From c1e2a3a9b33ecae2000d623a164d7377df6f78a2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Atgeirr=20Fl=C3=B8=20Rasmussen?= <atgeirr@sintef.no>
Date: Mon, 12 Aug 2024 11:56:48 +0200
Subject: [PATCH] Add workaround from libc++ incomplete from_chars().

Float version not included in current version (15).
---
 opm/models/utils/parametersystem.hh | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/opm/models/utils/parametersystem.hh b/opm/models/utils/parametersystem.hh
index f5f489132..7c6584abe 100644
--- a/opm/models/utils/parametersystem.hh
+++ b/opm/models/utils/parametersystem.hh
@@ -41,6 +41,7 @@
 #include <dune/common/classname.hh>
 #include <dune/common/parametertree.hh>
 
+#include <cstdlib>
 #include <charconv>
 #include <fstream>
 #include <iostream>
@@ -924,7 +925,18 @@ auto Get(bool errorIfNotRegistered)
         defaultValue = defVal == "1";
     }
     else {
+#ifdef _LIBCPP_VERSION // If this macro is defined, clang's libc++ is used
+        // For floating point types, libc++ (the llvm/clang library implementation)
+        // does not yet (as of clang 15) offer an implementation of std::from_chars().
+        if constexpr (std::is_integral_v<ParamType>) {
+            std::from_chars(defVal.data(), defVal.data() + defVal.size(), defaultValue);
+        } else {
+            // Floating point workaround.
+            defaultValue = std::strtod(defVal.c_str(), nullptr);
+        }
+#else
         std::from_chars(defVal.data(), defVal.data() + defVal.size(), defaultValue);
+#endif
     }
 
     // prefix the parameter name by the model's GroupName. E.g. If