scalar: add --no-maintenance option

These patches add a new --no-maintenance option to the scalar register and scalar clone commands. My motivation is based on setting up Scalar clones in automated environments that set up a repo onto a disk image for use later. If background maintenance runs during later setup steps, then this introduces a variable that is unexpected at minimum and disruptive at worst. The disruption comes in if the automation has steps to run git maintenance run --task=<X> commands but those commands are blocked due to the maintenance.lock file.

Functionally, these leave the default behavior as-is but allow disabling the git maintenance start step when users opt-in to this difference. The idea of Scalar is to recommend the best practices for a typical user, but allowing customization for expert users.

Updates in v2
=============

* The previous use of toggle_maintenance() in register_dir() would run the 'git maintenance unregister --force' command. There is a new patch 1 that is explicit about whether this should or should not happen and new tests are added to verify this behavior in the later patches.
* A new patch 4 adds the --[no-]maintenance option to scalar reconfigure.

Updates in v3
=============

* Patch 4 converts the --[no-]maintenance option of scalar reconfigure to --maintenance=<mode> to keep the default behavior the same (enable maintenance) but also allow two other modes: disable maintenance and leave maintenance as configured.

Thanks, -Stolee

Derrick Stolee (4):
scalar: customize register_dir()'s behavior scalar register: add --no-maintenance option scalar clone: add --no-maintenance option scalar reconfigure: add --maintenance=<mode> option

 Documentation/scalar.adoc | 32 ++++++++++++++++---
 scalar.c                  | 65 +++++++++++++++++++++++++++++++--------
 t/t9210-scalar.sh         | 26 ++++++++++++++--
 t/t9211-scalar-clone.sh   | 11 ++++++-
 4 files changed, 114 insertions(+), 20 deletions(-)

base-commit: f65182a99e545d2f2bc22e6c1c2da192133b16a3
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1913%2Fderrickstolee%2Fscalar-no-maintenance-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1913/derrickstolee/scalar-no-maintenance-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/1913

Range-diff vs v2:

 1:  f3a3cfe3ef1 = 1:  f3a3cfe3ef1 scalar: customize register_dir()'s behavior
 2:  1b99a559520 = 2:  1b99a559520 scalar register: add --no-maintenance option
 3:  e52b1282d93 = 3:  e52b1282d93 scalar clone: add --no-maintenance option
 4:  6fac9c4c394 ! 4:  684f04aaf7e scalar reconfigure: add --no-maintenance option
     @@ Metadata
      Author: Derrick Stolee <[email protected]>
      
       ## Commit message ##
     -    scalar reconfigure: add --no-maintenance option
     +    scalar reconfigure: add --maintenance=<mode> option
      
          When users want to enable the latest and greatest configuration options
          recommended by Scalar after a Git upgrade, 'scalar reconfigure --all' is
     @@ Commit message
          However, this feature previously forced users to enable background
          maintenance. In some environments this is not preferred.
      
     -    Add a new --[no-]maintenance option to 'scalar reconfigure' that avoids
     -    running 'git maintenance start' on these enlistments.
     +    Add a new --maintenance=<mode> option to 'scalar reconfigure' that
     +    provides options for enabling (default), disabling, or leaving
     +    background maintenance config as-is.
      
     +    Helped-by: Junio C Hamano <[email protected]>
          Signed-off-by: Derrick Stolee <[email protected]>
      
       ## Documentation/scalar.adoc ##
     @@ Documentation/scalar.adoc: scalar list
       scalar unregister [<enlistment>]
       scalar run ( all | config | commit-graph | fetch | loose-objects | pack-files ) [<enlistment>]
      -scalar reconfigure [ --all | <enlistment> ]
     -+scalar reconfigure [--[no-]maintenance] [ --all | <enlistment> ]
     ++scalar reconfigure [--maintenance=<mode>] [ --all | <enlistment> ]
       scalar diagnose [<enlistment>]
       scalar delete <enlistment>
       
     @@ Documentation/scalar.adoc: After a Scalar upgrade, or when the configuration of
      +	registered with Scalar by the `scalar.repo` config key. Use this
      +	option after each upgrade to get the latest features.
      +
     -+--[no-]maintenance::
     ++--maintenance=<mode>::
      +	By default, Scalar configures the enlistment to use Git's
     -+	background maintenance feature. Use the `--no-maintenance` to skip
     -+	this configuration and leave the repositories in whatever state is
     -+	currently configured.
     ++	background maintenance feature; this is the same as using the
     ++	`--maintenance=enable` value for this option. Use the
     ++	`--maintenance=disable` to remove each considered enlistment
     ++	from background maintenance. Use `--maitnenance=keep' to leave
     ++	the background maintenance configuration untouched for These
     ++	repositories.
       
