conservatively introduce fmtlib (fmt migration take II)

Instead of trying juggle nix::fmt and fmt::, we'll just rename the fmt
namespace.

Change-Id: Iba51166a8f04386f1b13e506edfc462ef0d12928

meson.build

@@ -297,6 +297,8 @@ pegtl = dependency(
 
 nlohmann_json = dependency('nlohmann_json', required : true)
 
+fmt = dependency('fmt', required : true)
+
 # lix-doc is a Rust project provided via buildInputs and unfortunately doesn't have any way to be detected.
 # Just declare it manually to resolve this.
 #

package.nix

@@ -20,6 +20,7 @@
   doxygen,
   editline-lix ? __forDefaults.editline-lix,
   editline,
+  fmt,
   git,
   gtest,
   jq,
@@ -246,6 +247,7 @@ stdenv.mkDerivation (finalAttrs: {
       sqlite
       libarchive
       boost
+      fmt
       lowdown
       libsodium
       toml11

src/libutil/fmt.hh

@@ -10,6 +10,7 @@
 #define BOOST_STACKTRACE_GNU_SOURCE_NOT_REQUIRED
 #endif
 #include <boost/stacktrace.hpp>
+
 #include "ansicolor.hh"
 
 namespace nix {

src/libutil/meson.build

@@ -122,6 +122,7 @@ libutil = library(
     aws_s3,
     boehm,
     boost,
+    fmt,
     cpuid,
     seccomp,
     libarchive,