whatchanged: remove when built with WITH_BREAKING_CHANGES

As we made "git whatchanged" require "--i-still-use-this" and asked
the users to report if they still want to use it, the logical next
step is to allow us build Git without "whatchanged" to prepare for
its eventual removal.

If we were to follow the pattern established in 8ccc75c2 (remote:
announce removal of "branches/" and "remotes/", 2025-01-22), we can
do this together with the documentation update to officially list
that the command will be removed in the BreakingChanges document,
but let's just keep the changes separate just in case we want to
proceed a bit slower.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/format.adoc

@@ -68,9 +68,15 @@ format.encodeEmailHeaders::
 	Defaults to true.
 
 format.pretty::
+ifndef::with-breaking-changes[]
 	The default pretty format for log/show/whatchanged command.
 	See linkgit:git-log[1], linkgit:git-show[1],
 	linkgit:git-whatchanged[1].
+endif::with-breaking-changes[]
+ifdef::with-breaking-changes[]
+	The default pretty format for log/show command.
+	See linkgit:git-log[1], linkgit:git-show[1].
+endif::with-breaking-changes[]
 
 format.thread::
 	The default threading style for 'git format-patch'.  Can be

Documentation/config/log.adoc

@@ -1,6 +1,13 @@
 log.abbrevCommit::
-	If true, makes linkgit:git-log[1], linkgit:git-show[1], and
-	linkgit:git-whatchanged[1] assume `--abbrev-commit`. You may
+	If true, makes
+ifndef::with-breaking-changes[]
+	linkgit:git-log[1], linkgit:git-show[1], and
+	linkgit:git-whatchanged[1]
+endif::with-breaking-changes[]
+ifdef::with-breaking-changes[]
+	linkgit:git-log[1] and linkgit:git-show[1]
+endif::with-breaking-changes[]
+	assume `--abbrev-commit`. You may
 	override this option with `--no-abbrev-commit`.
 
 log.date::

Documentation/pretty-options.adoc

@@ -62,7 +62,12 @@ ifndef::git-rev-list[]
 --notes[=<ref>]::
 	Show the notes (see linkgit:git-notes[1]) that annotate the
 	commit, when showing the commit log message.  This is the default
+ifndef::with-breaking-changes[]
 	for `git log`, `git show` and `git whatchanged` commands when
+endif::with-breaking-changes[]
+ifdef::with-breaking-changes[]
+	for `git log` and `git show` commands when
+endif::with-breaking-changes[]
 	there is no `--pretty`, `--format`, or `--oneline` option given
 	on the command line.
 +

Documentation/rev-list-options.adoc

@@ -1074,8 +1074,13 @@ Commit Formatting
 
 ifdef::git-rev-list[]
 Using these options, linkgit:git-rev-list[1] will act similar to the
-more specialized family of commit log tools: linkgit:git-log[1],
-linkgit:git-show[1], and linkgit:git-whatchanged[1]
+more specialized family of commit log tools:
+ifndef::with-breaking-changes[]
+linkgit:git-log[1], linkgit:git-show[1], and linkgit:git-whatchanged[1].
+endif::with-breaking-changes[]
+ifdef::with-breaking-changes[]
+linkgit:git-log[1] and linkgit:git-show[1].
+endif::with-breaking-changes[]
 endif::git-rev-list[]
 
 include::pretty-options.adoc[]

Documentation/technical/sparse-checkout.adoc

@@ -442,7 +442,7 @@ understanding these differences can be beneficial.
       * blame (only matters when one or more -C flags are passed)
 	* and annotate
       * log
-      * whatchanged
+      * whatchanged (may not exist anymore)
       * ls-files
       * diff-index
       * diff-tree

builtin/log.c

@@ -114,12 +114,14 @@ struct log_config {
 	char *fmt_pretty;
 	char *default_date_mode;
 
+#ifndef WITH_BREAKING_CHANGES
 	/*
 	 * Note: git_log_config() does not touch this member and that
 	 * is very deliberate.  This member is only to be used to
 	 * resurrect whatchanged that is deprecated.
 	 */
 	int i_still_use_this;
+#endif
 };
 
 static void log_config_init(struct log_config *cfg)
@@ -274,8 +276,10 @@ static void cmd_log_init_finish(int argc, const char **argv, const char *prefix,
 		OPT__QUIET(&quiet, N_("suppress diff output")),
 		OPT_BOOL(0, "source", &source, N_("show source")),
 		OPT_BOOL(0, "use-mailmap", &mailmap, N_("use mail map file")),
+#ifndef WITH_BREAKING_CHANGES
 		OPT_HIDDEN_BOOL(0, "i-still-use-this", &cfg->i_still_use_this,
 				"<use this deprecated command>"),
+#endif
 		OPT_ALIAS(0, "mailmap", "use-mailmap"),
 		OPT_CALLBACK_F(0, "clear-decorations", NULL, NULL,
 			       N_("clear all previously-defined decoration filters"),
@@ -642,6 +646,7 @@ static int git_log_config(const char *var, const char *value,
 	return git_diff_ui_config(var, value, ctx, cb);
 }
 
