[cmake] Add a CMake toolchain file for "hermetic" Xcode builds.
Bug: 417604769
Change-Id: If50832ec1ab727046aa55437006793ed4497c05a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/243695
Reviewed-by: Brian Sheedy <bsheedy@google.com>
Commit-Queue: Brian Sheedy <bsheedy@google.com>
Auto-Submit: Kai Ninomiya <kainino@chromium.org>
diff --git a/src/cmake/HermeticXcode/HermeticXcode.cmake b/src/cmake/HermeticXcode/HermeticXcode.cmake
new file mode 100644
index 0000000..1354b69
--- /dev/null
+++ b/src/cmake/HermeticXcode/HermeticXcode.cmake
@@ -0,0 +1,46 @@
+# Copyright 2025 The Dawn & Tint Authors
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+# 1. Redistributions of source code must retain the above copyright notice, this
+# list of conditions and the following disclaimer.
+#
+# 2. Redistributions in binary form must reproduce the above copyright notice,
+# this list of conditions and the following disclaimer in the documentation
+# and/or other materials provided with the distribution.
+#
+# 3. Neither the name of the copyright holder nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+set(HERMETICXCODE_DAWN_ROOT "${CMAKE_CURRENT_LIST_DIR}/../../..")
+set(HERMETICXCODE_LLVM "${HERMETICXCODE_DAWN_ROOT}/third_party/llvm-build/Release+Asserts/bin")
+set(HERMETICXCODE_DEVELOPER "${HERMETICXCODE_DAWN_ROOT}/build/mac_files/xcode_binaries/Contents/Developer")
+
+set(CMAKE_C_COMPILER "${HERMETICXCODE_LLVM}/clang")
+set(CMAKE_CXX_COMPILER "${HERMETICXCODE_LLVM}/clang++")
+set(CMAKE_AR "${HERMETICXCODE_LLVM}/llvm-ar")
+set(CMAKE_INSTALL_NAME_TOOL "${HERMETICXCODE_LLVM}/llvm-install-name-tool")
+
+# ranlib is just a symlink to libtool in system CommandLineTools, so we have our
+# own correctly-name symlink to make this work
+set(CMAKE_RANLIB "${CMAKE_CURRENT_LIST_DIR}/ranlib")
+
+set(CMAKE_LINKER "${HERMETICXCODE_DEVELOPER}/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld")
+set(CMAKE_NM "${HERMETICXCODE_DEVELOPER}/Toolchains/XcodeDefault.xctoolchain/usr/bin/llvm-nm")
+set(CMAKE_OBJDUMP "${HERMETICXCODE_DEVELOPER}/Toolchains/XcodeDefault.xctoolchain/usr/bin/llvm-objdump")
+set(CMAKE_STRIP "${HERMETICXCODE_DEVELOPER}/Toolchains/XcodeDefault.xctoolchain/usr/bin/strip")
+
+set(CMAKE_OSX_SYSROOT "${HERMETICXCODE_DEVELOPER}/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk")
diff --git a/src/cmake/HermeticXcode/README.md b/src/cmake/HermeticXcode/README.md
new file mode 100644
index 0000000..a169f31
--- /dev/null
+++ b/src/cmake/HermeticXcode/README.md
@@ -0,0 +1,18 @@
+This is a cobbled-together CMake toolchain file for using "hermetic Xcode",
+rather than the system-installed one. It is not used by default. It is meant to
+be used on automated builder bots to avoid depending on system dependencies, but
+can also be used locally.
+
+Use this by passing `-DCMAKE_TOOLCHAIN_FILE=path/to/HermeticXcode.cmake` to
+`cmake`.
+
+Notes:
+
+- Not all of the variables set in the script are probably actually used
+ (and thus could break later on if they become used), but are included in an
+ attempt at completeness.
+- `ranlib` is a link to `libtool` because those are the same binary with
+ different names. (It needs to be a symlink because it chooses its behavior
+ based on its filename.)
+- It doesn't currently try to set up other things as hermetic, in particular
+ Python.
diff --git a/src/cmake/HermeticXcode/ranlib b/src/cmake/HermeticXcode/ranlib
new file mode 120000
index 0000000..48b9743
--- /dev/null
+++ b/src/cmake/HermeticXcode/ranlib
@@ -0,0 +1 @@
+../../../build/mac_files/xcode_binaries/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/libtool
\ No newline at end of file
