Add mp-units units library

Add a units library [0] to allow compile-time dimensional analysis. This
commit adds the README example as a unit test.

[0] https://github.com/mpusz/mp-units

Change-Id: I74eb111e2df7c65881e0ba893a3de58b2ebc8512

.clang-tidy

@@ -35,6 +35,9 @@ Checks: >
     # https://reviews.llvm.org/D95714?id=320393,
     -modernize-use-nullptr,
 
+    # segfaults with mp-units,
+    -modernize-use-trailing-return-type,
+
     # disable common aliases,
     -cppcoreguidelines-avoid-c-arrays,
     -cppcoreguidelines-avoid-magic-numbers,

WORKSPACE.bazel

@@ -179,6 +179,70 @@ cc_library(
     url = "https://github.com/kokkos/stdblas/archive/%s.tar.gz" % LINALG_VERSION,
 )
 
+GSL_LITE_VERSION = "a8c7e5bbbd08841836f9b92d72747fb8769dbec4"
+
+http_archive(
+    name = "gsl_lite",
+    build_file_content = """
+load("@rules_cc//cc:defs.bzl", "cc_library")
+
+cc_library(
+    name = "gsl_lite",
+    hdrs = ["include/gsl/gsl-lite.hpp"],
+    includes = ["include"],
+    visibility = ["//visibility:public"],
+)
+""",
+    sha256 = "f9edeec2b517dbb57c5688150db56c90f5c4922ef8aa8d15cfe532fa42058792",
+    strip_prefix = "gsl-lite-%s" % GSL_LITE_VERSION,
+    url = "https://github.com/gsl-lite/gsl-lite/archive/%s.tar.gz" % GSL_LITE_VERSION,
+)
+
+MP_UNITS_VERSION = "60a564a86700804e306f0d73a1521ea6e4abe377"
+
+http_archive(
+    name = "mp_units",
+    build_file_content = """
+load("@rules_cc//cc:defs.bzl", "cc_library")
+
+cc_library(
+    name = "mp_units",
+    hdrs = glob(["src/**"]),
+    includes = [
+        "src/core-fmt/include",
+        "src/core-io/include",
+        "src/core/include",
+        "src/systems/angular/include",
+        "src/systems/cgs/include",
+        "src/systems/hep/include",
+        "src/systems/iau/include",
+        "src/systems/iec80000/include",
+        "src/systems/imperial/include",
+        "src/systems/international/include",
+        "src/systems/isq/include",
+        "src/systems/isq_angle/include",
+        "src/systems/natural/include",
+        "src/systems/si/include",
+        "src/systems/typographic/include",
+        "src/systems/usc/include",
+        "src/utility/include",
+    ],
+    deps = [
+        "@gsl_lite",
+    ],
+    visibility = ["//visibility:public"],
+)
+""",
+    # Fix Clang builds by defining constructor as public
+    # https://github.com/mpusz/mp-units/issues/473
+    #
+    patch_args = ["-p1"],
+    patches = ["//third_party:mp-units-clang-priv-ctor.patch"],
+    sha256 = "2c48171815909da836300d50a40e396412cb4881794b4cb5d13dcef858c46da1",
+    strip_prefix = "mp-units-%s" % MP_UNITS_VERSION,
+    url = "https://github.com/mpusz/mp-units/archive/%s.tar.gz" % MP_UNITS_VERSION,
+)
+
 BOOST_UT_VERSION = "e53a47d37bc594e80bd5f1b8dc1ade8dce4429d3"
 
 http_archive(

test/BUILD.bazel

@@ -11,3 +11,14 @@ cc_test(
         "@mdspan",
     ],
 )
+
+cc_test(
+    name = "units_test",
+    timeout = "short",
+    srcs = ["units_test.cpp"],
+    deps = [
+        "@boost_ut",
+        "@fmt",
+        "@mp_units",
+    ],
+)

test/units_test.cpp

@@ -0,0 +1,51 @@
+#include <boost/ut.hpp>
+
+#include <fmt/core.h>
+#include <mp-units/format.h>
+#include <mp-units/ostream.h>
+#include <mp-units/systems/international/international.h>
+#include <mp-units/systems/isq/space_and_time.h>
+#include <mp-units/systems/si/si.h>
+#include <sstream>
+
+using namespace mp_units;
+
+constexpr QuantityOf<isq::speed> auto
+avg_speed(QuantityOf<isq::length> auto d, QuantityOf<isq::time> auto t)
+{
+  return d / t;
+}
+
+constexpr auto to_string(const auto& value)
+{
+  auto ss = std::stringstream{};
+  ss << value;
+  return ss.str();
+}
+
+auto main() -> int
+{
+  using ::boost::ut::expect;
+  using ::boost::ut::test;
+
+  test("units example") = [] {
+    using namespace mp_units::si::unit_symbols;
+    using namespace mp_units::international::unit_symbols;
+
+    constexpr auto v1 = 110 * (km / h);
+    constexpr auto v2 = 70 * mph;
+    constexpr auto v3 = avg_speed(220. * isq::distance[km], 2 * h);
+    constexpr auto v4 = avg_speed(isq::distance(140. * mi), 2 * h);
+    constexpr auto v5 = v3[m / s];
+    constexpr auto v6 = value_cast<m / s>(v4);
+    constexpr auto v7 = value_cast<int>(v6);
+
+    expect("110 km/h" == to_string(v1));
+    expect("70 mi/h" == to_string(v2));
+    expect("110 km/h" == fmt::format("{}", v3));
+    expect("***70 mi/h****" == fmt::format("{:*^14}", v4));
+    expect("30.5556 in m/s" == fmt::format("{:%Q in %q}", v5));
+    expect("31.2928 in m/s" == fmt::format("{0:%Q} in {0:%q}", v6));
+    expect("31" == fmt::format("{:%Q}", v7));
+  };
+}

third_party/BUILD.bazel

@@ -0,0 +1 @@
+exports_files(["mp-units-clang-priv-ctor.patch"])

third_party/mp-units-clang-priv-ctor.patch

@@ -0,0 +1,12 @@
+diff --git a/src/core/include/mp-units/quantity.h b/src/core/include/mp-units/quantity.h
+index 3d3642b3..5e16eff4 100644
+--- a/src/core/include/mp-units/quantity.h
++++ b/src/core/include/mp-units/quantity.h
+@@ -321,6 +321,7 @@ private:
+     requires quantity<R2, std::remove_cvref_t<Rep2>>::_rep_safe_constructible_
+   friend constexpr quantity<R2, std::remove_cvref_t<Rep2>> make_quantity(Rep2&&);
+
++public:
+   template<typename Value>
+     requires detail::RepSafeConstructibleFrom<rep, Value&&, unit>
+   constexpr explicit quantity(Value&& v) : number_(std::forward<Value>(v))