Improve error message for bad/missing clauses, closes #14569

Author: josevalim

lib/elixir/src/elixir_clauses.erl

@@ -571,18 +571,16 @@ format_error({recursive, Vars, TypeExpr}) ->
   );
 
 format_error({bad_or_missing_clauses, {Kind, Key}}) ->
-  io_lib:format("expected -> clauses for :~ts in \"~ts\"", [Key, Kind]);
-format_error({bad_or_missing_clauses, Kind}) ->
-  io_lib:format("expected -> clauses in \"~ts\"", [Kind]);
+  io_lib:format("invalid \"~ts\" block in \"~ts\", it expects \"pattern -> expr\" clauses", [Key, Kind]);
 
 format_error({duplicated_clauses, Kind, Key}) ->
-  io_lib:format("duplicate :~ts clauses given for \"~ts\"", [Key, Kind]);
+  io_lib:format("duplicate \"~ts\" clauses given for \"~ts\"", [Key, Kind]);
 
 format_error({unexpected_option, Kind, Option}) ->
   io_lib:format("unexpected option ~ts in \"~ts\"", ['Elixir.Macro':to_string(Option), Kind]);
 
 format_error({wrong_number_of_args_for_clause, Expected, Kind, Key}) ->
-  io_lib:format("expected ~ts for :~ts clauses (->) in \"~ts\"", [Expected, Key, Kind]);
+  io_lib:format("expected ~ts for \"~ts\" clauses (->) in \"~ts\"", [Expected, Key, Kind]);
 
 format_error(multiple_after_clauses_in_receive) ->
   "expected a single -> clause for :after in \"receive\"";

lib/elixir/test/elixir/kernel/errors_test.exs

@@ -446,7 +446,7 @@ defmodule Kernel.ErrorsTest do
 
   test "invalid case clauses" do
     assert_compile_error(
-      ["nofile:1:37", "expected one argument for :do clauses (->) in \"case\""],
+      ["nofile:1:37", "expected one argument for \"do\" clauses (->) in \"case\""],
       ~c"case nil do 0, z when not is_nil(z) -> z end"
     )
   end
@@ -959,15 +959,18 @@ defmodule Kernel.ErrorsTest do
   end
 
   test "def fails when rescue, else or catch don't have clauses" do
-    assert_compile_error(~r"expected -> clauses for :rescue in \"def\"", """
-    defmodule Example do
-      def foo do
-        bar()
-      rescue
-        baz()
+    assert_compile_error(
+      ~r"invalid \"rescue\" block in \"def\", it expects \"pattern -> expr\" clauses",
+      """
+      defmodule Example do
+        def foo do
+          bar()
+        rescue
+          baz()
+        end
       end
-    end
-    """)
+      """
+    )
   end
 
   test "duplicate map keys" do