setting the home project: --project command-line option

modified version of #27798

base/initdefs.jl

@@ -133,7 +133,9 @@ function init_load_path()
  paths = filter!(env -> env !== nothing,
  [env == "@" ? current_project() : env for env in DEFAULT_LOAD_PATH])
  end
- project = get(ENV, "JULIA_PROJECT", nothing)
+ project = (JLOptions().project != C_NULL ?
+ unsafe_string(Base.JLOptions().project) :
+ get(ENV, "JULIA_PROJECT", nothing))
  HOME_PROJECT[] =
  project == "" ? nothing :
  project == "@" ? current_project() : project

base/options.jl

@@ -11,6 +11,7 @@ struct JLOptions
  cpu_target::Ptr{UInt8}
  nprocs::Int32
  machine_file::Ptr{UInt8}
+ project::Ptr{UInt8}
  isinteractive::Int8
  color::Int8
  historyfile::Int8

src/jloptions.c

@@ -31,6 +31,7 @@ jl_options_t jl_options = { 0, // quiet
  -1, // banner
  NULL, // julia_bindir
  NULL, // julia_bin
+ NULL, // project
  NULL, // cmds
  NULL, // image_file (will be filled in below)
  NULL, // cpu_target ("native", "core2", etc...)
@@ -171,6 +172,7 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
  opt_sysimage_native_code,
  opt_compiled_modules,
  opt_machine_file,
+ opt_project,
  };
  static const char* const shortopts = "+vhqH:e:E:L:J:C:ip:O:g:";
  static const struct option longopts[] = {
@@ -194,6 +196,7 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
  { "procs", required_argument, 0, 'p' },
  { "machinefile", required_argument, 0, opt_machinefile }, // deprecated
  { "machine-file", required_argument, 0, opt_machine_file },
+ { "project", optional_argument, 0, opt_project },
  { "color", required_argument, 0, opt_color },
  { "history-file", required_argument, 0, opt_history_file },
  { "startup-file", required_argument, 0, opt_startup_file },
@@ -399,6 +402,9 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
  if (!jl_options.machine_file)
  jl_error("julia: failed to allocate memory");
  break;
+ case opt_project:
+ jl_options.project = optarg ? strdup(optarg) : "@";
+ break;
  case opt_color:
  if (!strcmp(optarg, "yes"))
  jl_options.color = JL_OPTIONS_COLOR_ON;

src/julia.h

@@ -1778,6 +1778,7 @@ typedef struct {
  const char *cpu_target;
  int32_t nprocs;
  const char *machine_file;
+ const char *project;
  int8_t isinteractive;
  int8_t color;
  int8_t historyfile;