extdiff: refactor cmdline and gui calculation login in a separate fn

This is some good logic with handling of many config items and various ways of
specifying it. I want to reuse in `diff --tool` and hence refatcored it in a
separate function of it's own.

hgext/extdiff.py

@@ -1,761 +1,783 b''
 # extdiff.py - external diff program support for mercurial
 #
 # Copyright 2006 Vadim Gelfer <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 '''command to allow external programs to compare revisions
 
 The extdiff Mercurial extension allows you to use external programs
 to compare revisions, or revision with working directory. The external
 diff programs are called with a configurable set of options and two
 non-option arguments: paths to directories containing snapshots of
 files to compare.
 
 If there is more than one file being compared and the "child" revision
 is the working directory, any modifications made in the external diff
 program will be copied back to the working directory from the temporary
 directory.
 
 The extdiff extension also allows you to configure new diff commands, so
 you do not need to type :hg:`extdiff -p kdiff3` always. ::
 
   [extdiff]
   # add new command that runs GNU diff(1) in 'context diff' mode
   cdiff = gdiff -Nprc5
   ## or the old way:
   #cmd.cdiff = gdiff
   #opts.cdiff = -Nprc5
 
   # add new command called meld, runs meld (no need to name twice).  If
   # the meld executable is not available, the meld tool in [merge-tools]
   # will be used, if available
   meld =
 
   # add new command called vimdiff, runs gvimdiff with DirDiff plugin
   # (see http://www.vim.org/scripts/script.php?script_id=102) Non
   # English user, be sure to put "let g:DirDiffDynamicDiffText = 1" in
   # your .vimrc
   vimdiff = gvim -f "+next" \\
             "+execute 'DirDiff' fnameescape(argv(0)) fnameescape(argv(1))"
 
 Tool arguments can include variables that are expanded at runtime::
 
   $parent1, $plabel1 - filename, descriptive label of first parent
   $child,   $clabel  - filename, descriptive label of child revision
   $parent2, $plabel2 - filename, descriptive label of second parent
   $root              - repository root
   $parent is an alias for $parent1.
 
 The extdiff extension will look in your [diff-tools] and [merge-tools]
 sections for diff tool arguments, when none are specified in [extdiff].
 
 ::
 
   [extdiff]
   kdiff3 =
 
   [diff-tools]
   kdiff3.diffargs=--L1 '$plabel1' --L2 '$clabel' $parent $child
 
 If a program has a graphical interface, it might be interesting to tell
 Mercurial about it. It will prevent the program from being mistakenly
 used in a terminal-only environment (such as an SSH terminal session),
 and will make :hg:`extdiff --per-file` open multiple file diffs at once
 instead of one by one (if you still want to open file diffs one by one,
 you can use the --confirm option).
 
 Declaring that a tool has a graphical interface can be done with the
 ``gui`` flag next to where ``diffargs`` are specified:
 
 ::
 
   [diff-tools]
   kdiff3.diffargs=--L1 '$plabel1' --L2 '$clabel' $parent $child
   kdiff3.gui = true
 
 You can use -I/-X and list of file or directory names like normal
 :hg:`diff` command. The extdiff extension makes snapshots of only
 needed files, so running the external diff program will actually be
 pretty fast (at least faster than having to compare the entire tree).
 '''
 
 from __future__ import absolute_import
 
 import os
 import re
 import shutil
 import stat
 import subprocess
 
 from mercurial.i18n import _
 from mercurial.node import (
     nullid,
     short,
 )
 from mercurial import (
     archival,
     cmdutil,
     encoding,
     error,
     filemerge,
     formatter,
     pycompat,
     registrar,
     scmutil,
     util,
 )
 from mercurial.utils import (
     procutil,
     stringutil,
 )
 
 cmdtable = {}
 command = registrar.command(cmdtable)
 
 configtable = {}
 configitem = registrar.configitem(configtable)
 
 configitem(
     b'extdiff', br'opts\..*', default=b'', generic=True,
 )
 
 configitem(
     b'extdiff', br'gui\..*', generic=True,
 )
 
 configitem(
     b'diff-tools', br'.*\.diffargs$', default=None, generic=True,
 )
 
 configitem(
     b'diff-tools', br'.*\.gui$', generic=True,
 )
 
 # Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
 # extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
 # be specifying the version(s) of Mercurial they are tested with, or
 # leave the attribute unspecified.
 testedwith = b'ships-with-hg-core'
 
 
 def snapshot(ui, repo, files, node, tmproot, listsubrepos):
     '''snapshot files as of some revision
     if not using snapshot, -I/-X does not work and recursive diff
     in tools like kdiff3 and meld displays too many files.'''
     dirname = os.path.basename(repo.root)
     if dirname == b"":
         dirname = b"root"
     if node is not None:
         dirname = b'%s.%s' % (dirname, short(node))
     base = os.path.join(tmproot, dirname)
     os.mkdir(base)
     fnsandstat = []
 
     if node is not None:
         ui.note(
             _(b'making snapshot of %d files from rev %s\n')
             % (len(files), short(node))
         )
     else:
         ui.note(
             _(b'making snapshot of %d files from working directory\n')
             % (len(files))
         )
 
     if files:
         repo.ui.setconfig(b"ui", b"archivemeta", False)
 
         archival.archive(
             repo,
             base,
             node,
             b'files',
             match=scmutil.matchfiles(repo, files),
             subrepos=listsubrepos,
         )
 
         for fn in sorted(files):
             wfn = util.pconvert(fn)
             ui.note(b'  %s\n' % wfn)
 
             if node is None:
                 dest = os.path.join(base, wfn)
 
                 fnsandstat.append((dest, repo.wjoin(fn), os.lstat(dest)))
     return dirname, fnsandstat
 
 
 def formatcmdline(
     cmdline,
     repo_root,
     do3way,
     parent1,
     plabel1,
     parent2,
     plabel2,
     child,
     clabel,
 ):
     # Function to quote file/dir names in the argument string.
     # When not operating in 3-way mode, an empty string is
     # returned for parent2
     replace = {
         b'parent': parent1,
         b'parent1': parent1,
         b'parent2': parent2,
         b'plabel1': plabel1,
         b'plabel2': plabel2,
         b'child': child,
         b'clabel': clabel,
         b'root': repo_root,
     }
 
     def quote(match):
         pre = match.group(2)
         key = match.group(3)
         if not do3way and key == b'parent2':
             return pre
         return pre + procutil.shellquote(replace[key])
 
     # Match parent2 first, so 'parent1?' will match both parent1 and parent
     regex = (
         br'''(['"]?)([^\s'"$]*)'''
         br'\$(parent2|parent1?|child|plabel1|plabel2|clabel|root)\1'
     )
     if not do3way and not re.search(regex, cmdline):
         cmdline += b' $parent1 $child'
     return re.sub(regex, quote, cmdline)
 
 
 def _systembackground(cmd, environ=None, cwd=None):
     ''' like 'procutil.system', but returns the Popen object directly
         so we don't have to wait on it.
     '''
     env = procutil.shellenviron(environ)
     proc = subprocess.Popen(
         procutil.tonativestr(cmd),
         shell=True,
         close_fds=procutil.closefds,
         env=procutil.tonativeenv(env),
         cwd=pycompat.rapply(procutil.tonativestr, cwd),
     )
     return proc
 
 
 def _runperfilediff(
     cmdline,
     repo_root,
     ui,
     guitool,
     do3way,
     confirm,
     commonfiles,
     tmproot,
     dir1a,
     dir1b,
     dir2,
     rev1a,
     rev1b,
     rev2,
 ):
     # Note that we need to sort the list of files because it was
     # built in an "unstable" way and it's annoying to get files in a
     # random order, especially when "confirm" mode is enabled.
     waitprocs = []
     totalfiles = len(commonfiles)
     for idx, commonfile in enumerate(sorted(commonfiles)):
         path1a = os.path.join(dir1a, commonfile)
         label1a = commonfile + rev1a
         if not os.path.isfile(path1a):
             path1a = pycompat.osdevnull
 
         path1b = b''
         label1b = b''
         if do3way:
             path1b = os.path.join(dir1b, commonfile)
             label1b = commonfile + rev1b
             if not os.path.isfile(path1b):
                 path1b = pycompat.osdevnull
 
         path2 = os.path.join(dir2, commonfile)
         label2 = commonfile + rev2
 
         if confirm:
             # Prompt before showing this diff
             difffiles = _(b'diff %s (%d of %d)') % (
                 commonfile,
                 idx + 1,
                 totalfiles,
             )
             responses = _(
                 b'[Yns?]'
                 b'$$ &Yes, show diff'
                 b'$$ &No, skip this diff'
                 b'$$ &Skip remaining diffs'
                 b'$$ &? (display help)'
             )
             r = ui.promptchoice(b'%s %s' % (difffiles, responses))
             if r == 3:  # ?
                 while r == 3:
                     for c, t in ui.extractchoices(responses)[1]:
                         ui.write(b'%s - %s\n' % (c, encoding.lower(t)))
                     r = ui.promptchoice(b'%s %s' % (difffiles, responses))
             if r == 0:  # yes
                 pass
             elif r == 1:  # no
                 continue
             elif r == 2:  # skip
                 break
 
