Add binary for simplified bot comment training

This allows us to use the same infrastructure we use for PR metadata
validation, but in a more controlled setting for learning what a bot
comment is.

The comment it leaves is fairly artificial, but should be easy for
people to understand and act on.

Author: illicitonion

src/bin/dummy-code-of-conduct-validator.rs

@@ -0,0 +1,73 @@
+/// This binary exists to be a lightweight teaching version of the pr-metadata-validator.
+/// Its purpose is to train trainees in the idea that bots will comment on their PRs, and they should follow their advice.
+/// It is installed in https://github.com/CodeYourFuture/github_issues_prs_practice as a GitHub Action.
+use std::process::exit;
+
+use const_format::concatcp;
+use trainee_tracker::{
+    octocrab::octocrab_for_token,
+    pr_comments::{PullRequest, close_existing_comments, leave_tagged_comment},
+};
+
+#[tokio::main]
+async fn main() {
+    let Ok([_argv0, pr_url]) = <[_; _]>::try_from(std::env::args().collect::<Vec<_>>()) else {
+        eprintln!("Expected one arg - PR URL");
+        exit(1);
+    };
+    let pr_metadata = PullRequest::from_html_url(&pr_url).expect("Failed to parse PR URL");
+    let github_token =
+        std::env::var("GH_TOKEN").expect("GH_TOKEN wasn't set - must be set to a GitHub API token");
+    let octocrab = octocrab_for_token(github_token.to_owned()).expect("Failed to get octocrab");
+
+    let pr_from_rest = octocrab
+        .pulls(&pr_metadata.org, &pr_metadata.repo)
+        .get(pr_metadata.number)
+        .await
+        .expect("Failed to get PR");
+    if pr_from_rest
+        .body
+        .unwrap_or_default()
+        .ends_with(EXPECTED_SUFFIX)
+    {
+        let result = close_existing_comments(&octocrab, &pr_metadata, TAG).await;
+        if let Err(err) = result {
+            eprintln!("Failed to close existing comments: {:?}", err);
+        }
+    } else {
+        leave_tagged_comment(&octocrab, &pr_metadata, &[TAG], COMMENT_TO_LEAVE.to_owned())
+            .await
+            .expect("Failed to leave comment");
+    }
+}
+
+const EXPECTED_SUFFIX: &str = "I agree to follow the code of conduct for this organisation.";
+
+const TAG: &str = "dummy-code-of-conduct-validator";
+
+const COMMENT_TO_LEAVE: &str = concatcp!(
+    COMMENT_TO_LEAVE_PREFIX,
+    EXPECTED_SUFFIX,
+    COMMENT_TO_LEAVE_SUFFIX
+);
+
+const COMMENT_TO_LEAVE_PREFIX: &str = r#"This is a comment from a bot.
+
+You should read it, make sure you understand it, and take the action it suggests.
+
+If you don't understand the action it suggests, ask a volunteer or another trainee for help.
+
+## ⚠️ Problem detected
+
+In this repository, all pull request descriptions must end with the sentence:
+
+> "#;
+
+const COMMENT_TO_LEAVE_SUFFIX: &str = r#"
+
+Your pull request description does not currently end with this sentence.
+
+Please edit your pull request description to add this sentence at the end.
+
+If you are successful in doing this, this comment will get automatically hidden within about a minute.
+"#;