Adding upstream version 1:2.30.2.upstream/1%2.30.2upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1536 insertions, 0 deletions

diff --git a/graph.c b/graph.c
new file mode 100644
index 0000000..c128ad0
--- /dev/null
+++ b/graph.c
@@ -0,0 +1,1536 @@
+#include "cache.h"
+#include "config.h"
+#include "commit.h"
+#include "color.h"
+#include "graph.h"
+#include "revision.h"
+#include "strvec.h"
+
+/* Internal API */
+
+/*
+ * Output a padding line in the graph.
+ * This is similar to graph_next_line().  However, it is guaranteed to
+ * never print the current commit line.  Instead, if the commit line is
+ * next, it will simply output a line of vertical padding, extending the
+ * branch lines downwards, but leaving them otherwise unchanged.
+ */
+static void graph_padding_line(struct git_graph *graph, struct strbuf *sb);
+
+/*
+ * Print a strbuf.  If the graph is non-NULL, all lines but the first will be
+ * prefixed with the graph output.
+ *
+ * If the strbuf ends with a newline, the output will end after this
+ * newline.  A new graph line will not be printed after the final newline.
+ * If the strbuf is empty, no output will be printed.
+ *
+ * Since the first line will not include the graph output, the caller is
+ * 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.
+ * If a NULL graph is supplied, the strbuf is printed as-is.
+ */
+static void graph_show_strbuf(struct git_graph *graph,
+			      FILE *file,
+			      struct strbuf const *sb);
+
+/*
+ * TODO:
+ * - Limit the number of columns, similar to the way gitk does.
+ *   If we reach more than a specified number of columns, omit
+ *   sections of some columns.
+ */
+
+struct column {
+	/*
+	 * The parent commit of this column.
+	 */
+	struct commit *commit;
+	/*
+	 * The color to (optionally) print this column in.  This is an
+	 * index into column_colors.
+	 */
+	unsigned short color;
+};
+
+enum graph_state {
+	GRAPH_PADDING,
+	GRAPH_SKIP,
+	GRAPH_PRE_COMMIT,
+	GRAPH_COMMIT,
+	GRAPH_POST_MERGE,
+	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;
+
+static void parse_graph_colors_config(struct strvec *colors, const char *string)
+{
+	const char *end, *start;
+
+	start = string;
+	end = string + strlen(string);
+	while (start < end) {
+		const char *comma = strchrnul(start, ',');
+		char color[COLOR_MAXLEN];
+
+		if (!color_parse_mem(start, comma - start, color))
+			strvec_push(colors, color);
+		else
+			warning(_("ignore invalid color '%.*s' in log.graphColors"),
+				(int)(comma - start), start);
+		start = comma + 1;
+	}
+	strvec_push(colors, GIT_COLOR_RESET);
+}
+
+void graph_set_column_colors(const char **colors, unsigned short colors_max)
+{
+	column_colors = colors;
+	column_colors_max = colors_max;
+}
+
+static const char *column_get_color_code(unsigned short color)
+{
+	return column_colors[color];
+}
+
+struct graph_line {
+	struct strbuf *buf;
+	size_t width;
+};
+
+static inline void graph_line_addch(struct graph_line *line, int c)
+{
+	strbuf_addch(line->buf, c);
+	line->width++;
+}
+
+static inline void graph_line_addchars(struct graph_line *line, int c, size_t n)
+{
+	strbuf_addchars(line->buf, c, n);
+	line->width += n;
+}
+
+static inline void graph_line_addstr(struct graph_line *line, const char *s)
+{
+	strbuf_addstr(line->buf, s);
+	line->width += strlen(s);
+}
+
+static inline void graph_line_addcolor(struct graph_line *line, unsigned short color)
+{
+	strbuf_addstr(line->buf, column_get_color_code(color));
+}
+
+static void graph_line_write_column(struct graph_line *line, const struct column *c,
+				    char col_char)
+{
+	if (c->color < column_colors_max)
+		graph_line_addcolor(line, c->color);
+	graph_line_addch(line, col_char);
+	if (c->color < column_colors_max)
+		graph_line_addcolor(line, column_colors_max);
+}
+
+struct git_graph {
+	/*
+	 * The commit currently being processed
+	 */
+	struct commit *commit;
+	/* The rev-info used for the current traversal */
+	struct rev_info *revs;
+	/*
+	 * The number of interesting parents that this commit has.
+	 *
+	 * Note that this is not the same as the actual number of parents.
+	 * This count excludes parents that won't be printed in the graph
+	 * output, as determined by graph_is_interesting().
+	 */
+	int num_parents;
+	/*
+	 * The width of the graph output for this commit.
+	 * All rows for this commit are padded to this width, so that
+	 * messages printed after the graph output are aligned.
+	 */
+	int width;
+	/*
+	 * The next expansion row to print
+	 * when state is GRAPH_PRE_COMMIT
+	 */
+	int expansion_row;
+	/*
+	 * The current output state.
+	 * This tells us what kind of line graph_next_line() should output.
+	 */
+	enum graph_state state;
+	/*
+	 * The output state for the previous line of output.
+	 * This is primarily used to determine how the first merge line
+	 * should appear, based on the last line of the previous commit.
+	 */
+	enum graph_state prev_state;
+	/*
+	 * The index of the column that refers to this commit.
+	 *
+	 * If none of the incoming columns refer to this commit,
+	 * this will be equal to num_columns.
+	 */
+	int commit_index;
+	/*
+	 * The commit_index for the previously displayed commit.
+	 *
+	 * This is used to determine how the first line of a merge
+	 * graph output should appear, based on the last line of the
+	 * previous commit.
+	 */
+	int prev_commit_index;
+	/*
+	 * Which layout variant to use to display merge commits. If the
+	 * commit's first parent is known to be in a column to the left of the
+	 * merge, then this value is 0 and we use the layout on the left.