         curcmdline = formatcmdline(
             cmdline,
             repo_root,
             do3way=do3way,
             parent1=path1a,
             plabel1=label1a,
             parent2=path1b,
             plabel2=label1b,
             child=path2,
             clabel=label2,
         )
 
         if confirm or not guitool:
             # Run the comparison program and wait for it to exit
             # before we show the next file.
             # This is because either we need to wait for confirmation
             # from the user between each invocation, or because, as far
             # as we know, the tool doesn't have a GUI, in which case
             # we can't run multiple CLI programs at the same time.
             ui.debug(
                 b'running %r in %s\n' % (pycompat.bytestr(curcmdline), tmproot)
             )
             ui.system(curcmdline, cwd=tmproot, blockedtag=b'extdiff')
         else:
             # Run the comparison program but don't wait, as we're
             # going to rapid-fire each file diff and then wait on
             # the whole group.
             ui.debug(
                 b'running %r in %s (backgrounded)\n'
                 % (pycompat.bytestr(curcmdline), tmproot)
             )
             proc = _systembackground(curcmdline, cwd=tmproot)
             waitprocs.append(proc)
 
     if waitprocs:
         with ui.timeblockedsection(b'extdiff'):
             for proc in waitprocs:
                 proc.wait()
 
 
 def diffpatch(ui, repo, node1, node2, tmproot, matcher, cmdline):
     template = b'hg-%h.patch'
     # write patches to temporary files
     with formatter.nullformatter(ui, b'extdiff', {}) as fm:
         cmdutil.export(
             repo,
             [repo[node1].rev(), repo[node2].rev()],
             fm,
             fntemplate=repo.vfs.reljoin(tmproot, template),
             match=matcher,
         )
     label1 = cmdutil.makefilename(repo[node1], template)
     label2 = cmdutil.makefilename(repo[node2], template)
     file1 = repo.vfs.reljoin(tmproot, label1)
     file2 = repo.vfs.reljoin(tmproot, label2)
     cmdline = formatcmdline(
         cmdline,
         repo.root,
         # no 3way while comparing patches
         do3way=False,
         parent1=file1,
         plabel1=label1,
         # while comparing patches, there is no second parent
         parent2=None,
         plabel2=None,
         child=file2,
         clabel=label2,
     )
     ui.debug(b'running %r in %s\n' % (pycompat.bytestr(cmdline), tmproot))
     ui.system(cmdline, cwd=tmproot, blockedtag=b'extdiff')
     return 1
 
 
 def diffrevs(
     ui,
     repo,
     node1a,
     node1b,
     node2,
     matcher,
     tmproot,
     cmdline,
     do3way,
     guitool,
     opts,
 ):
 
     subrepos = opts.get(b'subrepos')
 
     # calculate list of files changed between both revs
     st = repo.status(node1a, node2, matcher, listsubrepos=subrepos)
     mod_a, add_a, rem_a = set(st.modified), set(st.added), set(st.removed)
     if do3way:
         stb = repo.status(node1b, node2, matcher, listsubrepos=subrepos)
         mod_b, add_b, rem_b = (
             set(stb.modified),
             set(stb.added),
             set(stb.removed),
         )
     else:
         mod_b, add_b, rem_b = set(), set(), set()
     modadd = mod_a | add_a | mod_b | add_b
     common = modadd | rem_a | rem_b
     if not common:
         return 0
 
     # Always make a copy of node1a (and node1b, if applicable)
     # dir1a should contain files which are:
     #   * modified or removed from node1a to node2
     #   * modified or added from node1b to node2
     #     (except file added from node1a to node2 as they were not present in
     #     node1a)
     dir1a_files = mod_a | rem_a | ((mod_b | add_b) - add_a)
     dir1a = snapshot(ui, repo, dir1a_files, node1a, tmproot, subrepos)[0]
     rev1a = b'@%d' % repo[node1a].rev()
     if do3way:
         # file calculation criteria same as dir1a
         dir1b_files = mod_b | rem_b | ((mod_a | add_a) - add_b)
         dir1b = snapshot(ui, repo, dir1b_files, node1b, tmproot, subrepos)[0]
         rev1b = b'@%d' % repo[node1b].rev()
     else:
         dir1b = None
         rev1b = b''
 
     fnsandstat = []
 
