Remove implementation details from stub flags in sdk snapshot

Previously, the build applied the same filtering to remove
implementation details from the sdk snapshot's stub-flags.csv file as
it did for its all-flags.csv, i.e. removing the signatures that only
had a "blocked" flag. Unfortunately, that had no effect on the stub
flags as the implementation signatures had no flags, not a single
blocked flag. That meant that the sdk snapshot's
filtered-stub-flags.csv file contained a lot of implementation details.

This change removes signatures from stub-flags.csv that have no flags
which removes all implementation details from the sdk snapshot.

Bug: 194063708
Test: atest --host verify_overlaps_test
      m out/soong/hiddenapi/hiddenapi-flags.csv
      m art-module-sdk
      # Check contents of its filtered-stub-flags.csv file
Change-Id: I30edc77348fad118ea732e787ae8e206c8841f84

scripts/hiddenapi/verify_overlaps_test.py

@@ -221,7 +221,8 @@ Ljava/lang/Object;->hashCode()I,public-api,system-api,test-api
         modular = self.read_signature_csv_from_string_as_dict("""
 Ljava/lang/Object;->hashCode()I,public-api,system-api,test-api
 """)
-        mismatches = vo.compare_signature_flags(monolithic, modular)
+        mismatches = vo.compare_signature_flags(monolithic, modular,
+                                                ["blocked"])
         expected = []
         self.assertEqual(expected, mismatches)
 
@@ -232,7 +233,8 @@ Ljava/lang/Object;->toString()Ljava/lang/String;,public-api
         modular = self.read_signature_csv_from_string_as_dict("""
 Ljava/lang/Object;->toString()Ljava/lang/String;,public-api,system-api,test-api
 """)
-        mismatches = vo.compare_signature_flags(monolithic, modular)
+        mismatches = vo.compare_signature_flags(monolithic, modular,
+                                                ["blocked"])
         expected = [
             (
                 "Ljava/lang/Object;->toString()Ljava/lang/String;",
@@ -249,7 +251,8 @@ Ljava/lang/Object;->toString()Ljava/lang/String;,blocked
         modular = self.read_signature_csv_from_string_as_dict("""
 Ljava/lang/Object;->toString()Ljava/lang/String;,public-api,system-api,test-api
 """)
-        mismatches = vo.compare_signature_flags(monolithic, modular)
+        mismatches = vo.compare_signature_flags(monolithic, modular,
+                                                ["blocked"])
         expected = [
             (
                 "Ljava/lang/Object;->toString()Ljava/lang/String;",
@@ -266,7 +269,8 @@ Ljava/lang/Object;->toString()Ljava/lang/String;,public-api,system-api,test-api
         modular = self.read_signature_csv_from_string_as_dict("""
 Ljava/lang/Object;->toString()Ljava/lang/String;,blocked
 """)
-        mismatches = vo.compare_signature_flags(monolithic, modular)
+        mismatches = vo.compare_signature_flags(monolithic, modular,
+                                                ["blocked"])
         expected = [
             (
                 "Ljava/lang/Object;->toString()Ljava/lang/String;",
@@ -281,7 +285,8 @@ Ljava/lang/Object;->toString()Ljava/lang/String;,blocked
         modular = self.read_signature_csv_from_string_as_dict("""
 Ljava/lang/Object;->toString()Ljava/lang/String;,public-api,system-api,test-api
 """)
-        mismatches = vo.compare_signature_flags(monolithic, modular)
+        mismatches = vo.compare_signature_flags(monolithic, modular,
+                                                ["blocked"])
         expected = [
             (
                 "Ljava/lang/Object;->toString()Ljava/lang/String;",
@@ -296,7 +301,8 @@ Ljava/lang/Object;->toString()Ljava/lang/String;,public-api,system-api,test-api
 Ljava/lang/Object;->hashCode()I,public-api,system-api,test-api
 """)
         modular = {}
-        mismatches = vo.compare_signature_flags(monolithic, modular)
+        mismatches = vo.compare_signature_flags(monolithic, modular,
+                                                ["blocked"])
         expected = [
             (
                 "Ljava/lang/Object;->hashCode()I",
@@ -311,7 +317,47 @@ Ljava/lang/Object;->hashCode()I,public-api,system-api,test-api
 Ljava/lang/Object;->hashCode()I,blocked
 """)
         modular = {}
-        mismatches = vo.compare_signature_flags(monolithic, modular)
+        mismatches = vo.compare_signature_flags(monolithic, modular,
+                                                ["blocked"])
+        expected = []
+        self.assertEqual(expected, mismatches)
+
+    def test_match_treat_missing_from_modular_as_empty(self):
+        monolithic = self.read_signature_csv_from_string_as_dict("")
+        modular = self.read_signature_csv_from_string_as_dict("""
+Ljava/lang/Object;->toString()Ljava/lang/String;,public-api,system-api,test-api
+""")
+        mismatches = vo.compare_signature_flags(monolithic, modular, [])
+        expected = [
+            (
+                "Ljava/lang/Object;->toString()Ljava/lang/String;",
+                ["public-api", "system-api", "test-api"],
+                [],
+            ),
+        ]
+        self.assertEqual(expected, mismatches)
+
+    def test_mismatch_treat_missing_from_modular_as_empty(self):
+        monolithic = self.read_signature_csv_from_string_as_dict("""
+Ljava/lang/Object;->hashCode()I,public-api,system-api,test-api
+""")
+        modular = {}
+        mismatches = vo.compare_signature_flags(monolithic, modular, [])
+        expected = [
+            (
+                "Ljava/lang/Object;->hashCode()I",
+                [],
+                ["public-api", "system-api", "test-api"],
+            ),
+        ]
+        self.assertEqual(expected, mismatches)
+
+    def test_empty_missing_from_modular(self):
+        monolithic = self.read_signature_csv_from_string_as_dict("""
+Ljava/lang/Object;->hashCode()I
+""")
+        modular = {}
+        mismatches = vo.compare_signature_flags(monolithic, modular, [])
         expected = []
         self.assertEqual(expected, mismatches)