Make ES6 module transpilation a "real" compiler pass.

This moves it from happening at the end of parsing into DefaultPassConfig,
where it can be more easily reordered around other passes.

Many of the existing passes were relying on module rewriting happening at parse time,
so much of the churn is from porting those.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=159139260

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

@@ -1823,10 +1823,6 @@ Node parseInputs() {
         if (!inputsToRewrite.isEmpty()) {
           forceToEs6Modules(inputsToRewrite.values());
         }
-
-        if (options.needsTranspilationFrom(FeatureSet.ES6_MODULES)) {
-          processEs6Modules();
-        }
       } else {
         // Use an empty module loader if we're not actually dealing with modules.
         this.moduleLoader = ModuleLoader.EMPTY;
@@ -2060,10 +2056,6 @@ Map<String, String> processJsonInputs(List<CompilerInput> inputsToProcess) {
     return rewriteJson.getPackageJsonMainEntries();
   }
 
-  void processEs6Modules() {
-    processEs6Modules(parsePotentialModules(inputs));
-  }
-
   void forceToEs6Modules(Collection<CompilerInput> inputsToProcess) {
     for (CompilerInput input : inputsToProcess) {
       input.setCompiler(this);
@@ -2098,20 +2090,6 @@ private List<CompilerInput> parsePotentialModules(List<CompilerInput> inputsToPr
     return filteredInputs;
   }
 
-  void processEs6Modules(List<CompilerInput> inputsToProcess) {
-    for (CompilerInput input : inputsToProcess) {
-      input.setCompiler(this);
-      Node root = input.getAstRoot(this);
-      if (root == null) {
-        continue;
-      }
-      if (Es6RewriteModules.isEs6ModuleRoot(root)) {
-        new Es6RewriteModules(this).processFile(root);
-      }
-    }
-    setFeatureSet(featureSet.without(Feature.MODULES));
-  }
-
   /**
    * Transforms AMD and CJS modules to something closure compiler can
    * process and creates JSModules and the corresponding dependency tree

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

@@ -1915,6 +1915,11 @@ public boolean needsTranspilationFrom(FeatureSet languageLevel) {
         && !getLanguageOut().toFeatureSet().contains(languageLevel);
   }
 
+  public boolean needsTranspilationOf(FeatureSet.Feature feature) {
+    return getLanguageIn().toFeatureSet().has(feature)
+        && !getLanguageOut().toFeatureSet().has(feature);
+  }
+
   /**
    * Set which set of builtin externs to use.
    */

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

@@ -191,6 +191,10 @@ protected List<PassFactory> getTranspileOnlyPasses() {
       passes.add(convertEs6TypedToEs6);
     }
 
+    if (options.needsTranspilationOf(FeatureSet.Feature.MODULES)) {
+      TranspilationPasses.addEs6ModulePass(passes);
+    }
+
     passes.add(checkMissingSuper);
     passes.add(checkVariableReferencesForTranspileOnly);
 
@@ -261,6 +265,7 @@ protected List<PassFactory> getChecks() {
     List<PassFactory> checks = new ArrayList<>();
 
     if (options.shouldGenerateTypedExterns()) {
+      TranspilationPasses.addEs6ModulePass(checks);
       checks.add(closureGoogScopeAliases);
       checks.add(closureRewriteClass);
       checks.add(generateIjs);
@@ -273,6 +278,14 @@ protected List<PassFactory> getChecks() {
     // Verify JsDoc annotations
     checks.add(checkJsDoc);
 
+    if (options.needsTranspilationFrom(TYPESCRIPT)) {
+      checks.add(convertEs6TypedToEs6);
+    }
+
+    if (options.needsTranspilationOf(FeatureSet.Feature.MODULES)) {
+      TranspilationPasses.addEs6ModulePass(checks);
+    }
+
     if (options.enables(DiagnosticGroups.LINT_CHECKS)) {
       checks.add(lintChecks);
     }
@@ -294,10 +307,6 @@ protected List<PassFactory> getChecks() {
       checks.add(closureRewriteModule);
     }
 
-    if (options.needsTranspilationFrom(TYPESCRIPT)) {
-      checks.add(convertEs6TypedToEs6);
-    }
-
     if (options.declaredGlobalExternsOnWindow) {
       checks.add(declaredGlobalExternsOnWindow);
     }

src/com/google/javascript/jscomp/Es6RewriteModules.java

@@ -15,6 +15,8 @@
  */
 package com.google.javascript.jscomp;
 
