[fix] [#381] Handle possible invalid stacktrace fonts

Pretty v2 introduced an incompatible change to its font format.

Few (if any?) Timbre users actually customize these fonts beyond
possibly disabling them, so this shouldn't affect most folks.

But to be on the safe side, this commit introduces handling for
possible v1 style fonts.

There's 2 cases:

  1. [Compile-time] Invalid default fonts (set via environment variable / JVM property).
     In this case Timbre will throw, preventing compilation.

  2. [Runtime] Invalid fonts in output opts.
     In this case Timbre will log an error and ignore the invalid fonts.

src/taoensso/timbre.cljc

@@ -899,13 +899,34 @@
      :output-opts {:arg->str-fn (fn [_] "x")}}))
 
 #?(:clj
-   (def ^:private default-stacktrace-fonts
-     (enc/get-env
-       {:as      :edn
-        :default clj-commons.format.exceptions/default-fonts}
-       [:taoensso.timbre.default-stacktrace-fonts<.edn> ; Undocumented
-        :timbre-defaut-stacktrace-fonts<.edn>           ; Legacy
-        ])))
+   (do
+     ;; Pretty v1 used string fonts, v2 uses unrelated keywords
+     (def ^:private invalid-stacktrace-fonts-msg "Invalid Timbre stacktrace fonts (see `org.clj-commons/pretty` docs)")
+     (def ^:private   valid-stacktrace-fonts? (fn [st-fonts] (not (enc/rsome-kv (fn [k v] (string? v)) st-fonts))))
+     (def ^:private default-stacktrace-fonts
+       (let [st-fonts
+             (enc/get-env
+               {:as :edn :default fmt-ex/default-fonts}
+               [:taoensso.timbre.default-stacktrace-fonts<.edn> ; Undocumented
+                :timbre-defaut-stacktrace-fonts<.edn>           ; Legacy
+                ])]
+
+         (if (valid-stacktrace-fonts? st-fonts) ; May be nil or {}
+           (do                        st-fonts)
+           (throw
+             (ex-info invalid-stacktrace-fonts-msg
+               {:given-fonts               st-fonts
+                :default-fonts fmt-ex/default-fonts})))))
+
+     (def ^:private valid-stacktrace-fonts!
+       (enc/fmemoize
+         (fn [st-fonts]
+           (if (valid-stacktrace-fonts? st-fonts)
+             (do                        st-fonts)
+             (do
+               ;; Log error on first encounter
+               (error invalid-stacktrace-fonts-msg st-fonts)
+               default-stacktrace-fonts)))))))
 
 (defn default-output-error-fn
   "Default (fn [data]) -> string, used by `default-output-fn` to
@@ -935,10 +956,13 @@
                  (assoc data :?err c))))))
 
        :clj
-       (binding [fmt-ex/*fonts*
-                 (get output-opts :stacktrace-fonts
-                   default-stacktrace-fonts)]
-         (fmt-ex/format-exception err)))))
+       (let [st-fonts
+             (if-let [e (find output-opts :stacktrace-fonts)]
+               (valid-stacktrace-fonts! (val e))
+               default-stacktrace-fonts)]
+
+         (binding [fmt-ex/*fonts* st-fonts]
+          (fmt-ex/format-exception err))))))
 
 (comment
   (default-output-error-fn

wiki/1-Getting-started.md

@@ -109,9 +109,9 @@ lein cljsbuild once # Compile js with appropriate logging calls excluded
 lein uberjar        # Compile jar ''
 ```
 
-## Stacktrace colors
+## Stacktrace fonts
 
-ANSI colors are enabled by default for Clojure stacktraces. To turn these off (e.g. for log files or emails), you can add the following entry to your top-level config or individual appender map/s:
+ANSI fonts are enabled by default for Clojure stacktraces being printed to a console. To disable these, add the following entry to your top-level config or individual appender map/s:
 
 ```clojure
 :output-opts {:stacktrace-fonts {}}