interpreter: Fix spurious warning in include_directories()

When doing include_directories('.') at the root of the subproject we
should not warn about sandboxing violation.

mesonbuild/interpreter.py

@@ -4601,7 +4601,7 @@ different subdirectory.
 ''')
             else:
                 try:
-                    self.validate_within_subproject(a, '')
+                    self.validate_within_subproject(self.subdir, a)
                 except InterpreterException:
                     mlog.warning('include_directories sandbox violation!')
                     print(f'''The project is trying to access the directory {a} which belongs to a different
@@ -4830,6 +4830,8 @@ Try setting b_lundef to false instead.'''.format(self.coredata.options[OptionKey
             # /opt/vendorsdk/src/file_with_license_restrictions.c
             return
         project_root = Path(srcdir, self.root_subdir)
+        if norm == project_root:
+            return
         if project_root not in norm.parents:
             raise InterpreterException(f'Sandbox violation: Tried to grab {inputtype} {norm.name} outside current (sub)project.')
         if project_root / self.subproject_dir in norm.parents:

test cases/common/240 includedir violation/meson.build

@@ -1,5 +1,9 @@
 project('foo', 'c')
 
+# It is fine to include the root source dir
+include_directories('.')
+subproject('sub')
+
 # This is here rather than in failing because this needs a
 # transition period to avoid breaking existing projects.
 # Once this becomes an error, move this under failing tests.

test cases/common/240 includedir violation/subprojects/sub/meson.build

@@ -1,3 +1,3 @@
 project('subproj', 'c')
 
-# This is never actually executed, just here for completeness.
+include_directories('.')

test cases/common/240 includedir violation/test.json

@@ -1,7 +1,9 @@
 {
   "stdout": [
     {
-      "line": "WARNING: include_directories sandbox violation!"
+      "line": ".*WARNING: include_directories sandbox violation!",
+      "match": "re",
+      "count": 1
     }
   ]
 }