tmp: Split up process_cli

This is part 1 of 2 for applying the changes recommended in #7600,
keeping the diff minimal by breaking process_cli into three pieces so we
can extract startup_context_from_env() from the middle.

This will be squashed into the prior commit before merging. Kept it
separate for now, just to make the changes easier to review.

Co-authored-by: Heikki Linnakangas <heikki@neon.tech>

compute_tools/src/bin/compute_ctl.rs

@@ -71,12 +71,18 @@ const BUILD_TAG_DEFAULT: &str = "latest";
 fn main() -> Result<()> {
     let (build_tag, clap_args) = init()?;
 
-    let (startup_context_guard, cli_result) = process_cli(&clap_args)?;
+    let cli_args = process_cli(&clap_args)?;
 
-    let wait_spec_result = wait_spec(build_tag, cli_result)?;
+    // Enter startup tracing context
+    let startup_context_guard = startup_context_from_env();
+
+    let cli_spec = try_spec_from_cli(&clap_args, &cli_args)?;
+
+    let wait_spec_result = wait_spec(build_tag, cli_args, cli_spec)?;
 
     let (pg_handle, start_pg_result) = start_postgres(&clap_args, wait_spec_result)?;
 
+    // PostgreSQL is now running, if startup was successful. Wait until it exits.
     let wait_pg_result = wait_postgres(pg_handle, startup_context_guard)?;
 
     cleanup_and_exit(start_pg_result, wait_pg_result)
@@ -100,9 +106,7 @@ fn init() -> Result<(String, clap::ArgMatches)> {
     Ok((build_tag, cli().get_matches()))
 }
 
-fn process_cli(
-    matches: &clap::ArgMatches,
-) -> Result<(Option<opentelemetry::ContextGuard>, ProcessCliResult)> {
+fn process_cli(matches: &clap::ArgMatches) -> Result<ProcessCliResult> {
     let pgbin_default = "postgres";
     let pgbin = matches
         .get_one::<String>("pgbin")
@@ -134,6 +138,28 @@ fn process_cli(
     let spec_json = matches.get_one::<String>("spec");
     let spec_path = matches.get_one::<String>("spec-path");
 
+    Ok(ProcessCliResult {
+        connstr,
+        pgdata,
+        pgbin,
+        ext_remote_storage,
+        http_port,
+        spec_json,
+        spec_path,
+    })
+}
+
+struct ProcessCliResult<'clap> {
+    connstr: &'clap str,
+    pgdata: &'clap str,
+    pgbin: &'clap str,
+    ext_remote_storage: Option<&'clap str>,
+    http_port: u16,
+    spec_json: Option<&'clap String>,
+    spec_path: Option<&'clap String>,
+}
+
+fn startup_context_from_env() -> Option<opentelemetry::ContextGuard> {
     // Extract OpenTelemetry context for the startup actions from the
     // TRACEPARENT and TRACESTATE env variables, and attach it to the current
     // tracing context.
@@ -170,7 +196,7 @@ fn process_cli(
     if let Ok(val) = std::env::var("TRACESTATE") {
         startup_tracing_carrier.insert("tracestate".to_string(), val);
     }
-    let startup_context_guard = if !startup_tracing_carrier.is_empty() {
+    if !startup_tracing_carrier.is_empty() {
         use opentelemetry::propagation::TextMapPropagator;
         use opentelemetry::sdk::propagation::TraceContextPropagator;
         let guard = TraceContextPropagator::new()
@@ -180,8 +206,17 @@ fn process_cli(
         Some(guard)
     } else {
         None
-    };
+    }
+}
 
+fn try_spec_from_cli(
+    matches: &clap::ArgMatches,
+    ProcessCliResult {
+        spec_json,
+        spec_path,
+        ..
+    }: &ProcessCliResult,
+) -> Result<CliSpecParams> {
     let compute_id = matches.get_one::<String>("compute-id");
     let control_plane_uri = matches.get_one::<String>("control-plane-uri");
 
@@ -222,30 +257,13 @@ fn process_cli(
         }
     };
 
-    let result = ProcessCliResult {
-        // directly from CLI:
-        connstr,
-        pgdata,
-        pgbin,
-        ext_remote_storage,
-        http_port,
-        // others:
+    Ok(CliSpecParams {
         spec,
         live_config_allowed,
-    };
-
-    // TODO: Move startup_context_guard out of this function. It's here right now only because
-    // that's where it was before, and moving it would've made the diff big.
-    Ok((startup_context_guard, result))
+    })
 }
 
-struct ProcessCliResult<'clap> {
-    connstr: &'clap str,
-    pgdata: &'clap str,
-    pgbin: &'clap str,
-    ext_remote_storage: Option<&'clap str>,
-    http_port: u16,
-
+struct CliSpecParams {
     /// If a spec was provided via CLI or file, the [`ComputeSpec`]
     spec: Option<ComputeSpec>,
     live_config_allowed: bool,
@@ -259,9 +277,12 @@ fn wait_spec(
         pgbin,
         ext_remote_storage,
         http_port,
+        ..
+    }: ProcessCliResult,
+    CliSpecParams {
         spec,
         live_config_allowed,
-    }: ProcessCliResult,
+    }: CliSpecParams,
 ) -> Result<WaitSpecResult> {
     let mut new_state = ComputeState::new();
     let spec_set;