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Building with the source directory rooted in the libc subdirectory isn't
tested in CI and can lead to subtle build problems (cf. #118871).

Let's fail fast with a helpful error message instead to help users
configure libc correctly.

set(LLVM_SUBPROJECT_TITLE "libc")

if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
message(FATAL_ERROR "Builds rooted in the libc directory are not supported. "
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Seems nicer to me to error out, but I'm open to changing this to a warning instead.

@llvmbot
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llvmbot commented Dec 10, 2024

@llvm/pr-subscribers-libc

Author: Carlo Cabrera (carlocab)

Changes

Building with the source directory rooted in the libc subdirectory isn't
tested in CI and can lead to subtle build problems (cf. #118871).

Let's fail fast with a helpful error message instead to help users
configure libc correctly.


Full diff: https://github.com/llvm/llvm-project/pull/119426.diff

1 Files Affected:

  • (modified) libc/CMakeLists.txt (+6)
diff --git a/libc/CMakeLists.txt b/libc/CMakeLists.txt
index 6d48489284faef..3ad549a66f14e6 100644
--- a/libc/CMakeLists.txt
+++ b/libc/CMakeLists.txt
@@ -1,6 +1,12 @@
 cmake_minimum_required(VERSION 3.20.0)
 set(LLVM_SUBPROJECT_TITLE "libc")
 
+if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+  message(FATAL_ERROR "Builds rooted in the libc directory are not supported. "
+    "Please see the documentation at https://libc.llvm.org/usage_modes.html for links to build "
+    "instructions depending how you plan to use libc.")
+endif()
+
 # Include LLVM's cmake policies.
 if(NOT DEFINED LLVM_COMMON_CMAKE_UTILS)
   set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)

@carlocab carlocab force-pushed the libc-standalone-error branch from 750beba to 0a88f17 Compare December 10, 2024 18:30
Building with the source directory rooted in the libc subdirectory isn't
tested in CI and can lead to subtle build problems (cf. llvm#118871).

Let's fail fast with a helpful error message instead to help users
configure libc correctly.

Co-authored-by: Nick Desaulniers <[email protected]>
@nickdesaulniers
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cc @RossComputerGuy

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@michaelrj-google michaelrj-google left a comment

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LGTM

@carlocab carlocab merged commit e84566f into llvm:main Dec 12, 2024
10 of 11 checks passed
@carlocab carlocab deleted the libc-standalone-error branch December 12, 2024 09:17
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4 participants