Removing unused ExcHandlers blocks

[Away-pp]

Removing unused ExcHandlers blocks in order to fix some decompilation errors caused by Unreachable blocks.

The root of this problem (for the current fix) is that some trys may never actually throw an exception.
Therefore the related catch may become unreachable.

The solution is that at the end of the try/catch processing, to look for unreachable blocks from the exception handlers.

An example of method that was not decompiled before:

Original code

https://cs.android.com/android/platform/superproject/main/+/main:frameworks/base/core/java/android/provider/FontsContract.java;l=726?q=prepareFontData

Decompiled code

    private static Map<Uri, ByteBuffer> prepareFontData(Context context, FontInfo[] fonts, CancellationSignal cancellationSignal) {
        HashMap<Uri, ByteBuffer> out = new HashMap<>();
        ContentResolver resolver = context.getContentResolver();
        for (FontInfo font : fonts) {
            if (font.getResultCode() == 0) {
                Uri uri = font.getUri();
                if (!out.containsKey(uri)) {
                    ByteBuffer buffer = null;
                    try {
                        ParcelFileDescriptor pfd = resolver.openFileDescriptor(uri, "r", cancellationSignal);
                        if (pfd != null) {
                            try {
                                FileInputStream fis = new FileInputStream(pfd.getFileDescriptor());
                                try {
                                    FileChannel fileChannel = fis.getChannel();
                                    long size = fileChannel.size();
                                    buffer = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0L, size);
                                    fis.close();
                                } finally {
                                    break;
                                }
                            } catch (IOException e) {
                            } catch (Throwable th) {
                                if (pfd == null) {
                                    throw th;
                                }
                                try {
                                    pfd.close();
                                    throw th;
                                } catch (Throwable th2) {
                                    th.addSuppressed(th2);
                                    throw th;
                                }
                            }
                        }
                        if (pfd != null) {
                            pfd.close();
                        }
                    } catch (IOException e2) {
                    }
                    out.put(uri, buffer);
                }
            }
        }
        return Collections.unmodifiableMap(out);
    }

[skylot]

Looks good, just small requests to improve code.
Also, please add simple Smali test (just copy whole method, also add disableCompilation(), code will not compile because of external classes).

[nitram84]

Here is a minimized standalone example for this issue that could be used for a unit test. Steps to reproduce: compile with openjdk8, "use dx/d8 to convert java bytecode" [x], "Plugins > Java convert > convert mode": "d8"

With convert mode "dx" there is still a NPE.

import java.io.FileInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class UnusedExceptionHandlers1 implements AutoCloseable {
  public static void doSomething(final Object unused1, final Object[] array, final Object o1,
      final Object o2, final Object unused2) {
    for (final Object item : array) {
      ByteBuffer buffer = null;
      try (final UnusedExceptionHandlers1 u = doSomething2(o1, "", o2)) {
        try (final FileInputStream fis = new FileInputStream(u.getFilename())) {
          final FileChannel fileChannel = fis.getChannel();
          buffer = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0, 42);
        } catch (final IOException e) {
          // ignore
        }
      } catch (final IOException e) {
        // ignore
      }
    }
  }

  private String getFilename() {
    return null;
  }

  private static UnusedExceptionHandlers1 doSomething2(final Object o1, final String s,
      final Object o2) {
    return null;
  }

  @Override
  public void close() throws IOException {}
}

[Away-pp]

Ok, I will add this test also.
I have compiled an APK with this method, but could not trigger NPE with dx.
It seemed ok.

[skylot]

@Away-pp great! Thank you for your work 👍