[PATCH v9 3/4] graph: add a 2 commit buffer for lookahead
From: Pablo Sabater <hidden>
Date: 2026-07-11 13:38:06
Subsystem:
the rest · Maintainer:
Linus Torvalds
In a subsequent commit the graph renderer needs to know if the next commit is a visual root or if it is the last commit to be shown. This requires peeking 2 commits ahead. Commits are pre-fetched in get_revision() through next_commit_to_show() where they are also marked as SHOWN, regardless the source they come from. Update graph_is_interesting() so it considers commits inside the lookahead buffer as interesting as well. Helped-by: Kristofer Karlsson [off-list ref] Signed-off-by: Pablo Sabater <redacted> --- graph.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ graph.h | 17 +++++++++++++++++ revision.c | 18 ++++++++++++++++-- 3 files changed, 84 insertions(+), 2 deletions(-)
diff --git a/graph.c b/graph.c
index 842282685f..89ebcf7540 100644
--- a/graph.c
+++ b/graph.c@@ -315,6 +315,14 @@ struct git_graph { * diff_output_prefix_callback(). */ struct strbuf prefix_buf; + + /* + * Lookahead buffer: up to 2 pre-fetched commits that will be shown. + * Populated by get_revision() so graph_peek_next_visible() can use + * actual walk results instead of peeking at rev_info internals. + */ + struct commit *lookahead[2]; + int lookahead_nr; }; static inline int graph_needs_truncation(struct git_graph *graph, int lane)
@@ -388,6 +396,9 @@ struct git_graph *graph_init(struct rev_info *opt) graph->num_columns = 0; graph->num_new_columns = 0; graph->mapping_size = 0; + graph->lookahead[0] = NULL; + graph->lookahead[1] = NULL; + graph->lookahead_nr = 0; /* * Start the column color at the maximum value, since we'll * always increment it for the first commit we output.
@@ -456,6 +467,15 @@ static void graph_ensure_capacity(struct git_graph *graph, int num_columns) */ static int graph_is_interesting(struct git_graph *graph, struct commit *commit) { + /* + * Commits in the lookahead buffer have been pre-fetched by + * get_revision() and will be shown in the future. They already have + * the SHOWN flag set when they were pre-fetched but the graph still + * needs to treat them as interesting parents. + */ + for (int i = 0; i < graph->lookahead_nr; i++) + if (graph->lookahead[i] == commit) + return 1; /* * If revs->boundary is set, commits whose children have * been shown are always interesting, even if they have the
@@ -763,6 +783,37 @@ static int graph_needs_pre_commit_line(struct git_graph *graph) graph->expansion_row < graph_num_expansion_rows(graph); } +struct commit *graph_pop_lookahead(struct git_graph *graph) +{ + struct commit *c; + + if (!graph->lookahead_nr) + return NULL; + + c = graph->lookahead[0]; + if (!c) + BUG("lookahead buffer has %d entries but the first one is NULL", + graph->lookahead_nr); + + graph->lookahead[0] = graph->lookahead[1]; + graph->lookahead[1] = NULL; + graph->lookahead_nr--; + return c; +} + +int graph_get_lookahead_room(struct git_graph *graph) +{ + return (int)ARRAY_SIZE(graph->lookahead) - graph->lookahead_nr; +} + +void graph_push_lookahead(struct git_graph *graph, struct commit *c) +{ + if (!graph_get_lookahead_room(graph)) + BUG("pushing into lookahead buffer when it is already full"); + + graph->lookahead[graph->lookahead_nr++] = c; +} + void graph_update(struct git_graph *graph, struct commit *commit) { struct commit_list *parent;
diff --git a/graph.h b/graph.h
index 3fd1dcb2e9..1193711fb8 100644
--- a/graph.h
+++ b/graph.h@@ -262,4 +262,21 @@ void graph_show_commit_msg(struct git_graph *graph, FILE *file, struct strbuf const *sb); +/* + * Pop the first commit from the graph's lookahead buffer. + * Returns NULL if the buffer is empty. + */ +struct commit *graph_pop_lookahead(struct git_graph *graph); + +/* + * Returns how many more commits can be added to the lookahead buffer. + */ +int graph_get_lookahead_room(struct git_graph *graph); + +/* + * Push a commit into the lookahead buffer. Must only be called when + * graph_get_lookahead_room() returns > 0. + */ +void graph_push_lookahead(struct git_graph *graph, struct commit *c); + #endif /* GRAPH_H */
diff --git a/revision.c b/revision.c
index 288935943f..258c3cf782 100644
--- a/revision.c
+++ b/revision.c@@ -4715,10 +4715,24 @@ struct commit *get_revision(struct rev_info *revs) return c; } - c = next_commit_to_show(revs); + if (revs->graph) { + c = graph_pop_lookahead(revs->graph); + if (!c) + c = next_commit_to_show(revs); + } else { + c = next_commit_to_show(revs); + } - if (c && revs->graph) + if (c && revs->graph) { + while (graph_get_lookahead_room(revs->graph)) { + struct commit *next = next_commit_to_show(revs); + if (!next) + break; + graph_push_lookahead(revs->graph, next); + } graph_update(revs->graph, c); + } + if (!c) { free_saved_parents(revs); commit_list_free(revs->previous_parents);
--
2.54.0