/
hints.cljs
155 lines (128 loc) · 6.55 KB
/
hints.cljs
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(ns devtools.hints
(:require-macros [devtools.compiler :refer [check-compiler-options!]]
[devtools.oops :refer [unchecked-aget]])
(:require [devtools.prefs :refer [pref]]
[devtools.context :as context]
[cljs.stacktrace :as stacktrace]))
; cljs.stacktrace does not play well in :advanced mode optimizations, see https://github.com/binaryage/cljs-devtools/issues/37
(check-compiler-options!)
(defn ^:dynamic available? []
true)
; Question: How much time have you lost staring at "Cannot read property 'call' of null" kind of errors?
;
; ---------------------------------------------------------------------------------------------------------------------------
;
; The idea is to try enhance error object's .stack and .message fields with additional info about
; the call site causing null type error. With optimizations :none the name of the null call site can be seen.
;
; The enhancing handler function tries to:
; 1) parse error's stack trace.
; 2) look original javascript source file up (via sync AJAX fetch by default).
; 3) locate reported line and column.
; 4) presents problematic line with a column hint as addition to .stack or .message strings.
; Technically the trick here is to override TypeError.prototype.toString
; and global window.onerror handler to enhance uncaught errors.
;
; With that we should handle two situations:
; 1) either error gets printed (typically in user's catch via console), so patched toString() method gets called.
; 2) or it is uncaught and our global error handler should take care of possible enhancement
; before devtools present it to the user themselves.
;
; note: Tested under Chrome only
(def ^:dynamic *installed* false)
(def ^:dynamic *original-global-error-handler* nil)
(def ^:dynamic *original-type-error-prototype-to-string* nil)
(def processed-errors (volatile! nil))
; ---------------------------------------------------------------------------------------------------------------------------
(defn set-processed-errors! [val]
(vreset! processed-errors val))
(defn get-processed-errors! []
(if-let [val @processed-errors]
val
(if (exists? js/WeakSet)
(set-processed-errors! (js/WeakSet.)))))
; ---------------------------------------------------------------------------------------------------------------------------
(defn empty-as-nil [str]
(if (empty? str) nil str))
(defn ajax-reader [url]
(let [xhr (js/XMLHttpRequest.)]
(.open xhr "GET" url false)
(.send xhr)
(empty-as-nil (.-responseText xhr))))
(defn retrieve-javascript-source [where]
(let [reader (or (pref :file-reader) ajax-reader)]
(reader where)))
(defn get-line [lines line-number]
(unchecked-aget lines (dec line-number))) ; line numbering is 1-based
(defn extend-content [content lines line-number min-length]
(if (or (> (count content) min-length)
(not (pos? line-number)))
content
(let [prev-line-number (dec line-number)
prev-line (get-line lines prev-line-number)
new-content (str prev-line "\n" content)]
(extend-content new-content lines prev-line-number min-length))))
(defn mark-call-closed-at-column [line column]
(let [n (dec column) ; column number is 1-based
prefix (.substring line 0 n)
postfix (.substring line n)]
(str prefix " <<< ☢ NULL ☢ <<< " postfix)))
(defn mark-null-call-site-location [file line-number column]
(let [content (retrieve-javascript-source file)
lines (.split content "\n")
line (get-line lines line-number)
marked-line (mark-call-closed-at-column line column)
min-length (or (pref :sanity-hint-min-length) 128)]
(extend-content marked-line lines line-number min-length)))
(defn make-sense-of-the-error [message file line-number column]
(cond
(re-matches #"Cannot read property 'call' of.*" message) (mark-null-call-site-location file line-number column)
:else nil))
(defn parse-stacktrace [native-stack-trace]
(stacktrace/parse-stacktrace {} native-stack-trace {:ua-product :chrome} {:asset-root ""}))
(defn error-object-sense [error]
(try
(let [native-stack-trace (.-stack error)
stack-trace (parse-stacktrace native-stack-trace)
top-item (second stack-trace) ; first line is just an error message
{:keys [file line column]} top-item]
(make-sense-of-the-error (.-message error) file line column))
(catch :default _e
; silently fail in case of troubles parsing stack trace
false)))
(defn type-error-to-string [self]
(if-let [seen-errors (get-processed-errors!)]
(when-not (.has seen-errors self)
(.add seen-errors self)
(when-let [sense (error-object-sense self)]
(set! (.-message self) (str (.-message self) ", a sanity hint:\n" sense))))) ; this is dirty, patch message field before it gets used
(.call *original-type-error-prototype-to-string* self))
(defn global-error-handler [message url line column error]
(let [res (if *original-global-error-handler*
(*original-global-error-handler* message url line column error))]
(if-not res
(when-let [sense (error-object-sense error)]
(.info (context/get-console) "A sanity hint for incoming uncaught error:\n" sense)
false)
true)))
(defn install-type-error-enhancer []
(set! *original-global-error-handler* (.-onerror (context/get-root)))
(set! (.-onerror (context/get-root)) global-error-handler)
(let [prototype (.-prototype js/TypeError)]
(set! *original-type-error-prototype-to-string* (.-toString prototype))
(set! (.-toString prototype) #(this-as self (type-error-to-string self))))) ; work around http://dev.clojure.org/jira/browse/CLJS-1545
; -- installation -----------------------------------------------------------------------------------------------------------
(defn installed? []
*installed*)
(defn install! []
(when-not *installed*
(set! *installed* true)
(install-type-error-enhancer)
true))
(defn uninstall! []
(when *installed*
(set! *installed* false)
(assert *original-type-error-prototype-to-string*)
(set! (.-onerror (context/get-root)) *original-global-error-handler*)
(let [prototype (.-prototype js/TypeError)]
(set! (.-toString prototype) *original-type-error-prototype-to-string*))))