+	 * Otherwise, the value is 1 and the layout on the right is used. This
+	 * field tells us how many columns the first parent occupies.
+	 *
+	 * 		0)			1)
+	 *
+	 * 		| | | *-.		| | *---.
+	 * 		| |_|/|\ \		| | |\ \ \
+	 * 		|/| | | | |		| | | | | *
+	 */
+	int merge_layout;
+	/*
+	 * The number of columns added to the graph by the current commit. For
+	 * 2-way and octopus merges, this is usually one less than the
+	 * number of parents:
+	 *
+	 * 		| | |			| |    \
+	 *		| * |			| *---. \
+	 *		| |\ \			| |\ \ \ \
+	 *		| | | |         	| | | | | |
+	 *
+	 *		num_parents: 2		num_parents: 4
+	 *		edges_added: 1		edges_added: 3
+	 *
+	 * For left-skewed merges, the first parent fuses with its neighbor and
+	 * so one less column is added:
+	 *
+	 *		| | |			| |  \
+	 *		| * |			| *-. \
+	 *		|/| |			|/|\ \ \
+	 *		| | |			| | | | |
+	 *
+	 *		num_parents: 2		num_parents: 4
+	 *		edges_added: 0		edges_added: 2
+	 *
+	 * This number determines how edges to the right of the merge are
+	 * displayed in commit and post-merge lines; if no columns have been
+	 * added then a vertical line should be used where a right-tracking
+	 * line would otherwise be used.
+	 *
+	 *		| * \			| * |
+	 *		| |\ \			|/| |
+	 *		| | * \			| * |
+	 */
+	int edges_added;
+	/*
+	 * The number of columns added by the previous commit, which is used to
+	 * smooth edges appearing to the right of a commit in a commit line
+	 * following a post-merge line.
+	 */
+	int prev_edges_added;
+	/*
+	 * The maximum number of columns that can be stored in the columns
+	 * and new_columns arrays.  This is also half the number of entries
+	 * that can be stored in the mapping and old_mapping arrays.
+	 */
+	int column_capacity;
+	/*
+	 * The number of columns (also called "branch lines" in some places)
+	 */
+	int num_columns;
+	/*
+	 * The number of columns in the new_columns array
+	 */
+	int num_new_columns;
+	/*
+	 * The number of entries in the mapping array
+	 */
+	int mapping_size;
+	/*
+	 * The column state before we output the current commit.
+	 */
+	struct column *columns;
+	/*
+	 * The new column state after we output the current commit.
+	 * Only valid when state is GRAPH_COLLAPSING.
+	 */
+	struct column *new_columns;
+	/*
+	 * An array that tracks the current state of each
+	 * character in the output line during state GRAPH_COLLAPSING.
+	 * Each entry is -1 if this character is empty, or a non-negative
+	 * integer if the character contains a branch line.  The value of
+	 * the integer indicates the target position for this branch line.
+	 * (I.e., this array maps the current column positions to their
+	 * desired positions.)
+	 *
+	 * The maximum capacity of this array is always
+	 * sizeof(int) * 2 * column_capacity.
+	 */
+	int *mapping;
+	/*
+	 * A copy of the contents of the mapping array from the last commit,
+	 * which we use to improve the display of columns that are tracking
+	 * from right to left through a commit line.  We also use this to
+	 * avoid allocating a fresh array when we compute the next mapping.
+	 */
+	int *old_mapping;
+	/*
+	 * The current default column color being used.  This is
+	 * stored as an index into the array column_colors.
+	 */
+	unsigned short default_column_color;
+};
+
+static struct strbuf *diff_output_prefix_callback(struct diff_options *opt, void *data)
+{
+	struct git_graph *graph = data;
+	static struct strbuf msgbuf = STRBUF_INIT;
+
+	assert(opt);
+
+	strbuf_reset(&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));
+
+	if (!column_colors) {
+		char *string;
+		if (git_config_get_string("log.graphcolors", &string)) {
+			/* not configured -- use default */
+			graph_set_column_colors(column_colors_ansi,
+						column_colors_ansi_max);
+		} else {
+			static struct strvec custom_colors = STRVEC_INIT;
+			strvec_clear(&custom_colors);
+			parse_graph_colors_config(&custom_colors, string);
+			free(string);
+			/* graph_set_column_colors takes a max-index, not a count */
+			graph_set_column_colors(custom_colors.v,
+						custom_colors.nr - 1);
+		}
+	}
+
+	graph->commit = NULL;
+	graph->revs = opt;
+	graph->num_parents = 0;
+	graph->expansion_row = 0;
+	graph->state = GRAPH_PADDING;
+	graph->prev_state = GRAPH_PADDING;
+	graph->commit_index = 0;
+	graph->prev_commit_index = 0;
+	graph->merge_layout = 0;
+	graph->edges_added = 0;
+	graph->prev_edges_added = 0;
+	graph->num_columns = 0;
+	graph->num_new_columns = 0;
+	graph->mapping_size = 0;
+	/*
+	 * Start the column color at the maximum value, since we'll
+	 * always increment it for the first commit we output.
+	 * This way we start at 0 for the first commit.
+	 */
+	graph->default_column_color = column_colors_max - 1;
+
+	/*
+	 * Allocate a reasonably large default number of columns
+	 * We'll automatically grow columns later if we need more room.
+	 */
+	graph->column_capacity = 30;
+	ALLOC_ARRAY(graph->columns, graph->column_capacity);
+	ALLOC_ARRAY(graph->new_columns, graph->column_capacity);
+	ALLOC_ARRAY(graph->mapping, 2 * graph->column_capacity);
+	ALLOC_ARRAY(graph->old_mapping, 2 * graph->column_capacity);
+
+	/*
+	 * The diff output prefix callback, with this we can make
+	 * all the diff output to align with the graph lines.
