fix #37393: interpolation in for outer (#37402)

Author: simeonschaub

src/julia-parser.scm

@@ -1690,33 +1690,27 @@
 
 ;; as above, but allows both "i=r" and "i in r"
 (define (parse-iteration-spec s)
-  (let* ((outer? (if (eq? (peek-token s) 'outer)
-                     (begin
-                       (take-token s)
-                       (let ((nxt (peek-token s)))
-                         (if (or (memq nxt '(= in ∈))
-                                 (not (symbol? nxt))
-                                 (operator? nxt))
-                             (begin (ts:put-back! s 'outer #t)
-                                    #f)
-                             #t)))
-                     #f))
-         (lhs (parse-pipe< s))
-         (t   (peek-token s)))
-    (cond ((memq t '(= in ∈))
-           (take-token s)
-           (let* ((rhs (parse-pipe< s))
-                  (t   (peek-token s)))
-             #;(if (not (or (closing-token? t) (newline? t)))
-                 ;; should be: (error "invalid iteration specification")
-                 (parser-depwarn s (string "for " (deparse `(= ,lhs ,rhs)) " " t)
-                                 (string "for " (deparse `(= ,lhs ,rhs)) "; " t)))
-             (if outer?
-                 `(= (outer ,lhs) ,rhs)
-                 `(= ,lhs ,rhs))))
-          ((and (eq? lhs ':) (closing-token? t))
-           ':)
-          (else (error "invalid iteration specification")))))
+  ;; FIXME: this is just for backwards compatibility, allows newline before =/in/∈ in
+  ;; generator expressions
+  (define (peek-token- s)
+    (let ((t (peek-token s)))
+      (if (and for-generator (newline? t))
+          (begin (take-token s)
+                 (peek-token s))
+          t)))
+  (let* ((lhs (let ((lhs- (with-space-sensitive (parse-pipe< s))))
+                (if (eq? lhs- 'outer)
+                    (let ((nxt (peek-token- s)))
+                      (if (memq nxt '(= in ∈))
+                          lhs-
+                          `(outer ,(parse-pipe< s))))
+                    lhs-)))
+         (t (peek-token- s)))
+    (if (memq t '(= in ∈))
+        (begin
+          (take-token s)
+          `(= ,lhs ,(parse-pipe< s)))
+        (error "invalid iteration specification"))))
 
 (define (parse-comma-separated-iters s)
   (let loop ((ranges '()))

test/syntax.jl

@@ -2461,3 +2461,32 @@ import .TestImportAs.Mod2 as M2
     @test Meta.parse("a'ᵀb") == Expr(:call, :*, Expr(:call, Symbol("'ᵀ"), :a), :b)
     @test Meta.parse("a'⁻¹b") == Expr(:call, :*, Expr(:call, Symbol("'⁻¹"), :a), :b)
 end
+
+@testset "issue #37393" begin
+    @test :(for outer i = 1:3; end) == Expr(:for, Expr(:(=), Expr(:outer, :i), :(1:3)), :(;;))
+    i = :i
+    @test :(for outer $i = 1:3; end) == Expr(:for, Expr(:(=), Expr(:outer, :i), :(1:3)), :(;;))
+    @test :(for outer = 1:3; end) == Expr(:for, Expr(:(=), :outer, :(1:3)), :(;;))
+    # TIL that this is possible
+    for outer $ i = 1:3
+        @test 1 $ 2 in 1:3
+    end
+
+    # 😭
+    @test Meta.isexpr(Meta.parse("""
+        [i for i
+        in 1:3]"""), :comprehension)
+    @test Meta.isexpr(Meta.parse("""
+        [i for outer
+        in 1:3]"""), :comprehension)
+    @test Meta.isexpr(Meta.parse("""
+        [i for outer
+        i in 1:3]"""), :comprehension)
+    @test Meta.isexpr(Meta.parse("""
+        f(i for i
+        in 1:3)""").args[2], :generator)
+    @test_throws Meta.ParseError Meta.parse("""
+        for i
+            in 1:3
+        end""")
+end