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• RewriteJsonToModule.java

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/*
 * Copyright 2016 The Closure Compiler Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.javascript.jscomp;

import static com.google.common.base.Preconditions.checkState;

import com.google.common.collect.ImmutableMap;
import com.google.javascript.jscomp.deps.ModuleLoader;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.JSDocInfoBuilder;
import com.google.javascript.rhino.Node;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Rewrites a JSON file to be a module export. So that the JSON file parses correctly, it is wrapped
 * in an EXPR_RESULT. The pass makes only basic checks that the file provided is valid JSON. It is
 * not a full JSON validator.
 *
 * 
Looks for JSON files named "package.json" so that the "main" property can be used as an alias
 * in module name resolution. See https://docs.npmjs.com/files/package.json#main
 */
public class RewriteJsonToModule extends NodeTraversal.AbstractPostOrderCallback
    implements CompilerPass {
  public static final DiagnosticType JSON_UNEXPECTED_TOKEN =
      DiagnosticType.error("JSC_JSON_UNEXPECTED_TOKEN", "Unexpected JSON token");

  private final Map packageJsonMainEntries;
  private final AbstractCompiler compiler;

  /**
   * Creates a new RewriteJsonToModule instance which can be used to rewrite JSON files to modules.
   *
   * @param compiler The compiler
   */
  public RewriteJsonToModule(AbstractCompiler compiler) {
    this.compiler = compiler;
    this.packageJsonMainEntries = new HashMap<>();
  }

  public ImmutableMap getPackageJsonMainEntries() {
    return ImmutableMap.copyOf(packageJsonMainEntries);
  }

  /**
   * Module rewriting is done a on per-file basis prior to main compilation. The root node for each
   * file is a SCRIPT - not the typical jsRoot of other passes.
   */
  @Override
  public void process(Node externs, Node root) {
    checkState(root.isScript());
    NodeTraversal.traverse(compiler, root, this);
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    switch (n.getToken()) {
      case SCRIPT:
        if (!n.hasOneChild()) {
          compiler.report(JSError.make(n, JSON_UNEXPECTED_TOKEN));
        } else {
          visitScript(t, n);
        }
        return;

      case OBJECTLIT:
      case ARRAYLIT:
      case NUMBER:
      case TRUE:
      case FALSE:
      case NULL:
      case STRING:
        break;

      case STRING_KEY:
        if (!n.isQuotedString() || !n.hasOneChild()) {
          compiler.report(JSError.make(n, JSON_UNEXPECTED_TOKEN));
        }
        break;

      case EXPR_RESULT:
        if (!parent.isScript()) {
          compiler.report(JSError.make(n, JSON_UNEXPECTED_TOKEN));
        }
        break;

      default:
        compiler.report(JSError.make(n, JSON_UNEXPECTED_TOKEN));
        break;
    }

    if (n.getLineno() == 1) {
      // We wrapped the expression in parens so our first-line columns are off by one.
      // We need to correct for this.
      n.setCharno(n.getCharno() - 1);
      t.reportCodeChange();
    }
  }

  /**
   * For script nodes of JSON objects, add a module variable assignment so the result is exported.
   *
   * 
If the file path ends with "/package.json", look for main entries in their specified order
   * in the object literal and track them as module aliases. Main entries default to "main" and can
   * be overridden with the `--package_json_entry_names` option.
   */
  private void visitScript(NodeTraversal t, Node n) {
    if (!n.hasOneChild() || !n.getFirstChild().isExprResult()) {
      compiler.report(JSError.make(n, JSON_UNEXPECTED_TOKEN));
      return;
    }

    JSDocInfoBuilder jsdoc = new JSDocInfoBuilder(false);
    jsdoc.recordFileOverview("Suppresses undefined var goog error");
    jsdoc.addSuppression("undefinedVars");
    n.setJSDocInfo(jsdoc.build());

    Node jsonObject = n.getFirstFirstChild().detach();
    n.removeFirstChild();

    String moduleName = t.getInput().getPath().toModuleName();

    n.addChildToFront(
        IR.var(IR.name(moduleName).useSourceInfoFrom(jsonObject), jsonObject)
            .useSourceInfoFrom(jsonObject));

    n.addChildToFront(
        IR.exprResult(
                IR.call(IR.getprop(IR.name("goog"), IR.string("provide")), IR.string(moduleName)))
            .useSourceInfoIfMissingFromForTree(n));

    String inputPath = t.getInput().getSourceFile().getOriginalPath();
    if (inputPath.endsWith("/package.json") && jsonObject.isObjectLit()) {
      List possibleMainEntries = compiler.getOptions().getPackageJsonEntryNames();

      for (String entryName : possibleMainEntries) {
        Node entry = NodeUtil.getFirstPropMatchingKey(jsonObject, entryName);

        if (entry != null && (entry.isString() || entry.isObjectLit())) {
          String dirName = inputPath.substring(0, inputPath.length() - "package.json".length());

          if (entry.isString()) {
            packageJsonMainEntries.put(inputPath, dirName + entry.getString());
            break;
          } else if (entry.isObjectLit()) {
            checkState(entryName.equals("browser"), entryName);

            // don't break if we're processing a browser field that is an object literal
            // because one of its entries may override the package.json main, which
            // we will get in the next iteration.
            processBrowserFieldAdvancedUsage(dirName, entry);
          }
        }
      }
    }

    t.reportCodeChange();
  }

  /**
   * For browser field entries in package.json files that are used in an advanced manner
   * (https://github.com/defunctzombie/package-browser-field-spec/#replace-specific-files---advanced),
   * track the entries in that object literal as module file replacements.
   */
  private void processBrowserFieldAdvancedUsage(String dirName, Node entry) {
    for (Node child : entry.children()) {
      Node value = child.getFirstChild();

      checkState(child.isStringKey() && (value.isString() || value.isFalse()));

      String path = child.getString();

      if (path.startsWith(ModuleLoader.DEFAULT_FILENAME_PREFIX)) {
        path = path.substring(ModuleLoader.DEFAULT_FILENAME_PREFIX.length());
      }

      String replacement =
          value.isString()
              ? dirName + value.getString()
              : ModuleLoader.JSC_BROWSER_BLACKLISTED_MARKER;

      packageJsonMainEntries.put(dirName + path, replacement);
    }
  }
}