cli: Add required --experimental flag for experimental features (e.g. --trim) (JuliaLang#56045)

The intention here is to clearly signal when a feature is "not yet fully
implemented" vs. "feature-complete and in pre-release" vs. "fully
released and ready for production use"

The only feature gated behind this right now is `--trim`. Trim has its
core functionality implemented (and folks seem to be enjoying it!) but
the deployment / linking story in particular is still in its very early
stages, esp. because our existing techniques for, e.g., pre-loading
`libunwind`, `libstdc++`, etc. no longer work in a shared library
context.

Once `--trim` is ready for a broader chunk of the ecosystem / language,
we can peel off the `--experimental` flag

Author: topolarity

base/options.jl

@@ -39,6 +39,7 @@ struct JLOptions
     worker::Int8
     cookie::Ptr{UInt8}
     handle_signals::Int8
+    use_experimental_features::Int8
     use_sysimage_native_code::Int8
     use_compiled_modules::Int8
     use_pkgimages::Int8

src/jloptions.c

@@ -130,6 +130,7 @@ JL_DLLEXPORT void jl_init_options(void)
                         0,    // worker
                         NULL, // cookie
                         JL_OPTIONS_HANDLE_SIGNALS_ON,
+                        JL_OPTIONS_USE_EXPERIMENTAL_FEATURES_NO,
                         JL_OPTIONS_USE_SYSIMAGE_NATIVE_CODE_YES,
                         JL_OPTIONS_USE_COMPILED_MODULES_YES,
                         JL_OPTIONS_USE_PKGIMAGES_YES,
@@ -150,7 +151,7 @@ JL_DLLEXPORT void jl_init_options(void)
                         0, // permalloc_pkgimg
                         0, // heap-size-hint
                         0, // trace_compile_timing
-                        0, // trim
+                        JL_TRIM_NO, // trim
     };
     jl_options_initialized = 1;
 }
@@ -303,6 +304,7 @@ static const char opts_hidden[]  =
     "                                               functions\n\n"
 
     // compiler debugging and experimental (see the devdocs for tips on using these options)
+    " --experimental                                Enable the use of experimental (alpha) features\n"
     " --output-unopt-bc <name>                      Generate unoptimized LLVM bitcode (.bc)\n"
     " --output-bc <name>                            Generate LLVM bitcode (.bc)\n"
     " --output-asm <name>                           Generate an assembly file (.s)\n"
@@ -372,6 +374,7 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
            opt_gc_threads,
            opt_permalloc_pkgimg,
            opt_trim,
+           opt_experimental_features,
     };
     static const char* const shortopts = "+vhqH:e:E:L:J:C:it:p:O:g:m:";
     static const struct option longopts[] = {
@@ -427,6 +430,7 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
         { "math-mode",       required_argument, 0, opt_math_mode },
         { "handle-signals",  required_argument, 0, opt_handle_signals },
         // hidden command line options
+        { "experimental",    no_argument,       0, opt_experimental_features },
         { "worker",          optional_argument, 0, opt_worker },
         { "bind-to",         required_argument, 0, opt_bind_to },
         { "lisp",            no_argument,       0, 1 },
@@ -570,6 +574,9 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
             else
                 jl_errorf("julia: invalid argument to --banner={yes|no|auto|short} (%s)", optarg);
             break;
+        case opt_experimental_features:
+            jl_options.use_experimental_features = JL_OPTIONS_USE_EXPERIMENTAL_FEATURES_YES;
+            break;
         case opt_sysimage_native_code:
             if (!strcmp(optarg,"yes"))
                 jl_options.use_sysimage_native_code = JL_OPTIONS_USE_SYSIMAGE_NATIVE_CODE_YES;
@@ -977,6 +984,10 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
         }
     }
     parsing_args_done:
+    if (!jl_options.use_experimental_features) {
+        if (jl_options.trim != JL_TRIM_NO)
+            jl_errorf("julia: --trim is an experimental feature, you must enable it with --experimental");
+    }
     jl_options.code_coverage = codecov;
     jl_options.malloc_log = malloclog;
     int proc_args = *argcp < optind ? *argcp : optind;

src/jloptions.h

@@ -43,6 +43,7 @@ typedef struct {
     int8_t worker;
     const char *cookie;
     int8_t handle_signals;
+    int8_t use_experimental_features;
     int8_t use_sysimage_native_code;
     int8_t use_compiled_modules;
     int8_t use_pkgimages;

src/julia.h

@@ -2599,6 +2599,9 @@ JL_DLLEXPORT int jl_generating_output(void) JL_NOTSAFEPOINT;
 #define JL_OPTIONS_HANDLE_SIGNALS_ON 1
 #define JL_OPTIONS_HANDLE_SIGNALS_OFF 0
 
+#define JL_OPTIONS_USE_EXPERIMENTAL_FEATURES_YES 1
+#define JL_OPTIONS_USE_EXPERIMENTAL_FEATURES_NO 0
+
 #define JL_OPTIONS_USE_SYSIMAGE_NATIVE_CODE_YES 1
 #define JL_OPTIONS_USE_SYSIMAGE_NATIVE_CODE_NO 0