+	 */
+	opt->diffopt.output_prefix = diff_output_prefix_callback;
+	opt->diffopt.output_prefix_data = graph;
+
+	return graph;
+}
+
+static void graph_update_state(struct git_graph *graph, enum graph_state s)
+{
+	graph->prev_state = graph->state;
+	graph->state = s;
+}
+
+static void graph_ensure_capacity(struct git_graph *graph, int num_columns)
+{
+	if (graph->column_capacity >= num_columns)
+		return;
+
+	do {
+		graph->column_capacity *= 2;
+	} while (graph->column_capacity < num_columns);
+
+	REALLOC_ARRAY(graph->columns, graph->column_capacity);
+	REALLOC_ARRAY(graph->new_columns, graph->column_capacity);
+	REALLOC_ARRAY(graph->mapping, graph->column_capacity * 2);
+	REALLOC_ARRAY(graph->old_mapping, graph->column_capacity * 2);
+}
+
+/*
+ * Returns 1 if the commit will be printed in the graph output,
+ * and 0 otherwise.
+ */
+static int graph_is_interesting(struct git_graph *graph, struct commit *commit)
+{
+	/*
+	 * If revs->boundary is set, commits whose children have
+	 * been shown are always interesting, even if they have the
+	 * UNINTERESTING or TREESAME flags set.
+	 */
+	if (graph->revs && graph->revs->boundary) {
+		if (commit->object.flags & CHILD_SHOWN)
+			return 1;
+	}
+
+	/*
+	 * Otherwise, use get_commit_action() to see if this commit is
+	 * interesting
+	 */
+	return get_commit_action(graph->revs, commit) == commit_show;
+}
+
+static struct commit_list *next_interesting_parent(struct git_graph *graph,
+						   struct commit_list *orig)
+{
+	struct commit_list *list;
+
+	/*
+	 * If revs->first_parent_only is set, only the first
+	 * parent is interesting.  None of the others are.
+	 */
+	if (graph->revs->first_parent_only)
+		return NULL;
+
+	/*
+	 * Return the next interesting commit after orig
+	 */
+	for (list = orig->next; list; list = list->next) {
+		if (graph_is_interesting(graph, list->item))
+			return list;
+	}
+
+	return NULL;
+}
+
+static struct commit_list *first_interesting_parent(struct git_graph *graph)
+{
+	struct commit_list *parents = graph->commit->parents;
+
+	/*
+	 * If this commit has no parents, ignore it
+	 */
+	if (!parents)
+		return NULL;
+
+	/*
+	 * If the first parent is interesting, return it
+	 */
+	if (graph_is_interesting(graph, parents->item))
+		return parents;
+
+	/*
+	 * Otherwise, call next_interesting_parent() to get
+	 * the next interesting parent
+	 */
+	return next_interesting_parent(graph, parents);
+}
+
+static unsigned short graph_get_current_column_color(const struct git_graph *graph)
+{
+	if (!want_color(graph->revs->diffopt.use_color))
+		return column_colors_max;
+	return graph->default_column_color;
+}
+
+/*
+ * Update the graph's default column color.
+ */
+static void graph_increment_column_color(struct git_graph *graph)
+{
+	graph->default_column_color = (graph->default_column_color + 1) %
+		column_colors_max;
+}
+
+static unsigned short graph_find_commit_color(const struct git_graph *graph,
+					      const struct commit *commit)
+{
+	int i;
+	for (i = 0; i < graph->num_columns; i++) {
+		if (graph->columns[i].commit == commit)
+			return graph->columns[i].color;
+	}
+	return graph_get_current_column_color(graph);
+}
+
+static int graph_find_new_column_by_commit(struct git_graph *graph,
+					   struct commit *commit)
+{
+	int i;
+	for (i = 0; i < graph->num_new_columns; i++) {
+		if (graph->new_columns[i].commit == commit)
+			return i;
+	}
+	return -1;
+}
+
+static void graph_insert_into_new_columns(struct git_graph *graph,
+					  struct commit *commit,
+					  int idx)
+{
+	int i = graph_find_new_column_by_commit(graph, commit);
+	int mapping_idx;
+
+	/*
+	 * If the commit is not already in the new_columns array, then add it
+	 * and record it as being in the final column.
+	 */
+	if (i < 0) {
+		i = graph->num_new_columns++;
+		graph->new_columns[i].commit = commit;
+		graph->new_columns[i].color = graph_find_commit_color(graph, commit);
+	}
+
+	if (graph->num_parents > 1 && idx > -1 && graph->merge_layout == -1) {
+		/*
+		 * If this is the first parent of a merge, choose a layout for
+		 * the merge line based on whether the parent appears in a
+		 * column to the left of the merge
+		 */
+		int dist, shift;
+
+		dist = idx - i;
+		shift = (dist > 1) ? 2 * dist - 3 : 1;
+
+		graph->merge_layout = (dist > 0) ? 0 : 1;
+		graph->edges_added = graph->num_parents + graph->merge_layout  - 2;
+
+		mapping_idx = graph->width + (graph->merge_layout - 1) * shift;
+		graph->width += 2 * graph->merge_layout;
+
+	} else if (graph->edges_added > 0 && i == graph->mapping[graph->width - 2]) {
+		/*
+		 * If some columns have been added by a merge, but this commit
+		 * was found in the last existing column, then adjust the
+		 * numbers so that the two edges immediately join, i.e.:
+		 *
+		 *		* |		* |
+		 *		|\ \	=>	|\|
+		 *		| |/		| *
+		 *		| *
+		 */
+		mapping_idx = graph->width - 2;
+		graph->edges_added = -1;
+	} else {
+		mapping_idx = graph->width;
+		graph->width += 2;
+	}
+
+	graph->mapping[mapping_idx] = i;
+}
+
+static void graph_update_columns(struct git_graph *graph)
+{
+	struct commit_list *parent;
+	int max_new_columns;
+	int i, seen_this, is_commit_in_columns;
+
+	/*
+	 * Swap graph->columns with graph->new_columns
+	 * graph->columns contains the state for the previous commit,
+	 * and new_columns now contains the state for our commit.
