Non-transitive R classes: Allow empty dependencies

It is possible to have a library with no dependencies, and in the
process of serialization of compiler arguments the difference between
empty string (serializing an empty list) and null is lost.

Just relax the assertion here, a reference to a resource that doesn't
exist will still be caught by the compiler.

Bug: 216667498
Test: Added unit test
Change-Id: Iaeb8494de85e9356ea68134804f9e92f2ba754c8

4 files changed, 32 insertions, 12 deletions

diff --git a/BUILD.bazel b/BUILD.bazel
index 6670d54a..b4022c82 100644
--- a/BUILD.bazel
+++ b/BUILD.bazel
@@ -314,6 +314,7 @@ kotlin_test(
         "@maven//:com.google.truth.truth",
         "@maven//:commons-io.commons-io",
         "@maven//:junit.junit",
+        "@maven//:org.jetbrains.kotlin.kotlin-test",
         "@maven//:org.mockito.mockito-core",
     ],
 )
diff --git a/compiler/build.gradle b/compiler/build.gradle
index e744f865..be805379 100644
--- a/compiler/build.gradle
+++ b/compiler/build.gradle
@@ -48,6 +48,7 @@ dependencies {
     implementation libs.juniversalchardet
     implementation libs.jaxb_runtime
     testImplementation libs.junit
+    testImplementation libs.kotlin_test
     testImplementation libs.mockito_core
     testImplementation libs.compile_testing
     testImplementation libs.truth
diff --git a/compiler/src/main/java/android/databinding/tool/util/SymbolTableUtil.kt b/compiler/src/main/java/android/databinding/tool/util/SymbolTableUtil.kt
index ab57d62e..1b6a4481 100644
--- a/compiler/src/main/java/android/databinding/tool/util/SymbolTableUtil.kt
+++ b/compiler/src/main/java/android/databinding/tool/util/SymbolTableUtil.kt
@@ -84,18 +84,10 @@ fun parseRTxtFiles(
     val symbolTables = ImmutableList.builder<SymbolTable>()
     // local resources at the front of the list
     symbolTables.add(parseLocalRTxt(localRFile))
-    when {
-        dependenciesRFiles != null -> {
-            // then add the rest of the dependencies, in order
-            dependenciesRFiles.forEach { symbolTables.add(parsePackageAwareRTxt(it)) }
-        }
-        mergedDependenciesRFile != null -> {
-            parseMergedPackageAwareRTxt(mergedDependenciesRFile, symbolTables)
-        }
-        else -> {
-            error("Unexpected error: Missing dependency resources")
-        }
-    }
+
+    // then add the rest of the dependencies, in order
+    dependenciesRFiles?.forEach { symbolTables.add(parsePackageAwareRTxt(it)) }
+    mergedDependenciesRFile?.let { parseMergedPackageAwareRTxt(it, symbolTables) }
 
     return Resources(symbolTables.build())
 }
diff --git a/compiler/src/test/java/android/databinding/tool/util/SymbolTableUtilTest.kt b/compiler/src/test/java/android/databinding/tool/util/SymbolTableUtilTest.kt
index f33738c6..2c23649c 100644
--- a/compiler/src/test/java/android/databinding/tool/util/SymbolTableUtilTest.kt
+++ b/compiler/src/test/java/android/databinding/tool/util/SymbolTableUtilTest.kt
@@ -17,11 +17,13 @@
 package android.databinding.tool.util
 
 import com.google.common.collect.ImmutableList
+import com.google.common.truth.Truth.assertThat
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
 import org.junit.Test
 import java.lang.IllegalStateException
 import java.nio.file.Files
+import kotlin.test.assertFailsWith
 
 class SymbolTableUtilTest {
 
@@ -118,6 +120,30 @@ class SymbolTableUtilTest {
     }
 
     @Test
+    fun testParsingWithEmptyDependencies() {
+        val localFile = Files.createTempFile("local", "R.txt")
+        Files.write(
+            localFile,
+            """
+                // This is a comment expected in package-aware R.txt
+                local
+                string first
+                """.trimIndent().toByteArray())
+        val result =
+            parseRTxtFiles(localFile.toFile(), null, null)
+
+        assertEquals(result.symbolTables!!.size, 1)
+        assertEquals(result.symbolTables!![0].rPackage, "")
+
+        assertEquals(result.getRPackagePrefix(null, "string", "first"), "")
+        val failure = assertFailsWith<Exception> {
+            result.getRPackagePrefix(null, "string", "second")
+        }
+        assertThat(failure).hasMessageThat().contains("not found")
+        assertEquals(result.getRPackagePrefix("android", "string", "not_found"), "android.")
+    }
+
+    @Test
     fun testParsingMergedDependencies() {
         val mergedR = Files.createTempFile("merged", "R.txt")
         Files.write(