Add Base.invoke_in_world and _apply_in_world builtin (#35844)

New builtin `Core._apply_in_world` to allow frozen-world APIs to be
implemented in pure Julia code. Also add an internal, experimental API
`Base.invoke_in_world()` in analogy to `Base.invokelatest()` to make this
easier to use (especially for keyword args) and to give us a place to
put some documentation.

base/essentials.jl

@@ -716,6 +716,40 @@ function invokelatest(@nospecialize(f), @nospecialize args...; kwargs...)
     Core._apply_latest(inner)
 end
 
+"""
+    invoke_in_world(world, f, args...; kwargs...)
+
+Call `f(args...; kwargs...)` in a fixed world age, `world`.
+
+This is useful for infrastructure running in the user's Julia session which is
+not part of the user's program. For example, things related to the REPL, editor
+support libraries, etc. In these cases it can be useful to prevent unwanted
+method invalidation and recompilation latency, and to prevent the user from
+breaking supporting infrastructure by mistake.
+
+The current world age can be queried using [`Base.get_world_counter()`](@ref)
+and stored for later use within the lifetime of the current Julia session, or
+when serializing and reloading the system image.
+
+Technically, `invoke_in_world` will prevent any function called by `f` from
+being extended by the user during their Julia session. That is, generic
+function method tables seen by `f` (and any functions it calls) will be frozen
+as they existed at the given `world` age. In a sense, this is like the opposite
+of [`invokelatest`](@ref).
+
+!!! note
+    It is not valid to store world ages obtained in precompilation for later use.
+    This is because precompilation generates a "parallel universe" where the
+    world age refers to system state unrelated to the main Julia session.
+"""
+function invoke_in_world(world::UInt, @nospecialize(f), @nospecialize args...; kwargs...)
+    if isempty(kwargs)
+        return Core._apply_in_world(world, f, args)
+    end
+    inner() = f(args...; kwargs...)
+    Core._apply_in_world(world, inner)
+end
+
 # TODO: possibly make this an intrinsic
 inferencebarrier(@nospecialize(x)) = Ref{Any}(x)[]
 

src/builtin_proto.h

@@ -24,6 +24,7 @@ DECLARE_BUILTIN(typeof);     DECLARE_BUILTIN(sizeof);
 DECLARE_BUILTIN(issubtype);  DECLARE_BUILTIN(isa);
 DECLARE_BUILTIN(_apply);     DECLARE_BUILTIN(_apply_pure);
 DECLARE_BUILTIN(_apply_latest); DECLARE_BUILTIN(_apply_iterate);
+DECLARE_BUILTIN(_apply_in_world);
 DECLARE_BUILTIN(isdefined);  DECLARE_BUILTIN(nfields);
 DECLARE_BUILTIN(tuple);      DECLARE_BUILTIN(svec);
 DECLARE_BUILTIN(getfield);   DECLARE_BUILTIN(setfield);

src/builtins.c

@@ -707,6 +707,24 @@ JL_CALLABLE(jl_f__apply_latest)
     return ret;
 }
 
+// Like `_apply`, but runs in the specified world.
+// If world > jl_world_counter, run in the latest world.
+JL_CALLABLE(jl_f__apply_in_world)
+{
+    JL_NARGSV(_apply_in_world, 2);
+    jl_ptls_t ptls = jl_get_ptls_states();
+    size_t last_age = ptls->world_age;
+    JL_TYPECHK(_apply_in_world, ulong, args[0]);
+    size_t world = jl_unbox_ulong(args[0]);
+    world = world <= jl_world_counter ? world : jl_world_counter;
+    if (!ptls->in_pure_callback) {
+        ptls->world_age = world;
+    }
+    jl_value_t *ret = do_apply(NULL, args+1, nargs-1, NULL);
+    ptls->world_age = last_age;
+    return ret;
+}
+
 // tuples ---------------------------------------------------------------------
 
