git-diff: complain about >=8 consecutive spaces in initial indent

This introduces a new whitespace error type, "indent-with-non-tab".
The error is about starting a line with 8 or more SP, instead of
indenting it with a HT.

This is not enabled by default, as some projects employ an
indenting policy to use only SPs and no HTs.

The kernel folks and git contributors may want to enable this
detection with:

	[core]
		whitespace = indent-with-non-tab

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/diff.c b/diff.c
index 211235376d..6bb902f4af 100644
--- a/diff.c
+++ b/diff.c
@@ -502,8 +502,11 @@ static void emit_line_with_ws(int nparents,
 	int i;
 	int tail = len;
 	int need_highlight_leading_space = 0;
-	/* The line is a newly added line.  Does it have funny leading
-	 * whitespaces?  In indent, SP should never precede a TAB.
+	/*
+	 * The line is a newly added line.  Does it have funny leading
+	 * whitespaces?  In indent, SP should never precede a TAB.  In
+	 * addition, under "indent with non tab" rule, there should not
+	 * be more than 8 consecutive spaces.
 	 */
 	for (i = col0; i < len; i++) {
 		if (line[i] == '\t') {
@@ -517,6 +520,13 @@ static void emit_line_with_ws(int nparents,
 		else
 			break;
 	}
+	if ((whitespace_rule & WS_INDENT_WITH_NON_TAB) &&
+	    0 <= last_space_in_indent &&
+	    last_tab_in_indent < 0 &&
+	    8 <= (i - col0)) {
+		last_tab_in_indent = i;
+		need_highlight_leading_space = 1;
+	}
 	fputs(set, stdout);
 	fwrite(line, col0, 1, stdout);
 	fputs(reset, stdout);