Example: Building dynamic libraries on Linux using overlay triplets

docs/examples/overlay-triplets-linux-dynamic.md

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+# Overlay triplets example: build dynamic libraries on Linux
+
+Using **vcpkg** you can build libraries for the following triplets:
+
+<div>
+    <ul style="columns: 3;">
+        <li> arm-uwp</li>
+        <li> arm-windows</li>
+        <li> arm64-uwp</li>
+        <li> arm64-windows</li>
+        <li> x86-uwp</li>
+        <li> x86-windows</li>
+        <li> x86-windows-static</li>
+        <li> x64-uwp</li>
+        <li> x64-linux</li>
+        <li> x64-osx</li>
+        <li> x64-windows</li>
+        <li> x64-windows-static</li>
+    </ul>
+</div>
+
+
+
+By design **vcpkg** builds only static libraries for Linux and Mac OS.
+However, this doesn't mean that you cannot use **vcpkg** to build your dynamic libraries on these platforms.
+
+This document will guide you through creating your own custom triplets to build dynamic libraries on Linux using **vcpkg**.
+
+### Step 1: Create a folder to contain your custom triplets
+
+```
+~/vcpkg$ mkdir ../custom-triplets
+```
+
+### Step 2: Create the custom triplet files
+
+To save time, copy the existing `x64-linux.cmake` triplet file.
+
+```
+~/vcpkg$ cp ./triplets/x64-linux.cmake ../custom-triplets/x64-linux-dynamic.cmake
+```
+
+And modify `custom-triplets/x64-linux-dynamic.cmake` to match the contents below:
+```
+set(VCPKG_TARGET_ARCHITECTURE x64)
+set(VCPKG_CRT_LINKAGE dynamic)
+# Change VCPKG_LIBRARY_LINKAGE from static to dynamic
+set(VCPKG_LIBRARY_LINKAGE dynamic)
+
+set(VCPKG_CMAKE_SYSTEM_NAME Linux)
+```
+
+### Step 3: Use `--overlay-triplets` to build dynamic libraries
+
+Use the `--overlay-triplets` option to include the triplets in the `custom-triplets` directory. 
+
+```
+./vcpkg install sqlite3:x64-linux-dynamic --overlay-triplets=../custom-triplets
+The following packages will be built and installed:
+    sqlite3[core]:x64-linux
+Starting package 1/1: sqlite3:x64-linux-dynamic
+Building package sqlite3[core]:x64-linux-dynamic...
+-- Loading triplet configuration from: /home/custom-triplets/x64-linux-dynamic.cmake
+-- Downloading https://sqlite.org/2019/sqlite-amalgamation-3280000.zip...
+-- Extracting source /home/victor/git/vcpkg/downloads/sqlite-amalgamation-3280000.zip
+-- Applying patch fix-arm-uwp.patch
+-- Using source at /home/victor/git/vcpkg/buildtrees/sqlite3/src/3280000-6a3ff7ce92
+-- Configuring x64-linux-dynamic-dbg
+-- Configuring x64-linux-dynamic-rel
+-- Building x64-linux-dynamic-dbg
+-- Building x64-linux-dynamic-rel
+-- Performing post-build validation
+-- Performing post-build validation done
+Building package sqlite3[core]:x64-linux-dynamic... done
+Installing package sqlite3[core]:x64-linux-dynamic...
+Installing package sqlite3[core]:x64-linux-dynamic... done
+Elapsed time for package sqlite3:x64-linux-dynamic: 44.82 s
+
+Total elapsed time: 44.82 s
+
+The package sqlite3:x64-linux-dynamic provides CMake targets:
+
+    find_package(sqlite3 CONFIG REQUIRED)
+    target_link_libraries(main PRIVATE sqlite3)
+```
+
+Overlay triplets will add your custom triplet files when using `vcpkg install`, `vcpkg update`, `vcpkg upgrade`, and `vcpkg remove`.
+
+When using the `--overlay-triplets` option, a message like the following lets you know that a custom triplet is being used: 
+
+```
+-- Loading triplet configuration from: /home/custom-triplets/x64-linux-dynamic.cmake
+```
+
+## Overriding default triplets
+
+As you may have noticed, the default triplets for Windows (`x86-windows` and `x64-windows`) install dynamic libraries, while a suffix (`-static`) is needed for static libraries. This is inconsistent with Linux and Mac OS where only static libraries are built.
+
+Using `--overlay-ports` it is possible to override the default triplets to accomplish the same behavior on Linux:
+
+* `x64-linux`: Builds dynamic libraries,
+* `x64-linux-static`: Builds static libraries.
+
+### Step 1: Create the overriden triplet
+
+Using the custom triplet created in the previous example, rename `custom-triplets/x64-linux-dynamic.cmake` to `custom-triplets/x64-linux.cmake`.
+
+```
+~/vcpkg$ mv ../custom-triplets/x64-linux-dynamic.cmake ../custom-triplets/x64-linux.cmake
+```
+
+### Step 2: Copy and rename the default triplet
+
+Then, copy the default `x64-linux` triplet (which builds static libraries) in your `/custom-triplets` folder and rename it to `x64-linux-static.cmake`.
+
+```
+~/vcpkg$ cp ./triplets/x64-linux.cmake ../custom-triplets/x64-linux-static.cmake
+```
+
+### Step 3: Use `--overlay-ports` to override default triplets
+
+Use the `--overlay-triplets` option to include the triplets in the `custom-triplets` directory.
+
+```
+./vcpkg install sqlite3:x64-linux --overlay-triplets=../custom-triplets
+The following packages will be built and installed:
+    sqlite3[core]:x64-linux
+Starting package 1/1: sqlite3:x64-linux
+Building package sqlite3[core]:x64-linux...
+-- Loading triplet configuration from: /home/custom-triplets/x64-linux.cmake
+-- Downloading https://sqlite.org/2019/sqlite-amalgamation-3280000.zip...
+-- Extracting source /home/victor/git/vcpkg/downloads/sqlite-amalgamation-3280000.zip
+-- Applying patch fix-arm-uwp.patch
+-- Using source at /home/victor/git/vcpkg/buildtrees/sqlite3/src/3280000-6a3ff7ce92
+-- Configuring x64-linux-dbg
+-- Configuring x64-linux-rel
+-- Building x64-linux-dbg
+-- Building x64-linux-rel
+-- Performing post-build validation
+-- Performing post-build validation done
+Building package sqlite3[core]:x64-linux... done
+Installing package sqlite3[core]:x64-linux...
+Installing package sqlite3[core]:x64-linux... done
+Elapsed time for package sqlite3:x64-linux: 44.82 s
+
+Total elapsed time: 44.82 s
+
+The package sqlite3:x64-linux provides CMake targets:
+
+    find_package(sqlite3 CONFIG REQUIRED)
+    target_link_libraries(main PRIVATE sqlite3)
+```
+
+Note that the default triplet is masked by your custom triplet:
+
+```
+-- Loading triplet configuration from: /home/custom-triplets/x64-linux.cmake
+```