+import static com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature.MODULES;
+
 import com.google.common.base.Preconditions;
 import com.google.common.base.Splitter;
 import com.google.common.collect.ImmutableSet;
@@ -34,13 +36,13 @@
 import java.util.Set;
 
 /**
- * Rewrites a ES6 module into a form that can be safely concatenated.
- * Note that we treat a file as an ES6 module if it has at least one import or
- * export statement.
+ * Rewrites a ES6 module into a form that can be safely concatenated. Note that we treat a file as
+ * an ES6 module if it has at least one import or export statement.
  *
  * @author moz@google.com (Michael Zhou)
  */
-public final class Es6RewriteModules extends AbstractPostOrderCallback {
+public final class Es6RewriteModules extends AbstractPostOrderCallback
+    implements HotSwapCompilerPass {
   private static final String DEFAULT_EXPORT_NAME = "$jscompDefaultExport";
 
   static final DiagnosticType LHS_OF_GOOG_REQUIRE_MUST_BE_CONST =
@@ -54,13 +56,13 @@ public final class Es6RewriteModules extends AbstractPostOrderCallback {
           "Namespace imports ('goog:some.Namespace') cannot use import * as. "
               + "Did you mean to import {0} from ''{1}'';?");
 
-  private final Compiler compiler;
-  private int scriptNodeCount = 0;
+  private final AbstractCompiler compiler;
+  private int scriptNodeCount;
 
   /**
    * Maps exported names to their names in current module.
    */
-  private Map<String, NameNodePair> exportMap = new LinkedHashMap<>();
+  private Map<String, NameNodePair> exportMap;
 
   /**
    * Maps symbol names to a pair of (moduleName, originalName). The original
@@ -69,12 +71,12 @@ public final class Es6RewriteModules extends AbstractPostOrderCallback {
    * object. Eg: "import {foo as f} from 'm'" maps 'f' to the pair ('m', 'foo').
    * In the entry for "import * as ns", the originalName will be the empty string.
    */
-  private Map<String, ModuleOriginalNamePair> importMap = new HashMap<>();
+  private Map<String, ModuleOriginalNamePair> importMap;
 
-  private Set<String> classes = new HashSet<>();
-  private Set<String> typedefs = new HashSet<>();
+  private Set<String> classes;
+  private Set<String> typedefs;
 
-  private Set<String> alreadyRequired = new HashSet<>();
+  private Set<String> alreadyRequired;
 
   private boolean forceRewrite;
 
@@ -84,7 +86,7 @@ public final class Es6RewriteModules extends AbstractPostOrderCallback {
    * Creates a new Es6RewriteModules instance which can be used to rewrite
    * ES6 modules to a concatenable form.
    */
-  public Es6RewriteModules(Compiler compiler) {
+  public Es6RewriteModules(AbstractCompiler compiler) {
     this.compiler = compiler;
   }
 
@@ -104,6 +106,8 @@ public static boolean isEs6ModuleRoot(Node scriptNode) {
    * "import" or "export" statements. Fails if the file contains a goog.provide or goog.module.
    *
    * @return True, if the file is now an ES6 module. False, if the file must remain a script.
+   * TODO(blickly): Move this logic out of this pass, since it is independent of whether or
+   * not we are actually transpiling modules
    */
   public boolean forceToEs6Module(Node root) {
     if (isEs6ModuleRoot(root)) {
@@ -120,15 +124,42 @@ public boolean forceToEs6Module(Node root) {
     return true;
   }
 
+  @Override
+  public void process(Node externs, Node root) {
+    Preconditions.checkState(compiler.getOptions().getLanguageIn().toFeatureSet().has(MODULES));
+    for (Node file = root.getFirstChild(); file != null; file = file.getNext()) {
+      hotSwapScript(file, null);
+    }
+    compiler.setFeatureSet(compiler.getFeatureSet().without(MODULES));
+  }
+
+  @Override
+  public void hotSwapScript(Node scriptNode, Node originalRoot) {
+    if (isEs6ModuleRoot(scriptNode)) {
+      processFile(scriptNode);
+    }
+  }
+
   /**
    * Rewrite a single ES6 module file to a global script version.
    */
-  public void processFile(Node root) {
+  private void processFile(Node root) {
     Preconditions.checkArgument(isEs6ModuleRoot(root), root);
-    this.forceRewrite = true;
+    clearState();
     NodeTraversal.traverseEs6(compiler, root, this);
   }
 
