Throw exception for unknown :fn/* function keywords (#670)

CHANGELOG.adoc

@@ -33,6 +33,7 @@ A release with an intentional breaking changes is marked with:
 ** {issue}661[#661]: Fix `:fn/enabled`. ({person}dgr[@dgr])
 ** {issue}663[#663]: `query` throws a more accurate exception with a more accurate error message when provided with an empty query vector. ({person}dgr[@dgr])
 ** {issue}666[#666]: Previously, in some error conditions, Etaoin would throw a very generic `clojure.lang.Exception` object. Some of those cases have been replaced by throwing a map with Slingshot, providing more information about the problem. ({person}dgr[@dgr])
+** {issue}668[#668]: Throw an exception for unknown `:fn/*` keywords in map queries.
 * Docs
 ** {issue}656[#656]: Correctly describe behavior when query's parameter is a string. The User Guide and `query` doc strings say that a string passed to `query` is interpreted as an XPath expression. In fact, `query` interprets this as either XPath or CSS depending on the setting of the driver's `:locator` parameter, which can be changed. ({person}dgr[@dgr])
 * Quality

src/etaoin/impl/xpath.clj

@@ -1,6 +1,7 @@
 (ns ^:no-doc etaoin.impl.xpath
   "A special module to work with XPath language."
-  (:require [clojure.string :as string]))
+  (:require [clojure.string :as string]
+            [slingshot.slingshot :refer [throw+]]))
 
 (set! *warn-on-reflection* true)
 
@@ -49,7 +50,16 @@
 
 (defmethod clause :default
   [[attr text]]
-  (node-equals (format "@%s" (to-str attr)) text))
+  ;; If we fall through to the default case and yet the attribute
+  ;; looks like a query function, then the user probably has a typo
+  ;; in their program, so we throw.
+  ;; Else treat it like an attribute
+  (if (and (keyword? attr) (= (namespace attr) "fn"))
+    (throw+ {:type :etaoin/argument
+             :message "Unknown query function"
+             :fn attr
+             :arg text})
+    (node-equals (format "@%s" (to-str attr)) text)))
 
 (defmethod clause :fn/text
   [[_ text]]

test/etaoin/api_test.clj

@@ -935,7 +935,10 @@
     ;; 3. malformed XPath
     ;; 4. malformed CSS
     ;; 5. query isn't a string, map, or vector. Perhaps a list and set.
-    ;; 6. bad :fn/... keywords
+    ;; 6. unknown :fn/... keywords
+    (testing "unknown :fn/* keywords"
+      ;; ":fn/indx" is probably a typo and the user really wants ":fn/index"
+      (is (thrown+? [:type :etaoin/argument] (e/query *driver* {:tag :div :fn/indx 1}))))
     ;; 7. vector queries with vector elements (vectors in vectors)
     ))