From 62a745327b6330024b6a3a4d6e5c1a6d325a894d Mon Sep 17 00:00:00 2001
From: Fernando Chorney <djsbx@djsbx.com>
Date: Thu, 11 Jun 2020 14:12:43 -0500
Subject: [PATCH] Add 2 arg @inferred (#706)

* Add 2 arg @inferred

* Update version to 3.12.0

* Update src/Compat.jl

Use using instead of import

Co-authored-by: Curtis Vogt <curtis.vogt@gmail.com>

Co-authored-by: Curtis Vogt <curtis.vogt@gmail.com>
---
 Project.toml     |  2 +-
 README.md        |  3 +++
 src/Compat.jl    | 50 ++++++++++++++++++++++++++++++++++++++++++++++++
 test/runtests.jl |  9 +++++++++
 4 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/Project.toml b/Project.toml
index 0f346dbfb..3884a49e2 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "Compat"
 uuid = "34da2185-b29b-5c13-b0c7-acf172513d20"
-version = "3.11.0"
+version = "3.12.0"
 
 [deps]
 Base64 = "2a0f44e3-6c83-55bd-87e4-b1978d98bd5f"
diff --git a/README.md b/README.md
index ee611674e..cfe74e35f 100644
--- a/README.md
+++ b/README.md
@@ -44,6 +44,8 @@ Please check the list below for the specific syntax you need.
 
 ## Supported features
 
+* `@inferred [AllowedType] f(x)` is defined ([#27516]). (since Compat 3.12.0)
+
 * Search a character in a string with `findfirst`, `findnext`, `findlast` and `findprev` ([#31664]). (since Compat 3.12.0)
 
 * `∘(f) = f` is defined ([#34251]). (since Compat 3.11.0)
@@ -160,3 +162,4 @@ Note that you should specify the correct minimum version for `Compat` in the
 [#30268]: https://github.com/JuliaLang/julia/pull/30268
 [#34251]: https://github.com/JuliaLang/julia/pull/34251
 [#35577]: https://github.com/JuliaLang/julia/pull/35577
+[#27516]: https://github.com/JuliaLang/julia/pull/27516
diff --git a/src/Compat.jl b/src/Compat.jl
index 76596c381..f379c44e3 100644
--- a/src/Compat.jl
+++ b/src/Compat.jl
@@ -414,6 +414,56 @@ if VERSION < v"1.5.0-DEV.681"
     Base.union(r::Base.OneTo, s::Base.OneTo) = Base.OneTo(max(r.stop,s.stop))
 end
 
+# https://github.com/JuliaLang/julia/pull/27516
+if VERSION < v"1.2.0-DEV.77"
+    import Test: @inferred
+    using Core.Compiler: typesubtract
+
+    macro inferred(allow, ex)
+        _inferred(ex, __module__, allow)
+    end
+
+    function _inferred(ex, mod, allow = :(Union{}))
+        if Meta.isexpr(ex, :ref)
+            ex = Expr(:call, :getindex, ex.args...)
+        end
+        Meta.isexpr(ex, :call)|| error("@inferred requires a call expression")
+        farg = ex.args[1]
+        if isa(farg, Symbol) && first(string(farg)) == '.'
+            farg = Symbol(string(farg)[2:end])
+            ex = Expr(:call, GlobalRef(Base.Test, :_materialize_broadcasted),
+                farg, ex.args[2:end]...)
+        end
+        Base.remove_linenums!(quote
+            let
+                allow = $(esc(allow))
+                allow isa Type || throw(ArgumentError("@inferred requires a type as second argument"))
+                $(if any(a->(Meta.isexpr(a, :kw) || Meta.isexpr(a, :parameters)), ex.args)
+                    # Has keywords
+                    args = gensym()
+                    kwargs = gensym()
+                    quote
+                        $(esc(args)), $(esc(kwargs)), result = $(esc(Expr(:call, _args_and_call, ex.args[2:end]..., ex.args[1])))
+                        inftypes = $(gen_call_with_extracted_types(mod, Base.return_types, :($(ex.args[1])($(args)...; $(kwargs)...))))
+                    end
+                else
+                    # No keywords
+                    quote
+                        args = ($([esc(ex.args[i]) for i = 2:length(ex.args)]...),)
+                        result = $(esc(ex.args[1]))(args...)
+                        inftypes = Base.return_types($(esc(ex.args[1])), Base.typesof(args...))
+                    end
+                end)
+                @assert length(inftypes) == 1
+                rettype = result isa Type ? Type{result} : typeof(result)
+                rettype <: allow || rettype == typesubtract(inftypes[1], allow) || error("return type $rettype does not match inferred return type $(inftypes[1])")
+                result
+            end
+        end)
+    end
+    #export @inferred
+end
+
 include("deprecated.jl")
 
 end # module Compat
diff --git a/test/runtests.jl b/test/runtests.jl
index bfbb37079..fd08efe16 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -455,4 +455,13 @@ end
     @test union(Base.OneTo(3), Base.OneTo(4)) === Base.OneTo(4)
 end
 
+# https://github.com/JuliaLang/julia/pull/27516
+@testset "two arg @inferred" begin
+    g(a) = a < 10 ? missing : 1
+    @test ismissing(g(9))
+    @test g(10) == 1
+    @inferred Missing g(9)
+    @inferred Missing g(10)
+end
+
 nothing