difftool: move 'git-difftool' out of contrib

This prepares 'git-difftool' and its documentation for
mainstream use.

'git-difftool-helper' became 'git-difftool--helper'
since users should not use it directly.

'git-difftool' was added to the list of commands as
an ancillaryinterrogator.

Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 115 insertions, 0 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 3afd12474..94ef1a62f 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -667,6 +667,24 @@ diff.suppressBlankEmpty::
 	A boolean to inhibit the standard behavior of printing a space
 	before each empty output line. Defaults to false.
 
+diff.tool::
+	Controls which diff tool is used.  `diff.tool` overrides
+	`merge.tool` when used by linkgit:git-difftool[1] and has
+	the same valid values as `merge.tool` minus "tortoisemerge"
+	and plus "kompare".
+
+difftool.<tool>.path::
+	Override the path for the given tool.  This is useful in case
+	your tool is not in the PATH.
+
+difftool.<tool>.cmd::
+	Specify the command to invoke the specified diff tool.
+	The specified command is evaluated in shell with the following
+	variables available:  'LOCAL' is set to the name of the temporary
+	file containing the contents of the diff pre-image and 'REMOTE'
+	is set to the name of the temporary file containing the contents
+	of the diff post-image.
+
 diff.wordRegex::
 	A POSIX Extended Regular Expression used to determine what is a "word"
 	when performing word-by-word difference calculations.  Character
diff --git a/Documentation/git-difftool.txt b/Documentation/git-difftool.txt
new file mode 100644
index 000000000..af68466eb
--- /dev/null
+++ b/Documentation/git-difftool.txt
@@ -0,0 +1,97 @@
+git-difftool(1)
+===============
+
+NAME
+----
+git-difftool - Show changes using common diff tools
+
+SYNOPSIS
+--------
+'git difftool' [--tool=<tool>] [-y|--no-prompt] [<'git diff' options>]
+
+DESCRIPTION
+-----------
+'git-difftool' is a git command that allows you to compare and edit files
+between revisions using common diff tools.  'git difftool' is a frontend
+to 'git-diff' and accepts the same options and arguments.
+
+OPTIONS
+-------
+-y::
+--no-prompt::
+	Do not prompt before launching a diff tool.
+
+-t <tool>::
+--tool=<tool>::
+	Use the diff tool specified by <tool>.
+	Valid merge tools are:
+	kdiff3, kompare, tkdiff, meld, xxdiff, emerge, vimdiff, gvimdiff,
+	ecmerge, diffuse and opendiff
++
+If a diff tool is not specified, 'git-difftool'
+will use the configuration variable `diff.tool`.  If the
+configuration variable `diff.tool` is not set, 'git-difftool'
+will pick a suitable default.
++
+You can explicitly provide a full path to the tool by setting the
+configuration variable `difftool.<tool>.path`. For example, you
+can configure the absolute path to kdiff3 by setting
+`difftool.kdiff3.path`. Otherwise, 'git-difftool' assumes the
+tool is available in PATH.
++
+Instead of running one of the known diff tools,
+'git-difftool' can be customized to run an alternative program
+by specifying the command line to invoke in a configuration
+variable `difftool.<tool>.cmd`.
++
+When 'git-difftool' is invoked with this tool (either through the
+`-t` or `--tool` option or the `diff.tool` configuration variable)
+the configured command line will be invoked with the following
+variables available: `$LOCAL` is set to the name of the temporary
+file containing the contents of the diff pre-image and `$REMOTE`
+is set to the name of the temporary file containing the contents
+of the diff post-image.  `$BASE` is provided for compatibility
+with custom merge tool commands and has the same value as `$LOCAL`.
+
+See linkgit:git-diff[1] for the full list of supported options.
+
+CONFIG VARIABLES
+----------------
+'git-difftool' falls back to 'git-mergetool' config variables when the
+difftool equivalents have not been defined.
+
+diff.tool::
+	The default diff tool to use.
+
+difftool.<tool>.path::
+	Override the path for the given tool.  This is useful in case
+	your tool is not in the PATH.
+
+difftool.<tool>.cmd::
+	Specify the command to invoke the specified diff tool.
++
+See the `--tool=<tool>` option above for more details.
+
+SEE ALSO
+--------
+linkgit:git-diff[1]::
+	 Show changes between commits, commit and working tree, etc
+
+linkgit:git-mergetool[1]::
+	Run merge conflict resolution tools to resolve merge conflicts
+
+linkgit:git-config[1]::
+	 Get and set repository or global options
+
+
+AUTHOR
+------
+Written by David Aguilar <davvid@gmail.com>.
+
+Documentation
+--------------
+Documentation by David Aguilar and the git-list <git@vger.kernel.org>.
+
+GIT
+---
+Part of the linkgit:git[1] suite