From 8db14eeead45e0f1961532f55061d5e4dd0f78be Mon Sep 17 00:00:00 2001
From: Paul Wise <pabs3@bonedaddy.net>
Date: Thu, 26 Aug 2021 22:03:00 +0800
Subject: [PATCH] Add a mode to build against system versions of dependencies

Make the default be to use system versions when available,
but allow always using them or never using them.

Add searching for and using system versions of fmt/googletest/pybind11,
which are currently pulled directly from git using FetchContent.

This will allow distributions that do not allow network access at build
time to depend on and build against these packages.

Fixes: https://github.com/nu-book/zxing-cpp/issues/248
---
 CMakeLists.txt                 |  7 +++++++
 test/blackbox/CMakeLists.txt   | 18 +++++++++++++-----
 1 files changed, 54 insertions(+), 21 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1361792..2b522e0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -8,6 +8,7 @@ option (BUILD_EXAMPLES "Build the example barcode reader/writer applicatons" ON)
 option (BUILD_BLACKBOX_TESTS "Build the black box reader/writer tests" ON)
 option (BUILD_UNIT_TESTS "Build the unit tests (don't enable for production builds)" OFF)
 option (BUILD_PYTHON_MODULE "Build the python module" OFF)
+set(BUILD_SYSTEM_DEPS "AUTO" CACHE STRING "Use system dependencies (AUTO/ALWAYS/NEVER)")
 
 if (WIN32)
     option (BUILD_SHARED_LIBS "Build and link as shared library" OFF)
@@ -53,6 +54,12 @@ if (BUILD_UNIT_TESTS)
     endif()
 endif()
 
+set(BUILD_SYSTEM_DEPS_LIST AUTO ALWAYS NEVER)
+set_property(CACHE BUILD_SYSTEM_DEPS PROPERTY STRINGS ${BUILD_SYSTEM_DEPS_LIST})
+if(NOT BUILD_SYSTEM_DEPS IN_LIST BUILD_SYSTEM_DEPS_LIST)
+    message(FATAL_ERROR "BUILD_SYSTEM_DEPS must be one of ${BUILD_SYSTEM_DEPS_LIST}")
+endif()
+
 add_subdirectory (core)
 
 enable_testing()
diff --git a/test/blackbox/CMakeLists.txt b/test/blackbox/CMakeLists.txt
index 3da26dd..9d79e8e 100644
--- a/test/blackbox/CMakeLists.txt
+++ b/test/blackbox/CMakeLists.txt
@@ -1,10 +1,18 @@
 cmake_minimum_required(VERSION 3.14)
 
-include(FetchContent)
-FetchContent_Declare (fmtlib
-        GIT_REPOSITORY https://github.com/fmtlib/fmt.git
-        GIT_TAG 7.1.2)
-FetchContent_MakeAvailable (fmtlib) # Adds fmt::fmt
+if (BUILD_SYSTEM_DEPS STREQUAL "AUTO")
+    find_package (fmt)
+elseif (BUILD_SYSTEM_DEPS STREQUAL "ALWAYS")
+    find_package (fmt REQUIRED)
+endif()
+
+if (NOT fmt_FOUND)
+    include(FetchContent)
+    FetchContent_Declare (fmtlib
+            GIT_REPOSITORY https://github.com/fmtlib/fmt.git
+            GIT_TAG 7.1.2)
+    FetchContent_MakeAvailable (fmtlib) # Adds fmt::fmt
+endif()
 
 if (BUILD_READERS)
     add_executable (ReaderTest
-- 
2.33.1