Handle aliases to source files (#67)

Previously an alias to a source file ended up not hashing the source
file because the file didn't exist in the same configuration as the
depender.

pkg/hash_cache.go

@@ -515,11 +515,24 @@ func hashRule(thc *TargetHashCache, rule *build.Rule, configuration *analysis.Co
 				return nil, fmt.Errorf("failed to parse ruleInput label %s: %w", ruleInputLabelString, err)
 			}
 			var depConfigurations []Configuration
+			// Aliases don't transition, and we've seen aliases expanding across configurations cause dependency cycles for nogo targets.
 			if rule.GetRuleClass() == "alias" {
-				// Aliases don't transition, and we've seen aliases expanding across configurations cause dependency cycles for nogo targets.
-				// Narrow just to the current configuration in this case.
-				depConfiguration := NormalizeConfiguration(configuration.GetChecksum())
-				depConfigurations = []Configuration{depConfiguration}
+				knownDepConfigurations := thc.context[ruleInputLabel]
+				isSourceFile := true
+				for _, ct := range knownDepConfigurations {
+					if ct.GetTarget().GetType() != build.Target_SOURCE_FILE {
+						isSourceFile = false
+					}
+				}
+
+				if isSourceFile {
+					// If it's a source file, it doesn't exist in the current configuration, but does exist in the empty configuration.
+					// Accordingly, we need to explicitly transition to the empty configuration.
+					depConfigurations = []Configuration{NormalizeConfiguration("")}
+				} else {
+					// If it's not a source file, narrow just to the current configuration - we know there was no transition, so we must be in the same configuration.
+					depConfigurations = []Configuration{NormalizeConfiguration(configuration.GetChecksum())}
+				}
 			} else {
 				depConfigurations = thc.KnownConfigurations(ruleInputLabel).SortedSlice()
 			}

tests/integration/java/com/github/bazel_contrib/target_determinator/integration/Tests.java

@@ -540,6 +540,12 @@ public void aliasTargetIsDetectedIfActualTargetChanged() throws Exception {
             Set.of("//java/example:ExampleTest", "//java/example:example_test"));
   }
 
+  @Test
+  public void aliasTargetIsDetectedIfActualFileChanged() throws Exception {
+    doTest(Commits.ALIAS_ADD_TARGET_TO_FILE, Commits.ALIAS_CHANGE_TARGET_THROUGH_ALIAS_TO_FILE,
+            Set.of("//java/example:ExampleTest", "//java/example:ExampleTestSource"));
+  }
+
   @Test
   public void aliasTargetIsDetectedIfActualLabelChanged() throws Exception {
     doTest(Commits.ALIAS_ADD_TARGET, Commits.ALIAS_CHANGE_ACTUAL,
@@ -692,4 +698,8 @@ class Commits {
   public static final String ALIAS_CHANGE_ACTUAL = "ec19104291a3ea7cb61fb54ecdeaee73127bf284";
 
   public static final String ALIAS_CHANGE_TARGET_THROUGH_ALIAS = "3d9788053a2eed1a2f3beb05070872526ebdf76e";
+
+  public static final String ALIAS_ADD_TARGET_TO_FILE = "7be0f96f26742daec661c2ebfbb08b88b6355a3b";
+
+  public static final String ALIAS_CHANGE_TARGET_THROUGH_ALIAS_TO_FILE = "68fbd3661f3626e2df6a55b079444adbf76b5a3b";
 }