fix some parsing issues with end and blocks inside expressions

- `end` should only be special inside indexing expressions, not cat
- Blocks introduced by words (e.g. `if`, `begin`) should revert to
  normal parsing context, so `for` is no longer special. Fixes JuliaLang#18935

src/julia-parser.scm

@@ -160,6 +160,15 @@
  (where-enabled #t))
  ,@body))
 
+(define-macro (with-normal-context . body)
+ `(with-bindings ((range-colon-enabled #t)
+ (space-sensitive #f)
+ (where-enabled #t)
+ (inside-vec #f)
+ (end-symbol #f)
+ (whitespace-newline #f))
+ ,@body))
+
 (define-macro (without-range-colon . body)
  `(with-bindings ((range-colon-enabled #f))
  ,@body))
@@ -1263,8 +1272,8 @@
 (define (parse-resword s word)
  (with-bindings
  ((expect-end-current-line (input-port-line (ts:port s))))
- (with-normal-ops
- (without-whitespace-newline
+ (with-normal-context
+ (begin
  (case word
  ((begin quote)
  (let ((loc (begin (skip-ws-and-comments (ts:port s))
@@ -1734,6 +1743,8 @@
  ((null? (cdr v)) (cons (car v) outer))
  (else (cons (fix 'row v) outer))))
  (define semicolon (eqv? (peek-token s) #\;))
+ ;; if a [ ] expression is a cat expression, `end` is not special
+ (with-bindings ((end-symbol #f))
  (let loop ((vec (list first))
  (outer '()))
  (let ((t (if (or (eqv? (peek-token s) #\newline) gotnewline)
@@ -1767,7 +1778,7 @@
  (if (and (pair? vec) (not (ts:space? s)))
  (error (string "expected separator between arguments to \"[ ]\"; got \""
  (deparse (car vec)) t "\"")))
- (loop (cons (parse-eq* s) vec) outer)))))))
+ (loop (cons (parse-eq* s) vec) outer))))))))
 
 (define (peek-non-newline-token s)
  (let loop ((t (peek-token s)))

test/parse.jl

@@ -1254,3 +1254,13 @@ end === (3, String)
 
 # issue #7479
 @test expand(Main, parse("(true &&& false)")) == Expr(:error, "misplaced \"&\" expression")
+
+# if an indexing expression becomes a cat expression, `end` is not special
+@test_throws ParseError parse("a[end end]")
+@test_throws ParseError parse("a[end;end]")
+#@test_throws ParseError parse("a[end;]") # this is difficult to fix
+
+# issue #18935
+@test [begin
+ @inbounds for i = 1:10 end
+ end for i = 1:5] == fill(nothing, 5)