https://github.com/eugeneepshteyn created
https://github.com/llvm/llvm-project/pull/222630
#221724 stopped exporting a project's targets file when that project is enabled
only as another project's dependency, but the build-tree `ClangConfig.cmake`
and `MLIRConfig.cmake` still include it unconditionally. `find_package()`
therefore finds the config and fails inside it:
```
CMake Error at build/lib/cmake/clang/ClangConfig.cmake:19 (include):
include could not find requested file:
build/lib/cmake/clang/ClangTargets.cmake
Call Stack (most recent call first):
CMakeLists.txt:90 (find_package)
```
This breaks any configuration that enables Flang without also enabling Clang or
MLIR explicitly: `runtimes/CMakeLists.txt` calls `find_package(Clang ...)`,
which is deliberately not `REQUIRED` and is expected to tolerate an unavailable
package — but a *half-generated* package is a hard error rather than a "not
found". Concretely, `-DLLVM_ENABLE_PROJECTS=flang
-DLLVM_ENABLE_RUNTIMES=flang-rt` fails at `runtimes-configure`, which is the
configuration premerge uses for flang-rt changes.
This patch guards the include the same way the export itself is guarded, so a
dependency-only project generates a config without a dangling include. The
install-tree path already handles this through `get_config_exports_includes()`;
only the build-tree path was missed.
MLIR has the same defect and is fixed here too. It is currently latent only
because `runtimes/CMakeLists.txt` calls `find_package(Clang)` and not
`find_package(MLIR)`; a `find_package(MLIR)` against a dependency-only build
tree fails identically at `MLIRConfig.cmake:33`.
**Verification** (configure-only, no build needed to reproduce):
Configuring with `-DLLVM_ENABLE_PROJECTS=flang -DLLVM_ENABLE_RUNTIMES=flang-rt`
and then running `find_package` against the generated build tree, exactly as
`runtimes/CMakeLists.txt` does:
| | `ClangConfig` | `ClangTargets` | config includes targets |
`find_package(Clang)` | `find_package(MLIR)` |
|---|---|---|---|---|---|
| before | present | absent | yes | **error** | **error** |
| after | present | absent | no | ok | ok |
Control, with `-DLLVM_ENABLE_PROJECTS='clang;mlir;flang'` (both explicitly
enabled): targets files are exported and the configs include them, as before —
unchanged by this patch.
An alternative fix would be to emit `include(... OPTIONAL)`, matching the
distribution path in `LLVMDistributionSupport.cmake`; I chose the explicit
guard because it mirrors the two existing `LLVM_DEPENDENCY_ONLY_PROJECTS`
checks in the same files. Happy to switch if you prefer the other form.
>From 27a3f3c279130f98ebd1a344a11909c6d7467a0c Mon Sep 17 00:00:00 2001
From: Eugene Epshteyn <[email protected]>
Date: Thu, 10 Sep 2026 05:35:08 -0700
Subject: [PATCH] [CMake] Don't reference unexported targets from
dependency-only configs
When a project is enabled only to satisfy another project's dependency, its
targets file is no longer exported, but the build-tree ClangConfig.cmake and
MLIRConfig.cmake still included it unconditionally. find_package() then found
the config and failed inside it:
CMake Error at build/lib/cmake/clang/ClangConfig.cmake:19 (include):
include could not find requested file:
build/lib/cmake/clang/ClangTargets.cmake
This breaks configurations that enable Flang without also enabling Clang or
MLIR explicitly, because runtimes/CMakeLists.txt calls find_package(Clang),
which is not REQUIRED and is expected to tolerate an unavailable package.
Guard the include the same way the export itself is guarded, so a
dependency-only project generates a config without a dangling include.
---
clang/cmake/modules/CMakeLists.txt | 6 +++++-
mlir/cmake/modules/CMakeLists.txt | 6 +++++-
2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/clang/cmake/modules/CMakeLists.txt
b/clang/cmake/modules/CMakeLists.txt
index 845250e4e0fd9..1dde1a0075fa9 100644
--- a/clang/cmake/modules/CMakeLists.txt
+++ b/clang/cmake/modules/CMakeLists.txt
@@ -30,7 +30,11 @@ endif()
# Generate ClangConfig.cmake for the build tree.
set(CLANG_CONFIG_CMAKE_DIR "${clang_cmake_builddir}")
set(CLANG_CONFIG_LLVM_CMAKE_DIR "${llvm_cmake_builddir}")
-set(CLANG_CONFIG_INCLUDE_EXPORTS
"include(\"${clang_cmake_builddir}/ClangTargets.cmake\")")
+if(NOT "clang" IN_LIST LLVM_DEPENDENCY_ONLY_PROJECTS)
+ set(CLANG_CONFIG_INCLUDE_EXPORTS
"include(\"${clang_cmake_builddir}/ClangTargets.cmake\")")
+else()
+ set(CLANG_CONFIG_INCLUDE_EXPORTS "")
+endif()
set(CLANG_CONFIG_INCLUDE_DIRS
"${CLANG_SOURCE_DIR}/include"
"${CLANG_BINARY_DIR}/include"
diff --git a/mlir/cmake/modules/CMakeLists.txt
b/mlir/cmake/modules/CMakeLists.txt
index 7030666ed927c..cf8f430c827c6 100644
--- a/mlir/cmake/modules/CMakeLists.txt
+++ b/mlir/cmake/modules/CMakeLists.txt
@@ -52,7 +52,11 @@ get_property(MLIR_CAPI_LIBS GLOBAL PROPERTY MLIR_CAPI_LIBS)
# Generate MlirConfig.cmake for the build tree.
set(MLIR_CONFIG_CMAKE_DIR "${mlir_cmake_builddir}")
set(MLIR_CONFIG_LLVM_CMAKE_DIR "${llvm_cmake_builddir}")
-set(MLIR_CONFIG_INCLUDE_EXPORTS
"include(\"\${MLIR_CMAKE_DIR}/MLIRTargets.cmake\")")
+if(NOT "mlir" IN_LIST LLVM_DEPENDENCY_ONLY_PROJECTS)
+ set(MLIR_CONFIG_INCLUDE_EXPORTS
"include(\"\${MLIR_CMAKE_DIR}/MLIRTargets.cmake\")")
+else()
+ set(MLIR_CONFIG_INCLUDE_EXPORTS "")
+endif()
set(MLIR_CONFIG_INCLUDE_DIRS
"${MLIR_SOURCE_DIR}/include"
"${MLIR_BINARY_DIR}/include"
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