 JL_CALLABLE(jl_f_tuple)
@@ -1527,6 +1545,7 @@ void jl_init_primitives(void) JL_GC_DISABLED
     jl_builtin_svec = add_builtin_func("svec", jl_f_svec);
     add_builtin_func("_apply_pure", jl_f__apply_pure);
     add_builtin_func("_apply_latest", jl_f__apply_latest);
+    add_builtin_func("_apply_in_world", jl_f__apply_in_world);
     add_builtin_func("_typevar", jl_f__typevar);
     add_builtin_func("_structtype", jl_f__structtype);
     add_builtin_func("_abstracttype", jl_f__abstracttype);

src/codegen.cpp

@@ -786,6 +786,7 @@ static const std::map<jl_fptr_args_t, JuliaFunction*> builtin_func_map = {
     { &jl_f__apply_iterate,     new JuliaFunction{"jl_f__apply_iterate", get_func_sig, get_func_attrs} },
     { &jl_f__apply_pure,        new JuliaFunction{"jl_f__apply_pure", get_func_sig, get_func_attrs} },
     { &jl_f__apply_latest,      new JuliaFunction{"jl_f__apply_latest", get_func_sig, get_func_attrs} },
+    { &jl_f__apply_in_world,    new JuliaFunction{"jl_f__apply_in_world", get_func_sig, get_func_attrs} },
     { &jl_f_throw,              new JuliaFunction{"jl_f_throw", get_func_sig, get_func_attrs} },
     { &jl_f_tuple,              jltuple_func },
     { &jl_f_svec,               new JuliaFunction{"jl_f_svec", get_func_sig, get_func_attrs} },

src/staticdata.c

@@ -117,7 +117,8 @@ void *native_functions;
 // This is a manually constructed dual of the fvars array, which would be produced by codegen for Julia code, for C.
 static const jl_fptr_args_t id_to_fptrs[] = {
     &jl_f_throw, &jl_f_is, &jl_f_typeof, &jl_f_issubtype, &jl_f_isa,
-    &jl_f_typeassert, &jl_f__apply, &jl_f__apply_iterate, &jl_f__apply_pure, &jl_f__apply_latest, &jl_f_isdefined,
+    &jl_f_typeassert, &jl_f__apply, &jl_f__apply_iterate, &jl_f__apply_pure,
+    &jl_f__apply_latest, &jl_f__apply_in_world, &jl_f_isdefined,
     &jl_f_tuple, &jl_f_svec, &jl_f_intrinsic_call, &jl_f_invoke_kwsorter,
     &jl_f_getfield, &jl_f_setfield, &jl_f_fieldtype, &jl_f_nfields,
     &jl_f_arrayref, &jl_f_const_arrayref, &jl_f_arrayset, &jl_f_arraysize, &jl_f_apply_type,

test/worlds.jl

@@ -324,3 +324,17 @@ w = worlds(mi)
 abstract type Colorant35855 end
 Base.convert(::Type{C}, c) where C<:Colorant35855 = false
 @test_broken worlds(mi) == w
+
+# invoke_in_world
+f_inworld(x) = "world one; x=$x"
+g_inworld(x; y) = "world one; x=$x, y=$y"
+wc_aiw1 = get_world_counter()
+# redefine f_inworld, g_inworld, and check that we can invoke both versions
+f_inworld(x) = "world two; x=$x"
+g_inworld(x; y) = "world two; x=$x, y=$y"
+wc_aiw2 = get_world_counter()
+@test Base.invoke_in_world(wc_aiw1, f_inworld, 2) == "world one; x=2"
+@test Base.invoke_in_world(wc_aiw2, f_inworld, 2) == "world two; x=2"
+@test Base.invoke_in_world(wc_aiw1, g_inworld, 2, y=3) == "world one; x=2, y=3"
+@test Base.invoke_in_world(wc_aiw2, g_inworld, 2, y=3) == "world two; x=2, y=3"
+