From f82ce5c89f3b319fd0b7692527ef28449c2a2795 Mon Sep 17 00:00:00 2001
From: Eric Davies <iamed2@gmail.com>
Date: Thu, 14 Jun 2018 16:19:12 -0500
Subject: [PATCH 1/3] Add hasfield to check for field existence

---
 base/exports.jl      |  1 +
 base/reflection.jl   | 21 +++++++++++++++++++++
 doc/src/base/base.md |  1 +
 3 files changed, 23 insertions(+)

diff --git a/base/exports.jl b/base/exports.jl
index b7492fc2a6b53..ad6fa04d4e828 100644
--- a/base/exports.jl
+++ b/base/exports.jl
@@ -714,6 +714,7 @@ export
     fieldname,
     fieldnames,
     fieldcount,
+    hasfield,
     propertynames,
     isabstracttype,
     isbitstype,
diff --git a/base/reflection.jl b/base/reflection.jl
index 12d7cbcd46540..2a9734a0f7000 100644
--- a/base/reflection.jl
+++ b/base/reflection.jl
@@ -560,6 +560,27 @@ function fieldindex(T::DataType, name::Symbol, err::Bool=true)
     return Int(ccall(:jl_field_index, Cint, (Any, Any, Cint), T, name, err)+1)
 end
 
+"""
+    hasfield(T, name::Symbol)
+
+Return `true` if a composite DataType `T` has a field called `name`.
+
+# Examples
+```jldoctest
+julia> struct Foo
+           x::Int64
+           y::String
+       end
+
+julia> Base.hasfield(Foo, :x)
+true
+
+julia> Base.hasfield(Foo, :balloon)
+false
+```
+"""
+hasfield(T::DataType, name::Symbol) = fieldindex(T, name, false) > 0
+
 argument_datatype(@nospecialize t) = ccall(:jl_argument_datatype, Any, (Any,), t)
 function argument_mt(@nospecialize t)
     dt = argument_datatype(t)
diff --git a/doc/src/base/base.md b/doc/src/base/base.md
index 030ffe3a837e4..4460b61da35bf 100644
--- a/doc/src/base/base.md
+++ b/doc/src/base/base.md
@@ -154,6 +154,7 @@ Base.isbitstype
 Core.fieldtype
 Base.fieldcount
 Base.fieldoffset
+Base.hasfield
 Base.datatype_alignment
 Base.datatype_haspadding
 Base.datatype_pointerfree

From cd302d093c35ecfb9fa98a08b11332e5df6f8e41 Mon Sep 17 00:00:00 2001
From: Eric Davies <iamed2@gmail.com>
Date: Fri, 15 Jun 2018 10:37:27 -0500
Subject: [PATCH 2/3] Add tests for hasfield

---
 test/reflection.jl | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/test/reflection.jl b/test/reflection.jl
index 6c57ba4bde132..c12bfeebbaf85 100644
--- a/test/reflection.jl
+++ b/test/reflection.jl
@@ -230,6 +230,11 @@ tlayout = TLayout(5,7,11)
 @test_throws ArgumentError fieldname(TLayout, 4)
 @test_throws BoundsError fieldoffset(TLayout, 4)
 
+for name in (:x, :y, :z)
+    @test hasfield(TLayout, name)
+end
+@test !hasfield(TLayout, :parameters)
+
 @test fieldtype(Tuple{Vararg{Int8}}, 1) === Int8
 @test fieldtype(Tuple{Vararg{Int8}}, 10) === Int8
 @test_throws BoundsError fieldtype(Tuple{Vararg{Int8}}, 0)

From da36b48eb2b2a4151c58eda6400d2aa76edb113f Mon Sep 17 00:00:00 2001
From: Eric Davies <iamed2@gmail.com>
Date: Fri, 15 Jun 2018 14:11:07 -0500
Subject: [PATCH 3/3] Add news for hasfield

---
 NEWS.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index df9d327cb2718..4a7ad9bae386c 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1269,6 +1269,8 @@ Deprecated or removed
 
   * `atan2` is now a 2-argument method of `atan` ([#27248]).
 
+  * `hasfield` was added to check if a composite type has a field of a given name ([#27582])
+
 Command-line option changes
 ---------------------------