Add a "check-config" command to validate config files & tests for it

src/cli.rs

@@ -12,6 +12,7 @@ use crate::{
     error, observability,
 };
 
+mod check_config;
 mod serve;
 
 /// Command line arguments
@@ -29,6 +30,18 @@ pub(crate) struct Args {
 pub(crate) enum Command {
     /// Run the server.
     Serve(ServeArgs),
+
+    /// Check the configuration file for syntax and semantic errors.
+    CheckConfig(CheckConfigArgs),
+}
+
+#[derive(clap::Args)]
+pub(crate) struct CheckConfigArgs {
+    #[clap(flatten)]
+    config: ConfigArg,
+
+    #[clap(flatten)]
+    observability: ObservabilityArgs,
 }
 
 /// Wrapper for the `--config` arg.
@@ -83,6 +96,9 @@ impl Args {
 
         match self.command {
             Command::Serve(args) => serve::run(args).await?,
+            Command::CheckConfig(args) => {
+                check_config::run(args.config).await?;
+            }
         }
         Ok(())
     }
@@ -93,6 +109,10 @@ impl Command {
         // All subcommands other than `serve` should return `Some`. Keep these
         // match arms sorted by the enum variant name.
         match self {
+            Command::CheckConfig(args) => Some((
+                args.observability.log_format,
+                args.observability.log_filter.clone(),
+            )),
             Command::Serve(_) => None,
         }
     }

src/cli/check_config.rs

@@ -0,0 +1,11 @@
+use tracing::info;
+
+use crate::{cli::ConfigArg, config, error};
+
+pub(crate) async fn run(
+    args: ConfigArg,
+) -> Result<(), error::CheckConfigCommand> {
+    let _config = config::load(args.config.as_ref()).await?;
+    info!("Configuration looks good");
+    Ok(())
+}

src/error.rs

@@ -45,6 +45,9 @@ pub(crate) enum Main {
 
     #[error("failed to install global default tracing subscriber")]
     SetSubscriber(#[from] tracing::subscriber::SetGlobalDefaultError),
+
+    #[error(transparent)]
+    CheckConfigCommand(#[from] CheckConfigCommand),
 }
 
 /// Errors returned from the `serve` CLI subcommand.
@@ -72,6 +75,16 @@ pub(crate) enum ServeCommand {
     ServerNameChanged(#[from] ServerNameChanged),
 }
 
+/// Errors returned from the `check-config` CLI subcommand.
+// Missing docs are allowed here since that kind of information should be
+// encoded in the error messages themselves anyway.
+#[allow(missing_docs)]
+#[derive(Error, Debug)]
+pub(crate) enum CheckConfigCommand {
+    #[error("failed to validate configuration")]
+    Config(#[from] Config),
+}
+
 /// Error generated if `server_name` has changed or if checking this failed
 // Missing docs are allowed here since that kind of information should be
 // encoded in the error messages themselves anyway.