+	 *
+	 * We'll re-use the old columns array as storage to compute the new
+	 * columns list for the commit after this one.
+	 */
+	SWAP(graph->columns, graph->new_columns);
+	graph->num_columns = graph->num_new_columns;
+	graph->num_new_columns = 0;
+
+	/*
+	 * Now update new_columns and mapping with the information for the
+	 * commit after this one.
+	 *
+	 * First, make sure we have enough room.  At most, there will
+	 * be graph->num_columns + graph->num_parents columns for the next
+	 * commit.
+	 */
+	max_new_columns = graph->num_columns + graph->num_parents;
+	graph_ensure_capacity(graph, max_new_columns);
+
+	/*
+	 * Clear out graph->mapping
+	 */
+	graph->mapping_size = 2 * max_new_columns;
+	for (i = 0; i < graph->mapping_size; i++)
+		graph->mapping[i] = -1;
+
+	graph->width = 0;
+	graph->prev_edges_added = graph->edges_added;
+	graph->edges_added = 0;
+
+	/*
+	 * Populate graph->new_columns and graph->mapping
+	 *
+	 * Some of the parents of this commit may already be in
+	 * graph->columns.  If so, graph->new_columns should only contain a
+	 * single entry for each such commit.  graph->mapping should
+	 * contain information about where each current branch line is
+	 * supposed to end up after the collapsing is performed.
+	 */
+	seen_this = 0;
+	is_commit_in_columns = 1;
+	for (i = 0; i <= graph->num_columns; i++) {
+		struct commit *col_commit;
+		if (i == graph->num_columns) {
+			if (seen_this)
+				break;
+			is_commit_in_columns = 0;
+			col_commit = graph->commit;
+		} else {
+			col_commit = graph->columns[i].commit;
+		}
+
+		if (col_commit == graph->commit) {
+			seen_this = 1;
+			graph->commit_index = i;
+			graph->merge_layout = -1;
+			for (parent = first_interesting_parent(graph);
+			     parent;
+			     parent = next_interesting_parent(graph, parent)) {
+				/*
+				 * If this is a merge, or the start of a new
+				 * childless column, increment the current
+				 * color.
+				 */
+				if (graph->num_parents > 1 ||
+				    !is_commit_in_columns) {
+					graph_increment_column_color(graph);
+				}
+				graph_insert_into_new_columns(graph, parent->item, i);
+			}
+			/*
+			 * We always need to increment graph->width by at
+			 * least 2, even if it has no interesting parents.
+			 * The current commit always takes up at least 2
+			 * spaces.
+			 */
+			if (graph->num_parents == 0)
+				graph->width += 2;
+		} else {
+			graph_insert_into_new_columns(graph, col_commit, -1);
+		}
+	}
+
+	/*
+	 * Shrink mapping_size to be the minimum necessary
+	 */
+	while (graph->mapping_size > 1 &&
+	       graph->mapping[graph->mapping_size - 1] < 0)
+		graph->mapping_size--;
+}
+
+static int graph_num_dashed_parents(struct git_graph *graph)
+{
+	return graph->num_parents + graph->merge_layout - 3;
+}
+
+static int graph_num_expansion_rows(struct git_graph *graph)
+{
+	/*
+	 * Normally, we need two expansion rows for each dashed parent line from
+	 * an octopus merge:
+	 *
+	 * 		| *
+	 * 		| |\
+	 * 		| | \
+	 * 		| |  \
+	 * 		| *-. \
+	 * 		| |\ \ \
+	 *
+	 * If the merge is skewed to the left, then its parents occupy one less
+	 * column, and we don't need as many expansion rows to route around it;
+	 * in some cases that means we don't need any expansion rows at all:
+	 *
+	 * 		| *
+	 * 		| |\
+	 * 		| * \
+	 * 		|/|\ \
+	 */
+	return graph_num_dashed_parents(graph) * 2;
+}
+
+static int graph_needs_pre_commit_line(struct git_graph *graph)
+{
+	return graph->num_parents >= 3 &&
+	       graph->commit_index < (graph->num_columns - 1) &&
+	       graph->expansion_row < graph_num_expansion_rows(graph);
+}
+
+void graph_update(struct git_graph *graph, struct commit *commit)
+{
+	struct commit_list *parent;
+
+	/*
+	 * Set the new commit
+	 */
+	graph->commit = commit;
+
+	/*
+	 * Count how many interesting parents this commit has
+	 */
+	graph->num_parents = 0;
+	for (parent = first_interesting_parent(graph);
+	     parent;
+	     parent = next_interesting_parent(graph, parent))
+	{
+		graph->num_parents++;
+	}
+
+	/*
+	 * Store the old commit_index in prev_commit_index.
+	 * graph_update_columns() will update graph->commit_index for this
+	 * commit.
+	 */
+	graph->prev_commit_index = graph->commit_index;
+
+	/*
+	 * Call graph_update_columns() to update
+	 * columns, new_columns, and mapping.
+	 */
+	graph_update_columns(graph);
+
+	graph->expansion_row = 0;
+
+	/*
+	 * Update graph->state.
+	 * Note that we don't call graph_update_state() here, since
+	 * we don't want to update graph->prev_state.  No line for
+	 * graph->state was ever printed.
+	 *
+	 * If the previous commit didn't get to the GRAPH_PADDING state,
+	 * it never finished its output.  Goto GRAPH_SKIP, to print out
+	 * a line to indicate that portion of the graph is missing.
