misc smaller improvements (#5527)

- finally add an `#[instrument]` to Timeline::create_image_layers,
making it easier to see that something is happening because we create
image layers
- format some macro context code
- add a warning not to create new validation functions a la parse do not
validate

Split off from #5198.

pageserver/src/lib.rs

@@ -149,6 +149,10 @@ fn ends_with_suffix(path: &Utf8Path, suffix: &str) -> bool {
     }
 }
 
+// FIXME: DO NOT ADD new query methods like this, which will have a next step of parsing timelineid
+// from the directory name. Instead create type "UninitMark(TimelineId)" and only parse it once
+// from the name.
+
 pub fn is_uninit_mark(path: &Utf8Path) -> bool {
     ends_with_suffix(path, TIMELINE_UNINIT_MARK_SUFFIX)
 }

pageserver/src/tenant.rs

@@ -1057,8 +1057,8 @@ impl Tenant {
                     TimelineId::try_from(timeline_uninit_mark_file.file_stem())
                         .with_context(|| {
                             format!(
-                            "Could not parse timeline id out of the timeline uninit mark name {timeline_uninit_mark_file}",
-                        )
+                                "Could not parse timeline id out of the timeline uninit mark name {timeline_uninit_mark_file}",
+                            )
                         })?;
                 let timeline_dir = self.conf.timeline_path(&self.tenant_id, &timeline_id);
                 if let Err(e) =

pageserver/src/tenant/timeline.rs

@@ -3079,6 +3079,7 @@ impl Timeline {
         Ok(false)
     }
 
+    #[tracing::instrument(skip_all, fields(%lsn, %force))]
     async fn create_image_layers(
         &self,
         partitioning: &KeyPartitioning,