graph: add support for --line-prefix on all graph-aware output

Add an extension to git-diff and git-log (and any other graph-aware
displayable output) such that "--line-prefix=<string>" will print the
additional line-prefix on every line of output.

To make this work, we have to fix a few bugs in the graph API that force
graph_show_commit_msg to be used only when you have a valid graph.
Additionally, we extend the default_diff_output_prefix handler to work
even when no graph is enabled.

This is somewhat of a hack on top of the graph API, but I think it
should be acceptable here.

This will be used by a future extension of submodule display which
displays the submodule diff as the actual diff between the pre and post
commit in the submodule project.

Add some tests for both git-log and git-diff to ensure that the prefix
is honored correctly.

Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/diff-options.txt

@@ -569,5 +569,8 @@ endif::git-format-patch[]
 --no-prefix::
 	Do not show any source or destination prefix.
 
+--line-prefix=<prefix>::
+	Prepend an additional prefix to every line of output.
+
 For more detailed explanation on these common options, see also
 linkgit:gitdiffcore[7].

builtin/rev-list.c

@@ -122,48 +122,40 @@ static void show_commit(struct commit *commit, void *data)
 		ctx.fmt = revs->commit_format;
 		ctx.output_encoding = get_log_output_encoding();
 		pretty_print_commit(&ctx, commit, &buf);
-		if (revs->graph) {
-			if (buf.len) {
-				if (revs->commit_format != CMIT_FMT_ONELINE)
-					graph_show_oneline(revs->graph);
-
-				graph_show_commit_msg(revs->graph, &buf);
-
-				/*
-				 * Add a newline after the commit message.
-				 *
-				 * Usually, this newline produces a blank
-				 * padding line between entries, in which case
-				 * we need to add graph padding on this line.
-				 *
-				 * However, the commit message may not end in a
-				 * newline.  In this case the newline simply
-				 * ends the last line of the commit message,
-				 * and we don't need any graph output.  (This
-				 * always happens with CMIT_FMT_ONELINE, and it
-				 * happens with CMIT_FMT_USERFORMAT when the
-				 * format doesn't explicitly end in a newline.)
-				 */
-				if (buf.len && buf.buf[buf.len - 1] == '\n')
-					graph_show_padding(revs->graph);
-				putchar('\n');
-			} else {
-				/*
-				 * If the message buffer is empty, just show
-				 * the rest of the graph output for this
-				 * commit.
-				 */
-				if (graph_show_remainder(revs->graph))
-					putchar('\n');
-				if (revs->commit_format == CMIT_FMT_ONELINE)
-					putchar('\n');
-			}
+		if (buf.len) {
+			if (revs->commit_format != CMIT_FMT_ONELINE)
+				graph_show_oneline(revs->graph);
+
+			graph_show_commit_msg(revs->graph, stdout, &buf);
+
+			/*
+			 * Add a newline after the commit message.
+			 *
+			 * Usually, this newline produces a blank
+			 * padding line between entries, in which case
+			 * we need to add graph padding on this line.
+			 *
+			 * However, the commit message may not end in a
+			 * newline.  In this case the newline simply
+			 * ends the last line of the commit message,
+			 * and we don't need any graph output.  (This
+			 * always happens with CMIT_FMT_ONELINE, and it
+			 * happens with CMIT_FMT_USERFORMAT when the
+			 * format doesn't explicitly end in a newline.)
+			 */
+			if (buf.len && buf.buf[buf.len - 1] == '\n')
+				graph_show_padding(revs->graph);
+			putchar('\n');
 		} else {
-			if (revs->commit_format != CMIT_FMT_USERFORMAT ||
-			    buf.len) {
-				fwrite(buf.buf, 1, buf.len, stdout);
-				putchar(info->hdr_termination);
-			}
+			/*
+			 * If the message buffer is empty, just show
+			 * the rest of the graph output for this
+			 * commit.
+			 */
+			if (graph_show_remainder(revs->graph))
+				putchar('\n');
+			if (revs->commit_format == CMIT_FMT_ONELINE)
+				putchar('\n');
 		}
 		strbuf_release(&buf);
 	} else {

diff.c

@@ -18,6 +18,7 @@
 #include "ll-merge.h"
 #include "string-list.h"
 #include "argv-array.h"
+#include "graph.h"
 
 #ifdef NO_FAST_WORKING_DIRECTORY
 #define FAST_WORKING_DIRECTORY 0
@@ -3966,6 +3967,12 @@ int diff_opt_parse(struct diff_options *options,
 		options->a_prefix = optarg;
 		return argcount;
 	}
+	else if ((argcount = parse_long_opt("line-prefix", av, &optarg))) {
+		options->line_prefix = optarg;
+		options->line_prefix_length = strlen(options->line_prefix);
+		graph_setup_line_prefix(options);
+		return argcount;
+	}
 	else if ((argcount = parse_long_opt("dst-prefix", av, &optarg))) {
 		options->b_prefix = optarg;
 		return argcount;

diff.h

@@ -115,6 +115,8 @@ struct diff_options {
 	const char *pickaxe;
 	const char *single_follow;
 	const char *a_prefix, *b_prefix;
+	const char *line_prefix;
+	size_t line_prefix_length;
 	unsigned flags;
 	unsigned touched_flags;
 

graph.c

@@ -2,7 +2,6 @@
 #include "commit.h"
 #include "color.h"
 #include "graph.h"
-#include "diff.h"
 #include "revision.h"
 
