add invokelatest function to work around world-age problems (JuliaLan…

…g#19774) without using eval

NEWS.md

@@ -132,6 +132,10 @@ Library improvements
     implemented; the semantics are as if the `Nullable` were a container with
     zero or one elements ([#16961]).
 
+  * New function `invokelatest(f, args...)` to call the latest version
+    of a function in circumstances where an older version may be called
+    instead (in a `cfunction` or a function calling `eval`) ([#19784]).
+
 Compiler/Runtime improvements
 -----------------------------
 

base/essentials.jl

@@ -239,3 +239,16 @@ function vector_any(xs::ANY...)
 end
 
 isempty(itr) = done(itr, start(itr))
+
+"""
+    invokelatest(f, args...)
+
+Calls `f(args...)`, but guarantees that the most recent method of `f`
+will be executed.   This is useful in specialized circumstances,
+especially `cfunction` callbacks that may extract a Julia `Function`
+from a pointer, or Julia functions that call `eval` or similar,
+in which case obsolete versions of `f` may otherwise be called.
+(The drawback is that `invokelatest` is somewhat slower than calling
+`f` directly, and the type of the result cannot be inferred by the compiler.)
+"""
+invokelatest(f, args...) = ccall(:jl_invoke_latest, Any, (Any,Any), f, args)

base/exports.jl

@@ -1066,6 +1066,7 @@ export
     atreplinit,
     clipboard,
     exit,
+    invokelatest,
     ntuple,
     quit,
 

doc/src/stdlib/base.md

@@ -121,6 +121,7 @@ Base.instances
 Base.method_exists
 Core.applicable
 Core.invoke
+Base.invokelatest
 Base.:(|>)
 ```
 

src/gf.c

@@ -2197,6 +2197,24 @@ JL_DLLEXPORT jl_value_t *jl_apply_generic(jl_value_t **args, uint32_t nargs)
     return verify_type(res);
 }
 
+JL_DLLEXPORT jl_value_t *jl_invoke_latest(jl_value_t *f, jl_value_t *argtuple)
+{
+    assert(jl_is_tuple(argtuple));
+    size_t nargs = jl_nfields(argtuple);
+    jl_value_t **argv;
+    JL_GC_PUSHARGS(argv, nargs+1);
+    argv[0] = f;
+    for(int i=1; i<nargs+1; i++)
+        argv[i] = jl_fieldref(argtuple, i-1);
+    jl_ptls_t ptls = jl_get_ptls_states();
+    size_t last_age = ptls->world_age;
+    ptls->world_age = jl_get_world_counter();
+    jl_value_t *v = jl_apply(argv, nargs+1);
+    ptls->world_age = last_age;
+    JL_GC_POP();
+    return v;
+}
+
 JL_DLLEXPORT jl_value_t *jl_gf_invoke_lookup(jl_datatype_t *types, size_t world)
 {
     jl_methtable_t *mt = ((jl_datatype_t*)jl_tparam0(types))->name->mt;

test/misc.jl

@@ -482,3 +482,12 @@ let
         eval(Base, :(have_color = $(old_have_color)))
     end
 end
+
+# invokelatest function for issue #19774
+issue19774(x) = 1
+let foo() = begin
+        eval(:(issue19774(x::Int) = 2))
+        return invokelatest(issue19774, 0)
+    end
+    @test foo() == 2
+end