Introduce inspect-last-exception op

Part of clojure-emacs/cider#3565

Author: vemv

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### New features
+
+* [cider#3565](https://github.com/clojure-emacs/cider/issues/3565): Add new [`inspect-last-exception`](https://docs.cider.mx/cider-nrepl/nrepl-api/ops.html#inspect-last-exception) op.
+
 ### Changes
 
 * [#828](https://github.com/clojure-emacs/cider-nrepl/issues/828): Warmup Orchard caches for exceptions in advance.

doc/modules/ROOT/pages/nrepl-api/ops.adoc

@@ -312,7 +312,6 @@ Optional parameters::
 * `:class` A Java class. If ``:ns`` is passed, it will be used for fully-qualifiying the class, if necessary.
 * `:context` A Compliment completion context, just like the ones already passed for the "complete" op,
 with the difference that the symbol at point should be entirely replaced by "\__prefix__".
-
 For Java interop queries, it helps inferring the precise type of the object the ``:sym`` or ``:member`` refers to,
 making the results more accurate (and less numerous).
 * `:member` A Java class member.
@@ -447,7 +446,6 @@ Optional parameters::
 * `:class` A Java class. If ``:ns`` is passed, it will be used for fully-qualifiying the class, if necessary.
 * `:context` A Compliment completion context, just like the ones already passed for the "complete" op,
 with the difference that the symbol at point should be entirely replaced by "\__prefix__".
-
 For Java interop queries, it helps inferring the precise type of the object the ``:sym`` or ``:member`` refers to,
 making the results more accurate (and less numerous).
 * `:member` A Java class member.
@@ -528,6 +526,24 @@ Returns::
 
 
 
+=== `inspect-last-exception`
+
+Returns an Inspector response for the last exception that has been processed through ``analyze-last-stacktrace`` for the current nrepl session.
+Assumes that ``analyze-last-stacktrace`` has been called first, returning "no-error" otherwise.
+
+Required parameters::
+* `:index` 0 for inspecting the top-level exception, 1 for its ex-cause, 2 for its ex-cause's ex-cause, and so on.
+
+
+Optional parameters::
+{blank}
+
+Returns::
+* `:status` "done", or "no-error" if ``analyze-last-stacktrace`` wasn't called beforehand (or the ``index`` was out of bounds).
+* `:value` A value, as produced by the Inspector middleware.
+
+
+
 === `inspect-next-page`
 
 Jumps to the next page in paginated collection view.

src/cider/nrepl.clj

@@ -627,6 +627,11 @@ if applicable, and re-render the updated value."
     :handles {"analyze-last-stacktrace" {:doc "Return messages describing each cause and stack frame of the most recent exception."
                                          :optional wrap-print-optional-arguments
                                          :returns {"status" "\"done\", or \"no-error\" if `*e` is nil"}}
+              "inspect-last-exception" {:doc "Returns an Inspector response for the last exception that has been processed through `analyze-last-stacktrace` for the current nrepl session.
+Assumes that `analyze-last-stacktrace` has been called first, returning \"no-error\" otherwise."
+                                        :requires {"index" "0 for inspecting the top-level exception, 1 for its ex-cause, 2 for its ex-cause's ex-cause, and so on."}
+                                        :returns {"status" "\"done\", or \"no-error\" if `analyze-last-stacktrace` wasn't called beforehand (or the `index` was out of bounds)."
+                                                  "value" "A value, as produced by the Inspector middleware."}}
               "analyze-stacktrace" {:doc "Parse and analyze the `:stacktrace`
 parameter and return messages describing each cause and stack frame. The
 stacktrace must be a string formatted in one of the following formats:

src/cider/nrepl/middleware/inspect.clj

@@ -24,16 +24,21 @@
                  (pr-str rendered))]
      (response-for msg resp {:value value}))))
 
-(defn inspect-reply
-  [{:keys [page-size transport max-atom-length max-coll-size] :as msg} eval-response]
-  (let [value (cljs/response-value msg eval-response)
-        page-size (or page-size 32)
+(defn inspect-reply*
+  [{:keys [page-size max-atom-length max-coll-size] :as msg} value]
+  (let [page-size (or page-size 32)
         inspector (swap-inspector! msg #(-> %
                                             (assoc :page-size page-size
                                                    :max-atom-length max-atom-length
                                                    :max-coll-size max-coll-size)
                                             (inspect/start value)))]
-    (transport/send transport (inspector-response msg inspector {}))))
+    (inspector-response msg inspector {})))
+
+(defn inspect-reply
+  [msg eval-response]
+  (let [value (cljs/response-value msg eval-response)]
+    (transport/send (:transport msg)
+                    (inspect-reply* msg value))))
 
