Fix racket#1146: Handle Row types and void in check-below

Added patterns to check-below to handle Row types from row-polymorphic
instantiation and void values from error propagation, preventing internal
errors when these cases occur.

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Closes racket#1146

Author: samth

typed-racket-lib/typed-racket/typecheck/check-below.rkt

@@ -18,11 +18,11 @@
          "tc-envops.rkt")
 
 (provide/cond-contract
- [check-below (-->i ([s (t) (if (Type? t)
+ [check-below (-->i ([s (t) (if (or (Type? t) (Row? t))
                                 (-or/c full-tc-results/c Type?)
                                 full-tc-results/c)]
-                     [t (-or/c Type? tc-results/c)])
-                    [_ (t) (if (Type? t) Type? full-tc-results/c)])]
+                     [t (-or/c Type? Row? tc-results/c)])
+                    [_ (t) (if (or (Type? t) (Row? t)) Type? full-tc-results/c)])]
  [cond-check-below (-->i ([s (-or/c Type? full-tc-results/c)]
                           [t (s) (-or/c #f (if (Type? s) Type? tc-results/c))])
                          [_ (s) (-or/c #f (if (Type? s) Type? full-tc-results/c))])])
@@ -193,6 +193,17 @@
        (expected-but-got t2 t1))
      (upgrade-trusted-rng t1 expected)]
 
+    ;; Handle void or other invalid inputs from error propagation
+    [((? void?) expected) (fix-results expected)]
+    [(actual (? void?)) actual]
+
+    ;; Handle Row types from row-polymorphic instantiation
+    ;; Row is not a Type?, so it needs special handling
+    [((tc-result1: t1 _ _) (? Row?))
+     ;; For row polymorphism, just return the actual type
+     ;; The row constraint checking happens elsewhere
+     t1]
+
     [(a b) (int-err "unexpected input for check-below: ~a ~a" a b)]))
 
 ;; shallow: if the top-level arrow on t1 is reliable, then upgrade the top-level arrow in t2

typed-racket-test/succeed/gh-issue-1146.rkt

@@ -0,0 +1,17 @@
+#lang typed/racket
+
+;; Issue #1146: Regression test - previously caused "unexpected input for check-below"
+;; internal error with row polymorphic types.
+;; Fixed by adding Row type handling in check-below.rkt.
+
+(: hi (All (r #:row)
+           (-> r r)))
+(define (hi a)
+  a)
+
+(define cls1
+  (class object%
+    (init-field [x : Real 0] [y : Real 0])
+    (super-new)))
+
+(hi cls1)