tests/test-import-context.t

rust: switch hg-core and hg-cpython to rust 2018 edition

Many interesting changes have happened in Rust since the Oxidation Plan was
introduced, like the 2018 edition and procedural macros:

    - Opting in to the 2018 edition is a clear benefit in terms of future
      proofing, new (nice to have) syntactical sugar notwithstanding. It
      also has a new non-lexical, non-AST based borrow checker that has
      fewer bugs(!) and allows us to write correct code that in some cases
      would have been rejected by the old one.
    - Procedural macros allow us to use the PyO3 crate which maintainers have
      expressed the clear goal of compiling on stable, which would help in
      code maintainability compared to rust-cpython.

In this patch are the following changes:
    - Removing most `extern crate` uses
    - Updating `use` clauses (`crate` keyword, nested `use`)
    - Removing `mod.rs` in favor of an aptly named module file

Like discussed in the mailing list (
https://www.mercurial-scm.org/pipermail/mercurial-devel/2019-July/132316.html
), until Rust integration in Mercurial is considered to be out of the
experimental phase, the maximum version of Rust allowed is whatever the latest
version Debian packages.

Differential Revision: https://phab.mercurial-scm.org/D6597

Test applying context diffs

  $ cat > writepatterns.py <<EOF
  > import sys
  > 
  > path = sys.argv[1]
  > lasteol = sys.argv[2] == '1'
  > patterns = sys.argv[3:]
  > 
  > fp = open(path, 'wb')
  > for i, pattern in enumerate(patterns):
  >     count = int(pattern[0:-1])
  >     char = pattern[-1].encode('utf8') + b'\n'
  >     if not lasteol and i == len(patterns) - 1:
  >         fp.write((char * count)[:-1])
  >     else:
  >         fp.write(char * count)
  > fp.close()
  > EOF
  $ cat > cat.py <<EOF
  > import sys
  > from mercurial import pycompat
  > from mercurial.utils import stringutil
  > pycompat.stdout.write(b'%s\n'
  >                       % stringutil.pprint(open(sys.argv[1], 'rb').read()))
  > EOF

Initialize the test repository

  $ hg init repo
  $ cd repo
  $ "$PYTHON" ../writepatterns.py a 0 5A 1B 5C 1D
  $ "$PYTHON" ../writepatterns.py b 1 1A 1B
  $ "$PYTHON" ../writepatterns.py c 1 5A
  $ "$PYTHON" ../writepatterns.py d 1 5A 1B
  $ hg add
  adding a
  adding b
  adding c
  adding d
  $ hg ci -m addfiles

Add file, missing a last end of line

  $ hg import --no-commit - <<EOF
  > *** /dev/null	2010-10-16 18:05:49.000000000 +0200
  > --- b/newnoeol	2010-10-16 18:23:26.000000000 +0200
  > ***************
  > *** 0 ****
  > --- 1,2 ----
  > + a
  > + b
  > \ No newline at end of file
  > *** a/a	Sat Oct 16 16:35:51 2010
  > --- b/a	Sat Oct 16 16:35:51 2010
  > ***************
  > *** 3,12 ****
  >   A
  >   A
  >   A
  > ! B
  >   C
  >   C
  >   C
  >   C
  >   C
  > ! D
  > \ No newline at end of file
  > --- 3,13 ----
  >   A
  >   A
  >   A
  > ! E
  >   C
  >   C
  >   C
  >   C
  >   C
  > ! F
  > ! F
  > 
  > *** a/b	2010-10-16 18:40:38.000000000 +0200
  > --- /dev/null	2010-10-16 18:05:49.000000000 +0200
  > ***************
  > *** 1,2 ****
  > - A
  > - B
  > --- 0 ----
  > *** a/c	Sat Oct 16 21:34:26 2010
  > --- b/c	Sat Oct 16 21:34:27 2010
  > ***************
  > *** 3,5 ****
  > --- 3,7 ----
  >   A
  >   A
  >   A
  > + B
  > + B
  > *** a/d	Sat Oct 16 21:47:20 2010
  > --- b/d	Sat Oct 16 21:47:22 2010
  > ***************
  > *** 2,6 ****
  >   A
  >   A
  >   A
  > - A
  > - B
  > --- 2,4 ----
  > EOF
  applying patch from stdin
  $ hg st
  M a
  M c
  M d
  A newnoeol
  R b

What's in a

  $ "$PYTHON" ../cat.py a
  'A\nA\nA\nA\nA\nE\nC\nC\nC\nC\nC\nF\nF\n'
  $ "$PYTHON" ../cat.py newnoeol
  'a\nb'
  $ "$PYTHON" ../cat.py c
  'A\nA\nA\nA\nA\nB\nB\n'
  $ "$PYTHON" ../cat.py d
  'A\nA\nA\nA\n'

  $ cd ..