Populate :msg for dispatch command errors

CHANGELOG.md

@@ -4,6 +4,10 @@ For breaking changes, check [here](#breaking-changes).
 
 [Babashka CLI](https://github.com/babashka/cli): turn Clojure functions into CLIs!
 
+## Unreleased
+
+- Populate `:msg` in the `:error-fn` data for `dispatch` command errors (`:no-match`, `:input-exhausted`), like option errors already carry it
+
 ## 0.12.81
 
 - Fix: a required `:inherit` option is no longer reported missing when supplied after its command

src/babashka/cli.cljc

@@ -1956,6 +1956,15 @@ $env.config.completions.external.completer = {|spans|
   [{:keys [tree dispatch prog inherit]}]
   (println (format-command-help {:table tree :cmds (or dispatch []) :prog prog :inherit inherit})))
 
+(defn- dispatch-error-msg
+  "The terse one-line `:msg` for a command-level dispatch error, or nil for an
+  option error (whose `:msg` comes from the parser)."
+  [cause wrong-input]
+  (case cause
+    :no-match (str "Unknown command: " wrong-input)
+    :input-exhausted "No command given."
+    nil))
+
 (defn format-command-error
   "Render a terse, helpful message (a string) for a dispatch error.
   It is given the data `dispatch` passes to its `:error-fn`:
@@ -1994,11 +2003,8 @@ $env.config.completions.external.completer = {|spans|
                                 [(str "Commands:\n" (format-table {:rows cmds :indent 2})) ""])
                               [hint]))))]
     (cond
-      (= :no-match cause)
-      (command-error (str "Unknown command: " wrong-input))
-
-      (= :input-exhausted cause)
-      (command-error "No command given.")
+      (or (= :no-match cause) (= :input-exhausted cause))
+      (command-error (or msg (dispatch-error-msg cause wrong-input)))
 
       ;; genuine option error (restrict / require / validate / coerce): terse.
       ;; The lib message already names the option the user typed.
@@ -2143,6 +2149,7 @@ $env.config.completions.external.completer = {|spans|
          (error-fn (thread-dispatch-context
                     (merge {:type :org.babashka/cli
                             :cause error
+                            :msg (dispatch-error-msg error (:wrong-input res))
                             :all-commands available-commands
                             :tree tree}
                            (select-keys res [:wrong-input :opts :dispatch]))

test/babashka/cli_test.cljc

@@ -598,11 +598,11 @@
                (-> (cli/dispatch
                     table
                     ["foo" "bar" "--version" "2000" "some-arg"])))))
-      (testing "dispatch errors return :dispatch key"
+      (testing "dispatch errors return :dispatch key, and a :msg like option errors do"
         ;; submap?: dispatch also enriches error data with :tree (and :prog/:inherit when set)
-        (is (submap? {:type :org.babashka/cli, :dispatch ["foo" "bar"], :all-commands '("baz"), :cause :input-exhausted, :opts {}}
+        (is (submap? {:type :org.babashka/cli, :dispatch ["foo" "bar"], :all-commands '("baz"), :cause :input-exhausted, :msg "No command given.", :opts {}}
                      (cli/dispatch [{:cmds ["foo" "bar" "baz"] :fn identity}] ["foo" "bar"] {:error-fn identity})))
-        (is (submap? {:type :org.babashka/cli, :dispatch ["foo" "bar"], :wrong-input "wrong", :all-commands '("baz"), :cause :no-match, :opts {}}
+        (is (submap? {:type :org.babashka/cli, :dispatch ["foo" "bar"], :wrong-input "wrong", :all-commands '("baz"), :cause :no-match, :msg "Unknown command: wrong", :opts {}}
                      (cli/dispatch [{:cmds ["foo" "bar" "baz"] :fn identity}] ["foo" "bar" "wrong"] {:error-fn identity})))))))
 
 (deftest table->tree-test