raise when using form as schema name in phx.gen.live (#6079)

Closes #5871.

Author: SteffenDE

lib/mix/tasks/phx.gen.live.ex

@@ -116,6 +116,8 @@ defmodule Mix.Tasks.Phx.Gen.Live do
     Mix.Phoenix.ensure_live_view_compat!(__MODULE__)
 
     {context, schema} = Gen.Context.build(args)
+    validate_context!(context)
+
     Gen.Context.prompt_for_code_injection(context)
 
     binding = [context: context, schema: schema, inputs: inputs(schema)]
@@ -129,6 +131,16 @@ defmodule Mix.Tasks.Phx.Gen.Live do
     |> print_shell_instructions()
   end
 
+  defp validate_context!(context) do
+    cond do
+      context.schema.singular == "form" ->
+        Gen.Context.raise_with_help("cannot use form as the schema name because it conflicts with the LiveView assigns!")
+
+      true ->
+        :ok
+    end
+  end
+
   defp prompt_for_conflicts(context) do
     context
     |> files_to_be_generated()

test/mix/tasks/phx.gen.live_test.exs

@@ -433,4 +433,10 @@ defmodule Mix.Tasks.Phx.Gen.LiveTest do
       end
     end
   end
+
+  test "raises on schema named form" do
+    assert_raise Mix.Error, ~r/cannot use form as the schema name because it conflicts with the LiveView assigns/, fn ->
+      Mix.Tasks.Phx.Gen.Live.run(~w(Blog Form forms title:string))
+    end
+  end
 end