Linux platform example app includes SHELL unconditionally. (#7205)

* Linux platform example app includes SHELL unconditionally.

Force defines and linkages as such, otherwise compilation with GN
without 'use shell' does not work.

TODO as followup: if shell is really optional, build it as such in linux
as well.

* remove the enable shell arg alltogether - it does not work because includes are already there

* Revert "Fix relative path for the markdown link (#7202)"

This reverts commit 7a172f3.
Apparently link checker is not fully working and this broke doxygen.

docs/README.md

@@ -6,7 +6,7 @@
     [the build guide](./BUILDING.md)
 -   Documentation about running [cirque](https://github.com/openweave/cirque)
     tests can be found in
-    [the cirque test guide](../src/test_driver/linux-cirque/README.md)
+    [the cirque test guide](src/test_driver/linux-cirque/README.md)
 -   Documentation about standard build & development flows using
     [Visual Studio Code](https://code.visualstudio.com/) can be found in
     [the development guide](./VSCODE_DEVELOPMENT.md)

examples/platform/linux/AppMain.cpp

@@ -112,15 +112,11 @@ int ChipLinuxAppInit(int argc, char ** argv)
 
 void ChipLinuxAppMainLoop()
 {
-#if CHIP_ENABLE_SHELL
     std::thread shellThread([]() { Engine::Root().RunMainLoop(); });
-#endif
 
     // Init ZCL Data Model and CHIP App Server
     InitServer();
 
     chip::DeviceLayer::PlatformMgr().RunEventLoop();
-#if CHIP_ENABLE_SHELL
     shellThread.join();
-#endif
 }

examples/platform/linux/BUILD.gn

@@ -19,10 +19,6 @@ config("app-main-config") {
   include_dirs = [ "." ]
 }
 
-declare_args() {
-  chip_enable_shell = false
-}
-
 source_set("app-main") {
   sources = [
     "AppMain.cpp",
@@ -40,12 +36,12 @@ source_set("app-main") {
   public_deps = [
     "${chip_root}/src/app/server",
     "${chip_root}/src/lib",
+    "${chip_root}/src/lib/shell",
+    "${chip_root}/src/lib/shell:shell_core",
   ]
 
-  if (chip_enable_shell) {
-    defines += [ "CHIP_ENABLE_SHELL" ]
-    public_deps += [ "${chip_root}/src/lib/shell" ]
-  }
+    public_deps += [ 
+    ]
 
   public_configs = [ ":app-main-config" ]
 }