Add systemapi as an APEX synonym for stub maps.

The apex tag is currently used for platform-to-APEX, APEX-to-APEX, and
APEX-to-platform, and it's difficult to tell when reviewing the map
files. Add a synonym so authors can be explicit about platform-to-APEX
since those have different stability rules.

Test: pytest
Test: mypy
Test: pylint
Test: treehugger
Bug: None
Change-Id: I0aee679a05b1b2d3749307434c19486bf4c7fe52

cc/ndkstubgen/__init__.py

@@ -108,7 +108,14 @@ def parse_args() -> argparse.Namespace:
     parser.add_argument(
         '--llndk', action='store_true', help='Use the LLNDK variant.')
     parser.add_argument(
-        '--apex', action='store_true', help='Use the APEX variant.')
+        '--apex',
+        action='store_true',
+        help='Use the APEX variant. Note: equivalent to --system-api.')
+    parser.add_argument(
+        '--system-api',
+        action='store_true',
+        dest='apex',
+        help='Use the SystemAPI variant. Note: equivalent to --apex.')
 
     parser.add_argument('--api-map',
                         type=resolved_path,

cc/symbolfile/__init__.py

@@ -83,7 +83,7 @@ class Tags:
     @property
     def has_apex_tags(self) -> bool:
         """Returns True if any APEX tags are set."""
-        return 'apex' in self.tags
+        return 'apex' in self.tags or 'systemapi' in self.tags
 
     @property
     def has_llndk_tags(self) -> bool:

cc/symbolfile/test_symbolfile.py

@@ -253,6 +253,21 @@ class OmitVersionTest(unittest.TestCase):
                 symbolfile.Version('foo', None, Tags.from_strs(['apex']), []),
                 Arch('arm'), 9, False, True))
 
+    def test_omit_systemapi(self) -> None:
+        self.assertTrue(
+            symbolfile.should_omit_version(
+                symbolfile.Version('foo', None, Tags.from_strs(['systemapi']),
+                                   []), Arch('arm'), 9, False, False))
+
+        self.assertFalse(
+            symbolfile.should_omit_version(
+                symbolfile.Version('foo', None, Tags(), []), Arch('arm'), 9,
+                False, True))
+        self.assertFalse(
+            symbolfile.should_omit_version(
+                symbolfile.Version('foo', None, Tags.from_strs(['systemapi']),
+                                   []), Arch('arm'), 9, False, True))
+
     def test_omit_arch(self) -> None:
         self.assertFalse(
             symbolfile.should_omit_version(
@@ -315,6 +330,20 @@ class OmitSymbolTest(unittest.TestCase):
                 symbolfile.Symbol('foo', Tags.from_strs(['apex'])),
                 Arch('arm'), 9, False, True))
 
+    def test_omit_systemapi(self) -> None:
+        self.assertTrue(
+            symbolfile.should_omit_symbol(
+                symbolfile.Symbol('foo', Tags.from_strs(['systemapi'])),
+                Arch('arm'), 9, False, False))
+
+        self.assertFalse(
+            symbolfile.should_omit_symbol(symbolfile.Symbol('foo', Tags()),
+                                          Arch('arm'), 9, False, True))
+        self.assertFalse(
+            symbolfile.should_omit_symbol(
+                symbolfile.Symbol('foo', Tags.from_strs(['systemapi'])),
+                Arch('arm'), 9, False, True))
+
     def test_omit_arch(self) -> None:
         self.assertFalse(
             symbolfile.should_omit_symbol(symbolfile.Symbol('foo', Tags()),

docs/map_files.md

@@ -70,9 +70,11 @@ the same line. The supported tags are:
 
 ### apex
 
-Indicates that the version or symbol is to be exposed in the APEX stubs rather
-than the NDK. May be used in combination with `llndk` if the symbol is exposed
-to both APEX and the LL-NDK.
+Indicates that the version or symbol is to be exposed by an APEX rather than the
+NDK. For APIs exposed by the platform *for* APEX, use `systemapi`.
+
+May be used in combination with `llndk` if the symbol is exposed to both APEX
+and the LL-NDK.
 
 ### future
 
@@ -144,6 +146,12 @@ for use by the NDK, LL-NDK, or APEX (similar to Java's `@SystemAPI`). It is
 preferable to keep such APIs in an entirely separate library to protect them
 from access via `dlsym`, but this is not always possible.
 
+### systemapi
+
+This is a synonym of the `apex` tag. It should be used to clarify that the API
+is an API exposed by the system for an APEX, whereas `apex` should be used for
+APIs exposed by an APEX to the platform or another APEX.
+
 ### var
 
 Used to define a public global variable. By default all symbols are exposed as