Don't try to allocate new binding partitions from static show (#56298)

In particular static show is used inside the GC for profiling, which
showed up as a segfault on CI, e.g. in

https://buildkite.com/julialang/julia-master/builds/41407#0192b628-47f3-49f9-a081-cd2708eb6121.

GC check didn't catch it because that file is explicitly exempt:
https://github.com/JuliaLang/julia/blob/master/src/Makefile#L504

src/julia.h

@@ -1848,6 +1848,7 @@ JL_DLLEXPORT jl_sym_t *jl_tagged_gensym(const char *str, size_t len);
 JL_DLLEXPORT jl_sym_t *jl_get_root_symbol(void);
 JL_DLLEXPORT jl_value_t *jl_get_binding_value(jl_binding_t *b JL_PROPAGATES_ROOT);
 JL_DLLEXPORT jl_value_t *jl_get_binding_value_if_const(jl_binding_t *b JL_PROPAGATES_ROOT);
+JL_DLLEXPORT jl_value_t *jl_get_binding_value_if_resolved_and_const(jl_binding_t *b JL_PROPAGATES_ROOT) JL_NOTSAFEPOINT;
 JL_DLLEXPORT jl_value_t *jl_declare_const_gf(jl_binding_t *b, jl_module_t *mod, jl_sym_t *name);
 JL_DLLEXPORT jl_method_t *jl_method_def(jl_svec_t *argdata, jl_methtable_t *mt, jl_code_info_t *f, jl_module_t *module);
 JL_DLLEXPORT jl_code_info_t *jl_code_for_staged(jl_method_instance_t *linfo, size_t world, jl_code_instance_t **cache);

src/module.c

@@ -48,6 +48,7 @@ jl_binding_partition_t *jl_get_binding_partition(jl_binding_t *b, size_t world)
             return bpart;
         jl_binding_partition_t *new_bpart = new_binding_partition();
         jl_atomic_store_relaxed(&new_bpart->next, bpart);
+        jl_gc_wb_fresh(new_bpart, bpart);
         if (bpart)
             new_bpart->min_world = jl_atomic_load_relaxed(&bpart->max_world) + 1;
         jl_atomic_store_relaxed(&new_bpart->max_world, max_world);
@@ -350,6 +351,26 @@ JL_DLLEXPORT jl_value_t *jl_get_binding_value_if_const(jl_binding_t *b)
     return decode_restriction_value(pku);
 }
 
+JL_DLLEXPORT jl_value_t *jl_get_binding_value_if_resolved_and_const(jl_binding_t *b)
+{
+    // Unlike jl_get_binding_value_if_const this doesn't try to allocate new binding partitions if they
+    // don't already exist, making this JL_NOTSAFEPOINT.
+    if (!b)
+        return NULL;
+    jl_binding_partition_t *bpart = jl_atomic_load_relaxed(&b->partitions);
+    if (!bpart)
+        return NULL;
+    size_t max_world = jl_atomic_load_relaxed(&bpart->max_world);
+    if (bpart->min_world > jl_current_task->world_age || jl_current_task->world_age > max_world)
+        return NULL;
+    jl_ptr_kind_union_t pku = jl_atomic_load_relaxed(&bpart->restriction);
+    if (jl_bkind_is_some_guard(decode_restriction_kind(pku)))
+        return NULL;
+    if (!jl_bkind_is_some_constant(decode_restriction_kind(pku)))
+        return NULL;
+    return decode_restriction_value(pku);
+}
+
 JL_DLLEXPORT jl_value_t *jl_bpart_get_restriction_value(jl_binding_partition_t *bpart)
 {
     jl_ptr_kind_union_t pku = jl_atomic_load_relaxed(&bpart->restriction);

src/rtutils.c

@@ -661,7 +661,7 @@ static int is_globname_binding(jl_value_t *v, jl_datatype_t *dv) JL_NOTSAFEPOINT
     jl_sym_t *globname = dv->name->mt != NULL ? dv->name->mt->name : NULL;
     if (globname && dv->name->module) {
         jl_binding_t *b = jl_get_module_binding(dv->name->module, globname, 0);
-        jl_value_t *bv = jl_get_binding_value_if_const(b);
+        jl_value_t *bv = jl_get_binding_value_if_resolved_and_const(b);
         // The `||` makes this function work for both function instances and function types.
         if (bv && (bv == v || jl_typeof(bv) == v))
             return 1;