 /* Internal API */
@@ -28,8 +27,15 @@ static void graph_padding_line(struct git_graph *graph, struct strbuf *sb);
  * responsible for printing this line's graph (perhaps via
  * graph_show_commit() or graph_show_oneline()) before calling
  * graph_show_strbuf().
+ *
+ * Note that unlike some other graph display functions, you must pass the file
+ * handle directly. It is assumed that this is the same file handle as the
+ * file specified by the graph diff options. This is necessary so that
+ * graph_show_strbuf can be called even with a NULL graph.
  */
-static void graph_show_strbuf(struct git_graph *graph, struct strbuf const *sb);
+static void graph_show_strbuf(struct git_graph *graph,
+			      FILE *file,
+			      struct strbuf const *sb);
 
 /*
  * TODO:
@@ -59,6 +65,17 @@ enum graph_state {
 	GRAPH_COLLAPSING
 };
 
+static void graph_show_line_prefix(const struct diff_options *diffopt)
+{
+	if (!diffopt || !diffopt->line_prefix)
+		return;
+
+	fwrite(diffopt->line_prefix,
+	       sizeof(char),
+	       diffopt->line_prefix_length,
+	       diffopt->file);
+}
+
 static const char **column_colors;
 static unsigned short column_colors_max;
 
@@ -195,13 +212,28 @@ static struct strbuf *diff_output_prefix_callback(struct diff_options *opt, void
 	static struct strbuf msgbuf = STRBUF_INIT;
 
 	assert(opt);
-	assert(graph);
 
 	strbuf_reset(&msgbuf);
-	graph_padding_line(graph, &msgbuf);
+	if (opt->line_prefix)
+		strbuf_add(&msgbuf, opt->line_prefix,
+			   opt->line_prefix_length);
+	if (graph)
+		graph_padding_line(graph, &msgbuf);
 	return &msgbuf;
 }
 
+static const struct diff_options *default_diffopt;
+
+void graph_setup_line_prefix(struct diff_options *diffopt)
+{
+	default_diffopt = diffopt;
+
+	/* setup an output prefix callback if necessary */
+	if (diffopt && !diffopt->output_prefix)
+		diffopt->output_prefix = diff_output_prefix_callback;
+}
+
+
 struct git_graph *graph_init(struct rev_info *opt)
 {
 	struct git_graph *graph = xmalloc(sizeof(struct git_graph));
@@ -1183,6 +1215,8 @@ void graph_show_commit(struct git_graph *graph)
 	struct strbuf msgbuf = STRBUF_INIT;
 	int shown_commit_line = 0;
 
+	graph_show_line_prefix(default_diffopt);
+
 	if (!graph)
 		return;
 
@@ -1200,8 +1234,10 @@ void graph_show_commit(struct git_graph *graph)
 		shown_commit_line = graph_next_line(graph, &msgbuf);
 		fwrite(msgbuf.buf, sizeof(char), msgbuf.len,
 			graph->revs->diffopt.file);
-		if (!shown_commit_line)
+		if (!shown_commit_line) {
 			putc('\n', graph->revs->diffopt.file);
+			graph_show_line_prefix(&graph->revs->diffopt);
+		}
 		strbuf_setlen(&msgbuf, 0);
 	}
 
@@ -1212,6 +1248,8 @@ void graph_show_oneline(struct git_graph *graph)
 {
 	struct strbuf msgbuf = STRBUF_INIT;
 
+	graph_show_line_prefix(default_diffopt);
+
 	if (!graph)
 		return;
 
@@ -1224,6 +1262,8 @@ void graph_show_padding(struct git_graph *graph)
 {
 	struct strbuf msgbuf = STRBUF_INIT;
 
+	graph_show_line_prefix(default_diffopt);
+
 	if (!graph)
 		return;
 
@@ -1237,6 +1277,8 @@ int graph_show_remainder(struct git_graph *graph)
 	struct strbuf msgbuf = STRBUF_INIT;
 	int shown = 0;
 
+	graph_show_line_prefix(default_diffopt);
+
 	if (!graph)
 		return 0;
 
@@ -1250,27 +1292,24 @@ int graph_show_remainder(struct git_graph *graph)
 		strbuf_setlen(&msgbuf, 0);
 		shown = 1;
 
