Add isnothing (#654)

Author: musm

README.md

@@ -120,6 +120,8 @@ Currently, the `@compat` macro supports the following syntaxes:
 
 ## New functions, macros, and methods
 
+* `isnothing` for testing if a variable is equal to `nothing` ([#29674]).
+
 * `Compat.readline` with `keep` keyword argument ([#25646])
 
 * `Compat.eachline` with `keep` keyword argument ([#25646])
@@ -573,3 +575,4 @@ includes this fix. Find the minimum version from there.
 [#28708]: https://github.com/JuliaLang/julia/issues/28708
 [#28850]: https://github.com/JuliaLang/julia/issues/28850
 [#29259]: https://github.com/JuliaLang/julia/issues/29259
+[#29674]: https://github.com/JuliaLang/julia/issues/29674

src/Compat.jl

@@ -924,6 +924,14 @@ end
     export Nothing, Cvoid
 end
 
+# https://github.com/JuliaLang/julia/pull/29679
+if VERSION < v"1.1.0-DEV.472"
+    export isnothing
+    isnothing(::Any) = false
+    isnothing(::Nothing) = true
+end
+
+
 @static if !isdefined(Base, :Some)
     import Base: promote_rule, convert
     struct Some{T}

test/runtests.jl

@@ -26,6 +26,10 @@ let s = "Koala test: 🐨"
     end
 end
 
+# julia#29679
+@test !isnothing(1)
+@test isnothing(nothing)
+
 # julia#26365
 @test Compat.tr([1 2; 3 5]) == 6