fix JuliaLang#42220: macro hygiene with unary :: (JuliaLang#42221)

src/macroexpand.scm

@@ -271,7 +271,9 @@
  (define (other x) (resolve-expansion-vars-with-new-env x env m parent-scope inarg))
  (case (car e)
  ((where) `(where ,(recur (cadr e)) ,@(map other (cddr e))))
- ((|::|) `(|::| ,(recur (cadr e)) ,(other (caddr e))))
+ ((|::|) (if (length= e 2)
+ `(|::| ,(other (cadr e)))
+ `(|::| ,(recur (cadr e)) ,(other (caddr e)))))
  ((call) `(call ,(other (cadr e))
  ,@(map (lambda (x)
  (resolve-expansion-vars-with-new-env x env m parent-scope #t))
@@ -397,13 +399,18 @@
  ((not (length> e 2)) e)
  ((and (pair? (cadr e))
  (eq? (caadr e) '|::|))
- `(kw (|::|
- ,(if inarg
- (resolve-expansion-vars- (cadr (cadr e)) env m parent-scope inarg)
- ;; in keyword arg A=B, don't transform "A"
- (unescape (cadr (cadr e))))
- ,(resolve-expansion-vars- (caddr (cadr e)) env m parent-scope inarg))
- ,(resolve-expansion-vars-with-new-env (caddr e) env m parent-scope inarg)))
+ (let* ((type-decl (cadr e)) ;; [argname]::type
+ (argname (and (length> type-decl 2) (cadr type-decl)))
+ (type (if argname (caddr type-decl) (cadr type-decl))))
+ `(kw (|::|
+ ,@(if argname
+ (list (if inarg
+ (resolve-expansion-vars- argname env m parent-scope inarg)
+ ;; in keyword arg A=B, don't transform "A"
+ (unescape argname)))
+ '())
+ ,(resolve-expansion-vars- type env m parent-scope inarg))
+ ,(resolve-expansion-vars-with-new-env (caddr e) env m parent-scope inarg))))
  (else
  `(kw ,(if inarg
  (resolve-expansion-vars- (cadr e) env m parent-scope inarg)

test/syntax.jl

@@ -2966,3 +2966,14 @@ end
 
 @generated g25678(x) = return :x
 @test g25678(7) === 7
+
+# issue 42220
+macro m42220()
+ return quote
+ function foo(::Type{T}=Float64) where {T}
+ return Vector{T}(undef, 10)
+ end
+ end
+end
+@test @m42220()() isa Vector{Float64}
+@test @m42220()(Bool) isa Vector{Bool}