survey: stub in new experimental git-survey command

Start work on a new `git survey` command to scan the repository
for monorepo performance and scaling problems.  The goal is to
measure the various known "dimensions of scale" and serve as a
foundation for adding additional measurements as we learn more
about Git monorepo scaling problems.

Results will be logged to the console and to Trace2.

The initial goal is to complement the scanning and analysis performed
by the GO-based `git-sizer` (https://github.com/github/git-sizer) tool.
It is hoped that by creating a builtin command, we may be able to take
advantage of internal Git data structures and code that is not
accessible from GO to gain further insight into potential scaling
problems.

Signed-off-by: Jeff Hostetler <jeffhostetler@github.com>

.gitignore

@@ -164,6 +164,7 @@
 /git-submodule
 /git-submodule--helper
 /git-subtree
+/git-survey
 /git-svn
 /git-switch
 /git-symbolic-ref

Documentation/git-survey.txt

@@ -0,0 +1,36 @@
+git-survey(1)
+=============
+
+NAME
+----
+git-survey - EXPERIMENTAL: Measure various repository dimensions of scale
+
+SYNOPSIS
+--------
+[verse]
+(EXPERIMENTAL!) `git survey` <options>
+
+DESCRIPTION
+-----------
+
+Survey the repository and measure various dimensions of scale.
+
+As repositories grow to "monorepo" size, certain data shapes can cause
+performance problems.  `git-survey` attempts to measure and report on
+known problem areas.
+
+OPTIONS
+-------
+
+--progress::
+	Show progress.  This is automatically enabled when interactive.
+
+OUTPUT
+------
+
+By default, `git survey` will print information about the repository in a
+human-readable format that includes overviews and tables.
+
+GIT
+---
+Part of the linkgit:git[1] suite

Makefile

@@ -1309,6 +1309,7 @@ BUILTIN_OBJS += builtin/sparse-checkout.o
 BUILTIN_OBJS += builtin/stash.o
 BUILTIN_OBJS += builtin/stripspace.o
 BUILTIN_OBJS += builtin/submodule--helper.o
+BUILTIN_OBJS += builtin/survey.o
 BUILTIN_OBJS += builtin/symbolic-ref.o
 BUILTIN_OBJS += builtin/tag.o
 BUILTIN_OBJS += builtin/unpack-file.o

builtin.h

@@ -238,6 +238,7 @@ int cmd_status(int argc, const char **argv, const char *prefix);
 int cmd_stash(int argc, const char **argv, const char *prefix);
 int cmd_stripspace(int argc, const char **argv, const char *prefix);
 int cmd_submodule__helper(int argc, const char **argv, const char *prefix);
+int cmd_survey(int argc, const char **argv, const char *prefix);
 int cmd_switch(int argc, const char **argv, const char *prefix);
 int cmd_symbolic_ref(int argc, const char **argv, const char *prefix);
 int cmd_tag(int argc, const char **argv, const char *prefix);

builtin/survey.c

@@ -0,0 +1,58 @@
+#include "builtin.h"
+#include "config.h"
+#include "parse-options.h"
+
+static const char * const survey_usage[] = {
+	N_("(EXPERIMENTAL!) git survey <options>"),
+	NULL,
+};
+
+struct survey_opts {
+	int verbose;
+	int show_progress;
+};
+
+static struct survey_opts survey_opts = {
+	.verbose = 0,
+	.show_progress = -1, /* defaults to isatty(2) */
+};
+
+static struct option survey_options[] = {
+	OPT__VERBOSE(&survey_opts.verbose, N_("verbose output")),
+	OPT_BOOL(0, "progress", &survey_opts.show_progress, N_("show progress")),
+	OPT_END(),
+};
+
+static int survey_load_config_cb(const char *var, const char *value,
+				 const struct config_context *ctx, void *pvoid)
+{
+	if (!strcmp(var, "survey.verbose")) {
+		survey_opts.verbose = git_config_bool(var, value);
+		return 0;
+	}
+	if (!strcmp(var, "survey.progress")) {
+		survey_opts.show_progress = git_config_bool(var, value);
+		return 0;
+	}
+
+	return git_default_config(var, value, ctx, pvoid);
+}
+
+static void survey_load_config(void)
+{
+	git_config(survey_load_config_cb, NULL);
+}
+
+int cmd_survey(int argc, const char **argv, const char *prefix)
+{
+	survey_load_config();
+
+	argc = parse_options(argc, argv, prefix, survey_options, survey_usage, 0);
+
+	prepare_repo_settings(the_repository);
+
+	if (survey_opts.show_progress < 0)
+		survey_opts.show_progress = isatty(2);
+
+	return 0;
+}

command-list.txt

@@ -186,6 +186,7 @@ git-stash                               mainporcelain
 git-status                              mainporcelain           info
 git-stripspace                          purehelpers
 git-submodule                           mainporcelain
+git-survey                              mainporcelain
 git-svn                                 foreignscminterface
 git-switch                              mainporcelain           history
 git-symbolic-ref                        plumbingmanipulators

git.c

@@ -622,6 +622,7 @@ static struct cmd_struct commands[] = {
 	{ "status", cmd_status, RUN_SETUP | NEED_WORK_TREE },
 	{ "stripspace", cmd_stripspace },
 	{ "submodule--helper", cmd_submodule__helper, RUN_SETUP },
+	{ "survey", cmd_survey, RUN_SETUP },
 	{ "switch", cmd_switch, RUN_SETUP | NEED_WORK_TREE },
 	{ "symbolic-ref", cmd_symbolic_ref, RUN_SETUP },
 	{ "tag", cmd_tag, RUN_SETUP | DELAY_PAGER_CONFIG },