+	 *
+	 * If there are 3 or more parents, we may need to print extra rows
+	 * before the commit, to expand the branch lines around it and make
+	 * room for it.  We need to do this only if there is a branch row
+	 * (or more) to the right of this commit.
+	 *
+	 * If there are less than 3 parents, we can immediately print the
+	 * commit line.
+	 */
+	if (graph->state != GRAPH_PADDING)
+		graph->state = GRAPH_SKIP;
+	else if (graph_needs_pre_commit_line(graph))
+		graph->state = GRAPH_PRE_COMMIT;
+	else
+		graph->state = GRAPH_COMMIT;
+}
+
+static int graph_is_mapping_correct(struct git_graph *graph)
+{
+	int i;
+
+	/*
+	 * The mapping is up to date if each entry is at its target,
+	 * or is 1 greater than its target.
+	 * (If it is 1 greater than the target, '/' will be printed, so it
+	 * will look correct on the next row.)
+	 */
+	for (i = 0; i < graph->mapping_size; i++) {
+		int target = graph->mapping[i];
+		if (target < 0)
+			continue;
+		if (target == (i / 2))
+			continue;
+		return 0;
+	}
+
+	return 1;
+}
+
+static void graph_pad_horizontally(struct git_graph *graph, struct graph_line *line)
+{
+	/*
+	 * Add additional spaces to the end of the strbuf, so that all
+	 * lines for a particular commit have the same width.
+	 *
+	 * This way, fields printed to the right of the graph will remain
+	 * aligned for the entire commit.
+	 */
+	if (line->width < graph->width)
+		graph_line_addchars(line, ' ', graph->width - line->width);
+}
+
+static void graph_output_padding_line(struct git_graph *graph,
+				      struct graph_line *line)
+{
+	int i;
+
+	/*
+	 * Output a padding row, that leaves all branch lines unchanged
+	 */
+	for (i = 0; i < graph->num_new_columns; i++) {
+		graph_line_write_column(line, &graph->new_columns[i], '|');
+		graph_line_addch(line, ' ');
+	}
+}
+
+
+int graph_width(struct git_graph *graph)
+{
+	return graph->width;
+}
+
+
+static void graph_output_skip_line(struct git_graph *graph, struct graph_line *line)
+{
+	/*
+	 * Output an ellipsis to indicate that a portion
+	 * of the graph is missing.
+	 */
+	graph_line_addstr(line, "...");
+
+	if (graph_needs_pre_commit_line(graph))
+		graph_update_state(graph, GRAPH_PRE_COMMIT);
+	else
+		graph_update_state(graph, GRAPH_COMMIT);
+}
+
+static void graph_output_pre_commit_line(struct git_graph *graph,
+					 struct graph_line *line)
+{
+	int i, seen_this;
+
+	/*
+	 * This function formats a row that increases the space around a commit
+	 * with multiple parents, to make room for it.  It should only be
+	 * called when there are 3 or more parents.
+	 *
+	 * We need 2 extra rows for every parent over 2.
+	 */
+	assert(graph->num_parents >= 3);
+
+	/*
+	 * graph->expansion_row tracks the current expansion row we are on.
+	 * It should be in the range [0, num_expansion_rows - 1]
+	 */
+	assert(0 <= graph->expansion_row &&
+	       graph->expansion_row < graph_num_expansion_rows(graph));
+
+	/*
+	 * Output the row
+	 */
+	seen_this = 0;
+	for (i = 0; i < graph->num_columns; i++) {
+		struct column *col = &graph->columns[i];
+		if (col->commit == graph->commit) {
+			seen_this = 1;
+			graph_line_write_column(line, col, '|');
+			graph_line_addchars(line, ' ', graph->expansion_row);
+		} else if (seen_this && (graph->expansion_row == 0)) {
+			/*
+			 * This is the first line of the pre-commit output.
+			 * If the previous commit was a merge commit and
+			 * ended in the GRAPH_POST_MERGE state, all branch
+			 * lines after graph->prev_commit_index were
+			 * printed as "\" on the previous line.  Continue
+			 * to print them as "\" on this line.  Otherwise,
+			 * print the branch lines as "|".
+			 */
+			if (graph->prev_state == GRAPH_POST_MERGE &&
+			    graph->prev_commit_index < i)
+				graph_line_write_column(line, col, '\\');
+			else
+				graph_line_write_column(line, col, '|');
+		} else if (seen_this && (graph->expansion_row > 0)) {
+			graph_line_write_column(line, col, '\\');
+		} else {
+			graph_line_write_column(line, col, '|');
+		}
+		graph_line_addch(line, ' ');
+	}
+
+	/*
+	 * Increment graph->expansion_row,
+	 * and move to state GRAPH_COMMIT if necessary
+	 */
+	graph->expansion_row++;
+	if (!graph_needs_pre_commit_line(graph))
+		graph_update_state(graph, GRAPH_COMMIT);
+}
+
+static void graph_output_commit_char(struct git_graph *graph, struct graph_line *line)
+{
+	/*
+	 * For boundary commits, print 'o'
+	 * (We should only see boundary commits when revs->boundary is set.)
+	 */
+	if (graph->commit->object.flags & BOUNDARY) {
+		assert(graph->revs->boundary);
+		graph_line_addch(line, 'o');
+		return;
+	}
+
+	/*
+	 * get_revision_mark() handles all other cases without assert()
+	 */
+	graph_line_addstr(line, get_revision_mark(graph->revs, graph->commit));
+}
+
+/*
+ * Draw the horizontal dashes of an octopus merge.
+ */
+static void graph_draw_octopus_merge(struct git_graph *graph, struct graph_line *line)
+{
+	/*
+	 * The parents of a merge commit can be arbitrarily reordered as they
+	 * are mapped onto display columns, for example this is a valid merge:
+	 *
+	 *	| | *---.