-		if (!graph_is_commit_finished(graph))
+		if (!graph_is_commit_finished(graph)) {
 			putc('\n', graph->revs->diffopt.file);
-		else
+			graph_show_line_prefix(&graph->revs->diffopt);
+		} else {
 			break;
+		}
 	}
 	strbuf_release(&msgbuf);
 
 	return shown;
 }
 
-
-static void graph_show_strbuf(struct git_graph *graph, struct strbuf const *sb)
+static void graph_show_strbuf(struct git_graph *graph,
+			      FILE *file,
+			      struct strbuf const *sb)
 {
 	char *p;
 
-	if (!graph) {
-		fwrite(sb->buf, sizeof(char), sb->len,
-			graph->revs->diffopt.file);
-		return;
-	}
-
 	/*
 	 * Print the strbuf line by line,
 	 * and display the graph info before each line but the first.
@@ -1285,37 +1324,28 @@ static void graph_show_strbuf(struct git_graph *graph, struct strbuf const *sb)
 		} else {
 			len = (sb->buf + sb->len) - p;
 		}
-		fwrite(p, sizeof(char), len, graph->revs->diffopt.file);
+		fwrite(p, sizeof(char), len, file);
 		if (next_p && *next_p != '\0')
 			graph_show_oneline(graph);
 		p = next_p;
 	}
 }
 
 void graph_show_commit_msg(struct git_graph *graph,
+			   FILE *file,
 			   struct strbuf const *sb)
 {
 	int newline_terminated;
 
-	if (!graph) {
-		/*
-		 * If there's no graph, just print the message buffer.
-		 *
-		 * The message buffer for CMIT_FMT_ONELINE and
-		 * CMIT_FMT_USERFORMAT are already missing a terminating
-		 * newline.  All of the other formats should have it.
-		 */
-		fwrite(sb->buf, sizeof(char), sb->len,
-			graph->revs->diffopt.file);
-		return;
-	}
-
-	newline_terminated = (sb->len && sb->buf[sb->len - 1] == '\n');
-
 	/*
 	 * Show the commit message
 	 */
-	graph_show_strbuf(graph, sb);
+	graph_show_strbuf(graph, file, sb);
+
+	if (!graph)
+		return;
+
+	newline_terminated = (sb->len && sb->buf[sb->len - 1] == '\n');
 
 	/*
 	 * If there is more output needed for this commit, show it now
@@ -1327,14 +1357,14 @@ void graph_show_commit_msg(struct git_graph *graph,
 		 * new line.
 		 */
 		if (!newline_terminated)
-			putc('\n', graph->revs->diffopt.file);
+			putc('\n', file);
 
 		graph_show_remainder(graph);
 
 		/*
 		 * If sb ends with a newline, our output should too.
 		 */
 		if (newline_terminated)
-			putc('\n', graph->revs->diffopt.file);
+			putc('\n', file);
 	}
 }

graph.h

@@ -1,9 +1,22 @@
 #ifndef GRAPH_H
 #define GRAPH_H
+#include "diff.h"
 
 /* A graph is a pointer to this opaque structure */
 struct git_graph;
 
+/*
+ * Called to setup global display of line_prefix diff option.
+ *
+ * Passed a diff_options structure which indicates the line_prefix and the
+ * file to output the prefix to. This is sort of a hack used so that the
+ * line_prefix will be honored by all flows which also honor "--graph"
+ * regardless of whether a graph has actually been setup. The normal graph
+ * flow will honor the exact diff_options passed, but a NULL graph will cause
+ * display of a line_prefix to stdout.
+ */
+void graph_setup_line_prefix(struct diff_options *diffopt);
+
 /*
  * Set up a custom scheme for column colors.
  *
@@ -113,7 +126,14 @@ int graph_show_remainder(struct git_graph *graph);
  * missing a terminating newline (including if it is empty), the output
  * printed by graph_show_commit_msg() will also be missing a terminating
  * newline.
+ *
+ * Note that unlike some other graph display functions, you must pass the file
+ * handle directly. It is assumed that this is the same file handle as the
+ * file specified by the graph diff options. This is necessary so that
+ * graph_show_commit_msg can be called even with a NULL graph.
  */
-void graph_show_commit_msg(struct git_graph *graph, struct strbuf const *sb);
+void graph_show_commit_msg(struct git_graph *graph,
+			   FILE *file,
+			   struct strbuf const *sb);
 
 #endif /* GRAPH_H */

log-tree.c

@@ -715,10 +715,7 @@ void show_log(struct rev_info *opt)
 	else
 		opt->missing_newline = 0;
 
-	if (opt->graph)
-		graph_show_commit_msg(opt->graph, &msgbuf);
-	else
-		fwrite(msgbuf.buf, sizeof(char), msgbuf.len, opt->diffopt.file);
+	graph_show_commit_msg(opt->graph, opt->diffopt.file, &msgbuf);
 	if (opt->use_terminator && !commit_format_is_empty(opt->commit_format)) {
 		if (!opt->missing_newline)
 			graph_show_padding(opt->graph);