docs: graph: remove unnecessary `graph_update()' call
[git/git.git] / Documentation / technical / api-history-graph.txt
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1history graph API
2=================
3
4The graph API is used to draw a text-based representation of the commit
5history. The API generates the graph in a line-by-line fashion.
6
7Functions
8---------
9
10Core functions:
11
12* `graph_init()` creates a new `struct git_graph`
13
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14* `graph_update()` moves the graph to a new commit.
15
16* `graph_next_line()` outputs the next line of the graph into a strbuf. It
17 does not add a terminating newline.
18
19* `graph_padding_line()` outputs a line of vertical padding in the graph. It
20 is similar to `graph_next_line()`, but is guaranteed to never print the line
21 containing the current commit. Where `graph_next_line()` would print the
22 commit line next, `graph_padding_line()` prints a line that simply extends
23 all branch lines downwards one row, leaving their positions unchanged.
24
25* `graph_is_commit_finished()` determines if the graph has output all lines
26 necessary for the current commit. If `graph_update()` is called before all
27 lines for the current commit have been printed, the next call to
28 `graph_next_line()` will output an ellipsis, to indicate that a portion of
29 the graph was omitted.
30
31The following utility functions are wrappers around `graph_next_line()` and
32`graph_is_commit_finished()`. They always print the output to stdout.
33They can all be called with a NULL graph argument, in which case no graph
34output will be printed.
35
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36* `graph_show_commit()` calls `graph_next_line()` and
37 `graph_is_commit_finished()` until one of them return non-zero. This prints
38 all graph lines up to, and including, the line containing this commit.
39 Output is printed to stdout. The last line printed does not contain a
40 terminating newline.
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41
42* `graph_show_oneline()` calls `graph_next_line()` and prints the result to
43 stdout. The line printed does not contain a terminating newline.
44
45* `graph_show_padding()` calls `graph_padding_line()` and prints the result to
46 stdout. The line printed does not contain a terminating newline.
47
48* `graph_show_remainder()` calls `graph_next_line()` until
49 `graph_is_commit_finished()` returns non-zero. Output is printed to stdout.
50 The last line printed does not contain a terminating newline. Returns 1 if
51 output was printed, and 0 if no output was necessary.
52
53* `graph_show_strbuf()` prints the specified strbuf to stdout, prefixing all
54 lines but the first with a graph line. The caller is responsible for
55 ensuring graph output for the first line has already been printed to stdout.
56 (This can be done with `graph_show_commit()` or `graph_show_oneline()`.) If
57 a NULL graph is supplied, the strbuf is printed as-is.
58
59* `graph_show_commit_msg()` is similar to `graph_show_strbuf()`, but it also
60 prints the remainder of the graph, if more lines are needed after the strbuf
61 ends. It is better than directly calling `graph_show_strbuf()` followed by
62 `graph_show_remainder()` since it properly handles buffers that do not end in
63 a terminating newline. The output printed by `graph_show_commit_msg()` will
64 end in a newline if and only if the strbuf ends in a newline.
65
66Data structure
67--------------
68`struct git_graph` is an opaque data type used to store the current graph
69state.
70
71Calling sequence
72----------------
73
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74* Create a `struct git_graph` by calling `graph_init()`. When using the
75 revision walking API, this is done automatically by `setup_revisions()` if
76 the '--graph' option is supplied.
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77
78* Use the revision walking API to walk through a group of contiguous commits.
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79 The `get_revision()` function automatically calls `graph_update()` each time
80 it is invoked.
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7fefda5c 82* For each commit, call `graph_next_line()` repeatedly, until
42ce44e0 83 `graph_is_commit_finished()` returns non-zero. Each call to
7fefda5c 84 `graph_next_line()` will output a single line of the graph. The resulting
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85 lines will not contain any newlines. `graph_next_line()` returns 1 if the
86 resulting line contains the current commit, or 0 if this is merely a line
87 needed to adjust the graph before or after the current commit. This return
88 value can be used to determine where to print the commit summary information
89 alongside the graph output.
90
91Limitations
92-----------
93
94* `graph_update()` must be called with commits in topological order. It should
95 not be called on a commit if it has already been invoked with an ancestor of
96 that commit, or the graph output will be incorrect.
97
98* `graph_update()` must be called on a contiguous group of commits. If
99 `graph_update()` is called on a particular commit, it should later be called
100 on all parents of that commit. Parents must not be skipped, or the graph
101 output will appear incorrect.
102+
103`graph_update()` may be used on a pruned set of commits only if the parent list
104has been rewritten so as to include only ancestors from the pruned set.
105
106* The graph API does not currently support reverse commit ordering. In
107 order to implement reverse ordering, the graphing API needs an
108 (efficient) mechanism to find the children of a commit.
109
110Sample usage
111------------
112
113------------
114struct commit *commit;
7528f27d 115struct git_graph *graph = graph_init(opts);
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116
117while ((commit = get_revision(opts)) != NULL) {
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118 while (!graph_is_commit_finished(graph))
119 {
120 struct strbuf sb;
121 int is_commit_line;
122
123 strbuf_init(&sb, 0);
124 is_commit_line = graph_next_line(graph, &sb);
125 fputs(sb.buf, stdout);
126
127 if (is_commit_line)
128 log_tree_commit(opts, commit);
129 else
130 putchar(opts->diffopt.line_termination);
131 }
132}
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133------------
134
135Sample output
136-------------
137
138The following is an example of the output from the graph API. This output does
139not include any commit summary information--callers are responsible for
140outputting that information, if desired.
141
142------------
143*
144*
7b60d0d3 145*
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146|\
147* |
148| | *
149| \ \
150| \ \
7b60d0d3 151*-. \ \
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152|\ \ \ \
153| | * | |
154| | | | | *
155| | | | | *
7b60d0d3 156| | | | | *
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157| | | | | |\
158| | | | | | *
159| * | | | | |
7b60d0d3 160| | | | | * \
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161| | | | | |\ |
162| | | | * | | |
163| | | | * | | |
164* | | | | | | |
165| |/ / / / / /
166|/| / / / / /
167* | | | | | |
168|/ / / / / /
169* | | | | |
170| | | | | *
171| | | | |/
172| | | | *
173------------