fix JuliaLang#9503, consistent parsing of <: expressions

NEWS.md

@@ -32,6 +32,9 @@ Language changes
   * A warning is always given when a method is overwritten (previously, this was done only when the new
     and old definitions were in separate modules) ([#14759]).
 
+  * `A <: B` is parsed as `Expr(:(<:), :A, :B)` in all cases ([#9503]). This also applies to the
+    `>:` operator.
+
 Command-line option changes
 ---------------------------
 
@@ -1690,6 +1693,7 @@ Too numerous to mention.
 [#9434]: https://github.com/JuliaLang/julia/issues/9434
 [#9452]: https://github.com/JuliaLang/julia/issues/9452
 [#9487]: https://github.com/JuliaLang/julia/issues/9487
+[#9503]: https://github.com/JuliaLang/julia/issues/9503
 [#9569]: https://github.com/JuliaLang/julia/issues/9569
 [#9575]: https://github.com/JuliaLang/julia/issues/9575
 [#9578]: https://github.com/JuliaLang/julia/issues/9578
@@ -1793,4 +1797,6 @@ Too numerous to mention.
 [#14469]: https://github.com/JuliaLang/julia/issues/14469
 [#14759]: https://github.com/JuliaLang/julia/issues/14759
 [#14798]: https://github.com/JuliaLang/julia/issues/14798
+[#15192]: https://github.com/JuliaLang/julia/issues/15192
 [#15242]: https://github.com/JuliaLang/julia/issues/15242
+[#15258]: https://github.com/JuliaLang/julia/issues/15258

src/julia-parser.scm

@@ -780,12 +780,21 @@
   (let loop ((ex (parse-pipes s))
              (first #t))
     (let ((t (peek-token s)))
-      (if (not (is-prec-comparison? t))
-          ex
-          (begin (take-token s)
-                 (if first
-                     (loop (list 'comparison ex t (parse-pipes s)) #f)
-                     (loop (append ex (list t (parse-pipes s))) #f)))))))
+      (cond ((is-prec-comparison? t)
+             (begin (take-token s)
+                    (if first
+                        (loop (list 'comparison ex t (parse-pipes s)) #f)
+                        (loop (append ex (list t (parse-pipes s))) #f))))
+            (first ex)
+            ((length= ex 4)
+             ;; only a single comparison; special chained syntax not required
+             (let ((op   (caddr ex))
+                   (arg1 (cadr ex))
+                   (arg2 (cadddr ex)))
+               (if (or (eq? op '|<:|) (eq? op '|>:|))
+                   `(,op ,arg1 ,arg2)
+                   ex)))
+            (else ex)))))
 
 (define closing-token?
   (let ((closer? (Set '(else elseif catch finally #\, #\) #\] #\} #\;))))
@@ -905,13 +914,6 @@
         (else
          ex)))))
 
-;; convert (comparison a <: b) to (<: a b)
-(define (subtype-syntax e)
-  (if (and (pair? e) (eq? (car e) 'comparison)
-           (length= e 4) (eq? (caddr e) '|<:|))
-      `(<: ,(cadr e) ,(cadddr e))
-      e))
-
 (define (parse-unary-prefix s)
   (let ((op (peek-token s)))
     (if (syntactic-unary-op? op)
@@ -1031,8 +1033,7 @@
                                      (string (deparse ex) " " (deparse t))
                                      (string (deparse ex) (deparse t))))
              (take-token s)
-             (loop (list* 'curly ex
-                          (map subtype-syntax (parse-arglist s #\} )))))
+             (loop (list* 'curly ex (parse-arglist s #\} ))))
             ((#\")
              (if (and (symbol? ex) (not (operator? ex))
                       (not (ts:space? s)))
@@ -1066,7 +1067,7 @@
                           " expected \"end\", got \"" t "\""))))))
 
 (define (parse-subtype-spec s)
-  (subtype-syntax (parse-comparison s)))
+  (parse-comparison s))
 
 ;; parse expressions or blocks introduced by syntactic reserved words
 (define (parse-resword s word)

src/julia-syntax.scm

@@ -1484,6 +1484,10 @@
                                             `(call (top next) ,coll ,state))
                    ,body))))))))
 
+;; convert an operator parsed as (op a b) to (call op a b)
+(define (syntactic-op-to-call e)
+  `(call ,(car e) ,(expand-forms (cadr e)) ,(expand-forms (caddr e))))
+
 ;; table mapping expression head to a function expanding that form
 (define expand-table
   (table
@@ -1520,9 +1524,9 @@
    (lambda (e)
      `(call (top getfield) ,(expand-forms (cadr e)) ,(expand-forms (caddr e))))
 
-   'in
-   (lambda (e)
-     `(call in ,(expand-forms (cadr e)) ,(expand-forms (caddr e))))
+   'in   syntactic-op-to-call
+   '|<:| syntactic-op-to-call
+   '|>:| syntactic-op-to-call
 
    'const  expand-const-decl
    'local  expand-local-or-global-decl

test/parse.jl

@@ -365,3 +365,9 @@ let a⊂b = reduce(&, x ∈ b for x in a) && length(b)>length(a)
     @test !([1,2] ⊂ [1,3,4])
     @test !([1,2] ⊂ [1,2])
 end
+
+# issue #9503
+@test parse("x<:y") == Expr(:(<:), :x, :y)
+@test parse("x>:y") == Expr(:(>:), :x, :y)
+@test parse("x<:y<:z").head === :comparison
+@test parse("x>:y<:z").head === :comparison