     # If node2 in not the wc or there is >1 change, copy it
     dir2root = b''
     rev2 = b''
     if node2:
         dir2 = snapshot(ui, repo, modadd, node2, tmproot, subrepos)[0]
         rev2 = b'@%d' % repo[node2].rev()
     elif len(common) > 1:
         # we only actually need to get the files to copy back to
         # the working dir in this case (because the other cases
         # are: diffing 2 revisions or single file -- in which case
         # the file is already directly passed to the diff tool).
         dir2, fnsandstat = snapshot(ui, repo, modadd, None, tmproot, subrepos)
     else:
         # This lets the diff tool open the changed file directly
         dir2 = b''
         dir2root = repo.root
 
     label1a = rev1a
     label1b = rev1b
     label2 = rev2
 
     if not opts.get(b'per_file'):
         # If only one change, diff the files instead of the directories
         # Handle bogus modifies correctly by checking if the files exist
         if len(common) == 1:
             common_file = util.localpath(common.pop())
             dir1a = os.path.join(tmproot, dir1a, common_file)
             label1a = common_file + rev1a
             if not os.path.isfile(dir1a):
                 dir1a = pycompat.osdevnull
             if do3way:
                 dir1b = os.path.join(tmproot, dir1b, common_file)
                 label1b = common_file + rev1b
                 if not os.path.isfile(dir1b):
                     dir1b = pycompat.osdevnull
             dir2 = os.path.join(dir2root, dir2, common_file)
             label2 = common_file + rev2
 
         # Run the external tool on the 2 temp directories or the patches
         cmdline = formatcmdline(
             cmdline,
             repo.root,
             do3way=do3way,
             parent1=dir1a,
             plabel1=label1a,
             parent2=dir1b,
             plabel2=label1b,
             child=dir2,
             clabel=label2,
         )
         ui.debug(b'running %r in %s\n' % (pycompat.bytestr(cmdline), tmproot))
         ui.system(cmdline, cwd=tmproot, blockedtag=b'extdiff')
     else:
         # Run the external tool once for each pair of files
         _runperfilediff(
             cmdline,
             repo.root,
             ui,
             guitool=guitool,
             do3way=do3way,
             confirm=opts.get(b'confirm'),
             commonfiles=common,
             tmproot=tmproot,
             dir1a=os.path.join(tmproot, dir1a),
             dir1b=os.path.join(tmproot, dir1b) if do3way else None,
             dir2=os.path.join(dir2root, dir2),
             rev1a=rev1a,
             rev1b=rev1b,
             rev2=rev2,
         )
 
     for copy_fn, working_fn, st in fnsandstat:
         cpstat = os.lstat(copy_fn)
         # Some tools copy the file and attributes, so mtime may not detect
         # all changes.  A size check will detect more cases, but not all.
         # The only certain way to detect every case is to diff all files,
         # which could be expensive.
         # copyfile() carries over the permission, so the mode check could
         # be in an 'elif' branch, but for the case where the file has
         # changed without affecting mtime or size.
         if (
             cpstat[stat.ST_MTIME] != st[stat.ST_MTIME]
             or cpstat.st_size != st.st_size
             or (cpstat.st_mode & 0o100) != (st.st_mode & 0o100)
         ):
             ui.debug(
                 b'file changed while diffing. '
                 b'Overwriting: %s (src: %s)\n' % (working_fn, copy_fn)
             )
             util.copyfile(copy_fn, working_fn)
 
     return 1
 
 
 def dodiff(ui, repo, cmdline, pats, opts, guitool=False):
     '''Do the actual diff:
 
     - copy to a temp structure if diffing 2 internal revisions
     - copy to a temp structure if diffing working revision with
       another one and more than 1 file is changed
     - just invoke the diff for a single file in the working dir
     '''
 
     cmdutil.check_at_most_one_arg(opts, b'rev', b'change')
     revs = opts.get(b'rev')
     change = opts.get(b'change')
     do3way = b'$parent2' in cmdline
 
     if change:
         ctx2 = scmutil.revsingle(repo, change, None)
         ctx1a, ctx1b = ctx2.p1(), ctx2.p2()
     else:
         ctx1a, ctx2 = scmutil.revpair(repo, revs)
         if not revs:
             ctx1b = repo[None].p2()
         else:
             ctx1b = repo[nullid]
 
     node1a = ctx1a.node()
     node1b = ctx1b.node()
     node2 = ctx2.node()
 
