docs/develop/ide: A quick guide for haiku code completion

* Works under a Linux "cross-compile" environment
* We can't check in compile_commands.json unforunetly because it
  highly depends on your build environment
* An in-tree .clangd is a thing, but our includes are complex
  and directory-spefific.
* Thanks to Pulkomandy for adding the flag to jam to do this!

Change-Id: I3be4084c43f7b822bb04ea7ec527c5fbe03d7289
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7158
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

.gitignore

@@ -22,3 +22,6 @@ build/user_config_headers
 
 # Project settings of the Genio IDE
 .genio
+
+# clangd related tooling for IDE code completion
+compile_commands.json

docs/develop/build/ide.rst

@@ -0,0 +1,29 @@
+Using an IDE
+===============
+
+Live Code Analysis
+------------------
+While developing the Haiku codebase, it is possible to generate an inventory of compile commands
+by passing the **-c** flag to jam. The resulting **compile_commands.json** document will assist
+tools such as clangd_ in live analyzing our source code.
+
+.. code-block::
+  :caption: Generating the **compile_commands.json** for clangd:
+
+  $ mkdir generated.clangd && cd generated.clangd
+  $ configure --build-cross-tools x86_64 --cross-tools-source ../../buildtools
+  $ jam -anc @nightly-anyboot
+  $ ln -sr compile_commands.json ../compile_commands.json
+
+
+When you use an editor which supports clangd_ such as helix_ or vim_ (with the clangd plugin),
+clangd_ will have knowledge of the relevant include paths and build flags for every source file
+within the Haiku codebase.
+
+.. TIP::
+   When new source code files are added, you will need to run though the process above for a
+   complete database.
+
+.. _helix: http://helix-editor.com
+.. _vim:   http://vim.org
+.. _clangd: http://clangd.llvm.org

docs/develop/build/index.rst

@@ -7,4 +7,5 @@ The build system
    /build/jam
    /build/sourcecode
    /build/compilers
+   /build/ide
    /build/repositories/README