[PATCH 2/7] diff.c: add --output-indicator-{new, old, context}

[Stefan Beller <sbeller@google.com>]

This will prove useful in range-diff in a later patch as we will be able to
differentiate between adding a new file (that line is starting with +++
and then the file name) and regular new lines.

It could also be useful for experimentation in new patch formats, i.e.
we could teach git to emit moved lines with lines other than +/-.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 diff.c | 21 +++++++++++++++++----
 diff.h |  5 +++++
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/diff.c b/diff.c
index 57a8a38755e..2e711809700 100644
--- a/diff.c
+++ b/diff.c
@@ -1032,7 +1032,7 @@ static void emit_diff_symbol_from_struct(struct diff_options *o,
 					 struct emitted_diff_symbol *eds)
 {
 	static const char *nneof = " No newline at end of file\n";
-	const char *context, *reset, *set, *set_sign, *meta, *fraginfo;
+	const char *context, *reset, *set, *set_sign, *meta, *fraginfo, *first;
 	struct strbuf sb = STRBUF_INIT;
 
 	enum diff_symbol s = eds->s;
@@ -1083,7 +1083,9 @@ static void emit_diff_symbol_from_struct(struct diff_options *o,
 			else if (c == '-')
 				set = diff_get_color_opt(o, DIFF_FILE_OLD);
 		}
-		emit_line_ws_markup(o, set_sign, set, reset, " ", line, len,
+		first = o->output_indicators[OI_CONTEXT] ?
+			o->output_indicators[OI_CONTEXT] : " ";
+		emit_line_ws_markup(o, set_sign, set, reset, first, line, len,
 				    flags & (DIFF_SYMBOL_CONTENT_WS_MASK), 0);
 		break;
 	case DIFF_SYMBOL_PLUS:
@@ -1126,7 +1128,10 @@ static void emit_diff_symbol_from_struct(struct diff_options *o,
 				set = diff_get_color_opt(o, DIFF_CONTEXT_BOLD);
 			flags |= WS_IGNORE_FIRST_SPACE;
 		}
-		emit_line_ws_markup(o, set_sign, set, reset, "+", line, len,
+
+		first = o->output_indicators[OI_NEW] ?
+			o->output_indicators[OI_NEW] : "+";
+		emit_line_ws_markup(o, set_sign, set, reset, first, line, len,
 				    flags & DIFF_SYMBOL_CONTENT_WS_MASK,
 				    flags & DIFF_SYMBOL_CONTENT_BLANK_LINE_EOF);
 		break;
@@ -1169,7 +1174,9 @@ static void emit_diff_symbol_from_struct(struct diff_options *o,
 			else
 				set = diff_get_color_opt(o, DIFF_CONTEXT_DIM);
 		}
-		emit_line_ws_markup(o, set_sign, set, reset, "-", line, len,
+		first = o->output_indicators[OI_OLD] ?
+			o->output_indicators[OI_OLD] : "-";
+		emit_line_ws_markup(o, set_sign, set, reset, first, line, len,
 				    flags & DIFF_SYMBOL_CONTENT_WS_MASK, 0);
 		break;
 	case DIFF_SYMBOL_WORDS_PORCELAIN:
@@ -4670,6 +4677,12 @@ int diff_opt_parse(struct diff_options *options,
 		 options->output_format |= DIFF_FORMAT_DIFFSTAT;
 	} else if (!strcmp(arg, "--no-compact-summary"))
 		 options->flags.stat_with_summary = 0;
+	else if (skip_prefix(arg, "--output-indicator-new=", &arg))
+		options->output_indicators[OI_NEW] = arg;
+	else if (skip_prefix(arg, "--output-indicator-old=", &arg))
+		options->output_indicators[OI_OLD] = arg;
+	else if (skip_prefix(arg, "--output-indicator-context=", &arg))
+		options->output_indicators[OI_CONTEXT] = arg;
 
 	/* renames options */
 	else if (starts_with(arg, "-B") ||
diff --git a/diff.h b/diff.h
index a08a3b2a293..b8bbe7baeb8 100644
--- a/diff.h
+++ b/diff.h
@@ -194,6 +194,11 @@ struct diff_options {
 	FILE *file;
 	int close_file;
 
+#define OI_NEW 0
+#define OI_OLD 1
+#define OI_CONTEXT 2
+	const char *output_indicators[3];
+
 	struct pathspec pathspec;
 	pathchange_fn_t pathchange;
 	change_fn_t change;
-- 
2.18.0.597.ga71716f1ad-goog