From fd4b37125217ba71223d7d1e1cfe6851bc5a2d2c Mon Sep 17 00:00:00 2001
From: "Steven G. Johnson" <stevenj@alum.mit.edu>
Date: Fri, 30 Dec 2016 16:56:30 -0500
Subject: [PATCH] add invokelatest function to work around world-age problems
 (#19774) without using eval

---
 NEWS.md                |  4 ++++
 base/essentials.jl     | 13 +++++++++++++
 base/exports.jl        |  1 +
 doc/src/stdlib/base.md |  1 +
 src/gf.c               | 18 ++++++++++++++++++
 test/misc.jl           |  9 +++++++++
 6 files changed, 46 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index 1e73f8b53a05a2..34f807cc559daa 100644
--- a/NEWS.md
+++ b/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
 -----------------------------
 
diff --git a/base/essentials.jl b/base/essentials.jl
index 8bd8d17ad6aaa2..40237820036998 100644
--- a/base/essentials.jl
+++ b/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)
diff --git a/base/exports.jl b/base/exports.jl
index 7109b9d136b228..ce341904e76d55 100644
--- a/base/exports.jl
+++ b/base/exports.jl
@@ -1066,6 +1066,7 @@ export
     atreplinit,
     clipboard,
     exit,
+    invokelatest,
     ntuple,
     quit,
 
diff --git a/doc/src/stdlib/base.md b/doc/src/stdlib/base.md
index 071b45b7cf03a3..d5c9caac62a447 100644
--- a/doc/src/stdlib/base.md
+++ b/doc/src/stdlib/base.md
@@ -121,6 +121,7 @@ Base.instances
 Base.method_exists
 Core.applicable
 Core.invoke
+Base.invokelatest
 Base.:(|>)
 ```
 
diff --git a/src/gf.c b/src/gf.c
index 60d98366878f68..b9df541937ba55 100644
--- a/src/gf.c
+++ b/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;
diff --git a/test/misc.jl b/test/misc.jl
index 7598c6d3f3eea2..052dc54562c5dc 100644
--- a/test/misc.jl
+++ b/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