Initialize JavaCommon.sources eagerly, rather than in initCommon().

This allows us to make the field final, and guarantees that it can't be
mutated after construction.

--
MOS_MIGRATED_REVID=115430793

src/main/java/com/google/devtools/build/lib/rules/java/JavaCommon.java

diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/JavaCommon.java b/src/main/java/com/google/devtools/build/lib/rules/java/JavaCommon.java
index cba5c47..2771da6 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/JavaCommon.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/JavaCommon.java
@@ -103,7 +103,7 @@
   private final ImmutableMap<ClasspathType, ImmutableList<TransitiveInfoCollection>>
       targetsTreatedAsDeps;
 
-  private ImmutableList<Artifact> sources = ImmutableList.of();
+  private final ImmutableList<Artifact> sources;
   private ImmutableList<JavaPluginInfoProvider> activePlugins = ImmutableList.of();
 
   private final RuleContext ruleContext;
@@ -112,6 +112,16 @@
 
   public JavaCommon(RuleContext ruleContext, JavaSemantics semantics) {
     this(ruleContext, semantics,
+        ruleContext.getPrerequisiteArtifacts("srcs", Mode.TARGET).list(),
+        collectTargetsTreatedAsDeps(ruleContext, semantics, ClasspathType.COMPILE_ONLY),
+        collectTargetsTreatedAsDeps(ruleContext, semantics, ClasspathType.RUNTIME_ONLY),
+        collectTargetsTreatedAsDeps(ruleContext, semantics, ClasspathType.BOTH));
+  }
+
+  public JavaCommon(RuleContext ruleContext, JavaSemantics semantics,
+      ImmutableList<Artifact> sources) {
+    this(ruleContext, semantics,
+        sources,
         collectTargetsTreatedAsDeps(ruleContext, semantics, ClasspathType.COMPILE_ONLY),
         collectTargetsTreatedAsDeps(ruleContext, semantics, ClasspathType.RUNTIME_ONLY),
         collectTargetsTreatedAsDeps(ruleContext, semantics, ClasspathType.BOTH));
@@ -122,8 +132,20 @@
       ImmutableList<TransitiveInfoCollection> compileDeps,
       ImmutableList<TransitiveInfoCollection> runtimeDeps,
       ImmutableList<TransitiveInfoCollection> bothDeps) {
+    this(ruleContext, semantics,
+        ruleContext.getPrerequisiteArtifacts("srcs", Mode.TARGET).list(),
+        compileDeps, runtimeDeps, bothDeps);
+  }
+
+  public JavaCommon(RuleContext ruleContext,
+      JavaSemantics semantics,
+      ImmutableList<Artifact> sources,
+      ImmutableList<TransitiveInfoCollection> compileDeps,
+      ImmutableList<TransitiveInfoCollection> runtimeDeps,
+      ImmutableList<TransitiveInfoCollection> bothDeps) {
     this.ruleContext = ruleContext;
     this.semantics = semantics;
+    this.sources = sources;
     this.targetsTreatedAsDeps = ImmutableMap.of(
         ClasspathType.COMPILE_ONLY, compileDeps,
         ClasspathType.RUNTIME_ONLY, runtimeDeps,
@@ -504,7 +526,6 @@
    */
   public JavaTargetAttributes.Builder initCommon(Collection<Artifact> extraSrcs) {
     Preconditions.checkState(javacOpts != null);
-    sources = ruleContext.getPrerequisiteArtifacts("srcs", Mode.TARGET).list();
     activePlugins = collectPlugins();
 
     JavaTargetAttributes.Builder javaTargetAttributes = new JavaTargetAttributes.Builder(semantics);

src/main/java/com/google/devtools/build/lib/rules/java/JavaImport.java

diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/JavaImport.java b/src/main/java/com/google/devtools/build/lib/rules/java/JavaImport.java
index fa3805b..46e4d81 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/JavaImport.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/JavaImport.java
@@ -63,7 +63,7 @@
             .addAll(ruleContext.getPrerequisites("exports", Mode.TARGET))
             .build();
     final JavaCommon common = new JavaCommon(
-        ruleContext, semantics, targets, targets, targets);
+        ruleContext, semantics, /*srcs=*/ImmutableList.<Artifact>of(), targets, targets, targets);
     semantics.checkRule(ruleContext, common);
 
     // No need for javac options - no compilation happening here.