From a39eb06554a662dedf14967fc83912cb376959ea Mon Sep 17 00:00:00 2001
From: David Feltell <david.feltell@foundry.com>
Date: Tue, 5 Sep 2023 14:08:55 +0100
Subject: [PATCH] [Core] Add fmtlib dependency

Closes #1070. fmtlib allows for easy, safe string substitution in C++,
adding advanced formatting functionality (e.g. rounding), and reducing
bloat.

So add as a new private build-only header-only dependency.

Using header-only increases compile times, but subjectively it's not
noticeable, and has the benefit of avoiding a possible public library
dependency (if OpenAssetIO is built as a static library).

Tweak a single existing, tested, log string to make use of libfmt, to
ensure basic usage is validated.

Signed-off-by: David Feltell <david.feltell@foundry.com>
---
 RELEASE_NOTES.md                             |  8 ++++++++
 cmake/ThirdParty.cmake                       |  7 +++++++
 resources/build/conanfile.py                 |  4 ++++
 src/openassetio-core/CMakeLists.txt          |  8 ++++++--
 src/openassetio-core/src/hostApi/Manager.cpp | 13 +++++++------
 5 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index cc0a36194..b8bfbb85f 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -1,6 +1,14 @@
 Release Notes
 =============
 
+v1.0.0-alpha.x
+---------------
+
+### Breaking changes
+
+- Added `fmtlib` as a new header-only private dependency.
+  [#1070](https://github.com/OpenAssetIO/OpenAssetIO/issues/1070)
+
 v1.0.0-alpha.14
 ---------------
 
diff --git a/cmake/ThirdParty.cmake b/cmake/ThirdParty.cmake
index b5d4c900b..8714fbc44 100644
--- a/cmake/ThirdParty.cmake
+++ b/cmake/ThirdParty.cmake
@@ -3,6 +3,13 @@
 
 find_package(tomlplusplus REQUIRED)
 
+
+#-----------------------------------------------------------------------
+# String formatting
+
+find_package(fmt REQUIRED)
+
+
 #-----------------------------------------------------------------------
 # Python
 
diff --git a/resources/build/conanfile.py b/resources/build/conanfile.py
index 08f48deb5..5348b12d7 100644
--- a/resources/build/conanfile.py
+++ b/resources/build/conanfile.py
@@ -40,3 +40,7 @@ def requirements(self):
         self.requires("catch2/2.13.8")
         # Mocking library
         self.requires("trompeloeil/42")
+        self.requires("fmt/10.1.1")
+
+    def configure(self):
+        self.options["fmt"].header_only = True
diff --git a/src/openassetio-core/CMakeLists.txt b/src/openassetio-core/CMakeLists.txt
index f5e69fc19..65a0637b2 100644
--- a/src/openassetio-core/CMakeLists.txt
+++ b/src/openassetio-core/CMakeLists.txt
@@ -90,9 +90,13 @@ target_include_directories(openassetio-core
     # Use includes from install tree for installed lib.
     "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>")
 
-target_link_libraries(openassetio-core
+target_link_libraries(
+    openassetio-core
     PRIVATE
-    $<BUILD_INTERFACE:tomlplusplus::tomlplusplus>)
+    # Header-only private dependencies:
+    $<BUILD_INTERFACE:tomlplusplus::tomlplusplus>
+    $<BUILD_INTERFACE:fmt::fmt-header-only>
+)
 
 #-----------------------------------------------------------------------
 # API export header
diff --git a/src/openassetio-core/src/hostApi/Manager.cpp b/src/openassetio-core/src/hostApi/Manager.cpp
index 7896e7444..b1fc6b2f8 100644
--- a/src/openassetio-core/src/hostApi/Manager.cpp
+++ b/src/openassetio-core/src/hostApi/Manager.cpp
@@ -3,6 +3,8 @@
 #include <stdexcept>
 #include <utility>
 
+#include <fmt/format.h>
+
 #include <openassetio/Context.hpp>
 #include <openassetio/TraitsData.hpp>
 #include <openassetio/constants.hpp>
@@ -53,12 +55,11 @@ std::optional<Str> entityReferencePrefixFromInfo(const log::LoggerInterfacePtr &
   if (auto iter = info.find(Str{constants::kInfoKey_EntityReferencesMatchPrefix});
       iter != info.end()) {
     if (const auto *prefixPtr = std::get_if<openassetio::Str>(&iter->second)) {
-      std::string msg = "Entity reference prefix '";
-      msg += *prefixPtr;
-      msg +=
-          "' provided by manager's info() dict. Subsequent calls to isEntityReferenceString will"
-          " use this prefix rather than call the manager's implementation.";
-      logger->debugApi(msg);
+      logger->debugApi(
+          fmt::format("Entity reference prefix '{}' provided by manager's info() dict. Subsequent"
+                      " calls to isEntityReferenceString will use this prefix rather than call the"
+                      " manager's implementation.",
+                      *prefixPtr));
 
       return *prefixPtr;
     }