From eeda7f1a134bbabb8dfae1c6a4a74585906ae00e Mon Sep 17 00:00:00 2001
From: Anton Kolesnyk <41349689+antkmsft@users.noreply.github.com>
Date: Tue, 23 Feb 2021 09:38:24 -0800
Subject: [PATCH] Get static/dynamic CRT link options in sync (#1715)

* Get static/dynamic CRT link options in sync

* Update docs

* PR feedback

* en-us

* Another 'en-us' in a link

* MSVC_USE_STATIC_CRT

* Update README.md

Co-authored-by: Anton Kolesnyk <antkmsft@users.noreply.github.com>
---
 CMakeLists.txt  | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 CONTRIBUTING.md |  5 +++++
 README.md       | 13 +++++++++++++
 3 files changed, 64 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d284cfa8d..11e2c2bd0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,6 +18,7 @@ option(BUILD_DOCUMENTATION "Create HTML based API documentation (requires Doxyge
 option(RUN_LONG_UNIT_TESTS "Tests that takes more than 5 minutes to complete. No effect if BUILD_TESTING is OFF" OFF)
 option(BUILD_STORAGE_SAMPLES "Build sample application for Azure Storage clients" OFF)
 option(BUILD_PERFORMANCE_TESTS "Build the performance test library" OFF)
+option(MSVC_USE_STATIC_CRT "(MSVC only) Set to ON to link SDK with static CRT (/MT or /MTd switch)." OFF)
 
 include(AzureTransportAdapters)
 include(AzureVcpkg)
@@ -29,6 +30,51 @@ project(azure-sdk LANGUAGES CXX)
 set(CMAKE_CXX_STANDARD 14)
 set(CMAKE_CXX_STANDARD_REQUIRED True)
 
+if(MSVC_USE_STATIC_CRT AND MSVC)
+  # 1. More about static/shared CRT:
+  # https://docs.microsoft.com/cpp/build/reference/md-mt-ld-use-run-time-library?view=msvc-160
+  #
+  # 2. MSVC_USE_STATIC_CRT build flag approach is used/inspired by libcurl
+  # (https://github.com/curl/curl/blob/master/CMakeLists.txt) and some other projects.
+  #
+  # 3. GTest would emit the following warning:
+  # warning LNK4098: defaultlib 'LIBCMTD' conflicts with use of other libs; use /NODEFAULTLIB:library
+  # AddGoogleTest.cmake uses gtest_force_shared_crt
+  # (see https://github.com/google/googletest/blob/master/googletest/README.md),
+  # which respects linker settings that we set below, and our settings below are all in sync.
+  #
+  # 4. Sometimes, the following approach is recommended instead:
+  # +-----------------------------------------------------------------------------------+
+  # | # Use the static runtime libraries when building statically                       |
+  # | # for consistency with vcpkg's arch-windows-static triplets:                      |
+  # | cmake_policy(SET CMP0091 NEW)                                                     |
+  # | # see https://cmake.org/cmake/help/v3.15/variable/CMAKE_MSVC_RUNTIME_LIBRARY.html |
+  # | if (NOT DEFINED CMAKE_MSVC_RUNTIME_LIBRARY)                                       |
+  # |   set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>")         |
+  # | endif()                                                                           |
+  # +-----------------------------------------------------------------------------------+
+  # However, it only works when cmake installed is 3.15+;
+  # we have to require a minimum of 3.13.
+  #
+  # 5. We "replace with empty string" (i.e. remove) first, then add, so that '/MT'
+  # will be present (and present once) even if '/MD' was not.
+
+  string(REGEX REPLACE "/MD" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /MT")
+  
+  string(REGEX REPLACE "/MD" "" CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}")
+  set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} /MT")
+
+  string(REGEX REPLACE "/MD" "" CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO}")
+  set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO} /MT")
+
+  string(REGEX REPLACE "/MD" "" CMAKE_CXX_FLAGS_MINSIZEREL "${CMAKE_CXX_FLAGS_MINSIZEREL}")
+  set(CMAKE_CXX_FLAGS_MINSIZEREL "${CMAKE_CXX_FLAGS_MINSIZEREL} /MT")
+  
+  string(REGEX REPLACE "/MDd" "" CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG}")
+  set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} /MTd")
+endif()
+
 if(BUILD_TESTING)
   include(AddGoogleTest)
   enable_testing ()  
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index fe7246b1f..edbfc7084 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -152,6 +152,11 @@ The following CMake options are available for adding/removing project features.
 <td>Build Doxygen documentation</td>
 <td>OFF</td>
 </tr>
+<tr>
+<td>MSVC_USE_STATIC_CRT</td>
+<td>On MSVC, link SDK with static CRT (use `/MT` or `/MTd` switch)</td>
+<td>OFF</td>
+</tr>
 </table>
 
 #### Testing the project
diff --git a/README.md b/README.md
index 79056f4e7..bf181bfb0 100644
--- a/README.md
+++ b/README.md
@@ -29,6 +29,19 @@ For a complete list of available packages, please see the [latest available pack
 
 Last stable versions of packages that are production-ready. These libraries provide similar functionalities to the beta packages, as they allow you to use and consume existing resources and interact with them, for example: upload a storage blob. They might not implement the [guidelines](https://azure.github.io/azure-sdk/cpp_introduction.html) or have the same feature set. They do however offer wider coverage of services.
 
+### VcPkg
+
+Released SDK library versions are available on [VcPkg](https://github.com/microsoft/vcpkg):
+* `azure-core-cpp`
+* `azure-identity-cpp`
+* `azure-storage-blobs-cpp`
+* `azure-storage-common-cpp`
+* `azure-storage-files-datalake-cpp`
+* `azure-storage-files-shares-cpp`
+
+> NOTE: In case of getting linker errors when consuming the SDK on Windows, make sure that [VcPkg trilet](https://vcpkg.readthedocs.io/en/latest/users/triplets/) being consumed matches the [CRT link flags](https://docs.microsoft.com/cpp/build/reference/md-mt-ld-use-run-time-library?view=msvc-160) being set for your app or library build. See also `MSVC_USE_STATIC_CRT` build flag.
+
+
 ## Need help
 
 - For reference documentation visit the [Azure SDK for C++ documentation](https://azure.github.io/azure-sdk-for-cpp).