Return type annotations fail to parse on functions with no body

[iamed2]

julia> function func()::Void end
syntax: malformed expression

julia> function func()::Void
       end
syntax: malformed expression

julia> function func()::Int
       end
syntax: malformed expression

julia> versioninfo()
Julia Version 0.5.1-pre+2
Commit f0d40ec* (2016-09-20 03:34 UTC)
Platform Info:
  System: Darwin (x86_64-apple-darwin16.0.0)
  CPU: Intel(R) Core(TM) i7-5557U CPU @ 3.10GHz
  WORD_SIZE: 64
  BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Haswell)
  LAPACK: libopenblas64_
  LIBM: libopenlibm
  LLVM: libLLVM-3.7.1 (ORCJIT, broadwell)

[ihnorton]

This won't do what you want (see #16432 (comment)), but we can give a better error message.

[iamed2]

I don't think any of these should error on definition. Given:

julia> function g() end
g (generic function with 1 method)

julia> @code_lowered g()
LambdaInfo template for g() at REPL[6]:1
:(begin
        nothing
        return
    end)

julia> function f()::Int
           nothing
       end
f (generic function with 1 method)

julia> @code_lowered f()
LambdaInfo template for f() at REPL[5]:2
:(begin
        nothing
        return (Base.convert)(Main.Int,Main.nothing)
    end)

julia> function h()::Int
           nothing
           return
       end
h (generic function with 1 method)

julia> @code_lowered h()
LambdaInfo template for h() at REPL[9]:2
:(begin
        nothing
        SSAValue(0) = Main.Int
        Main.nothing # line 3:
        return (Core.typeassert)((Base.convert)(SSAValue(0),nothing),SSAValue(0))
    end)

I would expect a call to this function:

function i()::Int
end

to lower to either:

:(begin
        SSAValue(0) = Main.Int
        Main.nothing
        return (Core.typeassert)((Base.convert)(SSAValue(0),nothing),SSAValue(0))
    end)

or

:(begin
        return (Base.convert)(Main.Int,Main.nothing)
    end)

[ihnorton]

@JeffBezanson this works, but not sure if there are other cases to handle:

diff --git a/src/julia-syntax.scm b/src/julia-syntax.scm
index 09f6459..0353684 100644
--- a/src/julia-syntax.scm
+++ b/src/julia-syntax.scm
@@ -3380,9 +3380,9 @@ f(x) = yt(x)
                           ;; strip filenames out of non-initial line nodes
                           (emit `(line ,(cadr e)))))
                      ((and (eq? (car e) 'meta) (length> e 2) (eq? (cadr e) 'ret-type))
-                      (assert (not value))
                       (assert (not rett))
-                      (set! rett (caddr e)))
+                      (set! rett (caddr e))
+                      (if (not value) (emit-return rett)))
                      (else
                       (emit e)))
                (if (and tail (not have-ret?))

[JeffBezanson]

The last line of that patch doesn't make sense; it says to return the value rett itself, i.e. return Void in this case.

[iamed2]

Is a backport possible?

[tkelman]

#19114 is already labeled. Be careful to declare your minimum version dependency as 0.5.1 if you want to rely on this working though.