devenv: Add more info how to get gdb scripts working

Now that top builddir is not the default workdir any more, the .gdbinit
file we write there won't be loaded automatically unless user cd there,
or use --init-command. There is also a global setting that user has to
set to allow automatically loading .gdbinit file.

mesonbuild/mdevenv.py

@@ -92,7 +92,7 @@ def add_gdb_auto_load(autoload_path: Path, gdb_helper: str, fname: Path) -> None
     except (FileExistsError, shutil.SameFileError):
         pass
 
-def write_gdb_script(privatedir: Path, install_data: 'InstallData') -> None:
+def write_gdb_script(privatedir: Path, install_data: 'InstallData', workdir: Path) -> None:
     if not shutil.which('gdb'):
         return
     bdir = privatedir.parent
@@ -122,7 +122,16 @@ def write_gdb_script(privatedir: Path, install_data: 'InstallData') -> None:
             gdbinit_path.write_text(gdbinit_line, encoding='utf-8')
             first_time = True
         if first_time:
-            mlog.log('Meson detected GDB helpers and added config in', mlog.bold(str(gdbinit_path)))
+            gdbinit_path = gdbinit_path.resolve()
+            workdir_path = workdir.resolve()
+            rel_path = gdbinit_path.relative_to(workdir_path)
+            mlog.log('Meson detected GDB helpers and added config in', mlog.bold(str(rel_path)))
+            mlog.log('To load it automatically you might need to:')
+            mlog.log(' - Add', mlog.bold(f'add-auto-load-safe-path {gdbinit_path.parent}'),
+                     'in', mlog.bold('~/.gdbinit'))
+            if gdbinit_path.parent != workdir_path:
+                mlog.log(' - Change current workdir to', mlog.bold(str(rel_path.parent)),
+                         'or use', mlog.bold(f'--init-command {rel_path}'))
 
 def run(options: argparse.Namespace) -> int:
     privatedir = Path(options.builddir) / 'meson-private'
@@ -142,7 +151,7 @@ def run(options: argparse.Namespace) -> int:
         return 0
 
     install_data = minstall.load_install_data(str(privatedir / 'install.dat'))
-    write_gdb_script(privatedir, install_data)
+    write_gdb_script(privatedir, install_data, workdir)
 
     setup_vsenv(b.need_vsenv)