of the LLVM project repository.
 
 ```bash
 git clone --depth=1 --branch release/21.x https://github.com/llvm/llvm-project.git

From 541711ea03fbafcb51564a252834cf7471d69299 Mon Sep 17 00:00:00 2001
From: mcbarton <matthew.c.barton@hotmail.co.uk>
Date: Mon, 15 Sep 2025 22:05:24 +0100
Subject: [PATCH 15/15] Update rest of docs for llvm 21

---
 docs/DevelopersDocumentation.rst       |  4 ++--
 docs/Emscripten-build-instructions.rst | 14 +++++++-------
 docs/InstallationAndUsage.rst          |  4 ++--
 docs/ReleaseNotes.md                   |  2 +-
 4 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/docs/DevelopersDocumentation.rst b/docs/DevelopersDocumentation.rst
index e586cc5d8..a440e05c6 100644
--- a/docs/DevelopersDocumentation.rst
+++ b/docs/DevelopersDocumentation.rst
@@ -34,11 +34,11 @@ library
  Setup Clang-REPL
 ******************
 
-Clone the 20.x release of the LLVM project repository.
+Clone the 21.x release of the LLVM project repository.
 
 .. code:: bash
 
-   git clone --depth=1 --branch release/20.x https://github.com/llvm/llvm-project.git
+   git clone --depth=1 --branch release/21.x https://github.com/llvm/llvm-project.git
    cd llvm-project
 
 ******************
diff --git a/docs/Emscripten-build-instructions.rst b/docs/Emscripten-build-instructions.rst
index 89e9be0d2..87de691ac 100644
--- a/docs/Emscripten-build-instructions.rst
+++ b/docs/Emscripten-build-instructions.rst
@@ -57,7 +57,7 @@ and on Windows execute in Powershell
    $env:PWD_DIR= $PWD.Path
    $env:SYSROOT_PATH="$env:EMSDK/upstream/emscripten/cache/sysroot"
 
-Now clone the 20.x release of the LLVM project repository and CppInterOp
+Now clone the 21.x release of the LLVM project repository and CppInterOp
 (the building of the emscripten version of llvm can be avoided by
 executing micromamba install llvm -c
 <https://repo.mamba.pm/emscripten-forge> and setting the LLVM_BUILD_DIR/$env:LLVM_BUILD_DIR
@@ -65,7 +65,7 @@ appropriately)
 
 .. code:: bash
 
-   git clone --depth=1 --branch release/20.x https://github.com/llvm/llvm-project.git
+   git clone --depth=1 --branch release/21.x https://github.com/llvm/llvm-project.git
    git clone --depth=1 https://github.com/compiler-research/CppInterOp.git
 
 Now move into the cloned llvm-project folder and apply the required patches. On Linux and osx this
@@ -74,16 +74,16 @@ executing
 .. code:: bash
 
    cd ./llvm-project/
-   git apply -v ../CppInterOp/patches/llvm/emscripten-clang20-*.patch
+   git apply -v ../CppInterOp/patches/llvm/emscripten-clang21-*.patch
 
 On Windows execute the following
 
 .. code:: powershell
 
    cd .\llvm-project\
-   cp -r ..\patches\llvm\emscripten-clang20*
-   git apply -v emscripten-clang20-2-shift-temporary-files-to-tmp-dir.patch
-   git apply -v emscripten-clang20-3-enable_exception_handling.patch
+   cp -r ..\patches\llvm\emscripten-clang21*
+   git apply -v emscripten-clang21-1-shift-temporary-files-to-tmp-dir.patch
+   git apply -v emscripten-clang21-2-enable_exception_handling.patch
 
 We are now in a position to build an emscripten build of llvm by executing the following on Linux
 and osx
@@ -365,7 +365,7 @@ build folder, you can build the wasm version of xeus-cpp by executing
 
    cd ../..
    git clone --depth=1 https://github.com/compiler-research/xeus-cpp.git
-   export LLVM_VERSION=20
+   export LLVM_VERSION=21
    cd ./xeus-cpp
    mkdir build
    cd build
diff --git a/docs/InstallationAndUsage.rst b/docs/InstallationAndUsage.rst
index 3ec6470b4..526e32882 100644
--- a/docs/InstallationAndUsage.rst
+++ b/docs/InstallationAndUsage.rst
@@ -34,11 +34,11 @@ library
  Setup Clang-REPL
 ******************
 
-Clone the 20.x release of the LLVM project repository.
+Clone the 21.x release of the LLVM project repository.
 
 .. code:: bash
 
-   git clone --depth=1 --branch release/20.x https://github.com/llvm/llvm-project.git
+   git clone --depth=1 --branch release/21.x https://github.com/llvm/llvm-project.git
    cd llvm-project
 
 ******************
diff --git a/docs/ReleaseNotes.md b/docs/ReleaseNotes.md
index 811519dea..a39ef6220 100644
--- a/docs/ReleaseNotes.md
+++ b/docs/ReleaseNotes.md
@@ -25,7 +25,7 @@ infrastructure are described first.
 ## External Dependencies
 
 - CppInterOp now works with:
-  - llvm20
+  - llvm21
 
 ## Introspection