rewrite negated assert/refute

Author: novaugust

CHANGELOG.md

@@ -5,6 +5,26 @@ they can and will change without that change being reflected in Styler's semanti
 
 ## main
 
+### Improvements
+
+- rewrite some negated asserts and refutes
+
+| before              | styled          |
+|---------------------|-----------------|
+| `assert x != nil`   | `assert x`      |
+| `assert !!x`        | `assert x`      |
+| `assert !x`         | `refute x`      |
+| `assert not x`      | `refute x`      |
+| `assert !is_nil(x)` | `assert x`      |
+| `assert x not in y` | `refute x in y` |
+| `refute !x`         | `assert x`      |
+| `refute not x`      | `assert x`      |
+| `refute x not in y` | `assert x in y` |
+| `assert x == nil`   | _no change_     |
+| `assert is_nil(x)`  | _no change_     |
+| `refute x`          | _no change_     |
+
+
 ### Fixes
 
 - alias lifting: fix bug lifting in snippets with a single ast node at the root level (like a credo config file) (#240, h/t @defndaines)

docs/general_styles.md

@@ -241,3 +241,22 @@ def save(
 # Params comment
 def save(%Socket{assigns: %{user: user, live_action: :new}} = initial_socket, params), do: :ok
 ```
+
+## Negated Assert/Refute
+
+Notably there are three ways to write "assert the thing is nil", but Styler doesn't yet feel like coercing codebases to a single style there.
+
+| before              | styled          |
+|---------------------|-----------------|
+| `assert x != nil`   | `assert x`      |
+| `assert !!x`        | `assert x`      |
+| `assert !x`         | `refute x`      |
+| `assert not x`      | `refute x`      |
+| `assert !is_nil(x)` | `assert x`      |
+| `assert x not in y` | `refute x in y` |
+| `refute !x`         | `assert x`      |
+| `refute not x`      | `assert x`      |
+| `refute x not in y` | `assert x in y` |
+| `assert x == nil`   | _no change_     |
+| `assert is_nil(x)`  | _no change_     |
+| `refute x`          | _no change_     |

lib/style/single_node.ex

@@ -37,6 +37,13 @@ defmodule Styler.Style.SingleNode do
 
   def run({node, meta}, ctx), do: {:cont, {style(node), meta}, ctx}
 
+  # reverse negated assert/refute
+  defp style({:assert, meta, [{:!=, _, [x, {:__block__, _, [nil]}]}]}), do: {:assert, meta, [x]}
+  defp style({:assert, meta, [{:!=, _, [{:__block__, _, [nil]}, y]}]}), do: {:assert, meta, [y]}
+  defp style({:assert, meta, [{n, _, [x]}]}) when n in [:!, :not], do: style({:refute, meta, [x]})
+  defp style({:refute, meta, [{n, _, [x]}]}) when n in [:!, :not], do: style({:assert, meta, [x]})
+  defp style({:refute, meta, [{:is_nil, _, [x]}]}), do: style({:assert, meta, [x]})
+
   # rewrite double-quote strings with >= 4 escaped double-quotes as sigils
   defp style({:__block__, [{:delimiter, ~s|"|} | meta], [string]} = node) when is_binary(string) do
     # running a regex against every double-quote delimited string literal in a codebase doesn't have too much impact

test/style/single_node_test.exs

@@ -11,6 +11,19 @@
 defmodule Styler.Style.SingleNodeTest do
   use Styler.StyleCase, async: true
 
+  test "assert/refute negation" do
+    assert_style "assert x != nil", "assert x"
+    assert_style "assert !!x", "assert x"
+    assert_style "assert !x", "refute x"
+    assert_style "assert not x", "refute x"
+    assert_style "assert !is_nil(x)", "assert x"
+    assert_style "assert x not in y", "refute x in y"
+
+    assert_style "refute !x", "assert x"
+    assert_style "refute not x", "assert x"
+    assert_style "refute x not in y", "assert x in y"
+  end
+
   test "string sigil rewrites" do
     assert_style ~s|""|
     assert_style ~s|"\\""|