Add support for javac-style @params files

Fixes #77

MOE_MIGRATED_REVID=172163309

core/src/main/java/com/google/googlejavaformat/java/CommandLineOptionsParser.java

@@ -14,9 +14,18 @@
 
 package com.google.googlejavaformat.java;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import com.google.common.base.CharMatcher;
 import com.google.common.base.Splitter;
 import com.google.common.collect.ImmutableRangeSet;
 import com.google.common.collect.Range;
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
 
@@ -25,11 +34,15 @@ final class CommandLineOptionsParser {
 
   private static final Splitter COMMA_SPLITTER = Splitter.on(',');
   private static final Splitter COLON_SPLITTER = Splitter.on(':');
+  private static final Splitter ARG_SPLITTER =
+      Splitter.on(CharMatcher.breakingWhitespace()).omitEmptyStrings().trimResults();
 
   /** Parses {@link CommandLineOptions}. */
   static CommandLineOptions parse(Iterable<String> options) {
     CommandLineOptions.Builder optionsBuilder = CommandLineOptions.builder();
-    Iterator<String> it = options.iterator();
+    List<String> expandedOptions = new ArrayList<>();
+    expandParamsFiles(options, expandedOptions);
+    Iterator<String> it = expandedOptions.iterator();
     while (it.hasNext()) {
       String option = it.next();
       if (!option.startsWith("-")) {
@@ -158,4 +171,29 @@ private static Range<Integer> parseRange(String arg) {
         throw new IllegalArgumentException(arg);
     }
   }
+
+  /**
+   * Pre-processes an argument list, expanding arguments of the form {@code @filename} by reading
+   * the content of the file and appending whitespace-delimited options to {@code arguments}.
+   */
+  private static void expandParamsFiles(Iterable<String> args, List<String> expanded) {
+    for (String arg : args) {
+      if (arg.isEmpty()) {
+        continue;
+      }
+      if (!arg.startsWith("@")) {
+        expanded.add(arg);
+      } else if (arg.startsWith("@@")) {
+        expanded.add(arg.substring(1));
+      } else {
+        Path path = Paths.get(arg.substring(1));
+        try {
+          String sequence = new String(Files.readAllBytes(path), UTF_8);
+          expandParamsFiles(ARG_SPLITTER.split(sequence), expanded);
+        } catch (IOException e) {
+          throw new UncheckedIOException(path + ": could not read file: " + e.getMessage(), e);
+        }
+      }
+    }
+  }
 }

core/src/main/java/com/google/googlejavaformat/java/UsageException.java

@@ -19,7 +19,7 @@
 import com.google.common.base.Joiner;
 
 /** Checked exception class for formatter command-line usage errors. */
-public final class UsageException extends Exception {
+final class UsageException extends Exception {
 
   private static final Joiner NEWLINE_JOINER = Joiner.on(System.lineSeparator());
 
@@ -37,7 +37,7 @@ public final class UsageException extends Exception {
     "  -",
     "    Format stdin -> stdout",
     "  --aosp, -aosp, -a",
-    "    Use AOSP style instead of Google Style (4-space indentation)",
+    "    Use AOSP style instead of Google Style (4-space indentation).",
     "  --fix-imports-only",
     "    Fix import order and remove any unused imports, but do no other formatting.",
     "  --skip-sorting-imports",
@@ -56,9 +56,11 @@ public final class UsageException extends Exception {
     "  --offset, -offset",
     "    Character offset to format (0-based; default is all).",
     "  --help, -help, -h",
-    "    Print this usage statement",
+    "    Print this usage statement.",
     "  --version, -version, -v",
     "    Print the version.",
+    "  @<filename>",
+    "    Read options and filenames from file.",
     "",
   };
 

core/src/test/java/com/google/googlejavaformat/java/CommandLineOptionsParserTest.java

@@ -15,19 +15,27 @@
 package com.google.googlejavaformat.java;
 
 import static com.google.common.truth.Truth.assertThat;
+import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.junit.Assert.fail;
 
 import com.google.common.collect.Range;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
 import java.util.Arrays;
 import java.util.Collections;
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
 
 /** {@link CommandLineOptionsParser}Test */
 @RunWith(JUnit4.class)
 public class CommandLineOptionsParserTest {
 
+  @Rule public TemporaryFolder testFolder = new TemporaryFolder();
+
   @Test
   public void defaults() {
     CommandLineOptions options = CommandLineOptionsParser.parse(Collections.<String>emptyList());
@@ -152,4 +160,19 @@ public void illegalLines() {
     }
   }
 
+  @Test
+  public void paramsFile() throws IOException {
+    Path outer = testFolder.newFile("outer").toPath();
+    Path exit = testFolder.newFile("exit").toPath();
+    Path nested = testFolder.newFile("nested").toPath();
+
+    String[] args = {"--dry-run", "@" + exit, "L", "@" + outer, "Q"};
+
+    Files.write(exit, "--set-exit-if-changed".getBytes(UTF_8));
+    Files.write(outer, ("M\n@" + nested.toAbsolutePath() + "\nP").getBytes(UTF_8));
+    Files.write(nested, "ℕ\n\n   \n@@O\n".getBytes(UTF_8));
+
+    CommandLineOptions options = CommandLineOptionsParser.parse(Arrays.asList(args));
+    assertThat(options.files()).containsExactly("L", "M", "ℕ", "@O", "P", "Q");
+  }
 }