bpart: Give a warning when accessing a backdated const binding

This implements the strategy proposed in #57102 (comment).
Example:
```
julia> function foo(i)
           eval(:(const x = $i))
           x
       end
foo (generic function with 1 method)

julia> foo(1)
WARNING: Detected access to binding Main.x in a world prior to its definition world.
  Julia 1.12 has introduced more strict world age semantics for global bindings.
  !!! This code may malfunction under Revise.
  !!! This code will error in future versions of Julia.
Hint: Add an appropriate `invokelatest` around the access to this binding.
1
```

The warning is triggered once per binding to avoid spamming for repeated access.

Author: Keno

Compiler/src/Compiler.jl

@@ -49,7 +49,8 @@ using Core: ABIOverride, Builtin, CodeInstance, IntrinsicFunction, MethodInstanc
 
 using Base
 using Base: @_foldable_meta, @_gc_preserve_begin, @_gc_preserve_end, @nospecializeinfer,
-    BINDING_KIND_GLOBAL, BINDING_KIND_UNDEF_CONST, Base, BitVector, Bottom, Callable, DataTypeFieldDesc,
+    BINDING_KIND_GLOBAL, BINDING_KIND_UNDEF_CONST, BINDING_KIND_BACKDATED_CONST,
+    Base, BitVector, Bottom, Callable, DataTypeFieldDesc,
     EffectsOverride, Filter, Generator, IteratorSize, JLOptions, NUM_EFFECTS_OVERRIDES,
     OneTo, Ordering, RefValue, SizeUnknown, _NAMEDTUPLE_NAME,
     _array_for, _bits_findnext, _methods_by_ftype, _uniontypes, all, allocatedinline, any,

Compiler/src/abstractinterpretation.jl

@@ -3524,6 +3524,11 @@ function abstract_eval_partition_load(interp::AbstractInterpreter, partition::Co
     end
 
     if is_defined_const_binding(kind)
+        if kind == BINDING_KIND_BACKDATED_CONST
+            # Infer this as guard. We do not want a later const definition to retroactively improve
+            # inference results in an earlier world.
+            return RTEffects(Any, UndefVarError, generic_getglobal_effects)
+        end
         rt = Const(partition_restriction(partition))
         return RTEffects(rt, Union{}, Effects(EFFECTS_TOTAL, inaccessiblememonly=is_mutation_free_argtype(rt) ? ALWAYS_TRUE : ALWAYS_FALSE))
     end

Compiler/src/ssair/slot2ssa.jl

@@ -137,10 +137,6 @@ function fixemup!(@specialize(slot_filter), @specialize(rename_slot), ir::IRCode
                 return nothing
             end
             op[] = x
-        elseif isa(val, GlobalRef) && !(isdefined(val.mod, val.name) && isconst(val.mod, val.name))
-            typ = typ_for_val(val, ci, ir, idx, Any[])
-            new_inst = NewInstruction(val, typ)
-            op[] = NewSSAValue(insert_node!(ir, idx, new_inst).id - length(ir.stmts))
         elseif isexpr(val, :static_parameter)
             ty = typ_for_val(val, ci, ir, idx, Any[])
             if isa(ty, Const)

Compiler/test/invalidation.jl

@@ -55,7 +55,7 @@ let mi = Base.method_instance(basic_caller, (Float64,))
 end
 
 # this redefinition below should invalidate the cache
-const BASIC_CALLER_WORLD = Base.get_world_counter()
+const BASIC_CALLER_WORLD = Base.get_world_counter()+1
 basic_callee(x) = x, x
 @test !isdefined(Base.method_instance(basic_callee, (Float64,)), :cache)
 let mi = Base.method_instance(basic_caller, (Float64,))

base/Base_compiler.jl

@@ -257,6 +257,10 @@ using .Order
 include("coreir.jl")
 include("invalidation.jl")
 
+# Because lowering inserts direct references, it is mandatory for this binding
+# to exist before we start inferring code.
+function string end
+
 # For OS specific stuff
 # We need to strcat things here, before strings are really defined
 function strcat(x::String, y::String)

base/boot.jl

@@ -717,7 +717,8 @@ macro __doc__(x)
 end
 
 isbasicdoc(@nospecialize x) = (isa(x, Expr) && x.head === :.) || isa(x, Union{QuoteNode, Symbol})
-iscallexpr(ex::Expr) = (isa(ex, Expr) && ex.head === :where) ? iscallexpr(ex.args[1]) : (isa(ex, Expr) && ex.head === :call)
+firstarg(arg1, args...) = arg1
+iscallexpr(ex::Expr) = (isa(ex, Expr) && ex.head === :where) ? iscallexpr(firstarg(ex.args...)) : (isa(ex, Expr) && ex.head === :call)
 iscallexpr(ex) = false
 function ignoredoc(source, mod, str, expr)
     (isbasicdoc(expr) || iscallexpr(expr)) && return Expr(:escape, nothing)

base/docs/bindings.jl

@@ -16,8 +16,8 @@ end
 
 bindingexpr(x) = Expr(:call, Binding, splitexpr(x)...)
 
