Cleanup backtraces, add Exception#capture_backtrace!

This adds a new protocol used to fill the backtrace that subclasses can
override if they wish.

Also, custom backtraces (Array of Strings) are better support and don't
master a true Backtrace object ever.

kernel/bootstrap/exception.rb

@@ -1,6 +1,5 @@
 class Exception
-  def fill_locations
-    Ruby.primitive :exception_fill_locations
-    raise PrimitiveFailure, "Unable to fill locations"
+  def capture_backtrace!(offset)
+    # replaced in delta with a real implementation
   end
 end

kernel/common/backtrace.rb

@@ -31,6 +31,8 @@ def initialize(locations)
     @inline_effect = "\033[0;4m"
 
     @width = Rubinius::TERMINAL_WIDTH
+
+    @mri_backtrace = nil
   end
 
   def [](index)
@@ -157,11 +159,35 @@ def each
     self
   end
 
+  def self.detect_backtrace(obj)
+    if bt = obj.instance_variable_get(:@rbx_backtrace)
+      return bt if bt.same_mri_backtrace?(obj)
+    end
+
+    return nil
+  end
+
   # HACK: This should be MRI compliant-ish. --rue
   #
-  def to_mri()
-    @locations.map do |loc|
+  def to_mri
+    return @mri_backtrace if @mri_backtrace
+
+    @mri_backtrace = @locations.map do |loc|
+      "#{loc.position}:in `#{loc.describe_method}'"
+    end
+
+    # A little extra magic, so we can carry the backtrace along and reuse it
+
+    @mri_backtrace.instance_variable_set(:@rbx_backtrace, self)
+
+    return @mri_backtrace
+  end
+
+  def same_mri_backtrace?(obj)
+    currently = @locations.map do |loc|
       "#{loc.position}:in `#{loc.describe_method}'"
     end
+
+    currently == obj
   end
 end

kernel/common/exception.rb

@@ -8,20 +8,15 @@ def initialize(message = nil)
     @message = message
     @locations = nil
     @backtrace = nil
+    @custom_backtrace = nil
   end
 
   # Needed to properly implement #exception, which must clone and call
   # #initialize again, BUT not a subclasses initialize.
   alias_method :__initialize__, :initialize
 
   def backtrace
-    if @backtrace
-      if @backtrace.kind_of? Array
-        return @backtrace
-      end
-
-      return @backtrace.to_mri
-    end
+    return @custom_backtrace if @custom_backtrace
 
     if @locations
       awesome_backtrace.to_mri
@@ -30,19 +25,40 @@ def backtrace
     end
   end
 
+  # Indicates if the Exception has a backtrace set
+  def backtrace?
+    (@backtrace || @locations) ? true : false
+  end
+
   def awesome_backtrace
-    @backtrace = Backtrace.backtrace(@locations)
+    @backtrace ||= Backtrace.backtrace(@locations)
   end
 
   def render(header="An exception occurred", io=STDOUT)
     io.puts header
     io.puts "    #{message} (#{self.class})"
+
+    if @custom_backtrace
+      io.puts "\nUser defined backtrace:"
+      @custom_backtrace.each do |line|
+        io.puts "    #{line}"
+      end
+    end
+
     io.puts "\nBacktrace:"
     io.puts awesome_backtrace.show
 
     extra = @parent
     while extra
       io.puts "\nCaused by: #{extra.message} (#{extra.class})"
+
+      if @custom_backtrace
+        io.puts "\nUser defined backtrace:"
+        @custom_backtrace.each do |line|
+          io.puts "    #{line}"
+        end
+      end
+
       io.puts "\nBacktrace:"
       io.puts extra.awesome_backtrace.show
 
@@ -52,7 +68,16 @@ def render(header="An exception occurred", io=STDOUT)
   end
 
   def set_backtrace(bt)
-    @backtrace = bt
+    if bt.kind_of? Backtrace
+      @backtrace = bt
+    else
+      # See if we stashed a Backtrace object away, and use it.
+      if hidden_bt = Backtrace.detect_backtrace(bt)
+        @backtrace = hidden_bt
+      else
+        @custom_backtrace = bt
+      end
+    end
   end
 
   def set_context(ctx)

kernel/delta/exception.rb

@@ -9,3 +9,9 @@
 
 class FatalError < Exception
 end
+
+class Exception
+  def capture_backtrace!(offset=1)
+    @locations = Rubinius::VM.backtrace offset
+  end
+end

kernel/delta/kernel.rb

@@ -30,9 +30,7 @@ def raise(exc=undefined, msg=undefined, ctx=nil)
 
     unless skip
       exc.set_context ctx if ctx
-      unless exc.locations
-        exc.locations = Rubinius::VM.backtrace 1
-      end
+      exc.capture_backtrace!(2) unless exc.backtrace?
     end
 
     if $DEBUG and $VERBOSE != nil