PP trick for long inspect code

lib/debug/server_dap.rb

@@ -441,6 +441,7 @@ def process_protocol_request req
 
       when 'stackTrace'
         tid = req.dig('arguments', 'threadId')
+
         if tc = find_waiting_tc(tid)
           request_tc [:dap, :backtrace, req]
         else
@@ -551,9 +552,10 @@ def dap_event args
 
       case type
       when :backtrace
-        result[:stackFrames].each.with_index{|fi, i|
+        result[:stackFrames].each{|fi|
+          frame_depth = fi[:id]
           fi[:id] = id = @frame_map.size + 1
-          @frame_map[id] = [req.dig('arguments', 'threadId'), i]
+          @frame_map[id] = [req.dig('arguments', 'threadId'), frame_depth]
           if fi[:source]
             if src = fi[:source][:sourceReference]
               src_id = @src_map.size + 1
@@ -620,27 +622,36 @@ def process_dap args
 
       case type
       when :backtrace
-        event! :dap_result, :backtrace, req, {
-          stackFrames: @target_frames.map{|frame|
-            path = frame.realpath || frame.path
-            source_name = path ? File.basename(path) : frame.location.to_s
-
-            if !UI_DAP.local_fs || !(path && File.exist?(path))
-              ref = frame.file_lines
-            end
+        start_frame = req.dig('arguments', 'startFrame') || 0
+        levels = req.dig('arguments', 'levels') || 1_000
+        frames = []
+        @target_frames.each_with_index do |frame, i|
+          next if i < start_frame
+          break if (levels -= 1) < 0
+
+          path = frame.realpath || frame.path
+          source_name = path ? File.basename(path) : frame.location.to_s
+
+          if !UI_DAP.local_fs || !(path && File.exist?(path))
+            ref = frame.file_lines
+          end
 
-            {
-              # id: ??? # filled by SESSION
-              name: frame.name,
-              line: frame.location.lineno,
-              column: 1,
-              source: {
-                name: source_name,
-                path: path,
-                sourceReference: ref,
-              },
-            }
+          frames << {
+            id: i, # id is refilled by SESSION
+            name: frame.name,
+            line: frame.location.lineno,
+            column: 1,
+            source: {
+              name: source_name,
+              path: path,
+              sourceReference: ref,
+            },
           }
+        end
+
+        event! :dap_result, :backtrace, req, {
+          stackFrames: frames,
+          totalFrames: @target_frames.size,
         }
       when :scopes
         fid = args.shift

lib/debug/session.rb

@@ -32,6 +32,7 @@
 require 'debug' # invalidate the $LOADED_FEATURE cache
 
 require 'json' if ENV['RUBY_DEBUG_TEST_UI'] == 'terminal'
+require 'pp'
 
 class RubyVM::InstructionSequence
   def traceable_lines_norec lines
@@ -2057,16 +2058,48 @@ def self.method_added tp
   end
 
   METHOD_ADDED_TRACKER = self.create_method_added_tracker
-
   SHORT_INSPECT_LENGTH = 40
 
-  def self.safe_inspect obj, max_length: SHORT_INSPECT_LENGTH, short: false
-    str = obj.inspect
+  class LimitedPP
+    def self.pp(obj, max=80)
+      out = self.new(max)
+      catch out do
+        PP.singleline_pp(obj, out)
+      end
+      out.buf
+    end
+
+    attr_reader :buf
+
+    def initialize max
+      @max = max
+      @cnt = 0
+      @buf = String.new
+    end
+
+    def <<(other)
+      @buf << other
 
-    if short && str.length > max_length
-      str[0...max_length] + '...'
+      if @buf.size >= @max
+        @buf = @buf[0..@max] + '...'
+        throw self
+      end
+    end
+  end
+
+  def self.safe_inspect obj, max_length: SHORT_INSPECT_LENGTH, short: false
+    if short
+      LimitedPP.pp(obj, max_length)
+    else
+      obj.inspect
+    end
+  rescue NoMethodError => e
+    klass, oid = M_CLASS.bind_call(obj), M_OBJECT_ID.bind_call(obj)
+    if obj == (r = e.receiver)
+      "<\##{klass.name}#{oid} does not have \#inspect>"
     else
-      str
+      rklass, roid = M_CLASS.bind_call(r), M_OBJECT_ID.bind_call(r)
+      "<\##{klass.name}:#{oid} contains <\##{rklass}:#{rid} and it does not have #inspect>"
     end
   rescue Exception => e
     str = "<#inspect raises #{e.inspect}>"