Print the problem line as context in error messages

PiperOrigin-RevId: 675207795

Author: cushon

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

@@ -16,10 +16,13 @@
 
 import static java.util.Locale.ENGLISH;
 
+import com.google.common.base.CharMatcher;
+import com.google.common.base.Splitter;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
 import com.google.googlejavaformat.FormatterDiagnostic;
 import java.util.List;
+import java.util.regex.Pattern;
 import javax.tools.Diagnostic;
 import javax.tools.JavaFileObject;
 
@@ -55,4 +58,22 @@ private static FormatterDiagnostic toFormatterDiagnostic(Diagnostic<?> input) {
     return FormatterDiagnostic.create(
         (int) input.getLineNumber(), (int) input.getColumnNumber(), input.getMessage(ENGLISH));
   }
+
+  public String formatDiagnostics(String path, String input) {
+    List<String> lines = Splitter.on(NEWLINE_PATTERN).splitToList(input);
+    StringBuilder sb = new StringBuilder();
+    for (FormatterDiagnostic diagnostic : diagnostics()) {
+      sb.append(path).append(":").append(diagnostic).append(System.lineSeparator());
+      int line = diagnostic.line();
+      int column = diagnostic.column();
+      if (line != -1 && column != -1) {
+        sb.append(CharMatcher.breakingWhitespace().trimTrailingFrom(lines.get(line - 1)))
+            .append(System.lineSeparator());
+        sb.append(" ".repeat(column)).append('^').append(System.lineSeparator());
+      }
+    }
+    return sb.toString();
+  }
+
+  private static final Pattern NEWLINE_PATTERN = Pattern.compile("\\R");
 }

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

@@ -20,7 +20,6 @@
 
 import com.google.common.io.ByteStreams;
 import com.google.common.util.concurrent.MoreExecutors;
-import com.google.googlejavaformat.FormatterDiagnostic;
 import com.google.googlejavaformat.java.JavaFormatterOptions.Style;
 import java.io.IOError;
 import java.io.IOException;
@@ -175,9 +174,7 @@ private int formatFiles(CommandLineOptions parameters, JavaFormatterOptions opti
     for (FormatFileCallable.Result result : results) {
       Path path = result.path();
       if (result.exception() != null) {
-        for (FormatterDiagnostic diagnostic : result.exception().diagnostics()) {
-          errWriter.println(path + ":" + diagnostic);
-        }
+        errWriter.print(result.exception().formatDiagnostics(path.toString(), result.input()));
         allOk = false;
         continue;
       }
@@ -224,9 +221,7 @@ private int formatStdin(CommandLineOptions parameters, JavaFormatterOptions opti
     FormatFileCallable.Result result =
         new FormatFileCallable(parameters, null, input, options).call();
     if (result.exception() != null) {
-      for (FormatterDiagnostic diagnostic : result.exception().diagnostics()) {
-        errWriter.println(stdinFilename + ":" + diagnostic);
-      }
+      errWriter.print(result.exception().formatDiagnostics(stdinFilename, input));
       ok = false;
     } else {
       String output = result.output();

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

@@ -635,4 +635,29 @@ public void reorderModifiersOptionTest() throws Exception {
                 .formatSource(source))
         .isEqualTo(source);
   }
+
+  @Test
+  public void badIdentifier() throws Exception {
+    Path path = testFolder.newFile("Test.java").toPath();
+    String[] input = {
+      "class Test {", //
+      "  void f(int package) {}",
+      "}",
+      "",
+    };
+    String source = joiner.join(input);
+    Files.writeString(path, source, UTF_8);
+    StringWriter out = new StringWriter();
+    StringWriter err = new StringWriter();
+    Main main = new Main(new PrintWriter(out, true), new PrintWriter(err, true), System.in);
+    int errorCode = main.format(path.toAbsolutePath().toString());
+    assertWithMessage("Error Code").that(errorCode).isEqualTo(1);
+    String[] expected = {
+      path + ":2:14: error: <identifier> expected", //
+      "  void f(int package) {}",
+      "             ^",
+      "",
+    };
+    assertThat(err.toString()).isEqualTo(joiner.join(expected));
+  }
 }