-defined(b::Binding) = isdefined(b.mod, b.var)
-resolve(b::Binding) = getfield(b.mod, b.var)
+defined(b::Binding) = invokelatest(isdefined, b.mod, b.var)
+resolve(b::Binding) = invokelatest(getfield, b.mod, b.var)
 
 function splitexpr(x::Expr)
     isexpr(x, :macrocall) ? splitexpr(x.args[1]) :

base/runtime_internals.jl

@@ -229,8 +229,9 @@ const BINDING_KIND_FAILED       = 0x6
 const BINDING_KIND_DECLARED     = 0x7
 const BINDING_KIND_GUARD        = 0x8
 const BINDING_KIND_UNDEF_CONST  = 0x9
+const BINDING_KIND_BACKDATED_CONST = 0xa
 
-is_defined_const_binding(kind::UInt8) = (kind == BINDING_KIND_CONST || kind == BINDING_KIND_CONST_IMPORT)
+is_defined_const_binding(kind::UInt8) = (kind == BINDING_KIND_CONST || kind == BINDING_KIND_CONST_IMPORT || kind == BINDING_KIND_BACKDATED_CONST)
 is_some_const_binding(kind::UInt8) = (is_defined_const_binding(kind) || kind == BINDING_KIND_UNDEF_CONST)
 is_some_imported(kind::UInt8) = (kind == BINDING_KIND_IMPLICIT || kind == BINDING_KIND_EXPLICIT || kind == BINDING_KIND_IMPORTED)
 is_some_guard(kind::UInt8) = (kind == BINDING_KIND_GUARD || kind == BINDING_KIND_DECLARED || kind == BINDING_KIND_FAILED || kind == BINDING_KIND_UNDEF_CONST)

base/show.jl

@@ -542,8 +542,8 @@ function show_function(io::IO, f::Function, compact::Bool, fallback::Function)
         fallback(io, f)
     elseif compact
         print(io, mt.name)
-    elseif isdefined(mt, :module) && isdefined(mt.module, mt.name) &&
-        getfield(mt.module, mt.name) === f
+    elseif isdefined(mt, :module) && isdefinedglobal(mt.module, mt.name) &&
+            getglobal(mt.module, mt.name) === f
         # this used to call the removed internal function `is_exported_from_stdlib`, which effectively
         # just checked for exports from Core and Base.
         mod = get(io, :module, UsesCoreAndBaseOnly)
@@ -1025,15 +1025,15 @@ function isvisible(sym::Symbol, parent::Module, from::Module)
     from_owner = ccall(:jl_binding_owner, Ptr{Cvoid}, (Any, Any), from, sym)
     return owner !== C_NULL && from_owner === owner &&
         !isdeprecated(parent, sym) &&
-        isdefined(from, sym) # if we're going to return true, force binding resolution
+        isdefinedglobal(from, sym) # if we're going to return true, force binding resolution
 end
 
 function is_global_function(tn::Core.TypeName, globname::Union{Symbol,Nothing})
     if globname !== nothing
         globname_str = string(globname::Symbol)
         if ('#' ∉ globname_str && '@' ∉ globname_str && isdefined(tn, :module) &&
-                isbindingresolved(tn.module, globname) && isdefined(tn.module, globname) &&
-                isconcretetype(tn.wrapper) && isa(getfield(tn.module, globname), tn.wrapper))
+                isbindingresolved(tn.module, globname) && isdefinedglobal(tn.module, globname) &&
+                isconcretetype(tn.wrapper) && isa(getglobal(tn.module, globname), tn.wrapper))
             return true
         end
     end
@@ -3364,7 +3364,10 @@ function print_partition(io::IO, partition::Core.BindingPartition)
     end
     print(io, " - ")
     kind = binding_kind(partition)
-    if is_defined_const_binding(kind)
+    if kind == BINDING_KIND_BACKDATED_CONST
+        print(io, "backdated constant binding to ")
+        print(io, partition_restriction(partition))
+    elseif is_defined_const_binding(kind)
         print(io, "constant binding to ")
         print(io, partition_restriction(partition))
     elseif kind == BINDING_KIND_UNDEF_CONST

src/codegen.cpp

@@ -3467,7 +3467,8 @@ static jl_cgval_t emit_globalref(jl_codectx_t &ctx, jl_module_t *mod, jl_sym_t *
                 break;
             pku = jl_atomic_load_acquire(&bpart->restriction);
         }
-        if (bpart && jl_bkind_is_some_constant(decode_restriction_kind(pku))) {
+        enum jl_partition_kind kind = decode_restriction_kind(pku);
+        if (bpart && (jl_bkind_is_some_constant(kind) && kind != BINDING_KIND_BACKDATED_CONST)) {
             jl_value_t *constval = decode_restriction_value(pku);
             if (!constval) {
                 undef_var_error_ifnot(ctx, ConstantInt::get(getInt1Ty(ctx.builder.getContext()), 0), name, (jl_value_t*)mod);