       Diagnose
       ~~~~~~~~
      
       ## scalar.c ##
      @@ scalar.c: static int remove_deleted_enlistment(struct strbuf *path)
     - 
       static int cmd_reconfigure(int argc, const char **argv)
       {
     --	int all = 0;
     -+	int all = 0, maintenance = 1;
     + 	int all = 0;
     ++	const char *maintenance_str = NULL;
     ++	int maintenance = 1; /* Enable maintenance by default. */
     ++
       	struct option options[] = {
       		OPT_BOOL('a', "all", &all,
       			 N_("reconfigure all registered enlistments")),
     -+		OPT_BOOL(0, "maintenance", &maintenance,
     -+			 N_("specify if background maintenance should be enabled")),
     ++		OPT_STRING(0, "maintenance", &maintenance_str,
     ++			 N_("<mode>"),
     ++			 N_("signal how to adjust background maintenance")),
       		OPT_END(),
       	};
       	const char * const usage[] = {
      -		N_("scalar reconfigure [--all | <enlistment>]"),
     -+		N_("scalar reconfigure [--[no-]maintenance] [--all | <enlistment>]"),
     ++		N_("scalar reconfigure [--maintenance=<mode>] [--all | <enlistment>]"),
       		NULL
       	};
       	struct string_list scalar_repos = STRING_LIST_INIT_DUP;
     +@@ scalar.c: static int cmd_reconfigure(int argc, const char **argv)
     + 		usage_msg_opt(_("--all or <enlistment>, but not both"),
     + 			      usage, options);
     + 
     ++	if (maintenance_str) {
     ++		if (!strcmp(maintenance_str, "enable"))
     ++			maintenance = 1;
     ++		else if (!strcmp(maintenance_str, "disable"))
     ++			maintenance = 0;
     ++		else if (!strcmp(maintenance_str, "keep"))
     ++			maintenance = -1;
     ++		else
     ++			die(_("unknown mode for --maintenance option: %s"),
     ++			    maintenance_str);
     ++	}
     ++
     + 	git_config(get_scalar_repos, &scalar_repos);
     + 
     + 	for (size_t i = 0; i < scalar_repos.nr; i++) {
      @@ scalar.c: static int cmd_reconfigure(int argc, const char **argv)
       		the_repository = old_repo;
       		repo_clear(&r);
       
      -		if (toggle_maintenance(1) >= 0)
     -+		if (maintenance &&
     -+		    toggle_maintenance(1) >= 0)
     ++		if (maintenance >= 0 &&
     ++		    toggle_maintenance(maintenance) >= 0)
       			succeeded = 1;
       
       loop_end:
     @@ t/t9210-scalar.sh: test_expect_success 'scalar reconfigure' '
      +	test_subcommand git maintenance start <reconfigure &&
      +	test_subcommand ! git maintenance unregister --force <reconfigure &&
      +
     -+	GIT_TRACE2_EVENT="$(pwd)/reconfigure-maint" scalar reconfigure --no-maintenance -a &&
     -+	test_subcommand ! git maintenance start <reconfigure-maint &&
     -+	test_subcommand ! git maintenance unregister --force <reconfigure-maint
     ++	GIT_TRACE2_EVENT="$(pwd)/reconfigure-maint-disable" \
     ++		scalar reconfigure -a --maintenance=disable &&
     ++	test_subcommand ! git maintenance start <reconfigure-maint-disable &&
     ++	test_subcommand git maintenance unregister --force <reconfigure-maint-disable &&
     ++
     ++	GIT_TRACE2_EVENT="$(pwd)/reconfigure-maint-keep" \
     ++		scalar reconfigure --maintenance=keep -a &&
     ++	test_subcommand ! git maintenance start <reconfigure-maint-keep &&
     ++	test_subcommand ! git maintenance unregister --force <reconfigure-maint-keep
       '
       
       test_expect_success 'scalar reconfigure --all with includeIf.onbranch' '

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