[PATCH 2/3] log: add a config option for --graph

[Alex Henrie <alexhenrie24@gmail.com>]

A coworker recently asked me how to turn on --graph by default in
`git log`. I googled it and found that several people have asked that
before on Stack Overflow, with no good solution:
https://stackoverflow.com/questions/43555256/how-do-i-make-git-log-graph-the-default

Add a log.graph option to turn on graph mode in the absence of any
incompatible options.

It would be nice to have a --no-graph command line option to countermand
log.graph=true, but it's not clear how that would work with topo_order
and rewrite_parents, which can be set by other options. In any case, it
is still possible to countermand log.graph=true per invocation with
`git -c log.graph=false log`.

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
---
 Documentation/config/log.txt |  5 +++++
 Documentation/git-log.txt    |  5 +++++
 builtin/log.c                | 17 +++++++++++++++++
 t/t4202-log.sh               | 35 +++++++++++++++++++++++++++++++++++
 4 files changed, 62 insertions(+)

diff --git a/Documentation/config/log.txt b/Documentation/config/log.txt
index 456eb07800..3e356cfce6 100644
--- a/Documentation/config/log.txt
+++ b/Documentation/config/log.txt
@@ -35,6 +35,11 @@ log.follow::
 	i.e. it cannot be used to follow multiple files and does not work well
 	on non-linear history.
 
+log.graph::
+	If true, makes linkgit:git-log[1], linkgit:git-show[1], and
+	linkgit:git-whatchanged[1] assume `--graph` unless an incompatible
+	option is also specified.
+
 log.graphColors::
 	A list of colors, separated by commas, that can be used to draw
 	history lines in `git log --graph`.
diff --git a/Documentation/git-log.txt b/Documentation/git-log.txt
index 20e87cecf4..7e9e0f8afe 100644
--- a/Documentation/git-log.txt
+++ b/Documentation/git-log.txt
@@ -214,6 +214,11 @@ log.follow::
 	i.e. it cannot be used to follow multiple files and does not work well
 	on non-linear history.
 
+log.graph::
+	If `true`, `git log` and related commands will act as if the
+	`--graph` option was passed to them unless an incompatible option is
+	also specified.
+
 log.showRoot::
 	If `false`, `git log` and related commands will not treat the
 	initial commit as a big creation event.  Any root commits in
diff --git a/builtin/log.c b/builtin/log.c
index 4b493408cc..1f0db54c84 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -35,6 +35,7 @@
 #include "repository.h"
 #include "commit-reach.h"
 #include "range-diff.h"
+#include "graph.h"
 
 #define MAIL_DEFAULT_WRAP 72
 #define COVER_FROM_AUTO_MAX_SUBJECT_LEN 100
@@ -48,6 +49,7 @@ static int default_show_root = 1;
 static int default_follow;
 static int default_show_signature;
 static int default_encode_email_headers = 1;
+static int default_graph;
 static int decoration_style;
 static int decoration_given;
 static int use_mailmap_config = 1;
@@ -234,6 +236,17 @@ static void cmd_log_init_finish(int argc, const char **argv, const char *prefix,
 		read_mailmap(rev->mailmap);
 	}
 
+	if (default_graph &&
+	    !rev->graph &&
+	    !rev->track_linear &&
+	    !rev->reverse &&
+	    !rev->reflog_info &&
+	    !rev->no_walk) {
+		rev->topo_order = 1;
+		rev->rewrite_parents = 1;
+		rev->graph = graph_init(rev);
+	}
+
 	if (rev->pretty_given && rev->commit_format == CMIT_FMT_RAW) {
 		/*
 		 * "log --pretty=raw" is special; ignore UI oriented
@@ -519,6 +532,10 @@ static int git_log_config(const char *var, const char *value, void *cb)
 		default_show_signature = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "log.graph")) {
+		default_graph = git_config_bool(var, value);
+		return 0;
+	}
 
 	if (grep_config(var, value, cb) < 0)
 		return -1;
diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index 5049559861..3b6f7aff23 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -1671,6 +1671,41 @@ test_expect_success 'log --graph with --name-only' '
 	test_cmp_graph --name-only tangle..reach
 '
 
+test_expect_success 'log.graph=true behaves like --graph' '
+	git log --graph >expect &&
+	test_config log.graph true &&
+	git log >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--show-linear-break ignores log.graph' '
+	git log --show-linear-break >expect &&
+	test_config log.graph true &&
+	git log --show-linear-break >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--reverse ignores log.graph' '
+	git log --reverse >expect &&
+	test_config log.graph true &&
+	git log --reverse >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--walk-reflogs ignores log.graph' '
+	git log --walk-reflogs >expect &&
+	test_config log.graph true &&
+	git log --walk-reflogs >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--no-walk ignores log.graph' '
+	git log --no-walk >expect &&
+	test_config log.graph true &&
+	git log --no-walk >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'dotdot is a parent directory' '
 	mkdir -p a/b &&
 	( echo sixth && echo fifth ) >expect &&
-- 
2.32.0.2645.gc109162a1f