 (defn inspector-transport
   [{:keys [^Transport transport] :as msg}]

src/cider/nrepl/middleware/stacktrace.clj

@@ -7,6 +7,7 @@
    [haystack.analyzer :as analyzer]
    [haystack.parser :as parser]
    [nrepl.middleware.print :as print]
+   [cider.nrepl.middleware.inspect :as middleware.inspect]
    [nrepl.misc :refer [response-for]]
    [nrepl.transport :as t]))
 
@@ -28,10 +29,14 @@
 
 ;; Analyze the last stacktrace
 
+(def ^:dynamic *last-exception* nil)
+
 (defn- analyze-last-stacktrace
   "Analyze the last exception."
   [{:keys [session ::print/print-fn] :as msg}]
-  (send-analysis msg (analyzer/analyze (@session #'*e) print-fn)))
+  (let [last-exception (@session #'*e)]
+    (swap! session assoc #'*last-exception* last-exception) ;; note that *e can change later, so this entry isn't redundant
+    (send-analysis msg (analyzer/analyze last-exception print-fn))))
 
 (defn- handle-analyze-last-stacktrace-op
   "Handle the analyze last stacktrace op."
@@ -66,10 +71,27 @@
   (handle-analyze-last-stacktrace-op msg)
   (notify-client msg "The `stacktrace` op is deprecated, please use `analyze-last-stacktrace` instead." :warning))
 
+(defn handle-inspect-last-exception-op [{:keys [index transport] :as msg}]
+  (let [le (when index
+             (some-> msg :session deref (get #'*last-exception*)))
+        cause (when le
+                (loop [n 0
+                       cause le]
+                  (if (= n index)
+                    cause
+                    (when cause
+                      (recur (inc n)
+                             (ex-cause cause))))))]
+    (if cause
+      (t/send transport (middleware.inspect/inspect-reply* msg cause))
+      (no-error msg))
+    (done msg)))
+
 (defn handle-stacktrace
   "Handle stacktrace ops."
   [_ {:keys [op] :as msg}]
   (case op
     "analyze-last-stacktrace" (handle-analyze-last-stacktrace-op msg)
-    "analyze-stacktrace" (handle-analyze-stacktrace-op msg)
-    "stacktrace" (handle-stacktrace-op msg)))
+    "inspect-last-exception"  (handle-inspect-last-exception-op msg)
+    "analyze-stacktrace"      (handle-analyze-stacktrace-op msg)
+    "stacktrace"              (handle-stacktrace-op msg)))

test/clj/cider/nrepl/middleware/stacktrace_test.clj

@@ -36,7 +36,27 @@
       (testing "returns the exception message"
         (is (= "Don't know how to create ISeq from: java.lang.Long" (:message response))))
       (testing "returns done status"
-        (is (= #{"done"} (:status response)))))))
+        (is (= #{"done"} (:status response)))))
+
+    (testing "`inspect-last-exception` op"
+      (testing "Index 0 for an exception without extra causes"
+        (let [{[^String first-value] :value} (session/message  {:op "inspect-last-exception" :index 0})]
+          (is (.startsWith first-value "(\"Class\" \": \" (:value")
+              "Returns an Inspector response")))
+      (testing "Index out of bounds"
+        (is (nil? (:value (session/message {:op "inspect-last-exception" :index 1})))))
+      (testing "Indices 0, 1, 2 for an exception with one extra cause"
+        (session/message {:op "eval" :code "(deref (future (/ 2 0)))"})
+        (session/message {:op "analyze-last-stacktrace"})
+        (is (seq (:value (session/message  {:op "inspect-last-exception" :index 0}))))
+        (let [{[^String first-value] :value} (session/message  {:op "inspect-last-exception" :index 0})]
+          (is (.startsWith first-value "(\"Class\" \": \" (:value \"java.util.concurrent.ExecutionException")
+              "Returns an Inspector response for index 0"))
+        (let [{[^String first-value] :value} (session/message  {:op "inspect-last-exception" :index 1})]
+          (is (.startsWith first-value "(\"Class\" \": \" (:value \"java.lang.ArithmeticException")
+              "Returns a different Inspector response for index 1"))
+        (is (nil? (:value (session/message {:op "inspect-last-exception" :index 2})))
+            "Doesn't return a value past the last index")))))
 
 (deftest analyze-last-stacktrace-unbound-test
   (testing "stacktrace op with most recent exception unbound"