Raise CompileError in case of duplicated clauses given for try

Author: lexmag

lib/elixir/src/elixir_exp_clauses.erl

@@ -107,6 +107,14 @@ do_receive(Meta, {Key, _}, _Acc, E) ->
 'try'(Meta, KV, E) when not is_list(KV) ->
   compile_error(Meta, ?m(E, file), "invalid arguments for try");
 'try'(Meta, KV, E) ->
+  RaiseError = fun(Kind) ->
+    compile_error(Meta, ?m(E, file), "duplicated ~ts clauses given for try", [Kind])
+  end,
+  ok = assert_at_most_once('do', KV, 0, RaiseError),
+  ok = assert_at_most_once('rescue', KV, 0, RaiseError),
+  ok = assert_at_most_once('catch', KV, 0, RaiseError),
+  ok = assert_at_most_once('else', KV, 0, RaiseError),
+  ok = assert_at_most_once('after', KV, 0, RaiseError),
   {lists:map(fun(X) -> do_try(Meta, X, E) end, KV), E}.
 
 do_try(_Meta, {'do', Expr}, E) ->
@@ -214,3 +222,11 @@ expand_without_export(Meta, Kind, Fun, {Key, Clauses}, E) when is_list(Clauses)
   {Key, lists:map(Transformer, Clauses)};
 expand_without_export(Meta, Kind, _Fun, {Key, _}, E) ->
   compile_error(Meta, ?m(E, file), "expected -> clauses for ~ts in ~ts", [Key, Kind]).
+
+assert_at_most_once(_Kind, [], _Count, _Fun) -> ok;
+assert_at_most_once(Kind, [{Kind, _} | _], 1, ErrorFun) ->
+  ErrorFun(Kind);
+assert_at_most_once(Kind, [{Kind, _} | Rest], Count, Fun) ->
+  assert_at_most_once(Kind, Rest, Count + 1, Fun);
+assert_at_most_once(Kind, [_ | Rest], Count, Fun) ->
+  assert_at_most_once(Kind, Rest, Count, Fun).

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

@@ -413,6 +413,28 @@ defmodule Kernel.ExpansionTest do
     end
   end
 
+  test "try: expects at most one clause" do
+    assert_raise CompileError, ~r"duplicated do clauses given for try", fn ->
+      expand(quote(do: try(do: e, do: f)))
+    end
+
+    assert_raise CompileError, ~r"duplicated rescue clauses given for try", fn ->
+      expand(quote(do: (try do e rescue x -> x rescue y -> y end)))
+    end
+
+    assert_raise CompileError, ~r"duplicated after clauses given for try", fn ->
+      expand(quote(do: (try do e after x = y after x = y end)))
+    end
+
+    assert_raise CompileError, ~r"duplicated else clauses given for try", fn ->
+      expand(quote(do: (try do e else x -> x else y -> y end)))
+    end
+
+    assert_raise CompileError, ~r"duplicated catch clauses given for try", fn ->
+      expand(quote(do: (try do e catch x -> x catch y -> y end)))
+    end
+  end
+
   ## Binaries
 
   test "bitstrings: size * unit" do