color-words: Support diff.wordregex config option

When diff is invoked with --color-words (w/o =regex), use the regular
expression the user has configured as diff.wordregex.

diff drivers configured via attributes take precedence over the
diff.wordregex-words setting.  If the user wants to change them, they have
their own configuration variables.

Signed-off-by: Boyd Stephen Smith Jr <bss@iguanasuicide.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -639,6 +639,12 @@ diff.suppress-blank-empty::
 	A boolean to inhibit the standard behavior of printing a space
 	before each empty output line. Defaults to false.
 
+diff.wordregex::
+	A POSIX Extended Regular Expression used to determine what is a "word"
+	when performing word-by-word difference calculations.  Character
+	sequences that match the regular expression are "words", all other
+	characters are *ignorable* whitespace.
+
 fetch.unpackLimit::
 	If the number of objects fetched over the git native
 	transfer is below this

Documentation/diff-options.txt

@@ -103,9 +103,10 @@ expression to make sure that it matches all non-whitespace characters.
 A match that contains a newline is silently truncated(!) at the
 newline.
 +
-The regex can also be set via a diff driver, see
+The regex can also be set via a diff driver or configuration option, see
-linkgit:gitattributes[1]; giving it explicitly overrides any diff
+linkgit:gitattributes[1] or linkgit:git-config[1].  Giving it explicitly
-driver setting.
+overrides any diff driver or configuration setting.  Diff drivers
+override configuration settings.
 
 --no-renames::
 	Turn off rename detection, even when the configuration

diff.c

@@ -23,6 +23,7 @@ static int diff_detect_rename_default;
 static int diff_rename_limit_default = 200;
 static int diff_suppress_blank_empty;
 int diff_use_color_default = -1;
+static const char *diff_word_regex_cfg;
 static const char *external_diff_cmd_cfg;
 int diff_auto_refresh_index = 1;
 static int diff_mnemonic_prefix;
@@ -92,6 +93,8 @@ int git_diff_ui_config(const char *var, const char *value, void *cb)
 	}
 	if (!strcmp(var, "diff.external"))
 		return git_config_string(&external_diff_cmd_cfg, var, value);
+	if (!strcmp(var, "diff.wordregex"))
+		return git_config_string(&diff_word_regex_cfg, var, value);
 
 	return git_diff_basic_config(var, value, cb);
 }
@@ -1550,6 +1553,8 @@ static void builtin_diff(const char *name_a,
 				o->word_regex = userdiff_word_regex(one);
 			if (!o->word_regex)
 				o->word_regex = userdiff_word_regex(two);
+			if (!o->word_regex)
+				o->word_regex = diff_word_regex_cfg;
 			if (o->word_regex) {
 				ecbdata.diff_words->word_regex = (regex_t *)
 					xmalloc(sizeof(regex_t));

t/t4034-diff-words.sh

@@ -77,6 +77,7 @@ a = b + c<RESET>
 
 <GREEN>aeff = aeff * ( aaa<RESET> )
 EOF
+cp expect expect.letter-runs-are-words
 
 test_expect_success 'word diff with a regular expression' '
 
@@ -92,7 +93,7 @@ post diff=testdriver
 EOF
 '
 
-test_expect_success 'option overrides default' '
+test_expect_success 'option overrides .gitattributes' '
 
 	word_diff --color-words="[a-z]+"
 
@@ -112,13 +113,53 @@ a = b + c<RESET>
 
 <GREEN>aeff = aeff * ( aaa )<RESET>
 EOF
+cp expect expect.non-whitespace-is-word
 
-test_expect_success 'use default supplied by driver' '
+test_expect_success 'use regex supplied by driver' '
 
 	word_diff --color-words
 
 '
 
+test_expect_success 'set diff.wordregex option' '
+	git config diff.wordregex "[[:alnum:]]+"
+'
+
+cp expect.letter-runs-are-words expect
+
+test_expect_success 'command-line overrides config' '
+	word_diff --color-words="[a-z]+"
+'
+
+cp expect.non-whitespace-is-word expect
+
+test_expect_success '.gitattributes override config' '
+	word_diff --color-words
+'
+
+test_expect_success 'remove diff driver regex' '
+	git config --unset diff.testdriver.wordregex
+'
+
+cat > expect <<\EOF
+<WHITE>diff --git a/pre b/post<RESET>
+<WHITE>index 330b04f..5ed8eff 100644<RESET>
+<WHITE>--- a/pre<RESET>
+<WHITE>+++ b/post<RESET>
+<BROWN>@@ -1,3 +1,7 @@<RESET>
+h(4),<GREEN>hh[44<RESET>]
+<RESET>
+a = b + c<RESET>
+
+<GREEN>aa = a<RESET>
+
+<GREEN>aeff = aeff * ( aaa<RESET> )
+EOF
+
+test_expect_success 'use configured regex' '
+	word_diff --color-words
+'
+
 echo 'aaa (aaa)' > pre
 echo 'aaa (aaa) aaa' > post