Fix docker run with arguments (#404)

Fixes an issue where `docker run` with a command was not working correctly. Before:

```
$ docker run --rm --entrypoint /cnb/lifecycle/launcher sample-app "echo 'hi'"
hi
⛄️ 3.4.2 🚀 /Users/rschneeman/Documents/projects/work/buildpacks-ruby (main)
$ docker run --rm sample-app "echo 'hi'"
bash: echo 'hi': No such file or directory
$ pack inspect sample-app | grep Processes: -A10
Processes:
  TYPE                 SHELL        COMMAND        ARGS                                                                                         WORK DIR
  web (default)                     bash           -c bundle exec rackup --host "[::]" --port "${PORT:?Error: PORT env var is not set!}"        /workspace
```

After:

```
$ cargo libcnb package && pack build sample-app \
  --buildpack packaged/x86_64-unknown-linux-musl/debug/heroku_ruby \
  --path buildpacks/ruby/tests/fixtures/default_ruby --clear-cache
$ docker run --rm sample-app "echo 'hi'"
hi
```

The root cause is that when you `docker run` something, it uses the default command and uses the arguments you provide as arguments to that command. In this case we want the full shell, so the command needs to be `bash -c <arguments>` instead of `bash <arguments>`.

Author: schneems

buildpacks/ruby/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- The `docker run` command no longer requires an entrypoint when using default processes provided by `heroku/ruby` directly (and not the `heroku/procfile` buildpack) ([#404](https://github.com/heroku/buildpacks-ruby/pull/404))
+
 ## [6.0.0] - 2025-03-12
 
 ### Changed

buildpacks/ruby/src/steps/get_default_process.rs

@@ -69,32 +69,26 @@ fn detect_web(gem_list: &GemList, app_path: &Path) -> WebProcess {
 }
 
 fn default_rack() -> Process {
-    ProcessBuilder::new(process_type!("web"), ["bash"])
-        .args([
-            "-c",
-            &[
-                "bundle exec rackup",
-                "--host \"[::]\"",
-                "--port \"${PORT:?Error: PORT env var is not set!}\"",
-            ]
-            .join(" "),
-        ])
+    ProcessBuilder::new(process_type!("web"), ["bash", "-c"])
+        .args([[
+            "bundle exec rackup",
+            "--host \"[::]\"",
+            "--port \"${PORT:?Error: PORT env var is not set!}\"",
+        ]
+        .join(" ")])
         .default(true)
         .build()
 }
 
 fn default_rails() -> Process {
-    ProcessBuilder::new(process_type!("web"), ["bash"])
-        .args([
-            "-c",
-            &[
-                "bin/rails server",
-                "--binding \"[::]\"",
-                "--port \"${PORT:?Error: PORT env var is not set!}\"",
-                "--environment \"$RAILS_ENV\"",
-            ]
-            .join(" "),
-        ])
+    ProcessBuilder::new(process_type!("web"), ["bash", "-c"])
+        .args([[
+            "bin/rails server",
+            "--binding \"[::]\"",
+            "--port \"${PORT:?Error: PORT env var is not set!}\"",
+            "--environment \"$RAILS_ENV\"",
+        ]
+        .join(" ")])
         .default(true)
         .build()
 }