From 3ba628ab389da57f3d9a492aa063ab4537867074 Mon Sep 17 00:00:00 2001
From: Kaan Ozkan <kaanozkan97@gmail.com>
Date: Wed, 13 May 2026 13:41:02 -0400
Subject: [PATCH] Warn when `--only-bootsnap-rbs-cache` runs without
 `TAPIOCA_RBS_CACHE=1`

Without the env var set, `bootsnap/setup` isn't required at boot and no
RBS cache gets populated. Previously the command would still print
"Bootsnap RBS cache populated", misleading users into thinking it had
done useful work.

Addresses https://github.com/Shopify/tapioca/pull/2617#discussion_r3209320189
---
 lib/tapioca/commands/dsl_generate.rb |  3 +++
 spec/tapioca/cli/dsl_spec.rb         | 24 ++++++++++++++++++++++--
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/lib/tapioca/commands/dsl_generate.rb b/lib/tapioca/commands/dsl_generate.rb
index 530cfb067..5fbb01496 100644
--- a/lib/tapioca/commands/dsl_generate.rb
+++ b/lib/tapioca/commands/dsl_generate.rb
@@ -18,6 +18,9 @@ def execute
         load_application
 
         if @only_bootsnap_rbs_cache
+          unless ENV["TAPIOCA_RBS_CACHE"] == "1"
+            say_error("Warning: --only-bootsnap-rbs-cache has no effect without TAPIOCA_RBS_CACHE=1", :yellow)
+          end
           say("Bootsnap RBS cache populated, exiting before RBI generation.", :green)
           return
         end
diff --git a/spec/tapioca/cli/dsl_spec.rb b/spec/tapioca/cli/dsl_spec.rb
index bc1c595da..3f35192f7 100644
--- a/spec/tapioca/cli/dsl_spec.rb
+++ b/spec/tapioca/cli/dsl_spec.rb
@@ -669,13 +669,33 @@ class Post
             end
           RB
 
-          result = @project.tapioca("dsl --only-bootsnap-rbs-cache Post")
+          result = @project.tapioca("dsl --only-bootsnap-rbs-cache Post", env: { "TAPIOCA_RBS_CACHE" => "1" })
 
           assert_stdout_includes(result, <<~OUT)
             Bootsnap RBS cache populated, exiting before RBI generation.
           OUT
 
-          assert_empty_stderr(result)
+          assert_stderr_includes(result, "bootsnap miss:")
+          refute_project_file_exist("sorbet/rbi/dsl/post.rbi")
+          assert_success_status(result)
+        end
+
+        it "warns when --only-bootsnap-rbs-cache is set without TAPIOCA_RBS_CACHE=1" do
+          @project.write!("lib/post.rb", <<~RB)
+            require "smart_properties"
+
+            class Post
+              include SmartProperties
+              property :title, accepts: String
+            end
+          RB
+
+          result = @project.tapioca("dsl --only-bootsnap-rbs-cache Post")
+
+          assert_stderr_includes(
+            result,
+            "Warning: --only-bootsnap-rbs-cache has no effect without TAPIOCA_RBS_CACHE=1",
+          )
           refute_project_file_exist("sorbet/rbi/dsl/post.rbi")
           assert_success_status(result)
         end