Ensure one arity catch is always expanded to :throw

Author: josevalim

lib/elixir/src/elixir_clauses.erl

@@ -406,7 +406,7 @@ expand_catch(Meta, [{'when', _, [_, _, _, _ | _]}], _, E) ->
 expand_catch(Meta, [{'when', WhenMeta, [Arg1, Arg2, Guard]}], S, E) ->
   guarded_head(Meta, WhenMeta, [Arg1, Arg2], Guard, S, E);
 expand_catch(Meta, [{'when', WhenMeta, [Arg1, Guard]}], S, E) ->
-  guarded_head(Meta, WhenMeta, [Arg1], Guard, S, E);
+  guarded_head(Meta, WhenMeta, [throw, Arg1], Guard, S, E);
 expand_catch(Meta, [Arg], S, E) ->
   head(Meta, [throw, Arg], S, E);
 expand_catch(Meta, [_, _] = Args, S, E) ->

lib/elixir/test/elixir/kernel/expansion_test.exs

@@ -1980,6 +1980,32 @@ defmodule Kernel.ExpansionTest do
       assert expand(before_expansion) == after_expansion
     end
 
+    test "expands catch with when" do
+      before_expansion =
+        quote do
+          try do
+            x
+          catch
+            x when x -> z = :erlang.-(x)
+          end
+
+          z
+        end
+
+      after_expansion =
+        quote do
+          try do
+            x()
+          catch
+            x when x -> z = :erlang.-(x)
+          end
+
+          z()
+        end
+
+      assert expand(before_expansion) == after_expansion
+    end
+
     test "expands after" do
       before_expansion =
         quote do