Tests for operator precedence and exponentiation.

All shells agree that -3 ** 2 = 9, i.e. that - has higher precedence
than **.

But Python and R do the opposite: ** has higher precedence than -.

Oil wil follow Python and R, but since all shells agree we aren't
changing OSH.

Unrelated: minor refactoring in bin/oil.py.

bin/oil.py

@@ -107,7 +107,7 @@ def OshMain(argv0, argv, login_shell):
                ['text', 'abbrev-text', 'html', 'abbrev-html', 'oheap', 'none'],
                default='abbrev-text')

  spec.LongFlag('--print-status')
  spec.LongFlag('--print-status')  # TODO: Replace with a shell hook
  spec.LongFlag('--hijack-shebang')  # TODO: Implement this

  # For benchmarks/*.sh
@@ -223,47 +223,48 @@ def OshMain(argv0, argv, login_shell):
                      status_out, ev)

    return main_loop.Interactive(opts, ex, c_parser, arena)
  else:
    # Parse the whole thing up front
    #print('Parsing file')

    # Do this after parsing the entire file.  There could be another option to
    # do it before exiting runtime?
    if opts.parser_mem_dump:
      # This might be superstition, but we want to let the value stabilize
      # after parsing.  bash -c 'cat /proc/$$/status' gives different results
      # with a sleep.
      time.sleep(0.001)
      input_path = '/proc/%d/status' % os.getpid()
      with open(input_path) as f, open(opts.parser_mem_dump, 'w') as f2:
        contents = f.read()
        f2.write(contents)
        log('Wrote %s to %s (--parser-mem-dump)', input_path,
            opts.parser_mem_dump)

    nodes_out = [] if exec_opts.noexec else None

    _tlog('Execute(node)')
    #status = ex.ExecuteAndRunExitTrap(node)
    status = main_loop.Batch(opts, ex, c_parser, arena, nodes_out=nodes_out)

    if nodes_out is not None:
      ui.PrintAst(nodes_out, opts)

    # NOTE: 'exit 1' is ControlFlow and gets here, but subshell/commandsub
    # don't because they call sys.exit().
    if opts.runtime_mem_dump:
      # This might be superstition, but we want to let the value stabilize
      # after parsing.  bash -c 'cat /proc/$$/status' gives different results
      # with a sleep.
      time.sleep(0.001)
      input_path = '/proc/%d/status' % os.getpid()
      with open(input_path) as f, open(opts.runtime_mem_dump, 'w') as f2:
        contents = f.read()
        f2.write(contents)
        log('Wrote %s to %s (--runtime-mem-dump)', input_path,
            opts.runtime_mem_dump)

  # Parse the whole thing up front
  #print('Parsing file')

  # Do this after parsing the entire file.  There could be another option to
  # do it before exiting runtime?
  if opts.parser_mem_dump:
    # This might be superstition, but we want to let the value stabilize
    # after parsing.  bash -c 'cat /proc/$$/status' gives different results
    # with a sleep.
    time.sleep(0.001)
    input_path = '/proc/%d/status' % os.getpid()
    with open(input_path) as f, open(opts.parser_mem_dump, 'w') as f2:
      contents = f.read()
      f2.write(contents)
      log('Wrote %s to %s (--parser-mem-dump)', input_path,
          opts.parser_mem_dump)

  nodes_out = [] if exec_opts.noexec else None

  _tlog('Execute(node)')
  #status = ex.ExecuteAndRunExitTrap(node)
  status = main_loop.Batch(opts, ex, c_parser, arena, nodes_out=nodes_out)

  if nodes_out is not None:
    ui.PrintAst(nodes_out, opts)

  # NOTE: 'exit 1' is ControlFlow and gets here, but subshell/commandsub
  # don't because they call sys.exit().
  if opts.runtime_mem_dump:
    # This might be superstition, but we want to let the value stabilize
    # after parsing.  bash -c 'cat /proc/$$/status' gives different results
    # with a sleep.
    time.sleep(0.001)
    input_path = '/proc/%d/status' % os.getpid()
    with open(input_path) as f, open(opts.runtime_mem_dump, 'w') as f2:
      contents = f.read()
      f2.write(contents)
      log('Wrote %s to %s (--runtime-mem-dump)', input_path,
          opts.runtime_mem_dump)

  # NOTE: We haven't closed the file opened with fd_state.Open
  return status

spec/arith.test.sh

@@ -328,3 +328,26 @@ echo "status=$?"
## N-I dash stdout: status=127
## N-I dash status: 0

#### Operator Precedence
echo $(( 1 + 2*3 - 8/2 ))
## stdout: 3

#### Exponentiation operator has buggy precedence
# NOTE: All shells agree on this, but R and Python give -9, which is more
# mathematically correct.
echo $(( -3 ** 2 ))
## osh stdout: 9
## N-I dash stdout-json: ""
## N-I dash status: 2
## N-I mksh stdout-json: ""
## N-I mksh status: 1

#### Negative exponennt
# bash explicitly disallows negative exponents!
echo $(( 2**-1 * 5 ))
## stdout: 2.5
## status: 0
## OK bash/mksh stdout-json: ""
## OK bash/mksh status: 1
## N-I dash stdout-json: ""
## N-I dash status: 2