fix JuliaLang#28576, parsing ? at end of input in conditional expression

Author: JeffBezanson

src/julia-parser.scm

@@ -779,7 +779,7 @@
            (begin (if (not (ts:space? s))
                       (error "space required before \"?\" operator"))
                   (take-token s) ; take the ?
-                  (let ((t (with-whitespace-newline (without-range-colon (peek-token s)))))
+                  (let ((t (with-whitespace-newline (without-range-colon (require-token s)))))
                     (if (not (ts:space? s))
                         (error "space required after \"?\" operator")))
                   (let ((then (without-range-colon (parse-eq* s))))
@@ -788,7 +788,7 @@
                     (if (not (ts:space? s))
                         (error "space required before colon in \"?\" expression"))
                     (take-token s) ; take the :
-                    (let ((t (with-whitespace-newline (peek-token s))))
+                    (let ((t (with-whitespace-newline (require-token s))))
                       (if (not (ts:space? s))
                           (error "space required after colon in \"?\" expression")))
                     (list 'if ex then (parse-eq* s)))))

test/syntax.jl

@@ -1642,3 +1642,7 @@ end
 for ex in [:([x=1]), :(T{x=1})]
     @test Meta.lower(@__MODULE__, ex) == Expr(:error, string("misplaced assignment statement in \"", ex, "\""))
 end
+
+# issue #28576
+@test Meta.isexpr(Meta.parse("1 == 2 ?"), :incomplete)
+@test Meta.isexpr(Meta.parse("1 == 2 ? 3 :"), :incomplete)