Fix the interaction between absolute path imports and module roots

Closes #2343

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=152771274

Author: ChadKillingsworth

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

@@ -1562,10 +1562,20 @@ Node parseInputs() {
                 options.moduleRoots,
                 inputs,
                 ModuleLoader.PathResolver.RELATIVE,
-                options.moduleResolutionMode);
+                options.moduleResolutionMode,
+                null);
 
         if (options.moduleResolutionMode == ModuleLoader.ResolutionMode.NODE) {
-          this.moduleLoader.setPackageJsonMainEntries(processJsonInputs(inputs));
+          // processJsonInputs requires a module loader to already be defined
+          // so we redefine it afterwards with the package.json inputs
+          this.moduleLoader =
+              new ModuleLoader(
+                  this,
+                  options.moduleRoots,
+                  inputs,
+                  ModuleLoader.PathResolver.RELATIVE,
+                  options.moduleResolutionMode,
+                  processJsonInputs(inputs));
         }
 
         if (options.lowerFromEs6()) {
@@ -1582,10 +1592,9 @@ Node parseInputs() {
         Map<String, CompilerInput> inputModuleIdentifiers = new HashMap<>();
         for (CompilerInput input : inputs) {
           if (input.getKnownProvides().isEmpty()) {
-            ModuleIdentifier modInfo =
-                ModuleIdentifier.forFile(input.getSourceFile().getOriginalPath());
-
-            inputModuleIdentifiers.put(modInfo.getClosureNamespace(), input);
+            ModuleLoader.ModulePath modPath =
+                moduleLoader.resolve(input.getSourceFile().getOriginalPath());
+            inputModuleIdentifiers.put(modPath.toModuleName(), input);
           }
         }
 

src/com/google/javascript/jscomp/deps/BrowserModuleResolver.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2017 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.deps;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import com.google.javascript.jscomp.CheckLevel;
+import com.google.javascript.jscomp.ErrorHandler;
+import com.google.javascript.jscomp.JSError;
+import javax.annotation.Nullable;
+
+/**
+ * Resolution algorithm for Browsers.
+ *
+ * <p>Only unambiguous paths are supported. Paths must specify a file extension.
+ */
+public class BrowserModuleResolver extends ModuleResolver {
+
+  public BrowserModuleResolver(
+      ImmutableSet<String> modulePaths,
+      ImmutableList<String> moduleRootPaths,
+      ErrorHandler errorHandler) {
+    super(modulePaths, moduleRootPaths, errorHandler);
+  }
+
+  @Override
+  @Nullable
+  public String resolveJsModule(
+      String scriptAddress, String moduleAddress, String sourcename, int lineno, int colno) {
+
+    if (ModuleLoader.isAmbiguousIdentifier(moduleAddress)) {
+      errorHandler.report(
+          CheckLevel.WARNING,
+          JSError.make(
+              sourcename,
+              lineno,
+              colno,
+              ModuleLoader.INVALID_MODULE_PATH,
+              moduleAddress,
+              "BROWSER"));
+      return null;
+    }
+
+    String loadAddress = locate(scriptAddress, moduleAddress);
+    if (loadAddress == null) {
+      errorHandler.report(
+          CheckLevel.WARNING,
+          JSError.make(sourcename, lineno, colno, ModuleLoader.LOAD_WARNING, moduleAddress));
+    }
+    return loadAddress;
+  }
+}

src/com/google/javascript/jscomp/deps/LegacyModuleResolver.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2017 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.deps;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import com.google.javascript.jscomp.CheckLevel;
+import com.google.javascript.jscomp.ErrorHandler;
+import com.google.javascript.jscomp.JSError;
+import javax.annotation.Nullable;
+
+/**
+ * Resolution algorithm historically used by the compiler.
+ *
+ * <p>Ambiguous paths are assumed to be absolute.
+ */
+public class LegacyModuleResolver extends ModuleResolver {
+
+  public LegacyModuleResolver(
+      ImmutableSet<String> modulePaths,
+      ImmutableList<String> moduleRootPaths,
+      ErrorHandler errorHandler) {
+    super(modulePaths, moduleRootPaths, errorHandler);
+  }
+
+  @Nullable
+  public String resolveJsModule(
+      String scriptAddress, String moduleAddress, String sourcename, int lineno, int colno) {
+    // Allow module names with or without the ".js" extension.
+    if (!moduleAddress.endsWith(".js")) {
+      moduleAddress += ".js";
+    }
+
+    String loadAddress = locate(scriptAddress, moduleAddress);
+
+    if (loadAddress == null) {
+      errorHandler.report(
+          CheckLevel.WARNING,
+          JSError.make(sourcename, lineno, colno, ModuleLoader.LOAD_WARNING, moduleAddress));
+      return canonicalizePath(scriptAddress, moduleAddress);
+    }
+    return loadAddress;
+  }
+}