src/main/java/net/starlark/java/cmd/Main.java

// Copyright 2016 The Bazel Authors. All rights reserved.
//
// 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 net.starlark.java.cmd;

import static java.nio.charset.StandardCharsets.UTF_8;

import java.io.BufferedReader;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.time.Duration;
import java.util.List;
import javax.annotation.Nullable;
import net.starlark.java.eval.CpuProfiler;
import net.starlark.java.eval.CpuProfilerNativeSupportImpl;
import net.starlark.java.eval.EvalException;
import net.starlark.java.eval.Module;
import net.starlark.java.eval.Mutability;
import net.starlark.java.eval.Starlark;
import net.starlark.java.eval.StarlarkSemantics;
import net.starlark.java.eval.StarlarkThread;
import net.starlark.java.syntax.FileOptions;
import net.starlark.java.syntax.ParserInput;
import net.starlark.java.syntax.StarlarkFile;
import net.starlark.java.syntax.Statement;
import net.starlark.java.syntax.SyntaxError;

/**
 * Main is a standalone interpreter for the core Starlark language. It does not yet support load
 * statements.
 *
 * <p>The sad class name is due to the linting tool, which forbids lowercase "starlark", and Java's
 * lack of renaming imports, which makes the name "Starlark" impractical due to conflicts with
 * eval.Starlark.
 */
class Main {
  private static final String START_PROMPT = ">> ";
  private static final String CONTINUATION_PROMPT = ".. ";

  private static final BufferedReader reader =
      new BufferedReader(new InputStreamReader(System.in, UTF_8));
  private static final StarlarkThread thread;
  private static final Module module = Module.create();

  // Variables bound by load in one REPL chunk are visible in the next.
  private static final FileOptions OPTIONS =
      FileOptions.DEFAULT.toBuilder().allowToplevelRebinding(true).loadBindsGlobally(true).build();

  static {
    maybeInstallCpuProfilerNativeSupport();
    Mutability mu = Mutability.create("interpreter");
    thread = StarlarkThread.createTransient(mu, StarlarkSemantics.DEFAULT);
    thread.setPrintHandler((th, msg) -> System.out.println(msg));
  }

  private static void maybeInstallCpuProfilerNativeSupport() {
    String osName = System.getProperty("os.name");
    if (osName.equals("Linux") || osName.equals("Mac OS X")) {
      CpuProfiler.setNativeSupport(new CpuProfilerNativeSupportImpl());
    }
  }

  // Prompts the user for a chunk of input, and returns it.
  @Nullable
  private static String prompt() {
    StringBuilder input = new StringBuilder();
    System.out.print(START_PROMPT);
    try {
      String lineSeparator = "";
      loop:
      while (true) {
        String line = reader.readLine();
        if (line == null) {
          return null;
        }
        if (line.isEmpty()) {
          break loop; // a blank line ends the chunk
        }
        input.append(lineSeparator).append(line);

        // Read lines until input produces valid statements, unless the last is if/def/for,
        // which can be multiline, in which case we must wait for a blank line.
        // TODO(adonovan): parse a compound statement, like the Python and
        //   go.starlark.net REPLs. This requires a new grammar production, and
        //   integration with the lexer so that it consumes new
        //   lines only until the parse is complete.
        StarlarkFile file = StarlarkFile.parse(ParserInput.fromString(input.toString(), "<stdin>"));
        if (file.ok()) {
          List<Statement> stmts = file.getStatements();
          if (!stmts.isEmpty()) {
            Statement last = stmts.get(stmts.size() - 1);
            switch (last.kind()) {
              case IF:
              case DEF:
              case FOR:
                break; // keep going until blank line
              default:
                break loop;
            }
          }
        }

        lineSeparator = "\n";
        System.out.print(CONTINUATION_PROMPT);
      }
    } catch (IOException e) {
      System.err.format("Error reading line: %s\n", e);
      return null;
    }
    return input.toString();
  }

  /** Provide a REPL evaluating Starlark code. */
  @SuppressWarnings("CatchAndPrintStackTrace")
  private static void readEvalPrintLoop() {
    module.setDocumentation("<REPL>"); // Do not retrieve a module docstring from REPL input.
    System.err.println("Welcome to Starlark (java.starlark.net)");
    String line;

    while ((line = prompt()) != null) {
      ParserInput input = ParserInput.fromString(line, "<stdin>");
      try {
        Object result = Starlark.execFile(input, OPTIONS, module, thread);
        if (result != Starlark.NONE) {
          System.out.println(Starlark.repr(result, thread.getSemantics()));
        }
      } catch (SyntaxError.Exception ex) {
        for (SyntaxError error : ex.errors()) {
          System.err.println(error);
        }
      } catch (EvalException ex) {
        // TODO(adonovan): provide a SourceReader. Requires that we buffer the
        // entire history so that line numbers don't reset in each chunk.
        System.err.println(ex.getMessageWithStack());
      } catch (InterruptedException ex) {
        System.err.println("Interrupted");
      }
    }
  }

  /** Execute a Starlark file. */
  private static int execute(ParserInput input) {
    try {
      Starlark.execFile(input, OPTIONS, module, thread);
      return 0;
    } catch (SyntaxError.Exception ex) {
      for (SyntaxError error : ex.errors()) {
        System.err.println(error);
      }
      return 1;
    } catch (EvalException ex) {
      System.err.println(ex.getMessageWithStack());
      return 1;
    } catch (InterruptedException e) {
      System.err.println("Interrupted");
      return 1;
    }
  }

  public static void main(String[] args) throws IOException {
    String file = null;
    String cmd = null;
    String cpuprofile = null;

    // parse flags
    int i;
    for (i = 0; i < args.length; i++) {
      if (!args[i].startsWith("-")) {
        break;
      }
      if (args[i].equals("--")) {
        i++;
        break;
      }
      if (args[i].equals("-c")) {
        if (i + 1 == args.length) {
          throw new IOException("-c <cmd> flag needs an argument");
        }
        cmd = args[++i];
      } else if (args[i].equals("-cpuprofile")) {
        if (i + 1 == args.length) {
          throw new IOException("-cpuprofile <file> flag needs an argument");
        }
        cpuprofile = args[++i];
      } else {
        throw new IOException("unknown flag: " + args[i]);
      }
    }
    // positional arguments
    if (i < args.length) {
      if (i + 1 < args.length) {
        throw new IOException("too many positional arguments");
      }
      file = args[i];
    }

    if (cpuprofile != null) {
      FileOutputStream out = new FileOutputStream(cpuprofile);
      Starlark.startCpuProfile(out, Duration.ofMillis(10));
    }

    int exit;
    if (file == null) {
      if (cmd != null) {
        exit = execute(ParserInput.fromString(cmd, "<command-line>"));
      } else {
        readEvalPrintLoop();
        exit = 0;
      }
    } else if (cmd == null) {
      try {
        exit = execute(ParserInput.readFile(file));
      } catch (IOException e) {
        // This results in such lame error messages as:
        // "Error reading a.star: java.nio.file.NoSuchFileException: a.star"
        System.err.format("Error reading %s: %s\n", file, e);
        exit = 1;
      }
    } else {
      System.err.println("usage: Starlark [-cpuprofile file] [-c cmd | file]");
      exit = 1;
    }

    if (cpuprofile != null) {
      Starlark.stopCpuProfile();
    }

    System.exit(exit);
  }
}