Move the externs hoisting after file ordering.

This allows externs to be sorted according to provides/requires

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=138003984

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

@@ -1587,8 +1587,7 @@ public Void call() throws Exception {
   }
 
   void orderInputs() {
-    hoistExterns();
-
+    hoistUnorderedExterns();
     // Check if the sources need to be re-ordered.
     boolean staleInputs = false;
     if (options.dependencyOptions.needsManagement()) {
@@ -1601,9 +1600,7 @@ void orderInputs() {
       }
 
       try {
-        inputs =
-            (moduleGraph == null ? new JSModuleGraph(modules) : moduleGraph)
-            .manageDependencies(options.dependencyOptions, inputs);
+        inputs = getDegenerateModuleGraph().manageDependencies(options.dependencyOptions, inputs);
         staleInputs = true;
       } catch (MissingProvideException e) {
         report(JSError.make(
@@ -1614,6 +1611,10 @@ void orderInputs() {
       }
     }
 
+    if (options.dependencyOptions.needsManagement() && options.allowGoogProvideInExterns()) {
+      hoistAllExterns();
+    }
+
     hoistNoCompileFiles();
 
     if (staleInputs) {
@@ -1622,46 +1623,72 @@ void orderInputs() {
   }
 
   /**
-   * Hoists inputs with the @externs annotation into the externs list.
+   * Hoists inputs with the @externs annotation and no provides or requires into the externs list.
    */
-  void hoistExterns() {
+  void hoistUnorderedExterns() {
     boolean staleInputs = false;
     for (CompilerInput input : inputs) {
-      if (!options.allowGoogProvideInExterns() && options.dependencyOptions.needsManagement()) {
+      if (options.dependencyOptions.needsManagement()) {
         // If we're doing scanning dependency info anyway, use that
         // information to skip sources that obviously aren't externs.
         if (!input.getProvides().isEmpty() || !input.getRequires().isEmpty()) {
           continue;
         }
       }
 
-      Node n = input.getAstRoot(this);
-
-      // Inputs can have a null AST on a parse error.
-      if (n == null) {
-        continue;
+      if (hoistIfExtern(input)) {
+        staleInputs = true;
       }
+    }
 
-      JSDocInfo info = n.getJSDocInfo();
-      if (info != null && info.isExterns()) {
-        // If the input file is explicitly marked as an externs file, then
-        // assume the programmer made a mistake and throw it into
-        // the externs pile anyways.
-        externsRoot.addChildToBack(n);
-        input.setIsExtern(true);
-
-        input.getModule().remove(input);
+    if (staleInputs) {
+      repartitionInputs();
+    }
+  }
 
-        externs.add(input);
+  /**
+   * Hoists inputs with the @externs annotation into the externs list.
+   */
+  void hoistAllExterns() {
+    boolean staleInputs = false;
+    for (CompilerInput input : inputs) {
+      if (hoistIfExtern(input)) {
         staleInputs = true;
       }
     }
-
     if (staleInputs) {
       repartitionInputs();
     }
   }
 
+  /**
+   * Hoists a compiler input to externs if it contains the @externs annotation.
+   * Return whether or not the given input was hoisted.
+   */
+  private boolean hoistIfExtern(CompilerInput input) {
+    Node n = input.getAstRoot(this);
+
+    // Inputs can have a null AST on a parse error.
+    if (n == null) {
+      return false;
+    }
+
+    JSDocInfo info = n.getJSDocInfo();
+    if (info != null && info.isExterns()) {
+      // If the input file is explicitly marked as an externs file, then
+      // assume the programmer made a mistake and throw it into
+      // the externs pile anyways.
+      externsRoot.addChildToBack(n);
+      input.setIsExtern(true);
+
+      input.getModule().remove(input);
+
+      externs.add(input);
+      return true;
+    }
+    return false;
+  }
+
   /**
    * Hoists inputs with the @nocompile annotation out of the inputs.
    */

test/com/google/javascript/jscomp/CompilerTest.java

@@ -918,6 +918,50 @@ public void testInputSerialization() throws Exception {
     assertTrue(ast.isEquivalentTo(newInput.getAstRoot(compiler)));
   }
 
+  public void testExternsDependencySorting() {
+    List<SourceFile> inputs = ImmutableList.of(
+        SourceFile.fromCode("leaf", "/** @externs */ goog.require('beer');"),
+        SourceFile.fromCode("beer", "/** @externs */ goog.provide('beer');\ngoog.require('hops');"),
+        SourceFile.fromCode("hops", "/** @externs */ goog.provide('hops');"));
+
+    CompilerOptions options = createNewFlagBasedOptions();
+    options.setIncrementalChecks(CompilerOptions.IncrementalCheckMode.CHECK_IJS);
+    options.dependencyOptions.setDependencySorting(true);
+
+    List<SourceFile> externs = ImmutableList.of();
+    Compiler compiler = new Compiler();
+    compiler.compile(externs, inputs, options);
+
+    assertThat(compiler.externsRoot.getChildCount()).isEqualTo(3);
+    assertExternIndex(compiler, 0, "hops");
+    assertExternIndex(compiler, 1, "beer");
+    assertExternIndex(compiler, 2, "leaf");
+  }
+
+  public void testExternsDependencyPruning() {
+    List<SourceFile> inputs = ImmutableList.of(
+        SourceFile.fromCode("unused", "/** @externs */ goog.provide('unused');"),
+        SourceFile.fromCode("moocher", "/** @externs */ goog.require('something');"),
+        SourceFile.fromCode("something", "/** @externs */ goog.provide('something');"));
+
+    CompilerOptions options = createNewFlagBasedOptions();
+    options.dependencyOptions.setDependencyPruning(true);
+    options.setIncrementalChecks(CompilerOptions.IncrementalCheckMode.CHECK_IJS);
+
+    List<SourceFile> externs = ImmutableList.of();
+    Compiler compiler = new Compiler();
+    compiler.compile(externs, inputs, options);
+
+    assertThat(compiler.externsRoot.getChildCount()).isEqualTo(2);
+    assertExternIndex(compiler, 0, "something");
+    assertExternIndex(compiler, 1, "moocher");
+  }
+
+  private void assertExternIndex(Compiler compiler, int index, String name) {
+    assertThat(compiler.externsRoot.getChildAtIndex(index))
+        .isSameAs(compiler.getInput(new InputId(name)).getAstRoot(compiler));
+  }
+
   public void testEs6ModuleEntryPoint() throws Exception {
     List<SourceFile> inputs = ImmutableList.of(
         SourceFile.fromCode(