Remove unnecessary entries from default backtrace

When the --backtrace (or --trace) command line option is not supplied
Rake lowers the noise level in exception backtraces by building
a regular expression containing all the system library paths and
using it to exclude backtrace entries that match.

This doesn't always go far enough, particularly in RVM environments when
many gem paths are added. This commit reverses that approach and only
include backtrace entries that fall within the Capfile and list of tasks
imported thereafter.

If the full unexpurgated backtrace is required then the --backtrace
and --trace options supply it as before.

CHANGELOG.md

@@ -6,6 +6,21 @@ Reverse Chronological Order:
 
 https://github.com/capistrano/capistrano/compare/v3.2.1...HEAD
 
+* Enhancement (@townsen): Remove unnecessary entries from default backtrace
+
+    When the `--backtrace` (or `--trace`) command line option is not supplied
+    Rake lowers the noise level in exception backtraces by building
+    a regular expression containing all the system library paths and
+    using it to exclude backtrace entries that match.
+
+    This does not always go far enough, particularly in RVM environments when
+    many gem paths are added. This commit reverses that approach and _only_
+    include backtrace entries that fall within the Capfile and list of tasks
+    imported thereafter. This makes reading exceptions much easier on the eye.
+
+    If the full unexpurgated backtrace is required then the --backtrace
+    and --trace options supply it as before.
+
 * Disable loading stages configs on `cap -T`
 * Enhancements (@townsen)
   * Fix matching on hosts with custom ports or users set

lib/capistrano/application.rb

@@ -61,6 +61,18 @@ module Capistrano
       end
     end
 
+    def display_error_message(ex)
+      unless options.backtrace
+        if loc = Rake.application.find_rakefile_location
+          whitelist = (@imported.dup << loc[0]).map{|f| File.absolute_path(f, loc[1])}
+          pattern = %r@^(?!#{whitelist.map{|p| Regexp.quote(p)}.join('|')})@
+          Rake.application.options.suppress_backtrace_pattern = pattern
+        end
+        trace "(Backtrace restricted to imported tasks)"
+      end
+      super
+    end
+
     def exit_because_of_exception(ex)
       if respond_to?(:deploying?) && deploying?
         exit_deploy_because_of_exception(ex)

lib/capistrano/dsl/task_enhancements.rb

@@ -53,7 +53,7 @@ module Capistrano
     end
 
     def exit_deploy_because_of_exception(ex)
-      warn t(:deploy_failed, ex: ex.inspect)
+      warn t(:deploy_failed, ex: ex.message)
       invoke 'deploy:failed'
       exit(false)
     end