Eliminate intermediate flow provenance when reporting Arith_ret_[XXX] errors

Summary: Ensures that the claim for `Arith_ret_[XXX]` errors is the same under extended reasons by traversing to the first element of a flow appearing inside one of these reasons.

Reviewed By: madgen

Differential Revision: D63456760

fbshipit-source-id: 6eea7b60b7634e7046d4b688a0b37caec7033a4a

Author: Michael Thomas

hphp/hack/src/typing/typing_reason.ml

@@ -2108,7 +2108,9 @@ let rec to_string : type a. string -> a t_ -> (Pos_or_decl.t * string) list =
   | Arith_ret_float (_, r, s) ->
     let rec find_last reason =
       match reason with
-      | Arith_ret_float (_, r, _) -> find_last r
+      | Flow { from = r; _ }
+      | Arith_ret_float (_, r, _) ->
+        find_last r
       | r -> r
     in
     let r_last = find_last r in
@@ -2125,7 +2127,9 @@ let rec to_string : type a. string -> a t_ -> (Pos_or_decl.t * string) list =
   | Arith_ret_num (_, r, s) ->
     let rec find_last reason =
       match reason with
-      | Arith_ret_num (_, r, _) -> find_last r
+      | Flow { from = r; _ }
+      | Arith_ret_num (_, r, _) ->
+        find_last r
       | r -> r
     in
     let r_last = find_last r in

hphp/hack/test/extended_reasons/num.php.debug.exp

@@ -2,9 +2,6 @@ error: Typing[4110] Invalid return type
 
 File "num.php", line 9, character 10 - line 9, character 15:
 
- 5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
  8 |   $x = 5 + $x;
  9 |   return »5 + $x«;
 10 | }
@@ -16,82 +13,22 @@ File "num.php", line 3, character 23 - line 3, character 28:
  3 | function foo(num $n): »string« {
  4 |   $x = 5 + $n;
  5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
 
 But got `float` because this is the result of an arithmetic operation with a `num` as the second argument, and no `float`s.
 
 File "num.php", line 9, character 10 - line 9, character 15:
 
- 5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
  8 |   $x = 5 + $x;
  9 |   return »5 + $x«;
 10 | }
 
-Here is why I think the argument is a `num`: this is a `num` because this is the result of an arithmetic operation with a `num` as the second argument, and no `float`s.
-
-File "num.php", line 8, character 8 - line 8, character 13:
-
- 5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
- 8 |   $x = »5 + $x«;
- 9 |   return 5 + $x;
-10 | }
-
-Here is why I think the argument is a `num`: this is a `num` because this is the result of an arithmetic operation with a `num` as the second argument, and no `float`s.
-
-File "num.php", line 7, character 8 - line 7, character 13:
-
- 5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = »5 + $x«;
- 8 |   $x = 5 + $x;
- 9 |   return 5 + $x;
-10 | }
-
-Here is why I think the argument is a `num`: this is a `num` because this is the result of an arithmetic operation with a `num` as the first argument, and no `float`s.
-
-File "num.php", line 6, character 8 - line 6, character 13:
-
- 5 |   $x = 5 + $x;
- 6 |   $x = »$x + 5«;
- 7 |   $x = 5 + $x;
- 8 |   $x = 5 + $x;
- 9 |   return 5 + $x;
-10 | }
-
-Here is why I think the argument is a `num`: this is a `num` because this is the result of an arithmetic operation with a `num` as the second argument, and no `float`s.
-
-File "num.php", line 5, character 8 - line 5, character 13:
-
- 3 | function foo(num $n): string {
- 4 |   $x = 5 + $n;
- 5 |   $x = »5 + $x«;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
-
-Here is why I think the argument is a `num`: this is a `num` because this is the result of an arithmetic operation with a `num` as the second argument, and no `float`s.
-
-File "num.php", line 4, character 8 - line 4, character 13:
-
- 3 | function foo(num $n): string {
- 4 |   $x = »5 + $n«;
- 5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
-
 Here is why I think the argument is a `num`: this is a `num`
 
 File "num.php", line 3, character 14 - line 3, character 16:
 
  3 | function foo(»num« $n): string {
  4 |   $x = 5 + $n;
  5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
 
 Derivation:
 {
@@ -747,9 +684,6 @@ error: Typing[4110] Invalid return type
 
 File "num.php", line 9, character 10 - line 9, character 15:
 
- 5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
  8 |   $x = 5 + $x;
  9 |   return »5 + $x«;
 10 | }
@@ -761,82 +695,22 @@ File "num.php", line 3, character 23 - line 3, character 28:
  3 | function foo(num $n): »string« {
  4 |   $x = 5 + $n;
  5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
 
 But got `int` because this is the result of an arithmetic operation with a `num` as the second argument, and no `float`s.
 
 File "num.php", line 9, character 10 - line 9, character 15:
 
- 5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
  8 |   $x = 5 + $x;
  9 |   return »5 + $x«;
 10 | }
 
-Here is why I think the argument is a `num`: this is a `num` because this is the result of an arithmetic operation with a `num` as the second argument, and no `float`s.
-
-File "num.php", line 8, character 8 - line 8, character 13:
-
- 5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
- 8 |   $x = »5 + $x«;
- 9 |   return 5 + $x;
-10 | }
-
-Here is why I think the argument is a `num`: this is a `num` because this is the result of an arithmetic operation with a `num` as the second argument, and no `float`s.
-
-File "num.php", line 7, character 8 - line 7, character 13:
-
- 5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = »5 + $x«;
- 8 |   $x = 5 + $x;
- 9 |   return 5 + $x;
-10 | }
-
-Here is why I think the argument is a `num`: this is a `num` because this is the result of an arithmetic operation with a `num` as the first argument, and no `float`s.
-
-File "num.php", line 6, character 8 - line 6, character 13:
-
- 5 |   $x = 5 + $x;
- 6 |   $x = »$x + 5«;
- 7 |   $x = 5 + $x;
- 8 |   $x = 5 + $x;
- 9 |   return 5 + $x;
-10 | }
-
-Here is why I think the argument is a `num`: this is a `num` because this is the result of an arithmetic operation with a `num` as the second argument, and no `float`s.
-
-File "num.php", line 5, character 8 - line 5, character 13:
-
- 3 | function foo(num $n): string {
- 4 |   $x = 5 + $n;
- 5 |   $x = »5 + $x«;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
-
-Here is why I think the argument is a `num`: this is a `num` because this is the result of an arithmetic operation with a `num` as the second argument, and no `float`s.
-
-File "num.php", line 4, character 8 - line 4, character 13:
-
- 3 | function foo(num $n): string {
- 4 |   $x = »5 + $n«;
- 5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
-
 Here is why I think the argument is a `num`: this is a `num`
 
 File "num.php", line 3, character 14 - line 3, character 16:
 
  3 | function foo(»num« $n): string {
  4 |   $x = 5 + $n;
  5 |   $x = 5 + $x;
- 6 |   $x = $x + 5;
- 7 |   $x = 5 + $x;
 
 Derivation:
 {