fix #45024, lost expected assignment after const error (#45344)

(cherry picked from commit 2d40898)

Author: JeffBezanson

src/julia-parser.scm

@@ -1355,11 +1355,19 @@
       (list 'where (rewrap-where x (cadr w)) (caddr w))
       x))
 
+(define (parse-struct-field s)
+  (let ((tok (peek-token s)))
+    ;; allow `const x` only as a struct field
+    (if (eq? tok 'const)
+        (begin (take-token s)
+               `(const ,(parse-eq s)))
+        (parse-eq s))))
+
 (define (parse-struct-def s mut? word)
   (if (reserved-word? (peek-token s))
       (error (string "invalid type name \"" (take-token s) "\"")))
   (let ((sig (parse-subtype-spec s)))
-    (begin0 (list 'struct (if mut? '(true) '(false)) sig (parse-block s))
+    (begin0 (list 'struct (if mut? '(true) '(false)) sig (parse-block s parse-struct-field))
             (expect-end s word))))
 
 ;; consume any number of line endings from a token stream
@@ -1456,7 +1464,13 @@
               `(const ,expr)
               expr)))
        ((const)
-        `(const ,(parse-eq s)))
+        (let ((assgn (parse-eq s)))
+          (if (not (and (pair? assgn)
+                        (or (eq? (car assgn) '=)
+                            (eq? (car assgn) 'global)
+                            (eq? (car assgn) 'local))))
+              (error "expected assignment after \"const\"")
+              `(const ,assgn))))
 
        ((function macro)
         (let* ((loc   (line-number-node s))

test/syntax.jl

@@ -3278,3 +3278,13 @@ demo44723()::Any = Base.Experimental.@opaque () -> true ? 1 : 2
 # issue #45162
 f45162(f) = f(x=1)
 @test first(methods(f45162)).called != 0
+
+# issue #45024
+@test_throws ParseError("expected assignment after \"const\"") Meta.parse("const x")
+@test_throws ParseError("expected assignment after \"const\"") Meta.parse("const x::Int")
+# these cases have always been caught during lowering, since (const (global x)) is not
+# ambiguous with the lowered form (const x), but that could probably be changed.
+@test Meta.lower(@__MODULE__, :(global const x)) == Expr(:error, "expected assignment after \"const\"")
+@test Meta.lower(@__MODULE__, :(global const x::Int)) == Expr(:error, "expected assignment after \"const\"")
+@test Meta.lower(@__MODULE__, :(const global x)) == Expr(:error, "expected assignment after \"const\"")
+@test Meta.lower(@__MODULE__, :(const global x::Int)) == Expr(:error, "expected assignment after \"const\"")