difftool: add support for a difftool.prompt config variable

difftool now supports difftool.prompt so that users do not have to
pass --no-prompt or hit enter each time a diff tool is launched.
The --prompt flag overrides the configuration variable.

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

Documentation/config.txt

@@ -685,6 +685,9 @@ difftool.<tool>.cmd::
 	is set to the name of the temporary file containing the contents
 	of the diff post-image.
 
+difftool.prompt::
+	Prompt before each invocation of the diff tool.
+
 diff.wordRegex::
 	A POSIX Extended Regular Expression used to determine what is a "word"
 	when performing word-by-word difference calculations.  Character

Documentation/git-difftool.txt

@@ -7,7 +7,7 @@ git-difftool - Show changes using common diff tools
 
 SYNOPSIS
 --------
-'git difftool' [--tool=<tool>] [-y|--no-prompt] [<'git diff' options>]
+'git difftool' [--tool=<tool>] [-y|--no-prompt|--prompt] [<'git diff' options>]
 
 DESCRIPTION
 -----------
@@ -21,6 +21,11 @@ OPTIONS
 --no-prompt::
 	Do not prompt before launching a diff tool.
 
+--prompt::
+	Prompt before each invocation of the diff tool.
+	This is the default behaviour; the option is provided to
+	override any configuration settings.
+
 -t <tool>::
 --tool=<tool>::
 	Use the diff tool specified by <tool>.
@@ -72,6 +77,9 @@ difftool.<tool>.cmd::
 +
 See the `--tool=<tool>` option above for more details.
 
+difftool.prompt::
+	Prompt before each invocation of the diff tool.
+
 SEE ALSO
 --------
 linkgit:git-diff[1]::

git-difftool--helper.sh

@@ -5,9 +5,15 @@
 #
 # Copyright (c) 2009 David Aguilar
 
-# Set GIT_DIFFTOOL_NO_PROMPT to bypass the per-file prompt.
+# difftool.prompt controls the default prompt/no-prompt behavior
+# and is overridden with $GIT_DIFFTOOL*_PROMPT.
 should_prompt () {
-	test -z "$GIT_DIFFTOOL_NO_PROMPT"
+	prompt=$(git config --bool difftool.prompt || echo true)
+	if test "$prompt" = true; then
+		test -z "$GIT_DIFFTOOL_NO_PROMPT"
+	else
+		test -n "$GIT_DIFFTOOL_PROMPT"
+	fi
 }
 
 # This function prepares temporary files and launches the appropriate

git-difftool.perl

@@ -2,9 +2,12 @@
 # Copyright (c) 2009 David Aguilar
 #
 # This is a wrapper around the GIT_EXTERNAL_DIFF-compatible
-# git-difftool--helper script.  This script exports
-# GIT_EXTERNAL_DIFF and GIT_PAGER for use by git, and
-# GIT_DIFFTOOL_NO_PROMPT and GIT_DIFF_TOOL for use by git-difftool--helper.
+# git-difftool--helper script.
+#
+# This script exports GIT_EXTERNAL_DIFF and GIT_PAGER for use by git.
+# GIT_DIFFTOOL_NO_PROMPT, GIT_DIFFTOOL_PROMPT, and GIT_DIFF_TOOL
+# are exported for use by git-difftool--helper.
+#
 # Any arguments that are unknown to this script are forwarded to 'git diff'.
 
 use strict;
@@ -62,6 +65,12 @@ sub generate_command
 		}
 		if ($arg eq '-y' || $arg eq '--no-prompt') {
 			$ENV{GIT_DIFFTOOL_NO_PROMPT} = 'true';
+			delete $ENV{GIT_DIFFTOOL_PROMPT};
+			next;
+		}
+		if ($arg eq '--prompt') {
+			$ENV{GIT_DIFFTOOL_PROMPT} = 'true';
+			delete $ENV{GIT_DIFFTOOL_NO_PROMPT};
 			next;
 		}
 		if ($arg eq '-h' || $arg eq '--help') {

t/t7800-difftool.sh

@@ -15,6 +15,7 @@ remove_config_vars()
 	# Unset all config variables used by git-difftool
 	git config --unset diff.tool
 	git config --unset difftool.test-tool.cmd
+	git config --unset difftool.prompt
 	git config --unset merge.tool
 	git config --unset mergetool.test-tool.cmd
 	return 0
@@ -26,11 +27,18 @@ restore_test_defaults()
 	remove_config_vars
 	unset GIT_DIFF_TOOL
 	unset GIT_MERGE_TOOL
+	unset GIT_DIFFTOOL_PROMPT
 	unset GIT_DIFFTOOL_NO_PROMPT
 	git config diff.tool test-tool &&
 	git config difftool.test-tool.cmd 'cat $LOCAL'
 }
 
+prompt_given()
+{
+	prompt="$1"
+	test "$prompt" = "Hit return to launch 'test-tool': branch"
+}
+
 # Create a file on master and change it on branch
 test_expect_success 'setup' '
 	echo master >file &&
@@ -116,6 +124,62 @@ test_expect_success 'GIT_DIFFTOOL_NO_PROMPT variable' '
 	restore_test_defaults
 '
 
+# git-difftool supports the difftool.prompt variable.
+# Test that GIT_DIFFTOOL_PROMPT can override difftool.prompt = false
+test_expect_success 'GIT_DIFFTOOL_PROMPT variable' '
+	git config difftool.prompt false &&
+	GIT_DIFFTOOL_PROMPT=true &&
+	export GIT_DIFFTOOL_PROMPT &&
+
+	prompt=$(echo | git difftool --prompt branch | tail -1) &&
+	prompt_given "$prompt" &&
+
+	restore_test_defaults
+'
+
+# Test that we don't have to pass --no-prompt when difftool.prompt is false
+test_expect_success 'difftool.prompt config variable is false' '
+	git config difftool.prompt false &&
+
+	diff=$(git difftool branch) &&
+	test "$diff" = "branch" &&
+
+	restore_test_defaults
+'
+
+# Test that the -y flag can override difftool.prompt = true
+test_expect_success 'difftool.prompt can overridden with -y' '
+	git config difftool.prompt true &&
+
+	diff=$(git difftool -y branch) &&
+	test "$diff" = "branch" &&
+
+	restore_test_defaults
+'
+
+# Test that the --prompt flag can override difftool.prompt = false
+test_expect_success 'difftool.prompt can overridden with --prompt' '
+	git config difftool.prompt false &&
+
+	prompt=$(echo | git difftool --prompt branch | tail -1) &&
+	prompt_given "$prompt" &&
+
+	restore_test_defaults
+'
+
+# Test that the last flag passed on the command-line wins
+test_expect_success 'difftool last flag wins' '
+	diff=$(git difftool --prompt --no-prompt branch) &&
+	test "$diff" = "branch" &&
+
+	restore_test_defaults &&
+
+	prompt=$(echo | git difftool --no-prompt --prompt branch | tail -1) &&
+	prompt_given "$prompt" &&
+
+	restore_test_defaults
+'
+
 # git-difftool falls back to git-mergetool config variables
 # so test that behavior here
 test_expect_success 'difftool + mergetool config variables' '