Allow macrocall as function sig (#55040)

@KristofferC requested that `function @main(args) end` should work. This
is currently a parse error. This PR makes it work as expected by
allowing macrocall as a valid signature in function (needs to exapand to
a call expr). Note that this is only the flisp changes. If this PR is
accepted, an equivalent change would need to be made in JuliaSyntax.

(cherry picked from commit b65f004)

Author: Keno

NEWS.md

@@ -50,6 +50,8 @@ Language changes
 * It is now an error to mark a binding as both `public` and `export`ed ([#53664]).
 * Errors during `getfield` now raise a new `FieldError` exception type instead of the generic
   `ErrorException` ([#54504]).
+* Macros in function-signature-position no longer require parentheses. E.g. `function @main(args) ... end` is now permitted, whereas `function (@main)(args) ... end` was required in prior Julia versions.
+
 
 Compiler/Runtime improvements
 -----------------------------

base/client.jl

@@ -605,7 +605,7 @@ The `@main` macro may be used standalone or as part of the function definition,
 case, parentheses are required. In particular, the following are equivalent:
 
 ```
-function (@main)(args)
+function @main(args)
     println("Hello World")
 end
 ```
@@ -624,7 +624,7 @@ imported into `Main`, it will be treated as an entrypoint in `Main`:
 ```
 module MyApp
     export main
-    (@main)(args) = println("Hello World")
+    @main(args) = println("Hello World")
 end
 using .MyApp
 # `julia` Will execute MyApp.main at the conclusion of script execution
@@ -634,7 +634,7 @@ Note that in particular, the semantics do not attach to the method
 or the name:
 ```
 module MyApp
-    (@main)(args) = println("Hello World")
+    @main(args) = println("Hello World")
 end
 const main = MyApp.main
 # `julia` Will *NOT* execute MyApp.main unless there is a separate `@main` annotation in `Main`
@@ -644,9 +644,6 @@ const main = MyApp.main
     This macro is new in Julia 1.11. At present, the precise semantics of `@main` are still subject to change.
 """
 macro main(args...)
-    if !isempty(args)
-        error("`@main` is expected to be used as `(@main)` without macro arguments.")
-    end
     if isdefined(__module__, :main)
         if Base.binding_module(__module__, :main) !== __module__
             error("Symbol `main` is already a resolved import in module $(__module__). `@main` must be used in the defining module.")
@@ -657,5 +654,9 @@ macro main(args...)
         global main
         global var"#__main_is_entrypoint__#"::Bool = true
     end)
-    esc(:main)
+    if !isempty(args)
+        Expr(:call, esc(:main), map(esc, args)...)
+    else
+        esc(:main)
+    end
 end

src/julia-parser.scm

@@ -1329,13 +1329,13 @@
 
 (define (valid-func-sig? paren sig)
   (and (pair? sig)
-       (or (eq? (car sig) 'call)
-           (eq? (car sig) 'tuple)
+       (or (memq (car sig) '(call tuple))
+           (and (not paren) (eq? (car sig) 'macrocall))
            (and paren (eq? (car sig) 'block))
            (and paren (eq? (car sig) '...))
            (and (eq? (car sig) '|::|)
                 (pair? (cadr sig))
-                (eq? (car (cadr sig)) 'call))
+                (memq (car (cadr sig)) '(call macrocall)))
            (and (eq? (car sig) 'where)
                 (valid-func-sig? paren (cadr sig))))))
 

test/syntax.jl

@@ -4051,6 +4051,38 @@ end
     using .Base: zero, zero
 end
 
+
+# PR# 55040 - Macrocall as function sig
+@test :(function @f()() end) == :(function (@f)() end)
+
+function callme end
+macro callmemacro(args...)
+    Expr(:call, esc(:callme), map(esc, args)...)
+end
+function @callmemacro(a::Int)
+    return 1
+end
+@callmemacro(b::Float64) = 2
+function @callmemacro(a::T, b::T) where T <: Int
+    return 3
+end
+function @callmemacro(a::Int, b::Int, c::Int)::Float64
+    return 4
+end
+function @callmemacro(d::String)
+    (a, b, c)
+    # ^ Should not be accidentally parsed as an argument list
+    return 4
+end
+
+@test callme(1) === 1
+@test callme(2.0) === 2
+@test callme(3, 3) === 3
+@test callme(4, 4, 4) === 4.0
+
+# Ambiguous 1-arg anymous vs macrosig
+@test_parseerror "function (@foo(a)) end"
+
 # #57267 - Missing `latestworld` after typealias
 abstract type A57267{S, T} end
 @test_nowarn @eval begin