+	 *	| | |\ \ \
+	 *	| | |/ / /
+	 *	| |/| | /
+	 *	| |_|_|/
+	 *	|/| | |
+	 *	3 1 0 2
+	 *
+	 * The numbers denote which parent of the merge each visual column
+	 * corresponds to; we can't assume that the parents will initially
+	 * display in the order given by new_columns.
+	 *
+	 * To find the right color for each dash, we need to consult the
+	 * mapping array, starting from the column 2 places to the right of the
+	 * merge commit, and use that to find out which logical column each
+	 * edge will collapse to.
+	 *
+	 * Commits are rendered once all edges have collapsed to their correct
+	 * logcial column, so commit_index gives us the right visual offset for
+	 * the merge commit.
+	 */
+
+	int i, j;
+	struct column *col;
+
+	int dashed_parents = graph_num_dashed_parents(graph);
+
+	for (i = 0; i < dashed_parents; i++) {
+		j = graph->mapping[(graph->commit_index + i + 2) * 2];
+		col = &graph->new_columns[j];
+
+		graph_line_write_column(line, col, '-');
+		graph_line_write_column(line, col, (i == dashed_parents - 1) ? '.' : '-');
+	}
+
+	return;
+}
+
+static void graph_output_commit_line(struct git_graph *graph, struct graph_line *line)
+{
+	int seen_this = 0;
+	int i;
+
+	/*
+	 * Output the row containing this commit
+	 * Iterate up to and including graph->num_columns,
+	 * since the current commit may not be in any of the existing
+	 * columns.  (This happens when the current commit doesn't have any
+	 * children that we have already processed.)
+	 */
+	seen_this = 0;
+	for (i = 0; i <= graph->num_columns; i++) {
+		struct column *col = &graph->columns[i];
+		struct commit *col_commit;
+		if (i == graph->num_columns) {
+			if (seen_this)
+				break;
+			col_commit = graph->commit;
+		} else {
+			col_commit = graph->columns[i].commit;
+		}
+
+		if (col_commit == graph->commit) {
+			seen_this = 1;
+			graph_output_commit_char(graph, line);
+
+			if (graph->num_parents > 2)
+				graph_draw_octopus_merge(graph, line);
+		} else if (seen_this && (graph->edges_added > 1)) {
+			graph_line_write_column(line, col, '\\');
+		} else if (seen_this && (graph->edges_added == 1)) {
+			/*
+			 * This is either a right-skewed 2-way merge
+			 * commit, or a left-skewed 3-way merge.
+			 * There is no GRAPH_PRE_COMMIT stage for such
+			 * merges, so this is the first line of output
+			 * for this commit.  Check to see what the previous
+			 * line of output was.
+			 *
+			 * If it was GRAPH_POST_MERGE, the branch line
+			 * coming into this commit may have been '\',
+			 * and not '|' or '/'.  If so, output the branch
+			 * line as '\' on this line, instead of '|'.  This
+			 * makes the output look nicer.
+			 */
+			if (graph->prev_state == GRAPH_POST_MERGE &&
+			    graph->prev_edges_added > 0 &&
+			    graph->prev_commit_index < i)
+				graph_line_write_column(line, col, '\\');
+			else
+				graph_line_write_column(line, col, '|');
+		} else if (graph->prev_state == GRAPH_COLLAPSING &&
+			   graph->old_mapping[2 * i + 1] == i &&
+			   graph->mapping[2 * i] < i) {
+			graph_line_write_column(line, col, '/');
+		} else {
+			graph_line_write_column(line, col, '|');
+		}
+		graph_line_addch(line, ' ');
+	}
+
+	/*
+	 * Update graph->state
+	 */
+	if (graph->num_parents > 1)
+		graph_update_state(graph, GRAPH_POST_MERGE);
+	else if (graph_is_mapping_correct(graph))
+		graph_update_state(graph, GRAPH_PADDING);
+	else
+		graph_update_state(graph, GRAPH_COLLAPSING);
+}
+
+static const char merge_chars[] = {'/', '|', '\\'};
+
+static void graph_output_post_merge_line(struct git_graph *graph, struct graph_line *line)
+{
+	int seen_this = 0;
+	int i, j;
+
+	struct commit_list *first_parent = first_interesting_parent(graph);
+	struct column *parent_col = NULL;
+
+	/*
+	 * Output the post-merge row
+	 */
+	for (i = 0; i <= graph->num_columns; i++) {
+		struct column *col = &graph->columns[i];
+		struct commit *col_commit;
+		if (i == graph->num_columns) {
+			if (seen_this)
+				break;
+			col_commit = graph->commit;
+		} else {
+			col_commit = col->commit;
+		}
+
+		if (col_commit == graph->commit) {
+			/*
+			 * Since the current commit is a merge find
+			 * the columns for the parent commits in
+			 * new_columns and use those to format the
+			 * edges.
