[PATCH v3 16/20] range-diff --dual-color: work around bogus white-space warning

From: Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>
Date: May 3, 2018, 01:11 UTC
Message-ID: <dfa7b1e71f7a39dfa608e1e205579d3b95d8a34f.1530617166.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.1.v3.git.gitgitgadget@gmail.com>

From: Johannes Schindelin <johannes.schindelin@gmx.de>

When displaying a diff of diffs, it is possible that there is an outer `+` before a context line. That happens when the context changed between old and new commit. When that context line starts with a tab (after the space that marks it as context line), our diff machinery spits out a white-space error (space before tab), but in this case, that is incorrect.

Work around this by detecting that situation and simply *not* printing the space in that case.

This is slightly improper a fix because it is conceivable that an output_prefix might be configured with *just* the right length to let that tab jump to a different tab stop depending whether we emit that space or not.

However, the proper fix would be relatively ugly and intrusive because it would have to *weaken* the WS_SPACE_BEFORE_TAB option in ws.c. Besides, we do not expose the --dual-color option in cases other than the `git range-diff` command, which only uses a hard-coded output_prefix of four spaces (which misses the problem by one column... ;-)).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 diff.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/diff.c b/diff.c
index 26445ffa1..325007167 100644
--- a/diff.c
+++ b/diff.c
@@ -1093,6 +1093,12 @@ static void emit_diff_symbol_from_struct(struct diff_options *o,
 				set = diff_get_color_opt(o, DIFF_FRAGINFO);
 			else if (c != '+')
 				set = diff_get_color_opt(o, DIFF_CONTEXT);
+			/* Avoid space-before-tab warning */
+			if (c == ' ' && (len < 2 || line[1] == '\t' ||
+					 line[1] == '\r' || line[1] == '\n')) {
+				line++;
+				len--;
+			}
 		}
 		emit_line_ws_markup(o, set, reset, line, len, set_sign, '+',
 				    flags & DIFF_SYMBOL_CONTENT_WS_MASK,

-- 
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