[libcxx-commits] [libcxxabi] [libcxxabi] Add test to assert that ItaniumDemangle.h is the same (PR #140323)

[Aiden Grossman via libcxx-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/140323

ItaniumDemangle.h exists in both llvm/ and libcxxabi/. These files are supposed to be copies of each other (minus the top two lines). This patch adds a test to assert that this is the case to enable tooling to automatically detect this as an issue, like in #139825. This makes it easier for contributors unfamiliar with the duplication to make changes/get appropriate reviews.

Ideally we would share the file and copy it from one place to the other but the ideal way to do this (based on previous discussion with libc++ maintainers) would be a new runtime library that clearly outlines requirements, so that is left for later with the test being used as a stopgap. This is a relatively common approach for structures shared between compiler-rt and LLVM.

This patch does make the test reference the LLVM source directory, but that should be fine given building libcxxabi is only supported through the runtimes build in the monorepo meaning it should always be available.

>From c945a23ad181deac70874531cfc9b63bc149768c Mon Sep 17 00:00:00 2001
From: Aiden Grossman <aidengrossman at google.com>
Date: Sat, 17 May 2025 00:28:53 +0000
Subject: [PATCH] [libcxxabi] Add test to assert that ItaniumDemangle.h is the
 same

ItaniumDemangle.h exists in both llvm/ and libcxxabi/. These files are
supposed to be copies of each other (minus the top two lines). This
patch adds a test to assert that this is the case to enable tooling to
automatically detect this as an issue, like in #139825. This makes it
easier for contributors unfamiliar with the duplication to make
changes/get appropriate reviews.

Ideally we would share the file and copy it from one place to the other
but the ideal way to do this (based on previous discussion with libc++
maintainers) would be a new runtime library that clearly outlines
requirements, so that is left for later with the test being used as a
stopgap. This is a relatively common approach for structures shared
between compiler-rt and LLVM.

This patch does make the test reference the LLVM source directory, but
that should be fine given building libcxxabi is only supported through
the runtimes build in the monorepo meaning it should always be
available.
---
 libcxxabi/test/configs/cmake-bridge.cfg.in           | 2 ++
 libcxxabi/test/itanium_demangle_matches_llvm.sh.test | 6 ++++++
 2 files changed, 8 insertions(+)
 create mode 100644 libcxxabi/test/itanium_demangle_matches_llvm.sh.test

diff --git a/libcxxabi/test/configs/cmake-bridge.cfg.in b/libcxxabi/test/configs/cmake-bridge.cfg.in
index edf80c8f2a732..1bdba32405ddd 100644
--- a/libcxxabi/test/configs/cmake-bridge.cfg.in
+++ b/libcxxabi/test/configs/cmake-bridge.cfg.in
@@ -27,6 +27,8 @@ config.test_exec_root = os.path.join('@LIBCXXABI_BINARY_DIR@', 'test')
 config.host_triple = '@LLVM_HOST_TRIPLE@'
 
 config.substitutions.append(('%{libcxx}', '@LIBCXXABI_LIBCXX_PATH@'))
+config.substitutions.append(('%{libcxxabi}', '@LIBCXXABI_SOURCE_DIR@'))
+config.substitutions.append(('%{llvm}', '@LLVM_MAIN_SRC_DIR@'))
 config.substitutions.append(('%{install-prefix}', '@LIBCXXABI_TESTING_INSTALL_PREFIX@'))
 config.substitutions.append(('%{include}', '@LIBCXXABI_TESTING_INSTALL_PREFIX@/include'))
 config.substitutions.append(('%{cxx-include}', '@LIBCXXABI_TESTING_INSTALL_PREFIX@/@LIBCXXABI_INSTALL_INCLUDE_DIR@'))
diff --git a/libcxxabi/test/itanium_demangle_matches_llvm.sh.test b/libcxxabi/test/itanium_demangle_matches_llvm.sh.test
new file mode 100644
index 0000000000000..31371d121fbdd
--- /dev/null
+++ b/libcxxabi/test/itanium_demangle_matches_llvm.sh.test
@@ -0,0 +1,6 @@
+# This test diffs the ItaniumDemangle.h header in libcxxabi and LLVM to ensure
+# that they are the same.
+
+# RUN: tail -n +3 %{libcxxabi}/src/demangle/ItaniumDemangle.h > %t.libcxxabi_demangle
+# RUN: tail -n +3 %{llvm}/include/llvm/Demangle/ItaniumDemangle.h > %t.llvm_demangle
+# RUN: diff %t.libcxxabi_demangle %t.llvm_demangle