+			 */
+			struct commit_list *parents = first_parent;
+			int par_column;
+			int idx = graph->merge_layout;
+			char c;
+			seen_this = 1;
+
+			for (j = 0; j < graph->num_parents; j++) {
+				par_column = graph_find_new_column_by_commit(graph, parents->item);
+				assert(par_column >= 0);
+
+				c = merge_chars[idx];
+				graph_line_write_column(line, &graph->new_columns[par_column], c);
+				if (idx == 2) {
+					if (graph->edges_added > 0 || j < graph->num_parents - 1)
+						graph_line_addch(line, ' ');
+				} else {
+					idx++;
+				}
+				parents = next_interesting_parent(graph, parents);
+			}
+			if (graph->edges_added == 0)
+				graph_line_addch(line, ' ');
+
+		} else if (seen_this) {
+			if (graph->edges_added > 0)
+				graph_line_write_column(line, col, '\\');
+			else
+				graph_line_write_column(line, col, '|');
+			graph_line_addch(line, ' ');
+		} else {
+			graph_line_write_column(line, col, '|');
+			if (graph->merge_layout != 0 || i != graph->commit_index - 1) {
+				if (parent_col)
+					graph_line_write_column(
+						line, parent_col, '_');
+				else
+					graph_line_addch(line, ' ');
+			}
+		}
+
+		if (col_commit == first_parent->item)
+			parent_col = col;
+	}
+
+	/*
+	 * Update graph->state
+	 */
+	if (graph_is_mapping_correct(graph))
+		graph_update_state(graph, GRAPH_PADDING);
+	else
+		graph_update_state(graph, GRAPH_COLLAPSING);
+}
+
+static void graph_output_collapsing_line(struct git_graph *graph, struct graph_line *line)
+{
+	int i;
+	short used_horizontal = 0;
+	int horizontal_edge = -1;
+	int horizontal_edge_target = -1;
+
+	/*
+	 * Swap the mapping and old_mapping arrays
+	 */
+	SWAP(graph->mapping, graph->old_mapping);
+
+	/*
+	 * Clear out the mapping array
+	 */
+	for (i = 0; i < graph->mapping_size; i++)
+		graph->mapping[i] = -1;
+
+	for (i = 0; i < graph->mapping_size; i++) {
+		int target = graph->old_mapping[i];
+		if (target < 0)
+			continue;
+
+		/*
+		 * Since update_columns() always inserts the leftmost
+		 * column first, each branch's target location should
+		 * always be either its current location or to the left of
+		 * its current location.
+		 *
+		 * We never have to move branches to the right.  This makes
+		 * the graph much more legible, since whenever branches
+		 * cross, only one is moving directions.
+		 */
+		assert(target * 2 <= i);
+
+		if (target * 2 == i) {
+			/*
+			 * This column is already in the
+			 * correct place
+			 */
+			assert(graph->mapping[i] == -1);
+			graph->mapping[i] = target;
+		} else if (graph->mapping[i - 1] < 0) {
+			/*
+			 * Nothing is to the left.
+			 * Move to the left by one
+			 */
+			graph->mapping[i - 1] = target;
+			/*
+			 * If there isn't already an edge moving horizontally
+			 * select this one.
+			 */
+			if (horizontal_edge == -1) {
+				int j;
+				horizontal_edge = i;
+				horizontal_edge_target = target;
+				/*
+				 * The variable target is the index of the graph
+				 * column, and therefore target*2+3 is the
+				 * actual screen column of the first horizontal
+				 * line.
+				 */
+				for (j = (target * 2)+3; j < (i - 2); j += 2)
+					graph->mapping[j] = target;
+			}
+		} else if (graph->mapping[i - 1] == target) {
+			/*
+			 * There is a branch line to our left
+			 * already, and it is our target.  We
+			 * combine with this line, since we share
+			 * the same parent commit.
+			 *
+			 * We don't have to add anything to the
+			 * output or mapping, since the
+			 * existing branch line has already taken
+			 * care of it.
+			 */
+		} else {
+			/*
+			 * There is a branch line to our left,
+			 * but it isn't our target.  We need to
+			 * cross over it.
+			 *
+			 * The space just to the left of this
+			 * branch should always be empty.
+			 */
+			assert(graph->mapping[i - 1] > target);
+			assert(graph->mapping[i - 2] < 0);
+			graph->mapping[i - 2] = target;
+			/*
+			 * Mark this branch as the horizontal edge to
+			 * prevent any other edges from moving
+			 * horizontally.
+			 */
+			if (horizontal_edge == -1) {
+				int j;
+				horizontal_edge_target = target;
+				horizontal_edge = i - 1;
+
+				for (j = (target * 2) + 3; j < (i - 2); j += 2)
+					graph->mapping[j] = target;
+			}
+		}
+	}
+
+	/*
+	 * Copy the current mapping array into old_mapping
+	 */
+	COPY_ARRAY(graph->old_mapping, graph->mapping, graph->mapping_size);
+
+	/*
+	 * The new mapping may be 1 smaller than the old mapping
+	 */
+	if (graph->mapping[graph->mapping_size - 1] < 0)
+		graph->mapping_size--;
+
+	/*
+	 * Output out a line based on the new mapping info
+	 */
+	for (i = 0; i < graph->mapping_size; i++) {
+		int target = graph->mapping[i];
+		if (target < 0)
+			graph_line_addch(line, ' ');
+		else if (target * 2 == i)
+			graph_line_write_column(line, &graph->new_columns[target], '|');
+		else if (target == horizontal_edge_target &&
+			 i != horizontal_edge - 1) {
+				/*
+				 * Set the mappings for all but the
+				 * first segment to -1 so that they
+				 * won't continue into the next line.
+				 */
+				if (i != (target * 2)+3)
+					graph->mapping[i] = -1;
+				used_horizontal = 1;
+			graph_line_write_column(line, &graph->new_columns[target], '_');
+		} else {
+			if (used_horizontal && i < horizontal_edge)
+				graph->mapping[i] = -1;
+			graph_line_write_column(line, &graph->new_columns[target], '/');
+
+		}
+	}
+
+	/*
+	 * If graph->mapping indicates that all of the branch lines
+	 * are already in the correct positions, we are done.
+	 * Otherwise, we need to collapse some branch lines together.
+	 */
+	if (graph_is_mapping_correct(graph))
+		graph_update_state(graph, GRAPH_PADDING);
+}
+
+int graph_next_line(struct git_graph *graph, struct strbuf *sb)
+{
+	int shown_commit_line = 0;
+	struct graph_line line = { .buf = sb, .width = 0 };
+
+	/*
+	 * We could conceivable be called with a NULL commit
+	 * if our caller has a bug, and invokes graph_next_line()
+	 * immediately after graph_init(), without first calling
+	 * graph_update().  Return without outputting anything in this
+	 * case.
