Initial implementation of readlink -f.

Addresses issue #96.

It uses the Python function os.path.realpath(), which we discovered has
different semantics than C's realpath().

Run demo with:

$ demo/readlink-demo.sh all

Run failing "gold" test with:

$ test/gold.sh readlink-case

- Changed the gold.sh test framework to add $REPO_ROOT/bin to the $PATH
  so we can test Oil's readlink against the one on the system.

Co-authored-by: Nicolas Hahn <nicolas@stonespring.org>

bin/oil.py

@@ -88,6 +88,7 @@ def _tlog(msg):

from tools import deps
from tools import osh2oil
from tools import readlink

log = util.log

@@ -592,6 +593,8 @@ def AppBundleMain(argv):
    return 0
  elif main_name == 'false':
    return 1
  elif main_name == 'readlink':
    return readlink.main(main_argv)
  else:
    raise args.UsageError('Invalid applet name %r.' % main_name)

build/common.sh

@@ -19,7 +19,7 @@ readonly PY27=Python-2.7.13
readonly PREPARE_DIR=_devbuild/cpython-full

# Used by scripts/run.sh and opy/build.sh
readonly OIL_SYMLINKS=(oil osh oshc sh wok boil true false)
readonly OIL_SYMLINKS=(oil osh oshc sh wok boil true false readlink)
readonly OPY_SYMLINKS=(opy opyc)

demo/readlink-demo-data.txt

@@ -0,0 +1 @@
--- this is data.txt ---

demo/readlink-demo-target.sh

@@ -0,0 +1,14 @@
#!/bin/bash

echo '--- readlink-demo-data.sh ---'

echo '$0 =' $0
#cat $(dirname $0)/readlink-demo-data.txt

script=$(readlink -f $0)
#script=$(readlink $0)
#script=$(bin/readlink -f $0)

echo "script = $script"

cat $(dirname $script)/readlink-demo-data.txt

demo/readlink-demo.sh

@@ -0,0 +1,32 @@
#!/bin/bash
#
# Usage:
#   ./readlink-demo.sh <function name>

set -o nounset
set -o pipefail
set -o errexit

two-file-symlinks() {
  # NOTE: Two levels of symlinks requires readlink -f, not readlink.
  ln -s -f $PWD/demo/readlink-demo-target.sh /tmp/demo.sh
  ln -s -f /tmp/demo.sh /tmp/demo-level2.sh
  /tmp/demo-level2.sh
}

dir-symlink() {
  ln -s -f --no-target-directory $PWD/demo/ /tmp/oil-demo
  /tmp/oil-demo/readlink-demo-target.sh
}

all() {
  echo 'Two files:'
  two-file-symlinks
  echo

  echo 'Dirs:'
  dir-symlink
  echo
}

"$@"

gold/readlink.sh

@@ -0,0 +1,18 @@
#!/bin/bash
#
# Usage:
#   ./readlink.sh <function name>

set -o nounset
set -o pipefail
#set -o errexit

dir-does-not-exist() {
  readlink -f /nonexistent
  echo $?

  readlink -f /nonexistent/foo
  echo $?
}

"$@"

test/gold.sh

@@ -14,13 +14,18 @@ set -o errexit

source test/common.sh  # for $OSH

# Runs an command (argv) the normal way (with its shebang) and then with
# OSH, and compares the stdout and exit code.
#
# Also puts $PWD/bin on the front of $PATH, in order to read bin/readlink
# and so forth.
_compare() {
  set +o errexit

  "$@" >_tmp/shebang.txt
  local expected_status=$?

  $OSH "$@" >_tmp/osh.txt
  PATH="$PWD/bin:$PATH" $OSH "$@" >_tmp/osh.txt
  local osh_status=$?

  set -o errexit
@@ -87,7 +92,7 @@ and-or() { _compare gold/and-or.sh test-simple; }

comments() { _compare gold/comments.sh; }
readonly_() { _compare gold/readonly.sh; }
export() { _compare gold/export.sh; }
export-case() { _compare gold/export.sh; }
glob() { _compare gold/glob.sh; }
no-op() { _compare scripts/count.sh; }
complex-here-docs() { _compare gold/complex-here-docs.sh; }
@@ -109,6 +114,9 @@ declare() { _compare gold/declare.sh demo; }
# Needs declare -p
scope() { _compare gold/scope.sh; }

readlink-case() {
  _compare gold/readlink.sh dir-does-not-exist
}

readonly -a PASSING=(
  # FLAKY: This one differs by timestamp
@@ -120,7 +128,7 @@ readonly -a PASSING=(

  comments
  readonly_
  export
  export-case
  glob
  no-op
  complex-here-docs

tools/readlink.py

@@ -0,0 +1,22 @@
#!/usr/bin/python
from __future__ import print_function
"""
readlink.py
"""

import os
from core import args, util

SPEC = args.BuiltinFlags()
SPEC.ShortFlag('-f')


def main(argv):
  arg, i = SPEC.Parse(argv)
  if not arg.f:
    util.error("-f must be passed")
    return 1
  for arg in argv[i:]:
    res = os.path.realpath(arg)
    print(res)
  return 0