Generate target id based on subdirectory instead of subproject

Allows creation of targets with same name in different subdirectories.
Closes #2861 and closes #1867

mesonbuild/build.py

@@ -310,11 +310,16 @@ a hard error in the future.''' % name)
     def get_id(self):
         # This ID must also be a valid file name on all OSs.
         # It should also avoid shell metacharacters for obvious
-        # reasons.
-        base = self.name + self.type_suffix()
-        if self.subproject == '':
-            return base
-        return self.subproject + '@@' + base
+        # reasons. '@' is not used as often as '_' in source code names.
+        # In case of collisions consider using checksums.
+        # FIXME replace with assert when slash in names is prohibited
+        name_part = self.name.replace('/', '@').replace('\\', '@')
+        assert not has_path_sep(self.type_suffix())
+        myid = name_part + self.type_suffix()
+        if self.subdir:
+            subdir_part = self.subdir.replace('/', '@').replace('\\', '@')
+            myid = subdir_part + '@@' + myid
+        return myid
 
     def process_kwargs(self, kwargs):
         if 'build_by_default' in kwargs:

run_unittests.py

@@ -1117,7 +1117,7 @@ class AllPlatformTests(BasePlatformTests):
         incs = [a for a in shlex.split(execmd) if a.startswith("-I")]
         self.assertEqual(len(incs), 9)
         # target private dir
-        self.assertPathEqual(incs[0], "-Isub4/someexe@exe")
+        self.assertPathEqual(incs[0], "-Isub4/sub4@@someexe@exe")
         # target build subdir
         self.assertPathEqual(incs[1], "-Isub4")
         # target source subdir
@@ -2601,8 +2601,8 @@ class LinuxlikeTests(BasePlatformTests):
     def test_unity_subproj(self):
         testdir = os.path.join(self.common_test_dir, '49 subproject')
         self.init(testdir, extra_args='--unity=subprojects')
-        self.assertPathExists(os.path.join(self.builddir, 'subprojects/sublib/sublib@@simpletest@exe/simpletest-unity.c'))
-        self.assertPathExists(os.path.join(self.builddir, 'subprojects/sublib/sublib@@sublib@sha/sublib-unity.c'))
+        self.assertPathExists(os.path.join(self.builddir, 'subprojects/sublib/subprojects@sublib@@simpletest@exe/simpletest-unity.c'))
+        self.assertPathExists(os.path.join(self.builddir, 'subprojects/sublib/subprojects@sublib@@sublib@sha/sublib-unity.c'))
         self.assertPathDoesNotExist(os.path.join(self.builddir, 'user@exe/user-unity.c'))
         self.build()