driver: properly clone stack traces from error objects, and never display long state traces on backend errors

packages/driver/src/config/bluebird.coffee

@@ -2,5 +2,4 @@ Promise = require("bluebird")
 
 Promise.config({
   cancellation: true
-  longStackTraces: true
 })

packages/driver/src/cypress.coffee

@@ -102,15 +102,15 @@ class $Cypress
     ## slice up the behavior
     config.isInteractive = !config.isTextTerminal
 
-    if not config.isInteractive
-      ## disable long stack traces when
-      ## we are running headlessly for
-      ## performance since users cannot
-      ## interact with the stack traces
-      ## anyway
-      Promise.config({
-        longStackTraces: false
-      })
+    ## enable long stack traces when
+    ## we not are running headlessly
+    ## for debuggability but disable
+    ## them when running headlessly for
+    ## performance since users cannot
+    ## interact with the stack traces
+    Promise.config({
+      longStackTraces: config.isInteractive
+    })
 
     {environmentVariables, remote} = config
 
@@ -359,7 +359,14 @@ class $Cypress
     new Promise (resolve, reject) =>
       fn = (reply) ->
         if e = reply.error
+          ## clone the error object
+          ## and set stack cleaned
+          ## to prevent bluebird from
+          ## attaching long stace traces
+          ## which otherwise make this err
+          ## unusably long
           err = $utils.cloneErr(e)
+          err.__stackCleaned__ = true
           err.backend = true
           reject(err)
         else

packages/driver/src/cypress/utils.coffee

@@ -54,11 +54,12 @@ module.exports = {
 
     return err
 
-  cloneErr: (err) ->
-    err2 = new Error(err.message)
-    err2.name = err.name
+  cloneErr: (obj) ->
+    err2 = new Error(obj.message)
+    err2.name = obj.name
+    err2.stack = obj.stack
 
-    for own prop, val of err
+    for own prop, val of obj
       if not err2[prop]
         err2[prop] = val
 

packages/driver/test/cypress/integration/cypress/cypress_spec.coffee

@@ -0,0 +1,22 @@
+describe "driver/src/cypress/index", ->
+  beforeEach ->
+    @Cypress = Cypress.$Cypress.create({})
+
+  context "#backend", ->
+    it "sets __stackCleaned__ on errors", (done) ->
+      cy.stub(@Cypress, "emit")
+      .withArgs("backend:request")
+      .yieldsAsync({
+        error: {
+          name: "Error"
+          message: "msg"
+          stack: "stack"
+        }
+      })
+
+      @Cypress.backend("foo")
+      .catch (err) ->
+        expect(err.backend).to.be.true
+        expect(err.stack).not.to.include("From previous event")
+
+        done()

packages/driver/test/cypress/integration/cypress/utils_spec.coffee

@@ -1,6 +1,23 @@
+_ = Cypress._
 $utils = Cypress.utils
 
 describe "driver/src/cypress/utils", ->
+  context ".cloneErr", ->
+    it "copies properies, message, stack", ->
+      obj = {
+        stack: "stack"
+        message: "message"
+        name: "Foo"
+        code: 123
+      }
+
+      err = $utils.cloneErr(obj)
+
+      expect(err).to.be.instanceof(top.Error)
+
+      for key, val of obj
+        expect(err[key], "key: #{key}").to.eq(obj[key])
+
   context ".appendErrMsg", ->
     it "appends error message", ->
       err = new Error("foo")