module: Tweak backdate-warning-turned error

This makes two changes to the backdate-warning-turned-error (#58266):
1. Fix a bug where the error would only trigger the first time. We do only want
   to print once per process, but of course, we do want to error every time if
   enabled.
2. If we are in speculative execution context (generators and speculatively run
   functions during inference), always use the UndefVarError. Effects from these
   functions are not supposed to be observable, and it's very confusing if the
   printed warning goes away when depwarns are enabled. This is marginally more
   breaking, but the burden is on generated function authors (which already have
   to be world-age aware and are somewhat more regularly broken) and is consistent
   with other things that are stronger errors in pure context.

Fixes #58648

Author: Keno

src/module.c

@@ -846,8 +846,6 @@ JL_DLLEXPORT jl_module_t *jl_get_module_of_binding(jl_module_t *m, jl_sym_t *var
 
 static NOINLINE void print_backdate_admonition(jl_binding_t *b) JL_NOTSAFEPOINT
 {
-    if (jl_options.depwarn == JL_OPTIONS_DEPWARN_ERROR)
-        jl_undefined_var_error(b->globalref->name, (jl_value_t*)b->globalref->mod);
     jl_safe_printf(
         "WARNING: Detected access to binding `%s.%s` in a world prior to its definition world.\n"
         "  Julia 1.12 has introduced more strict world age semantics for global bindings.\n"
@@ -860,9 +858,13 @@ static NOINLINE void print_backdate_admonition(jl_binding_t *b) JL_NOTSAFEPOINT
 
 static inline void check_backdated_binding(jl_binding_t *b, enum jl_partition_kind kind) JL_NOTSAFEPOINT
 {
-    if (__unlikely(kind == PARTITION_KIND_BACKDATED_CONST) &&
-        !(jl_atomic_fetch_or_relaxed(&b->flags, BINDING_FLAG_DID_PRINT_BACKDATE_ADMONITION) & BINDING_FLAG_DID_PRINT_BACKDATE_ADMONITION)) {
-        print_backdate_admonition(b);
+    if (__unlikely(kind == PARTITION_KIND_BACKDATED_CONST)) {
+        // We don't want functions that inference executes speculatively to print this warning, so turn those into
+        // an error for inference purposes.
+        if (jl_current_task->ptls->in_pure_callback || jl_options.depwarn == JL_OPTIONS_DEPWARN_ERROR)
+            jl_undefined_var_error(b->globalref->name, (jl_value_t*)b->globalref->mod);
+        if (!(jl_atomic_fetch_or_relaxed(&b->flags, BINDING_FLAG_DID_PRINT_BACKDATE_ADMONITION) & BINDING_FLAG_DID_PRINT_BACKDATE_ADMONITION))
+            print_backdate_admonition(b);
     }
 }