chore: Restore unity builds (#6328)

In certain cases, such as when modifying headers used by many compilation units, performing a unity build is slower than when performing a regular build with `ccache` enabled. There is also a benefit to a unity build in that it can detect things such as macro redefinitions within the group of files that are compiled together as a unit. This change therefore restores the ability to perform unity builds. However, instead of running every configuration with and without unity enabled, it is now only enabled for a single configuration to maintain lower computational use.

As part of restoring the code, it became clear that currently two configurations have coverage enabled, since the check doesn't focus specifically on Debian Bookworm so it also applies to Debian Trixie. This has been fixed too in this change.

.github/scripts/strategy-matrix/generate.py

@@ -196,11 +196,22 @@ def generate_strategy_matrix(all: bool, config: Config) -> list:
         # Enable code coverage for Debian Bookworm using GCC 15 in Debug on
         # linux/amd64
         if (
-            f"{os['compiler_name']}-{os['compiler_version']}" == "gcc-15"
+            f"{os['distro_name']}-{os['distro_version']}" == "debian-bookworm"
+            and f"{os['compiler_name']}-{os['compiler_version']}" == "gcc-15"
             and build_type == "Debug"
             and architecture["platform"] == "linux/amd64"
         ):
-            cmake_args = f"-Dcoverage=ON -Dcoverage_format=xml -DCODE_COVERAGE_VERBOSE=ON -DCMAKE_C_FLAGS=-O0 -DCMAKE_CXX_FLAGS=-O0 {cmake_args}"
+            cmake_args = f"{cmake_args} -Dcoverage=ON -Dcoverage_format=xml -DCODE_COVERAGE_VERBOSE=ON -DCMAKE_C_FLAGS=-O0 -DCMAKE_CXX_FLAGS=-O0"
+
+        # Enable unity build for Ubuntu Jammy using GCC 12 in Debug on
+        # linux/amd64.
+        if (
+            f"{os['distro_name']}-{os['distro_version']}" == "ubuntu-jammy"
+            and f"{os['compiler_name']}-{os['compiler_version']}" == "gcc-12"
+            and build_type == "Debug"
+            and architecture["platform"] == "linux/amd64"
+        ):
+            cmake_args = f"{cmake_args} -Dunity=ON"
 
         # Generate a unique name for the configuration, e.g. macos-arm64-debug
         # or debian-bookworm-gcc-12-amd64-release.
@@ -217,6 +228,8 @@ def generate_strategy_matrix(all: bool, config: Config) -> list:
         config_name += f"-{build_type.lower()}"
         if "-Dcoverage=ON" in cmake_args:
             config_name += "-coverage"
+        if "-Dunity=ON" in cmake_args:
+            config_name += "-unity"
 
         # Add the configuration to the list, with the most unique fields first,
         # so that they are easier to identify in the GitHub Actions UI, as long

BUILD.md

@@ -575,10 +575,16 @@ See [Sanitizers docs](./docs/build/sanitizers.md) for more details.
 | `assert`   | OFF           | Enable assertions.                                             |
 | `coverage` | OFF           | Prepare the coverage report.                                   |
 | `tests`    | OFF           | Build tests.                                                   |
+| `unity`    | OFF           | Configure a unity build.                                       |
 | `xrpld`    | OFF           | Build the xrpld application, and not just the libxrpl library. |
 | `werr`     | OFF           | Treat compilation warnings as errors                           |
 | `wextra`   | OFF           | Enable additional compilation warnings                         |
 
+[Unity builds][5] may be faster for the first build (at the cost of much more
+memory) since they concatenate sources into fewer translation units. Non-unity
+builds may be faster for incremental builds, and can be helpful for detecting
+`#include` omissions.
+
 ## Troubleshooting
 
 ### Conan
@@ -645,6 +651,7 @@ If you want to experiment with a new package, follow these steps:
 [1]: https://github.com/conan-io/conan-center-index/issues/13168
 [2]: https://en.cppreference.com/w/cpp/compiler_support/20
 [3]: https://docs.conan.io/en/latest/getting_started.html
+[5]: https://en.wikipedia.org/wiki/Unity_build
 [6]: https://github.com/boostorg/beast/issues/2648
 [7]: https://github.com/boostorg/beast/issues/2661
 [gcovr]: https://gcovr.com/en/stable/getting-started.html

cmake/XrplCore.cmake

@@ -4,7 +4,12 @@
 
 include(target_protobuf_sources)
 
+# Protocol buffers cannot participate in a unity build,
+# because all the generated sources
+# define a bunch of `static const` variables with the same names,
+# so we just build them as a separate library.
 add_library(xrpl.libpb)
+set_target_properties(xrpl.libpb PROPERTIES UNITY_BUILD OFF)
 target_protobuf_sources(xrpl.libpb xrpl/proto LANGUAGE cpp IMPORT_DIRS include/xrpl/proto
                         PROTOS include/xrpl/proto/xrpl.proto)
 

cmake/XrplSettings.cmake

@@ -30,6 +30,14 @@ if (tests)
     endif ()
 endif ()
 
+option(unity "Creates a build using UNITY support in cmake." OFF)
+if (unity)
+    if (NOT is_ci)
+        set(CMAKE_UNITY_BUILD_BATCH_SIZE 15 CACHE STRING "")
+    endif ()
+    set(CMAKE_UNITY_BUILD ON CACHE BOOL "Do a unity build")
+endif ()
+
 if (is_clang AND is_linux)
     option(voidstar "Enable Antithesis instrumentation." OFF)
 endif ()

conanfile.py

@@ -23,6 +23,7 @@ class Xrpl(ConanFile):
         "shared": [True, False],
         "static": [True, False],
         "tests": [True, False],
+        "unity": [True, False],
         "xrpld": [True, False],
     }
 
@@ -54,6 +55,7 @@ class Xrpl(ConanFile):
         "shared": False,
         "static": True,
         "tests": False,
+        "unity": False,
         "xrpld": False,
         "date/*:header_only": True,
         "ed25519/*:shared": False,
@@ -166,6 +168,7 @@ class Xrpl(ConanFile):
         tc.variables["rocksdb"] = self.options.rocksdb
         tc.variables["BUILD_SHARED_LIBS"] = self.options.shared
         tc.variables["static"] = self.options.static
+        tc.variables["unity"] = self.options.unity
         tc.variables["xrpld"] = self.options.xrpld
         tc.generate()
 

src/libxrpl/net/RegisterSSLCerts.cpp

@@ -85,8 +85,7 @@ registerSSLCerts(boost::asio::ssl::context& ctx, boost::system::error_code& ec,
 // There is a very unpleasant interaction between <wincrypt> and
 // openssl x509 types (namely the former has macros that stomp
 // on the latter), these undefs allow this TU to be safely used in
-// unity builds without messing up subsequent TUs. Although we
-// no longer use unity builds, leaving the undefs here does no harm.
+// unity builds without messing up subsequent TUs.
 #if BOOST_OS_WINDOWS
 #undef X509_NAME
 #undef X509_EXTENSIONS