check-flagged-apis: parse API versions XML

Teach check-flagged-apis to parse API versions XML; this represents the
APIs after metalava has processed the source and kept APIs as is, or
reverted them to the previous SDK snapshot, according to their
@FlaggedApi flags.

As with the API signature parser, limit support to fields to keep things
simple; support for classes and methods will be added in later CLs.

Note: `m sdk dist` will generate an API versions XML file.

Bug: 334870672
Test: atest --host check-flagged-apis-test
Test: check-flagged-apis --api-signature out/target/product/mainline_x86/obj/ETC/frameworks-base-api-current.txt_intermediates/frameworks-base-api-current.txt --flag-values out/soong/.intermediates/all_aconfig_declarations.pb --api-versions out/dist/data/api-versions.xml
Change-Id: I779a0d0cdb8a50536d3fc8d517fa38ba4b0dcd1c

tools/check-flagged-apis/src/com/android/checkflaggedapis/CheckFlaggedApisTest.kt

@@ -52,6 +52,18 @@ private val PARSED_FLAGS =
       ByteArrayInputStream(binaryProto.toByteArray())
     }()
 
+private val API_VERSIONS =
+    """
+      <?xml version="1.0" encoding="utf-8"?>
+      <api version="3">
+        <class name="android/Clazz" since="1">
+          <method name="&lt;init>()V"/>
+          <field name="FOO"/>
+        </class>
+      </api>
+"""
+        .trim()
+
 @RunWith(DeviceJUnit4ClassRunner::class)
 class CheckFlaggedApisTest : BaseHostJUnit4Test() {
   @Test
@@ -67,4 +79,11 @@ class CheckFlaggedApisTest : BaseHostJUnit4Test() {
     val actual = parseFlagValues(PARSED_FLAGS)
     assertEquals(expected, actual)
   }
+
+  @Test
+  fun testParseApiVersions() {
+    val expected: Set<Symbol> = setOf(Symbol("android.Clazz.FOO"))
+    val actual = parseApiVersions(API_VERSIONS.byteInputStream())
+    assertEquals(expected, actual)
+  }
 }

tools/check-flagged-apis/src/com/android/checkflaggedapis/Main.kt

@@ -28,6 +28,8 @@ import com.github.ajalt.clikt.parameters.options.option
 import com.github.ajalt.clikt.parameters.options.required
 import com.github.ajalt.clikt.parameters.types.path
 import java.io.InputStream
+import javax.xml.parsers.DocumentBuilderFactory
+import org.w3c.dom.Node
 
 /**
  * Class representing the fully qualified name of a class, method or field.
@@ -108,6 +110,16 @@ The tool will exit with a non-zero exit code if any flagged APIs are found to be
             """)
           .path(mustExist = true, canBeDir = false, mustBeReadable = true)
           .required()
+  private val apiVersionsPath by
+      option("--api-versions")
+          .help(
+              """
+            Path to API versions XML file.
+            Usually named xml-versions.xml.
+            Tip: `m sdk dist` will generate a file that includes all platform and mainline APIs.
+            """)
+          .path(mustExist = true, canBeDir = false, mustBeReadable = true)
+          .required()
 
   override fun run() {
     @Suppress("UNUSED_VARIABLE")
@@ -117,6 +129,8 @@ The tool will exit with a non-zero exit code if any flagged APIs are found to be
         }
     @Suppress("UNUSED_VARIABLE")
     val flags = flagValuesPath.toFile().inputStream().use { parseFlagValues(it) }
+    @Suppress("UNUSED_VARIABLE")
+    val exportedSymbols = apiVersionsPath.toFile().inputStream().use { parseApiVersions(it) }
     throw ProgramResult(0)
   }
 }
@@ -151,4 +165,24 @@ internal fun parseFlagValues(input: InputStream): Map<Flag, Boolean> {
       { it.getState() == Aconfig.flag_state.ENABLED })
 }
 
+internal fun parseApiVersions(input: InputStream): Set<Symbol> {
+  fun Node.getAttribute(name: String): String? = getAttributes()?.getNamedItem(name)?.getNodeValue()
+
+  val output = mutableSetOf<Symbol>()
+  val factory = DocumentBuilderFactory.newInstance()
+  val parser = factory.newDocumentBuilder()
+  val document = parser.parse(input)
+  val fields = document.getElementsByTagName("field")
+  // ktfmt doesn't understand the `..<` range syntax; explicitly call .rangeUntil instead
+  for (i in 0.rangeUntil(fields.getLength())) {
+    val field = fields.item(i)
+    val fieldName = field.getAttribute("name")
+    val className =
+        requireNotNull(field.getParentNode()) { "Bad XML: top level <field> element" }
+            .getAttribute("name")
+    output.add(Symbol.create("$className.$fieldName"))
+  }
+  return output
+}
+
 fun main(args: Array<String>) = CheckCommand().main(args)