Use FetchContent to get vcpkg. (#4484)

[SC-36205](https://app.shortcut.com/tiledb-inc/story/36205/use-fetchcontent-to-acquire-vcpkg)

Currently, building TileDB from a GitHub archive fails by default[^1],
because we use vcpkg from a submodule, and if we are not on a cloned
repository that submodules does not exist.

With this PR we change our approach to using CMake's
[`FetchContent`](https://cmake.org/cmake/help/latest/module/FetchContent.html)
module, and remove the `externals/vcpkg` submodule. [This is what the
Azure SDK for C++
does.](https://github.com/Azure/azure-sdk-for-cpp/blob/12407e8bfcb9bc1aa43b253c1d0ec93bf795ae3b/cmake-modules/AzureVcpkg.cmake#L14-L40)

This has the disadvantage that by default[^1] the vcpkg repository will
be downloaded for every clean configure. It can by mitigated by
specifying a `VCPKG_ROOT` environment variable to a local path of the
vcpkg repository.

[^1]: Unless the vcpkg toolchain file is manually specified.

---
TYPE: BUILD
DESC: Remove the vcpkg submodule and download it automatically when
configuring

.github/workflows/ci-linux_mac.yml

@@ -74,18 +74,6 @@ jobs:
             core.exportVariable('ACTIONS_CACHE_URL', process.env.ACTIONS_CACHE_URL || '');
             core.exportVariable('ACTIONS_RUNTIME_TOKEN', process.env.ACTIONS_RUNTIME_TOKEN || '');
 
-      - name: Setup vcpkg
-        uses: lukka/run-vcpkg@v11
-        id: runvcpkg
-        with:
-          vcpkgJsonGlob: 'vcpkg.json'
-          vcpkgDirectory: '${{ github.workspace }}/external/vcpkg'
-
-      - name: Prints output of run-vcpkg's action.
-        run: |
-          echo "run-vcpkg outputs:"
-          echo "${{ toJSON(steps.runvcpkg.outputs) }}"
-
       - name: Prevent vpckg from building debug variants
         run: python ./scripts/ci/patch_vcpkg_triplets.py
 

cmake/Options/TileDBToolchain.cmake

@@ -16,11 +16,20 @@ if (NOT DEFINED CMAKE_TOOLCHAIN_FILE)
         set(CMAKE_TOOLCHAIN_FILE
             "$ENV{VCPKG_ROOT}/scripts/buildsystems/vcpkg.cmake"
             CACHE STRING "Vcpkg toolchain file")
-    else()
-        include(init-submodule)
-        set(CMAKE_TOOLCHAIN_FILE
-            "${CMAKE_CURRENT_SOURCE_DIR}/external/vcpkg/scripts/buildsystems/vcpkg.cmake"
-            CACHE STRING "Vcpkg toolchain file")
+    elseif(NOT DEFINED ENV{TILEDB_DISABLE_AUTO_VCPKG})
+        # Inspired from https://github.com/Azure/azure-sdk-for-cpp/blob/azure-core_1.10.3/cmake-modules/AzureVcpkg.cmake
+        message("TILEDB_DISABLE_AUTO_VCPKG is not defined. Fetch a local copy of vcpkg.")
+        # To help with resolving conflicts, when you update the commit, also update its date.
+        set(VCPKG_COMMIT_STRING 1b4d69f3028d74401a001aa316986a670ca6289a) # 2023-09-27
+        message("Vcpkg commit string used: ${VCPKG_COMMIT_STRING}")
+        include(FetchContent)
+        FetchContent_Declare(
+            vcpkg
+            GIT_REPOSITORY https://github.com/microsoft/vcpkg.git
+            GIT_TAG        ${VCPKG_COMMIT_STRING}
+            )
+        FetchContent_MakeAvailable(vcpkg)
+        set(CMAKE_TOOLCHAIN_FILE "${vcpkg_SOURCE_DIR}/scripts/buildsystems/vcpkg.cmake" CACHE STRING "Vcpkg toolchain file")
     endif()
 endif()
 

scripts/ci/patch_vcpkg_triplets.py

@@ -1,8 +1,7 @@
 import os
 
 workspace = os.curdir
-triplet_paths = [os.path.join(workspace, "external", "vcpkg", "triplets"),
-                 os.path.join(workspace, "ports", "triplets")]
+triplet_paths = [os.path.join(workspace, "ports", "triplets")]
 
 for triplet_path in triplet_paths:
   for path, dnames, fnames in os.walk(triplet_path):