toolcontext: add nit_dir service

Use `NIT_DIR` or some heuristic to find the Nit directory.
In next commits, tools will use it.

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/src/toolcontext.nit b/src/toolcontext.nit
index 85d7cd6..a7d17ce 100644 (file)
--- a/src/toolcontext.nit
+++ b/src/toolcontext.nit
@@ -238,5 +238,31 @@ class ToolContext
                        # Make sure the output directory exists
                        log_directory.mkdir
                end
+
+               nit_dir = compute_nit_dir
+       end
+
+       # The identified root directory of the Nit project
+       var nit_dir: nullable String
+
+       private fun compute_nit_dir: nullable String
+       do
+               # a environ variable has precedence
+               var res = "NIT_DIR".environ
+               if not res.is_empty then return res
+
+               # find the runpath of the program from argv[0]
+               res = "{sys.program_name.dirname}/.."
+               if res.file_exists and "{res}/src/nit.nit".file_exists then return res.simplify_path
+
+               # find the runpath of the process from /proc
+               var exe = "/proc/self/exe"
+               if exe.file_exists then
+                       res = exe.realpath
+                       res = res.dirname.join_path("..")
+                       if res.file_exists and "{res}/src/nit.nit".file_exists then return res.simplify_path
+               end
+
+               return null
        end
 end