`@kwdef` fails on structs with supertypes

[arthurp]

This is best explained with an example:

julia> abstract type Super end

julia> Base.@kwdef struct S <: Super; v; end
ERROR: syntax: invalid function name "S <: Super"

julia> @macroexpand Base.@kwdef struct S <: Super; v; end
quote
    #= util.jl:660 =#
    begin
        $(Expr(:meta, :doc))
        struct S1 <: Super
            #= none:1 =#
            v
        end
    end
    (S1 <: Super)(; v) = (S1 <: Super)(v)
end

@kwdef is blindly taking the first argument of the struct Expr and using as the function name. But the first argument includes the supertype when it is present. This means the function name includes the supertype annotation which is invalid.

I think the fix for this is simple and safe: Check for the case where the struct "name" is not a Symbol and further deconstruct it to get the real struct name. Patch below.

From 22f0ccfe0e97ad157aca6a917ccc2c299a1329c8 Mon Sep 17 00:00:00 2001
From: Arthur Peters <amp@singingwizard.org>
Date: Fri, 21 Sep 2018 12:32:24 -0500
Subject: [PATCH] Fix invalid code generation in @kwdef when struct has
 supertype.

---
 base/util.jl | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/base/util.jl b/base/util.jl
index 80c7907..d27dc03 100644
--- a/base/util.jl
+++ b/base/util.jl
@@ -652,7 +652,12 @@ Stacktrace:
 """
 macro kwdef(expr)
     expr = macroexpand(__module__, expr) # to expand @static
-    T = expr.args[2]
+    if expr.args[2] isa Symbol
+        T = expr.args[2]
+    else
+        @assert expr.args[2].head == :<:
+        T = expr.args[2].args[1]
+    end
     params_ex = Expr(:parameters)
     call_ex = Expr(:call, T)
     _kwdef!(expr.args[3], params_ex, call_ex)
-- 
2.17.1

(I explicitly release my copy rights, if any, to this patch, putting my contribution to this patch in the public domain.)

[simonbyrne]

Thanks for the issue and the patch. It occurs to me we don't handle parametric types very well either: I'll open pull request.