[new] OpenTelemetry handler: support spans created outside Telemere

BEFORE this commit:

  Telemere captured OpenTelemetry context only when generating
  tracing signals (`trace!`, `spy!`, etc.).

AFTER this commit:

  Telemere always captures OpenTelemetry context when present.

Motivation for the change:

  Telemere users may have spans automatically created by the
  OpenTelemetry Java Agent, or manually created by other libs
  like clj-otel.

  By always capturing the OpenTelemetry context when present,
  this lets even non-tracing Telemere signals (like `log!`)
  include the relevant trace and span IDs for external tooling.

Thanks to @devurandom for suggesting this, and for helping
debug/identify the necessary changes 🙏

main/resources/docs/signal-options.txt

@@ -26,7 +26,7 @@ All options are available for all signal creator calls:
 
 `:elidable?` --- Should signal be subject to compile-time elision? (default true)
 `:allow?` ------ Custom override for usual runtime filtering (true => ALWAYS create signal)
-`:trace?` ------ Should tracing be enabled for `:run` form?
+`:trace?` ------ Should tracing be enabled for this signal? (default true iff `:run` provided or OpenTelemetry tracing enabled)
 
 `:sample` ------ Sample ?rate ∈ℝ[0,1] for random signal sampling (0.75 => allow 75% of signals, nil => allow all)
 `:when` -------- Arb ?form; when present, form must return truthy to allow signal

main/src/taoensso/telemere/impl.cljc

@@ -569,7 +569,10 @@
                  id-form    :id
                  level-form :level} opts
 
-                trace? (get opts :trace? run-form?)
+                otel?         (get opts :otel? (and clj? present:otel?)) ; Undocumented
+                otel-tracing? (and otel? enabled:otel-tracing?)
+
+                trace? (get opts :trace? (or run-form? otel-tracing?))
                 _
                 (when-not (contains? #{true false nil} trace?)
                   (truss/ex-info!
@@ -612,9 +615,9 @@
                               (dissoc opts
                                 :elidable? :coords :inst :uid :xfn :xfn+ :kvs+,
                                 :sample :ns :kind :id :level :filter :when #_:limit #_:limit-by,
-                                :ctx :ctx+ :parent #_:trace?, :do :let :data :msg :error,
+                                :ctx :ctx+ :parent :trace?, :do :let :data :msg :error,
                                 :run :run-form :run-val, :elide? :allow? #_:callsite-id,
-                                :host :thread :otel/context))]
+                                :host :thread :otel? :otel/context))]
 
                         (if-let [kvs+ (get opts :kvs+)] ; Undocumented
                           (if base
@@ -696,7 +699,7 @@
                             (catch :all t# (RunResult. nil        t#  (- (enc/now-nano*) t0#))))))]
 
                   ;; Trace without OpenTelemetry
-                  (or cljs? (not enabled:otel-tracing?))
+                  (or cljs? (not otel-tracing?))
                   `[~'__otel-context1 nil
                     ~'__uid  ~(auto-> uid-form `(taoensso.telemere/*uid-fn* (if ~'__root0 false true)))
                     ~'__root1 (or ~'__root0 ~(when trace? `{:id ~'__id, :uid ~'__uid}))
@@ -710,9 +713,9 @@
                               (catch :all t# (RunResult. nil        t#  (- (enc/now-nano*) t0#)))))))]
 
                   ;; Trace with OpenTelemetry
-                  (and clj? enabled:otel-tracing?)
+                  (and clj? otel-tracing?)
                   `[~'__otel-context0  ~(get opts :otel/context `(otel-context)) ; Context
-                    ~'__otel-context1  ~(if run-form? `(otel-context+span ~'__id ~'__inst ~'__otel-context0 ~(get opts :otel/span-kind)) ~'__otel-context0)
+                    ~'__otel-context1  ~(if run-form? `(otel-context+span ~'__id ~'__inst ~'__otel-context0 ~(get opts :otel/span-kind)) `~'__otel-context0)
                     ~'__uid            ~(auto-> uid-form `(or (otel-span-id ~'__otel-context1) (com.taoensso.encore.Ids/genHexId16)))
                     ~'__root1
                     (or ~'__root0

main/test/taoensso/telemere_tests.cljc

@@ -447,10 +447,10 @@
         (let [sv (with-sig (sig! {:level :info, :parent {:uid :uid1, :foo :bar}}))] (is (sm? sv {:parent {:id :submap/nx :uid      :uid1, :foo :bar}}) "Manual `:parent/uid`"))
         (let [sv (with-sig (sig! {:level :info, :root   {:id   :id1, :foo :bar}}))] (is (sm? sv {:root   {:id :id1       :uid :submap/nx, :foo :bar}}) "Manual `:root/id`"))
         (let [sv (with-sig (sig! {:level :info, :root   {:uid :uid1, :foo :bar}}))] (is (sm? sv {:root   {:id :submap/nx :uid      :uid1, :foo :bar}}) "Manual `:root/uid`"))
-        (let [sv (with-sig (sig! {:level :info}))                                 ] (is (sm? sv {:uid nil})))
+        (let [sv (with-sig (sig! {:level :info, :otel? false}))                   ] (is (sm? sv {:uid nil})))
         (let [sv (with-sig (sig! {:level :info, :uid :auto}))                     ] (is (sm? sv {:uid string?})))
         (let [sv (binding [tel/*uid-fn* (fn [_] "my-uid")]
-                   (with-sig (sig! {:level :info, :uid :auto})))                  ] (is (sm? sv {:uid "my-uid"})))])
+                   (with-sig (sig! {:level :info, :uid :auto, :otel? false})))    ] (is (sm? sv {:uid "my-uid"})))])
 
      (testing "Auto parent/root"
        [(testing "Tracing disabled"
@@ -882,7 +882,7 @@
              (is (= ((tel/pr-signal-fn {:pr-fn (fn [_] "str")}) sig) (str "str" utils/newline))))]))
 
       (testing "format-signal-fn"
-        (let [sig (with-sig :raw :trap (tel/event! ::ev-id {:inst t1, :msg ["a" "b"]}))]
+        (let [sig (with-sig :raw :trap (tel/event! ::ev-id {:inst t1, :msg ["a" "b"], :otel? false}))]
           [(is (enc/str-starts-with? ((tel/format-signal-fn)         sig       ) "2024-01-01T01:01:01.110Z INFO EVENT"))
            (is (enc/str-ends-with?   ((tel/format-signal-fn) (dissoc sig :host)) "::ev-id a b\n"))]))])])