     # Disable 3-way merge if there is only one parent
     if do3way:
         if node1b == nullid:
             do3way = False
 
     matcher = scmutil.match(repo[node2], pats, opts)
 
     if opts.get(b'patch'):
         if opts.get(b'subrepos'):
             raise error.Abort(_(b'--patch cannot be used with --subrepos'))
         if opts.get(b'per_file'):
             raise error.Abort(_(b'--patch cannot be used with --per-file'))
         if node2 is None:
             raise error.Abort(_(b'--patch requires two revisions'))
 
     tmproot = pycompat.mkdtemp(prefix=b'extdiff.')
     try:
         if opts.get(b'patch'):
             return diffpatch(ui, repo, node1a, node2, tmproot, matcher, cmdline)
 
         return diffrevs(
             ui,
             repo,
             node1a,
             node1b,
             node2,
             matcher,
             tmproot,
             cmdline,
             do3way,
             guitool,
             opts,
         )
 
     finally:
         ui.note(_(b'cleaning up temp directory\n'))
         shutil.rmtree(tmproot)
 
 
 extdiffopts = (
     [
         (
             b'o',
             b'option',
             [],
             _(b'pass option to comparison program'),
             _(b'OPT'),
         ),
         (b'r', b'rev', [], _(b'revision'), _(b'REV')),
         (b'c', b'change', b'', _(b'change made by revision'), _(b'REV')),
         (
             b'',
             b'per-file',
             False,
             _(b'compare each file instead of revision snapshots'),
         ),
         (
             b'',
             b'confirm',
             False,
             _(b'prompt user before each external program invocation'),
         ),
         (b'', b'patch', None, _(b'compare patches for two revisions')),
     ]
     + cmdutil.walkopts
     + cmdutil.subrepoopts
 )
 
 
 @command(
     b'extdiff',
     [(b'p', b'program', b'', _(b'comparison program to run'), _(b'CMD')),]
     + extdiffopts,
     _(b'hg extdiff [OPT]... [FILE]...'),
     helpcategory=command.CATEGORY_FILE_CONTENTS,
     inferrepo=True,
 )
 def extdiff(ui, repo, *pats, **opts):
     '''use external program to diff repository (or selected files)
 
     Show differences between revisions for the specified files, using
     an external program. The default program used is diff, with
     default options "-Npru".
 
     To select a different program, use the -p/--program option. The
     program will be passed the names of two directories to compare,
     unless the --per-file option is specified (see below). To pass
     additional options to the program, use -o/--option. These will be
     passed before the names of the directories or files to compare.
 
     When two revision arguments are given, then changes are shown
     between those revisions. If only one revision is specified then
     that revision is compared to the working directory, and, when no
     revisions are specified, the working directory files are compared
     to its parent.
 
     The --per-file option runs the external program repeatedly on each
     file to diff, instead of once on two directories. By default,
     this happens one by one, where the next file diff is open in the
     external program only once the previous external program (for the
     previous file diff) has exited. If the external program has a
     graphical interface, it can open all the file diffs at once instead
     of one by one. See :hg:`help -e extdiff` for information about how
     to tell Mercurial that a given program has a graphical interface.
 
     The --confirm option will prompt the user before each invocation of
     the external program. It is ignored if --per-file isn't specified.
     '''
     opts = pycompat.byteskwargs(opts)
     program = opts.get(b'program')
     option = opts.get(b'option')
     if not program:
         program = b'diff'
         option = option or [b'-Npru']
     cmdline = b' '.join(map(procutil.shellquote, [program] + option))
     return dodiff(ui, repo, cmdline, pats, opts)
 
 
 class savedcmd(object):
     """use external program to diff repository (or selected files)
 
     Show differences between revisions for the specified files, using
     the following program::
 
         %(path)s
 
     When two revision arguments are given, then changes are shown
     between those revisions. If only one revision is specified then
     that revision is compared to the working directory, and, when no
     revisions are specified, the working directory files are compared
     to its parent.
     """
 
     def __init__(self, path, cmdline, isgui):
         # We can't pass non-ASCII through docstrings (and path is
         # in an unknown encoding anyway), but avoid double separators on
         # Windows
         docpath = stringutil.escapestr(path).replace(b'\\\\', b'\\')
         self.__doc__ %= {'path': pycompat.sysstr(stringutil.uirepr(docpath))}
         self._cmdline = cmdline
         self._isgui = isgui
 
     def __call__(self, ui, repo, *pats, **opts):
         opts = pycompat.byteskwargs(opts)
         options = b' '.join(map(procutil.shellquote, opts[b'option']))
         if options:
             options = b' ' + options
         return dodiff(
             ui, repo, self._cmdline + options, pats, opts, guitool=self._isgui
         )
 
