more documentation updates for auto-recompilation

NEWS.md

@@ -30,7 +30,7 @@ New language features
 
   * Incremental compilation of modules: `Base.compile(module::Symbol)` imports the named module,
     but instead of loading it into the current session saves the result of compiling it in
-    `~/.julia/lib/v0.4` ([#8745]).
+    `~/.julia/lib/v0.4` ([#8745]).  The module will automatically be recompiled as needed ([#12458]).
 
       * See manual section on `Module initialization and precompilation` (under `Modules`) for details and errata.
 
@@ -1557,3 +1557,4 @@ Too numerous to mention.
 [#12137]: https://github.com/JuliaLang/julia/issues/12137
 [#12162]: https://github.com/JuliaLang/julia/issues/12162
 [#12393]: https://github.com/JuliaLang/julia/issues/12393
+[#12458]: https://github.com/JuliaLang/julia/issues/12458

doc/manual/modules.rst

@@ -266,6 +266,12 @@ recompile Julia after modifying the file ``base/userimg.jl`` to require the desi
 To create an incremental precompiled module file,
 call ``Base.compile(modulename::Symbol)``.
 The resulting cache files will be stored in ``Base.LOAD_CACHE_PATH[1]``.
+(This will also compile any modules that your module depends on.)
+Once it has been compiled, the module will automatically be recompiled
+as needed (if any of its ``include`` dependencies or imported modules
+have changed) when it is imported.  (The ``include_dependency(path)``
+function can be called in your module to declare a dependency on
+an arbitrary file that you did not ``include``.)
 
 In order to make your module work with precompilation,
 however, you may need to change your module to explicitly separate any