squash: add the maintaining doc for dependencies

Signed-off-by: Michael Dawson <mdawson@devrus.com>

doc/contributing/maintaining-dependencies.md

@@ -0,0 +1,106 @@
+# Maintaining Dependencies
+
+Node.js depends on additional components beyond the Node.js code
+itself. These dependencies provide both native and JavaScript code
+and are built together with the code under the `src` and `lib`
+directories to create the Node.js binaries.
+
+All dependencies are located within the `deps` directory.
+
+Any code which meets one or more of these conditions should
+be managed as a dependency:
+
+* originates in an upstream project and is maintained
+  in that upstream project.
+* is not built from the `preferred form of the work for
+  making modifications to it` (see
+  [GNU GPL v2, section 3.](https://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html)
+  when `make node` is run. A good example is
+  WASM code generated from JavaScript(the preferred form).
+  Typically generation is only supported on a subset of platforms, needs
+  additional tools, and is pre-built outside of the `make node`
+  step and then committed as a WASM binary in the directory
+  for the dependency under the `deps` directory.
+
+By default all dependencies are bundled into the Node.js
+binary, however, `configure` options should be available to
+use an externalized version at runtime when:
+
+* the dependency provides native code and is available as
+  a shared library in one or more of the common Node.js
+  distributions.
+* the dependency provides JavaScript and is not built
+  from the `preferred form of the work for making modifications
+  to it` when `make node` is run.
+
+Many distributions use externalized dependencies for one or
+more of these reasons:
+
+1. They have a requirement to build everything that they ship
+   from the `preferred form of the work for making
+   modifications to it`. This means that they need to
+   replace any pre-built components (for example WASM
+   binaries) with an equivalent that they have built.
+2. They manage the dependency separately as it is used by
+   more applications than just Node.js. Linking against
+   a shared library allows them to manage updates and
+   CVE fixes against the library instead of having to
+   patch all of the individual applications.
+3. They have a system wide configuration for the
+   dependency that all applications should respect.
+
+## Supporting externalized dependencies with native code.
+
+Support for externalized dependencies with native code for which a
+shared library is available can added by:
+
+* adding options to `configure.py`. These are added to the
+  shared\_optgroup and include an options to:
+  * enable use of a shared library
+  * set the name of the shared library
+  * set the path to the directory with the includes for the
+    shared library
+  * set the path to where to find the shared library at
+    runtime
+* add a call to configure\_library() to `configure.py` for the
+  library at the end of list of existing configure\_library() calls.
+  If there are additional libraries that are required it is
+  possible to list more than one with the `pkgname` option.
+* in `node.gypi` guard the build for the dependency
+  with `node_shared_depname` so that is is only built if
+  the dependency is being bundled into Node.js itself. For example:
+
+```text
+    [ 'node_shared_brotli=="false"', {
+      'dependencies': [ 'deps/brotli/brotli.gyp:brotli' ],
+    }],
+```
+
+## Supporting externalizable dependencies with JavaScript codeIZA
+
+Support for an externalizable dependency with JavaScript code
+can be added by:
+
+* adding an entry to the `sharable_builtins` map in
+  `configure.py`. The path should correspond to the file
+  within the deps directory that is normally bundled into
+  Node.js. For example `deps/cjs-module-lexer/lexer.js`.
+  This will add a new option for building with that dependency
+  externalized. After adding the entry you can see
+  the new option by running `./configure --help`.
+
+* adding a call to `AddExternalizedBuiltin` to the constructor
+  for BuildinLoader in `src/node_builtins.cc` for the
+  dependency using the `NODE_SHARED_BUILTLIN` #define generated for
+  the dependency. After running `./configure` with the new
+  option you can find the #define in `config.gypi`. You can cut and
+  paste one of the existing entries and then update to match the
+  inport name for the dependency and the #define generated.
+
+## Supporting non-externalized dependencies with JavaScript code
+
+If the depenency consists of JavaScript in the
+`preferred form of the work for making modifications to it`, it
+can be added as a non-externalizable dependency. In this case
+simply add the path to the JavaScript file in the `deps_files`
+list in the `node.gyp` file.