+  public void clearState() {
+    this.scriptNodeCount = 0;
+    this.exportMap = new LinkedHashMap<>();
+    this.importMap = new HashMap<>();
+    this.classes = new HashSet<>();
+    this.typedefs = new HashSet<>();
+    this.alreadyRequired = new HashSet<>();
+    this.forceRewrite = true;
+    this.googRequireInsertSpot = null;
+  }
+
   /**
    * Avoid processing if we find the appearance of goog.provide or goog.module.
    *
@@ -284,8 +315,7 @@ private void visitExport(NodeTraversal t, Node export, Node parent) {
       }
 
       if (name != null) {
-        Node decl = child.cloneTree();
-        decl.setJSDocInfo(child.getJSDocInfo());
+        Node decl = child.detach();
         parent.replaceChild(export, decl);
         exportMap.put("default", new NameNodePair(name, child));
       } else {
@@ -556,6 +586,7 @@ public void visit(NodeTraversal t, Node n, Node parent) {
             n.setString(newName);
             n.setOriginalName(name);
           }
+          t.reportCodeChange(n);
         } else if (var == null && importMap.containsKey(name)) {
           // Change to property access on the imported module object.
           if (parent.isCall() && parent.getFirstChild() == n) {
@@ -571,6 +602,7 @@ public void visit(NodeTraversal t, Node n, Node parent) {
                 IR.getprop(moduleAccess, IR.string(pair.originalName))
                     .useSourceInfoIfMissingFromForTree(n));
           }
+          t.reportCodeChange(moduleAccess);
         }
       }
     }

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

@@ -30,6 +30,10 @@
 public class TranspilationPasses {
   private TranspilationPasses() {}
 
+  public static void addEs6ModulePass(List<PassFactory> passes) {
+    passes.add(es6RewriteModule);
+  }
+
   public static void addEs2017Passes(List<PassFactory> passes) {
     passes.add(rewriteAsyncFunctions);
   }
@@ -73,6 +77,20 @@ public static void addRewritePolyfillPass(List<PassFactory> passes) {
     passes.add(rewritePolyfills);
   }
 
+  /** Rewrites ES6 modules */
+  private static final HotSwapPassFactory es6RewriteModule =
+      new HotSwapPassFactory("es6RewriteModule", true) {
+        @Override
+        protected HotSwapCompilerPass create(AbstractCompiler compiler) {
+          return new Es6RewriteModules(compiler);
+        }
+
+        @Override
+        protected FeatureSet featureSet() {
+          return FeatureSet.ES8_MODULES;
+        }
+      };
+
   private static final PassFactory rewriteAsyncFunctions =
       new PassFactory("rewriteAsyncFunctions", true) {
         @Override

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

@@ -1712,6 +1712,7 @@ private Compiler multistageSerializeAndDeserialize(
 
   private static void transpileToEs5(AbstractCompiler compiler, Node externsRoot, Node codeRoot) {
     List<PassFactory> factories = new ArrayList<>();
+    TranspilationPasses.addEs6ModulePass(factories);
     TranspilationPasses.addEs2017Passes(factories);
     TranspilationPasses.addEs6EarlyPasses(factories);
     TranspilationPasses.addEs6LatePasses(factories);

test/com/google/javascript/jscomp/Es6RewriteClassTest.java

@@ -22,7 +22,7 @@
 import static com.google.javascript.jscomp.Es6RewriteClass.DYNAMIC_EXTENDS_TYPE;
 import static com.google.javascript.jscomp.Es6ToEs3Converter.CANNOT_CONVERT;
 import static com.google.javascript.jscomp.Es6ToEs3Converter.CANNOT_CONVERT_YET;
-import static com.google.javascript.jscomp.parsing.parser.FeatureSet.ES6;
+import static com.google.javascript.jscomp.parsing.parser.FeatureSet.ES6_MODULES;
 
 import com.google.javascript.jscomp.CompilerOptions.LanguageMode;
 import com.google.javascript.jscomp.parsing.parser.FeatureSet;
@@ -84,7 +84,7 @@ protected CompilerPass create(AbstractCompiler compiler) {
 
       @Override
       protected FeatureSet featureSet() {
-        return ES6;
+        return ES6_MODULES;
       }
     };
   }