build: require at least major version 23 for llvm

Author: gf712

src/CMakeLists.txt

@@ -302,7 +302,10 @@ target_link_libraries(python-cpp
 )
 
 # LLVM backend
-find_package(LLVM CONFIG 23)
+# No version is requested here for the same reason as in executable/mlir: LLVM's
+# config-version file wants an exact major.minor match. The MLIR subdirectory has
+# already validated the major version by this point.
+find_package(LLVM CONFIG)
 if(ENABLE_LLVM_BACKEND AND NOT LLVM_FOUND)
   message(FATAL_ERROR "Could not find LLVM in the local environment")
 elseif(ENABLE_LLVM_BACKEND AND LLVM_FOUND)

src/executable/mlir/CMakeLists.txt

@@ -1,5 +1,15 @@
-find_package(LLVM 23 REQUIRED CONFIG)
-message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")
+# LLVMConfigVersion.cmake only accepts an exact major.minor match, so asking for
+# "23" means "23.0" and rejects the 23.1.x releases. Search without a version,
+# newest install first, and enforce the major version ourselves.
+set(CMAKE_FIND_PACKAGE_SORT_ORDER NATURAL)
+set(CMAKE_FIND_PACKAGE_SORT_DIRECTION DEC)
+find_package(LLVM REQUIRED CONFIG)
+if(LLVM_VERSION_MAJOR LESS 23)
+  message(FATAL_ERROR
+          "LLVM 23 or newer is required, found ${LLVM_PACKAGE_VERSION} in ${LLVM_DIR}. "
+          "Point CMake at a newer install with -DLLVM_DIR=<prefix>/lib/cmake/llvm")
+endif()
+message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR} (${LLVM_PACKAGE_VERSION})")
 
 find_package(MLIR CONFIG REQUIRED
              HINTS ${LLVM_DIR}/../lib/cmake/mlir)