[common] Add fmt_runtime compatibility shim for C++20 (RobotLocomotio…

…n#17958)

Add previously-overlooked C++17 flag to an acceptance test, now that
we use <string_view> in one of the headers (text_logging) that happens
to be covered by that acceptance test.

common/test/text_logging_test.cc

@@ -74,6 +74,12 @@ GTEST_TEST(TextLoggingTest, ConstantTest) {
   #endif
 }
 
+// Check that the "warn once" idiom compiles and doesn't crash at runtime.
+GTEST_TEST(TextLoggingTest, WarnOnceTest) {
+  static const drake::logging::Warn log_once(
+      "The log_once happened as expected.");
+}
+
 // Abuse gtest internals to verify that logging actually prints when enabled,
 // and that the default level is INFO.
 GTEST_TEST(TextLoggingTest, CaptureOutputTest) {

common/text_logging.h

@@ -92,6 +92,14 @@ used by Drake might be older.)
 
 namespace drake {
 
+#if FMT_VERSION >= 80000 || defined(DRAKE_DOXYGEN_CXX)
+/// When using fmt >= 8, this is an alias for fmt::runtime.
+/// When using fmt < 8, this is a no-op.
+inline auto fmt_runtime(std::string_view s) { return fmt::runtime(s); }
+#else
+inline auto fmt_runtime(std::string_view s) { return s; }
+#endif
+
 #ifdef HAVE_SPDLOG
 namespace logging {
 
@@ -195,7 +203,10 @@ sink* get_dist_sink();
 struct Warn {
   template <typename... Args>
   Warn(const char* a, const Args&... b) {
-    drake::log()->warn(a, b...);
+    // TODO(jwnimmer-tri) Ideally we would compile-time check our Warn format
+    // strings without using fmt_runtime here, but I haven't figured out how
+    // to forward the arguments properly for all versions of fmt.
+    drake::log()->warn(fmt_runtime(a), b...);
   }
 };
 

geometry/meshcat.cc

@@ -542,7 +542,8 @@ class Meshcat::Impl {
     // values) through to fmt to allow any fmt-specific exception to percolate.
     // Then, confirm that the user's pattern started with a valid protocol.
     const std::string url = fmt::format(
-        params.web_url_pattern, fmt::arg("host", "foo"), fmt::arg("port", 1));
+        fmt_runtime(params.web_url_pattern),
+        fmt::arg("host", "foo"), fmt::arg("port", 1));
     if (url.substr(0, 4) != "http") {
       throw std::logic_error("The web_url_pattern must be http:// or https://");
     }
@@ -611,7 +612,7 @@ class Meshcat::Impl {
     const bool is_localhost = host.empty() || host == "*";
     const std::string display_host = is_localhost ? "localhost" : host;
     return fmt::format(
-        params_.web_url_pattern,
+        fmt_runtime(params_.web_url_pattern),
         fmt::arg("host", display_host),
         fmt::arg("port", port_));
   }

systems/sensors/image_writer.cc

@@ -195,7 +195,7 @@ std::string ImageWriter::MakeFileName(const std::string& format,
 
   int64_t u_time = static_cast<int64_t>(time * 1e6 + 0.5);
   int m_time = static_cast<int>(time * 1e3 + 0.5);
-  return fmt::format(format, fmt::arg("port_name", port_name),
+  return fmt::format(fmt_runtime(format), fmt::arg("port_name", port_name),
                      fmt::arg("image_type", labels_.at(pixel_type)),
                      fmt::arg("time_double", time),
                      fmt::arg("time_usec", u_time),

tools/install/bazel/test/drake_bazel_installed_test.py

@@ -60,6 +60,7 @@ def main():
 cc_test(
     name = "text_logging_test",
     srcs = ["text_logging_test.cc"],
+    copts = ["--std=c++17"],
     # TODO(jwnimmer-tri) On macOS, we need to pkg-config fmt for this to pass.
     # For the moment, we'll say that :drake_shared_library is Ubuntu-only.
     tags = ["manual"] if OS_NAME == "mac os x" else [],