+#ifndef WITH_BREAKING_CHANGES
 int cmd_whatchanged(int argc,
 		    const char **argv,
 		    const char *prefix,
@@ -678,6 +683,7 @@ int cmd_whatchanged(int argc,
 	log_config_release(&cfg);
 	return ret;
 }
+#endif
 
 static void show_tagger(const char *buf, struct rev_info *rev)
 {

git.c

@@ -645,7 +645,9 @@ static struct cmd_struct commands[] = {
 	{ "verify-pack", cmd_verify_pack },
 	{ "verify-tag", cmd_verify_tag, RUN_SETUP },
 	{ "version", cmd_version },
+#ifndef WITH_BREAKING_CHANGES
 	{ "whatchanged", cmd_whatchanged, RUN_SETUP },
+#endif
 	{ "worktree", cmd_worktree, RUN_SETUP },
 	{ "write-tree", cmd_write_tree, RUN_SETUP },
 };

t/t4013-diff-various.sh

@@ -200,7 +200,15 @@ do
 	expect="$TEST_DIRECTORY/t4013/diff.$test"
 	actual="$pfx-diff.$test"
 
-	test_expect_success "git $cmd # magic is ${magic:-(not used)}" '
+	case "$cmd" in
+	whatchanged | whatchanged" "*)
+		prereq=WITHOUT_BREAKING_CHANGES
+		;;
+	*)
+		prereq=;;
+	esac
+
+	test_expect_success $prereq "git $cmd # magic is ${magic:-(not used)}" '
 		{
 			echo "$ git $cmd"
 
@@ -462,7 +470,7 @@ diff-tree --stat --compact-summary initial mode
 diff-tree -R --stat --compact-summary initial mode
 EOF
 
-test_expect_success 'whatchanged needs --i-still-use-this' '
+test_expect_success WITHOUT_BREAKING_CHANGES 'whatchanged needs --i-still-use-this' '
 	test_must_fail git whatchanged >message 2>&1 &&
 	test_grep "nominated for removal" message
 '

t/t4202-log.sh

@@ -486,7 +486,12 @@ test_expect_success !FAIL_PREREQS 'log with various grep.patternType configurati
 	)
 '
 
-for cmd in show whatchanged reflog format-patch
+cmds="show reflog format-patch"
+if test_have_prereq WITHOUT_BREAKING_CHANGES
+then
+	cmds="$cmds whatchanged"
+fi
+for cmd in $cmds
 do
 	case "$cmd" in
 	format-patch) myarg="HEAD~.." ;;
@@ -1202,7 +1207,7 @@ test_expect_success 'reflog is expected format' '
 	test_cmp expect actual
 '
 
-test_expect_success 'whatchanged is expected format' '
+test_expect_success WITHOUT_BREAKING_CHANGES 'whatchanged is expected format' '
 	whatchanged="whatchanged --i-still-use-this" &&
 	git log --no-merges --raw >expect &&
 	git $whatchanged >actual &&
@@ -1217,8 +1222,12 @@ test_expect_success 'log.abbrevCommit configuration' '
 	git log --pretty=raw >expect.log.raw &&
 	git reflog --abbrev-commit >expect.reflog.abbrev &&
 	git reflog --no-abbrev-commit >expect.reflog.full &&
-	git $whatchanged --abbrev-commit >expect.whatchanged.abbrev &&
-	git $whatchanged --no-abbrev-commit >expect.whatchanged.full &&
+
+	if test_have_prereq WITHOUT_BREAKING_CHANGES
+	then
+		git $whatchanged --abbrev-commit >expect.whatchanged.abbrev &&
+		git $whatchanged --no-abbrev-commit >expect.whatchanged.full
+	fi &&
 
 	test_config log.abbrevCommit true &&
 
@@ -1235,10 +1244,13 @@ test_expect_success 'log.abbrevCommit configuration' '
 	git reflog --no-abbrev-commit >actual &&
 	test_cmp expect.reflog.full actual &&
 
-	git $whatchanged >actual &&
-	test_cmp expect.whatchanged.abbrev actual &&
-	git $whatchanged --no-abbrev-commit >actual &&
-	test_cmp expect.whatchanged.full actual
+	if test_have_prereq WITHOUT_BREAKING_CHANGES
+	then
+		git $whatchanged >actual &&
+		test_cmp expect.whatchanged.abbrev actual &&
+		git $whatchanged --no-abbrev-commit >actual &&
+		test_cmp expect.whatchanged.full actual
+	fi
 '
 
 test_expect_success '--abbrev-commit with core.abbrev=false' '