Move formatexpr config in-tree, out of plugin

Introduces the `format` Python module which provides `clang_format()`
and `yapf()` functions which efficiently (compared to vimscript) invoke
`clang-format` or `yapf` respectively then apply the minimal number of
changes using `difflib.SequenceMatcher`.

Additionally, in order to invoke these Python functions add |autoload|
functions `format#clang_format()` and `format#yapf()` which can be
directly used by the 'formatexpr' setting.

Finally, add |ftplugin| files which set 'formatexpr' when the |autoload|
functions are available.

autoload/format.vim

@@ -0,0 +1,14 @@
+if !has('pythonx')
+  finish
+endif
+
+" set debug=msg,throw
+pythonx import format
+
+function! format#clang_format() abort
+  pythonx format.clang_format()
+endfunction
+
+function! format#yapf() abort
+  pythonx format.yapf()
+endfunction

ftplugin/c.vim

@@ -0,0 +1,3 @@
+if has('pythonx')
+  set formatexpr=format#clang_format()
+endif

ftplugin/cpp.vim

@@ -0,0 +1,3 @@
+if has('pythonx')
+  set formatexpr=format#clang_format()
+endif

ftplugin/java.vim

@@ -0,0 +1,3 @@
+if has('pythonx')
+  set formatexpr=format#clang_format()
+endif

ftplugin/javascript.vim

@@ -0,0 +1,3 @@
+if has('pythonx')
+  set formatexpr=format#clang_format()
+endif

ftplugin/objc.vim

@@ -0,0 +1,3 @@
+if has('pythonx')
+  set formatexpr=format#clang_format()
+endif

ftplugin/objcpp.vim

@@ -0,0 +1,3 @@
+if has('pythonx')
+  set formatexpr=format#clang_format()
+endif

ftplugin/proto.vim

@@ -0,0 +1,3 @@
+if has('pythonx')
+  set formatexpr=format#clang_format()
+endif

ftplugin/python.vim

@@ -0,0 +1,3 @@
+if has('pythonx')
+  set formatexpr=format#yapf()
+endif

plugin/format.vim

@@ -0,0 +1,8 @@
+if !has('pythonx')
+  finish
+endif
+
+let g:clang_format_path = get(g:, 'clang_format_path', 'clang-format')
+let g:clang_format_style = get(g:, 'clang_format_style', 'google')
+let g:yapf_path = get(g:, 'yapf_path', 'yapf')
+let g:yapf_style = get(g:, 'yapf_style', 'pep8')

pythonx/format.py

@@ -0,0 +1,117 @@
+"""Python formatexpr for clang-format & yapf"""
+
+import json
+import sys
+import subprocess
+import difflib
+
+import vim
+
+
+class FormatError(Exception):
+    """A formatting error."""
+
+
+def clang_format():
+    """Call clang-format on the current text object."""
+    clang_format = vim.vars['clang_format_path']
+    # TODO: The cursor position before gq is invoked is not preserved in the
+    # jump list, this expression will return the cursor position at the
+    # beginning of the motion or text object.
+    # Is there a way to get the cursor position immediately before gq is
+    # invoked? So that we can pass the position to clang-format in order for
+    # it to return the updated position to continue editing.
+    # Query the current absolute cursor positon.
+    cursor = int(vim.eval('line2byte(".") + col(".")')) - 2
+    if cursor < 0:
+        return
+    # Determine the lines to format.
+    startline = int(vim.eval('v:lnum'))
+    endline = startline + int(vim.eval('v:count')) - 1
+    lines = f'{startline}:{endline}'
+    fallback_style = vim.vars['clang_format_style']
+    # Construct the clang-format command to call.
+    command = [
+        clang_format, '-style', 'file', '-cursor',
+        str(cursor), '-lines', lines, '-fallback-style', fallback_style
+    ]
+    if vim.current.buffer.name:
+        command += ['-assume-filename', vim.current.buffer.name]
+    # Call the clang-format command.
+    output = call(command)
+    if not output:
+        return
+    # Read the clang-format json header.
+    header = json.loads(output[0])
+    if header.get('IncompleteFormat'):
+        raise FormatError('clang-format: incomplete (syntax errors).')
+    # Replace the formatted regions.
+    replace_regions(output[1:])
+    # Set the updated cursor position.
+    vim.command('goto %d' % (header['Cursor'] + 1))
+
+
+def yapf():
+    """Call yapf on the current text object."""
+    yapf = vim.vars['yapf_path']
+    # Determine the lines to format.
+    start = int(vim.eval('v:lnum'))
+    end = start + int(vim.eval('v:count'))
+    lines = '{0}-{1}'.format(start, end)
+    style = vim.vars['yapf_style']
+    # Construct the clang-format command to call.
+    command = [yapf, '--style', style, '--lines', lines]
+    # TODO: Since yapf is a Python package, we could import the module and
+    # call it directly instead. It would then be possible to output better
+    # error messages and act on the buffer directly.
+    # Call the yapf command.
+    output = call(command)
+    if not output:
+        return
+    # Replace the formatted regions.
+    replace_regions(output[:-1])
+
+
+def call(command):
+    """Call the command to format the text.
+
+    Arguments:
+        command (list): Formatting command to call.
+        text (str): Text to be passed to stdin of command.
+
+    Returns:
+        list: The output of the formatter split on new lines.
+        None: If the subprocess failed.
+    """
+    # Don't open a cmd prompt window on Windows.
+    startupinfo = None
+    if sys.platform.startswith('win32'):
+        startupinfo = subprocess.STARTUPINFO()
+        startupinfo.dwFlags |= subprocess.STARTF_USESHOWWINDOW
+        startupinfo.wShowWindow = subprocess.SW_HIDE
+    # Call the formatting command.
+    process = subprocess.Popen(command,
+                               stdout=subprocess.PIPE,
+                               stderr=subprocess.PIPE,
+                               stdin=subprocess.PIPE,
+                               startupinfo=startupinfo)
+    stdout, stderr = process.communicate(
+        input='\n'.join(vim.current.buffer).encode('utf-8'))
+    if stderr:
+        raise FormatError(stderr)
+    if not stdout:
+        raise FormatError('No output from {0}.'.format(command[0]))
+    # Split the lines into a list of elements.
+    return stdout.decode('utf-8').split('\n')
+
+
+def replace_regions(lines):
+    """Replace formatted regions in the current buffer.
+
+    Arguments:
+        lines (list): The formatted buffer lines.
+    """
+    matcher = difflib.SequenceMatcher(None, vim.current.buffer, lines)
+    for tag, i1, i2, j1, j2 in reversed(matcher.get_opcodes()):
+        if tag != 'equal':
+            vim.current.buffer[i1:i2] = lines[j1:j2]

vimrc

@@ -59,9 +59,6 @@ let g:ale_cmake_cmakelint_options =
 " Version control differences in the sign column
 Pack 'mhinz/vim-signify'
 
-" format.vim - format with text objects
-Pack 'git@bitbucket.org:infektor/format.vim.git'
-
 " vim-textobj-user - library for creating text objects
 Pack 'kana/vim-textobj-user'
 " vim-textobj-entire - Entire file text object