+	 */
+	if (!graph->commit)
+		return -1;
+
+	switch (graph->state) {
+	case GRAPH_PADDING:
+		graph_output_padding_line(graph, &line);
+		break;
+	case GRAPH_SKIP:
+		graph_output_skip_line(graph, &line);
+		break;
+	case GRAPH_PRE_COMMIT:
+		graph_output_pre_commit_line(graph, &line);
+		break;
+	case GRAPH_COMMIT:
+		graph_output_commit_line(graph, &line);
+		shown_commit_line = 1;
+		break;
+	case GRAPH_POST_MERGE:
+		graph_output_post_merge_line(graph, &line);
+		break;
+	case GRAPH_COLLAPSING:
+		graph_output_collapsing_line(graph, &line);
+		break;
+	}
+
+	graph_pad_horizontally(graph, &line);
+	return shown_commit_line;
+}
+
+static void graph_padding_line(struct git_graph *graph, struct strbuf *sb)
+{
+	int i;
+	struct graph_line line = { .buf = sb, .width = 0 };
+
+	if (graph->state != GRAPH_COMMIT) {
+		graph_next_line(graph, sb);
+		return;
+	}
+
+	/*
+	 * Output the row containing this commit
+	 * Iterate up to and including graph->num_columns,
+	 * since the current commit may not be in any of the existing
+	 * columns.  (This happens when the current commit doesn't have any
+	 * children that we have already processed.)
+	 */
+	for (i = 0; i < graph->num_columns; i++) {
+		struct column *col = &graph->columns[i];
+
+		graph_line_write_column(&line, col, '|');
+
+		if (col->commit == graph->commit && graph->num_parents > 2) {
+			int len = (graph->num_parents - 2) * 2;
+			graph_line_addchars(&line, ' ', len);
+		} else {
+			graph_line_addch(&line, ' ');
+		}
+	}
+
+	graph_pad_horizontally(graph, &line);
+
+	/*
+	 * Update graph->prev_state since we have output a padding line
+	 */
+	graph->prev_state = GRAPH_PADDING;
+}
+
+int graph_is_commit_finished(struct git_graph const *graph)
+{
+	return (graph->state == GRAPH_PADDING);
+}
+
+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;
+
+	/*
+	 * When showing a diff of a merge against each of its parents, we
+	 * are called once for each parent without graph_update having been
+	 * called.  In this case, simply output a single padding line.
+	 */
+	if (graph_is_commit_finished(graph)) {
+		graph_show_padding(graph);
+		shown_commit_line = 1;
+	}
+
+	while (!shown_commit_line && !graph_is_commit_finished(graph)) {
+		shown_commit_line = graph_next_line(graph, &msgbuf);
+		fwrite(msgbuf.buf, sizeof(char), msgbuf.len,
+			graph->revs->diffopt.file);
+		if (!shown_commit_line) {
+			putc('\n', graph->revs->diffopt.file);
+			graph_show_line_prefix(&graph->revs->diffopt);
+		}
+		strbuf_setlen(&msgbuf, 0);
+	}
+
+	strbuf_release(&msgbuf);
+}
+
+void graph_show_oneline(struct git_graph *graph)
+{
+	struct strbuf msgbuf = STRBUF_INIT;
+
+	graph_show_line_prefix(default_diffopt);
+
+	if (!graph)
+		return;
+
+	graph_next_line(graph, &msgbuf);
+	fwrite(msgbuf.buf, sizeof(char), msgbuf.len, graph->revs->diffopt.file);
+	strbuf_release(&msgbuf);
+}
+
+void graph_show_padding(struct git_graph *graph)
+{
+	struct strbuf msgbuf = STRBUF_INIT;
+
+	graph_show_line_prefix(default_diffopt);
+
+	if (!graph)
+		return;
+
+	graph_padding_line(graph, &msgbuf);
+	fwrite(msgbuf.buf, sizeof(char), msgbuf.len, graph->revs->diffopt.file);
+	strbuf_release(&msgbuf);
+}
+
+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;
+
+	if (graph_is_commit_finished(graph))
+		return 0;
+
+	for (;;) {
+		graph_next_line(graph, &msgbuf);
+		fwrite(msgbuf.buf, sizeof(char), msgbuf.len,
+			graph->revs->diffopt.file);
+		strbuf_setlen(&msgbuf, 0);
+		shown = 1;
+
+		if (!graph_is_commit_finished(graph)) {
+			putc('\n', graph->revs->diffopt.file);
+			graph_show_line_prefix(&graph->revs->diffopt);
+		} else {
+			break;
+		}
+	}
+	strbuf_release(&msgbuf);
+
+	return shown;
+}
+
+static void graph_show_strbuf(struct git_graph *graph,
+			      FILE *file,
+			      struct strbuf const *sb)
+{
+	char *p;
+
+	/*
+	 * Print the strbuf line by line,
+	 * and display the graph info before each line but the first.
+	 */
+	p = sb->buf;
+	while (p) {
+		size_t len;
+		char *next_p = strchr(p, '\n');
+		if (next_p) {
+			next_p++;
+			len = next_p - p;
+		} else {
+			len = (sb->buf + sb->len) - p;
+		}
+		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;
+
+	/*
+	 * Show the commit message
+	 */
+	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
+	 */
+	if (!graph_is_commit_finished(graph)) {
+		/*
+		 * If sb doesn't have a terminating newline, print one now,
+		 * so we can start the remainder of the graph output on a
+		 * new line.
+		 */
+		if (!newline_terminated)
+			putc('\n', file);
+
+		graph_show_remainder(graph);
+
+		/*
+		 * If sb ends with a newline, our output should too.
+		 */
+		if (newline_terminated)
+			putc('\n', file);
+	}
+}