Conditional compilation of plugins (#527)

* Conditional compilation of plugins. WITH_PLUGINS side is working.

* Conditional compilation of plugins according to specified cmake options.

* Refactoring to reduce redundancy.

Author: intjftw

doc/deps.md

@@ -303,3 +303,4 @@ relevant during compilation.
 | `DATABASE` | Database type. Possible values are **sqlite**, **pgsql**. The default value is `sqlite`. |
 | `TEST_DB` | The connection string for the database that will be used when executing tests with `make test`. Optional. |
 | `CODECOMPASS_LINKER` | The path of the linker, if the system's default linker is to be overridden. |
+| `WITH_PLUGIN`/`WITHOUT_PLUGIN` | The names of the plugins to be built/skipped at build. Possible values are **cpp**, **cpp_reparse**, **dummy**, **git**, **metrics**, **search**. The `metrics` and `search` plugins are fundamental, they will be compiled even if not included. `WITH_PLUGIN` **cannot** be used together with `WITHOUT_PLUGIN`. Example: `-DWITH_PLUGIN="cpp;git"` This will compile the cpp, git, metrics and search plugins. |

plugins/CMakeLists.txt

@@ -2,9 +2,35 @@
 include_directories(SYSTEM
   ${ODB_INCLUDE_DIRS})
 
+# Throw error if WITH_PLUGIN and WITHOUT_PLUGIN are used together
+if(WITH_PLUGIN AND WITHOUT_PLUGIN)
+  message(FATAL_ERROR "The WITH_PLUGIN and WITHOUT_PLUGIN options cannot be used together.")
+endif()
+
 # Add all subdirectories to the build
 file(GLOB plugins RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} "${CMAKE_CURRENT_SOURCE_DIR}/*")
 
+# Remove subdirectories according to the provided WITH_PLUGIN or WITHOUT_PLUGIN variables
+set(baseline "search")
+if(WITH_PLUGIN OR WITHOUT_PLUGIN)
+  foreach(_base ${baseline})
+    if((WITH_PLUGIN AND NOT ("${_base}" IN_LIST WITH_PLUGIN))
+       OR (WITHOUT_PLUGIN AND "${_base}" IN_LIST WITHOUT_PLUGIN))
+      message(WARNING "The ${_base} plugin cannot be left out, "
+              "it will be compiled anyway.")
+    endif()
+  endforeach()
+
+  foreach(_plugin ${plugins})
+    if(((WITH_PLUGIN AND NOT ("${_plugin}" IN_LIST WITH_PLUGIN))
+       OR (WITHOUT_PLUGIN AND ("${_plugin}" IN_LIST WITHOUT_PLUGIN)))
+       AND NOT ("${_plugin}" IN_LIST baseline)
+       AND IS_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/${_plugin}")
+      list(REMOVE_ITEM plugins ${_plugin})
+    endif()
+  endforeach()
+endif()
+
 # Set unique plugin directory variable for each plugin
 message(STATUS "Found the following CodeCompass plugins:")
 foreach(_plugin ${plugins})