cli: templates check: allow rendering to --out-dir

crates/cli/src/commands/templates.rs

@@ -6,6 +6,8 @@
 
 use std::process::ExitCode;
 
+use anyhow::{Context as _, bail};
+use camino::Utf8PathBuf;
 use clap::Parser;
 use figment::Figment;
 use mas_config::{
@@ -27,14 +29,19 @@ pub(super) struct Options {
 #[derive(Parser, Debug)]
 enum Subcommand {
     /// Check that the templates specified in the config are valid
-    Check,
+    Check {
+        /// If set, templates will be rendered to this directory.
+        /// The directory must either not exist or be empty.
+        #[arg(long = "out-dir")]
+        out_dir: Option<Utf8PathBuf>,
+    },
 }
 
 impl Options {
     pub async fn run(self, figment: &Figment) -> anyhow::Result<ExitCode> {
         use Subcommand as SC;
         match self.subcommand {
-            SC::Check => {
+            SC::Check { out_dir } => {
                 let _span = info_span!("cli.templates.check").entered();
 
                 let template_config = TemplatesConfig::extract_or_default(figment)
@@ -67,7 +74,39 @@ impl Options {
                 )?;
                 let templates =
                     templates_from_config(&template_config, &site_config, &url_builder).await?;
-                templates.check_render(clock.now(), &mut rng)?;
+                let all_renders = templates.check_render(clock.now(), &mut rng)?;
+
+                if let Some(out_dir) = out_dir {
+                    // Save renders to disk.
+                    if out_dir.exists() {
+                        let mut read_dir =
+                            tokio::fs::read_dir(&out_dir).await.with_context(|| {
+                                format!("could not read {out_dir} to check it's empty")
+                            })?;
+                        while let Some(x) = read_dir.next_entry().await? {
+                            bail!("Render directory {out_dir} is not empty, refusing to write.");
+                        }
+                    } else {
+                        tokio::fs::create_dir(&out_dir)
+                            .await
+                            .with_context(|| format!("could not create {out_dir}"))?;
+                    }
+
+                    for (template, template_renders) in &all_renders {
+                        let template_filename_base =
+                            template.trim_end_matches(".html").replace('/', "_");
+                        for (idx, render) in template_renders.iter().enumerate() {
+                            let render_path =
+                                out_dir.join(format!("{template_filename_base}-sample{idx}.html"));
+
+                            tokio::fs::write(&render_path, render.as_bytes())
+                                .await
+                                .with_context(|| {
+                                    format!("could not write render to {render_path}")
+                                })?;
+                        }
+                    }
+                }
 
                 Ok(ExitCode::SUCCESS)
             }