 
+def _gettooldetails(ui, cmd, path):
+    """
+    returns following things for a
+    ```
+    [extdiff]
+    <cmd> = <path>
+    ```
+    entry:
+
+    cmd: command/tool name
+    path: path to the tool
+    cmdline: the command which should be run
+    isgui: whether the tool uses GUI or not
+
+    Reads all external tools related configs, whether it be extdiff section,
+    diff-tools or merge-tools section, or its specified in an old format or
+    the latest format.
+    """
+    path = util.expandpath(path)
+    if cmd.startswith(b'cmd.'):
+        cmd = cmd[4:]
+        if not path:
+            path = procutil.findexe(cmd)
+            if path is None:
+                path = filemerge.findexternaltool(ui, cmd) or cmd
+        diffopts = ui.config(b'extdiff', b'opts.' + cmd)
+        cmdline = procutil.shellquote(path)
+        if diffopts:
+            cmdline += b' ' + diffopts
+        isgui = ui.configbool(b'extdiff', b'gui.' + cmd)
+    else:
+        if path:
+            # case "cmd = path opts"
+            cmdline = path
+            diffopts = len(pycompat.shlexsplit(cmdline)) > 1
+        else:
+            # case "cmd ="
+            path = procutil.findexe(cmd)
+            if path is None:
+                path = filemerge.findexternaltool(ui, cmd) or cmd
+            cmdline = procutil.shellquote(path)
+            diffopts = False
+        isgui = ui.configbool(b'extdiff', b'gui.' + cmd)
+    # look for diff arguments in [diff-tools] then [merge-tools]
+    if not diffopts:
+        key = cmd + b'.diffargs'
+        for section in (b'diff-tools', b'merge-tools'):
+            args = ui.config(section, key)
+            if args:
+                cmdline += b' ' + args
+                if isgui is None:
+                    isgui = ui.configbool(section, cmd + b'.gui') or False
+                break
+    return cmd, path, cmdline, isgui
+
+
 def uisetup(ui):
     for cmd, path in ui.configitems(b'extdiff'):
         if cmd.startswith(b'opts.') or cmd.startswith(b'gui.'):
             continue
-        path = util.expandpath(path)
-        if cmd.startswith(b'cmd.'):
-            cmd = cmd[4:]
-            if not path:
-                path = procutil.findexe(cmd)
-                if path is None:
-                    path = filemerge.findexternaltool(ui, cmd) or cmd
-            diffopts = ui.config(b'extdiff', b'opts.' + cmd)
-            cmdline = procutil.shellquote(path)
-            if diffopts:
-                cmdline += b' ' + diffopts
-            isgui = ui.configbool(b'extdiff', b'gui.' + cmd)
-        else:
-            if path:
-                # case "cmd = path opts"
-                cmdline = path
-                diffopts = len(pycompat.shlexsplit(cmdline)) > 1
-            else:
-                # case "cmd ="
-                path = procutil.findexe(cmd)
-                if path is None:
-                    path = filemerge.findexternaltool(ui, cmd) or cmd
-                cmdline = procutil.shellquote(path)
-                diffopts = False
-            isgui = ui.configbool(b'extdiff', b'gui.' + cmd)
-        # look for diff arguments in [diff-tools] then [merge-tools]
-        if not diffopts:
-            key = cmd + b'.diffargs'
-            for section in (b'diff-tools', b'merge-tools'):
-                args = ui.config(section, key)
-                if args:
-                    cmdline += b' ' + args
-                    if isgui is None:
-                        isgui = ui.configbool(section, cmd + b'.gui') or False
-                    break
+        cmd, path, cmdline, isgui = _gettooldetails(ui, cmd, path)
         command(
             cmd,
             extdiffopts[:],
             _(b'hg %s [OPTION]... [FILE]...') % cmd,
             helpcategory=command.CATEGORY_FILE_CONTENTS,
             inferrepo=True,
         )(savedcmd(path, cmdline, isgui))
 
 
 # tell hggettext to extract docstrings from these functions:
 i18nfunctions = [savedcmd]