Make sure STATIC_SOURCE_FILE PropListItem nodes are not duplicated un…

…necessarily.

This patch reduces the total number of STATIC_SOURCE_FILE nodes by 10x in a typical project.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=164177760

src/com/google/javascript/jscomp/CheckSideEffects.java

@@ -193,7 +193,7 @@ private void addExtern() {
     var.setJSDocInfo(builder.build());
     CompilerInput input = compiler.getSynthesizedExternsInput();
     name.setStaticSourceFile(input.getSourceFile());
-    var.setStaticSourceFile(input.getSourceFile());
+    var.setStaticSourceFileFrom(name);
     input.getAstRoot(compiler).addChildToBack(var);
     compiler.reportChangeToEnclosingScope(var);
   }

src/com/google/javascript/rhino/Node.java

@@ -1266,6 +1266,25 @@ private static void toStringTreeHelper(Node n, int level, Appendable sb)
   //==========================================================================
   // Source position management
 
+  public void setStaticSourceFileFrom(Node other) {
+    // Make sure source file prop nodes are not duplicated.
+    if (other.propListHead != null
+        && (this.propListHead == null
+            || (this.propListHead.propType == STATIC_SOURCE_FILE
+               && this.propListHead.next == null))) {
+      // Either the node has only STATIC_SOURCE_FILE as a property or has not properties.
+      PropListItem tail = other.propListHead;
+      while (tail.next != null) {
+        tail = tail.next;
+      }
+      if (tail.propType == STATIC_SOURCE_FILE) {
+        propListHead = tail;
+        return;
+      }
+    }
+    setStaticSourceFile(other.getStaticSourceFile());
+  }
+
   public void setStaticSourceFile(@Nullable StaticSourceFile file) {
     this.putProp(STATIC_SOURCE_FILE, file);
   }
@@ -2225,15 +2244,15 @@ public Node cloneTree(boolean cloneTypeExprs) {
   // TODO(nicksantos): The semantics of this method are ill-defined. Delete it.
   @Deprecated
   public Node useSourceInfoWithoutLengthIfMissingFrom(Node other) {
-    if (getProp(ORIGINALNAME_PROP) == null) {
-      putProp(ORIGINALNAME_PROP, other.getProp(ORIGINALNAME_PROP));
-    }
-
     if (getStaticSourceFile() == null) {
-      setStaticSourceFile(other.getStaticSourceFile());
+      setStaticSourceFileFrom(other);
       sourcePosition = other.sourcePosition;
     }
 
+    if (getProp(ORIGINALNAME_PROP) == null) {
+      putProp(ORIGINALNAME_PROP, other.getProp(ORIGINALNAME_PROP));
+    }
+
     return this;
   }
 
@@ -2258,8 +2277,8 @@ public Node useSourceInfoWithoutLengthIfMissingFromForTree(Node other) {
    * that of {@code other}.
    */
   public Node useSourceInfoFrom(Node other) {
+    setStaticSourceFileFrom(other);
     putProp(ORIGINALNAME_PROP, other.getProp(ORIGINALNAME_PROP));
-    setStaticSourceFile(other.getStaticSourceFile());
     sourcePosition = other.sourcePosition;
     length = other.length;
     return this;
@@ -2291,16 +2310,16 @@ public Node srcrefTree(Node other) {
    * that of {@code other} iff the source info is missing.
    */
   public Node useSourceInfoIfMissingFrom(Node other) {
-    if (getProp(ORIGINALNAME_PROP) == null) {
-      putProp(ORIGINALNAME_PROP, other.getProp(ORIGINALNAME_PROP));
-    }
-
     if (getStaticSourceFile() == null) {
-      setStaticSourceFile(other.getStaticSourceFile());
+      setStaticSourceFileFrom(other);
       sourcePosition = other.sourcePosition;
       length = other.length;
     }
 
+    if (getProp(ORIGINALNAME_PROP) == null) {
+      putProp(ORIGINALNAME_PROP, other.getProp(ORIGINALNAME_PROP));
+    }
+
     return this;
   }