Add pattern for contravariant projection on lower bounds

Summary: Adds an additional pattern to replicate the legacy `Contravariant_generic` and `Invariant_generic` reasons.

Reviewed By: patriciamckenzie

Differential Revision: D63897645

fbshipit-source-id: 5edab60a998f5358f4d0a1e56965c6c45b3285de

Author: Michael Thomas

hphp/hack/src/typing/typing_reason.ml

@@ -2073,7 +2073,6 @@ let rec to_string_help :
     to_string_help prefix solutions r
   | From_witness_locl witness -> [witness_locl_to_string prefix witness]
   | From_witness_decl witness -> [witness_decl_to_string prefix witness]
-  | Lower_bound { bound = r; _ }
   | Axiom { next = r; _ }
   | Def (_, r)
   | Prj_one { part = r; _ } ->
@@ -2093,7 +2092,33 @@ let rec to_string_help :
     | _ -> to_string_help prefix solutions into)
   | Solved { solution; of_; in_ = r } ->
     let solutions = Tvid.Map.add of_ solution solutions in
+
+    to_string_help prefix solutions r
+  | Lower_bound
+      {
+        bound = r;
+        of_ = Prj_both { prj = Prj_symm_ctor (_, class_name, _, Dir Contra); _ };
+      } ->
     to_string_help prefix solutions r
+    @ [
+        ( p,
+          "This type argument to "
+          ^ (strip_ns class_name |> Markdown_lite.md_codify)
+          ^ " only allows supertypes (it is contravariant)" );
+      ]
+  | Lower_bound
+      {
+        bound = r;
+        of_ = Prj_both { prj = Prj_symm_ctor (_, class_name, _, Inv _); _ };
+      } ->
+    to_string_help prefix solutions r
+    @ [
+        ( p,
+          "This type argument to "
+          ^ (strip_ns class_name |> Markdown_lite.md_codify)
+          ^ " must match exactly (it is invariant)" );
+      ]
+  | Lower_bound { bound = r; _ } -> to_string_help prefix solutions r
   | Prj_both
       {
         sub_prj = r_orig;

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

@@ -17,6 +17,15 @@ File "vector_invariant.php", line 3, character 24 - line 3, character 26:
 
 But got `string`
 
+File "vector_invariant.php", line 4, character 22 - line 4, character 24:
+
+ 3 | function foo(): Vector<int> {
+ 4 |   $x =  Vector { 1 , »'2'« };
+ 5 |   $y = $x;
+ 6 |   $z = $y;
+
+This type argument to `Vector` must match exactly (it is invariant)
+
 File "vector_invariant.php", line 4, character 22 - line 4, character 24:
 
  3 | function foo(): Vector<int> {

hphp/hack/test/extended_reasons/vector_invariant.php.diff.exp

@@ -2,11 +2,13 @@
 
 +++ test
 
-@@ -1,6 +1,5 @@
+@@ -1,7 +1,7 @@
 
  error: Typing[4110] Invalid return type [1]
  -> Expected int [2]
 --> This type argument to Vector must match exactly (it is invariant) [2]
  -> But got string [3]
++-> This type argument to Vector must match exactly (it is invariant) [3]
 
- hphp/hack/test/extended_reasons/vector_invariant.php:8:10
+ hphp/hack/test/extended_reasons/vector_invariant.php:8:10
+     1 | <?hh

hphp/hack/test/extended_reasons/vector_invariant.php.exp

@@ -20,6 +20,15 @@ File "vector_invariant.php", line 3, character 24 - line 3, character 26:
 
 But got `string`
 
+File "vector_invariant.php", line 4, character 22 - line 4, character 24:
+
+ 3 | function foo(): Vector<int> {
+ 4 |   $x =  Vector { 1 , »'2'« };
+ 5 |   $y = $x;
+ 6 |   $z = $y;
+
+This type argument to `Vector` must match exactly (it is invariant)
+
 File "vector_invariant.php", line 4, character 22 - line 4, character 24:
 
  3 | function foo(): Vector<int> {

hphp/hack/test/extended_reasons/vector_invariant.php.terse.exp

@@ -17,6 +17,15 @@ File "vector_invariant.php", line 3, character 24 - line 3, character 26:
 
 But got `string`
 
+File "vector_invariant.php", line 4, character 22 - line 4, character 24:
+
+ 3 | function foo(): Vector<int> {
+ 4 |   $x =  Vector { 1 , »'2'« };
+ 5 |   $y = $x;
+ 6 |   $z = $y;
+
+This type argument to `Vector` must match exactly (it is invariant)
+
 File "vector_invariant.php", line 4, character 22 - line 4, character 24:
 
  3 | function foo(): Vector<int> {

hphp/hack/test/extended_reasons/vector_invariant.php.verbose.exp

@@ -20,6 +20,15 @@ File "vector_invariant.php", line 3, character 24 - line 3, character 26:
 
 But got `string`
 
+File "vector_invariant.php", line 4, character 22 - line 4, character 24:
+
+ 3 | function foo(): Vector<int> {
+ 4 |   $x =  Vector { 1 , »'2'« };
+ 5 |   $y = $x;
+ 6 |   $z = $y;
+
+This type argument to `Vector` must match exactly (it is invariant)
+
 File "vector_invariant.php", line 4, character 22 - line 4, character 24:
 
  3 | function foo(): Vector<int> {