Fix bug in prefix/suffix strip operators.

I had to make a table to show that we always consider N prefixes and
suffixes, and that the order is exactly revesred for # vs ## an % and
%%.

Uncovered by k-script-build.

core/libstr.py

@@ -85,31 +85,35 @@ def DoUnarySuffixOp(s, op, arg):

  n = len(s)
  if op.op_id == Id.VOp1_Pound:  # shortest prefix
    for i in xrange(1, n):
    # 'abcd': match 'a', 'ab', 'abc', ...
    for i in xrange(1, n+1):
      #log('Matching pattern %r with %r', arg, s[:i])
      if libc.fnmatch(arg, s[:i]):
        return s[i:]
    else:
      return s

  elif op.op_id == Id.VOp1_DPound:  # longest prefix
    for i in xrange(-1, -n, -1):
    # 'abcd': match 'abc', 'ab', 'a'
    for i in xrange(n, 0, -1):
      #log('Matching pattern %r with %r', arg, s[:i])
      if libc.fnmatch(arg, s[:i]):
        return s[i:]
    else:
      return s

  elif op.op_id == Id.VOp1_Percent:  # shortest suffix
    for i in xrange(-1, -n, -1):
    # 'abcd': match 'abc', 'ab', 'a'
    for i in xrange(n-1, -1, -1):
      #log('Matching pattern %r with %r', arg, s[:i])
      if libc.fnmatch(arg, s[i:]):
        return s[:i]
    else:
      return s
    
  elif op.op_id == Id.VOp1_DPercent:  # longest suffix
    for i in xrange(1, n):
    # 'abcd': match 'abc', 'bc', 'c', ...
    for i in xrange(0, n):
      #log('Matching pattern %r with %r', arg, s[:i])
      if libc.fnmatch(arg, s[i:]):
        return s[:i]

core/libstr_test.py

@@ -0,0 +1,42 @@
#!/usr/bin/python -S
"""
libstr_test.py: Tests for libstr.py
"""

import unittest

import libstr  # module under test


class LibStrTest(unittest.TestCase):

  def testUnarySuffixOpDemo(self):
    s = 'abcd'
    n = len(s)

    # All of these loops test exactly 4.
    # NOTE: These are manually copied into DoUnarySuffixOp

    print('## shortest prefix')
    for i in xrange(1, n+1):
      print '%d test %06r return %06r' % (i, s[:i], s[i:])
    print

    print('# longest prefix')
    for i in xrange(n, 0, -1):
      print '%d test %06r return %06r' % (i, s[:i], s[i:])
    print

    print('% shortest suffix')
    for i in xrange(n-1, -1, -1):
      print '%d test %06r return %06r' % (i, s[i:], s[:i])
    print

    print('%% longest suffix')
    for i in xrange(0, n):
      print '%d test %06r return %06r' % (i, s[i:], s[:i])
    print


if __name__ == '__main__':
  unittest.main()

spec/var-op-strip.test.sh

@@ -67,3 +67,23 @@ echo ${v#?}  # ? is a glob that stands for one character
# stdout: -
# BUG dash/mksh stdout-repr: '\xbc-\n'
# BUG zsh stdout-repr: '\n'

### Bug fix: Test that you can remove everything with glob
s='--x--'
argv "${s%%-*}" "${s%-*}" "${s#*-}" "${s##*-}"
## STDOUT:
['', '--x-', '-x--', '']
## END

### Test that you can remove everything with const
s='abcd'
argv "${s%%abcd}" "${s%abcd}" "${s#abcd}" "${s##abcd}"
# failure case:
argv "${s%%abcde}" "${s%abcde}" "${s#abcde}" "${s##abcde}"
## STDOUT:
['', '', '', '']
['abcd', 'abcd', 'abcd', 'abcd']
## END