mirror of https://github.com/rails/rails
Add breakpoint section
Add breakpoint examples Add breakpoint options Some corrections Introduce chained debugging commands
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@ -468,6 +468,287 @@ instance variables:
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class variables: @@raise_on_missing_translations @@raise_on_open_redirects
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```
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### Breakpoints
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There are many ways to insert and trigger a breakpoint in the debugger. In additional to adding debugging statements (e.g. `debugger`) directly in your code, you can also insert breakpoints with commands:
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- `break` (or `b`)
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- `break` - list all breakpoints
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- `break <num>` - set a breakpoint on the `num` line of the current file
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- `break <file:num>` - set a breakpoint on the `num` line of `file`
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- `break <Class#method>` or `break <Class.method>` - set a breakpoint on `Class#method` or `Class.method`
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- `break <expr>.<method>` - sets a breakpoint on `<expr>` result's `<method>` method.
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- `catch <Exception>` - set a breakpoint that'll stop when `Exception` is raised
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- `watch <@ivar>` - set a breakpoint that'll stop when the result of current object's `@ivar` is changed (this is slow)
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And to remove them, you can use:
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- `delete` (or `del`)
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- `delete` - delete all breakpoints
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- `delete <num>` - delete the breakpoint with id `num`
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#### The break command
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**Set a breakpoint with specified line number - e.g. `b 28`**
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```rb
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[20, 29] in ~/projects/rails-guide-example/app/controllers/posts_controller.rb
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20| end
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21|
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22| # POST /posts or /posts.json
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23| def create
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24| @post = Post.new(post_params)
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=> 25| debugger
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26|
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27| respond_to do |format|
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28| if @post.save
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29| format.html { redirect_to @post, notice: "Post was successfully created." }
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=>#0 PostsController#create at ~/projects/rails-guide-example/app/controllers/posts_controller.rb:25
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#1 ActionController::BasicImplicitRender#send_action(method="create", args=[]) at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/actionpack-7.0.0.alpha2/lib/action_controller/metal/basic_implicit_render.rb:6
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# and 72 frames (use `bt' command for all frames)
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(rdbg) b 28 # break command
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#0 BP - Line /Users/st0012/projects/rails-guide-example/app/controllers/posts_controller.rb:28 (line)
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```
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```rb
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(rdbg) c # continue command
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[23, 32] in ~/projects/rails-guide-example/app/controllers/posts_controller.rb
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23| def create
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24| @post = Post.new(post_params)
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25| debugger
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26|
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27| respond_to do |format|
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=> 28| if @post.save
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29| format.html { redirect_to @post, notice: "Post was successfully created." }
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30| format.json { render :show, status: :created, location: @post }
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31| else
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32| format.html { render :new, status: :unprocessable_entity }
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=>#0 block {|format=#<ActionController::MimeResponds::Collec...|} in create at ~/projects/rails-guide-example/app/controllers/posts_controller.rb:28
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#1 ActionController::MimeResponds#respond_to(mimes=[]) at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/actionpack-7.0.0.alpha2/lib/action_controller/metal/mime_responds.rb:205
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# and 74 frames (use `bt' command for all frames)
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Stop by #0 BP - Line /Users/st0012/projects/rails-guide-example/app/controllers/posts_controller.rb:28 (line)
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```
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**Set a breakpoint on a given method call - e.g. `b @post.save`**
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```rb
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[20, 29] in ~/projects/rails-guide-example/app/controllers/posts_controller.rb
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20| end
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21|
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22| # POST /posts or /posts.json
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23| def create
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24| @post = Post.new(post_params)
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=> 25| debugger
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26|
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27| respond_to do |format|
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28| if @post.save
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29| format.html { redirect_to @post, notice: "Post was successfully created." }
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=>#0 PostsController#create at ~/projects/rails-guide-example/app/controllers/posts_controller.rb:25
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#1 ActionController::BasicImplicitRender#send_action(method="create", args=[]) at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/actionpack-7.0.0.alpha2/lib/action_controller/metal/basic_implicit_render.rb:6
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# and 72 frames (use `bt' command for all frames)
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(rdbg) b @post.save # break command
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#0 BP - Method @post.save at /Users/st0012/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/suppressor.rb:43
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```
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```rb
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(rdbg) c # continue command
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[39, 48] in ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/suppressor.rb
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39| SuppressorRegistry.suppressed[name] = previous_state
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40| end
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41| end
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42|
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43| def save(**) # :nodoc:
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=> 44| SuppressorRegistry.suppressed[self.class.name] ? true : super
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45| end
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46|
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47| def save!(**) # :nodoc:
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48| SuppressorRegistry.suppressed[self.class.name] ? true : super
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=>#0 ActiveRecord::Suppressor#save(#arg_rest=nil) at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/suppressor.rb:44
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#1 block {|format=#<ActionController::MimeResponds::Collec...|} in create at ~/projects/rails-guide-example/app/controllers/posts_controller.rb:28
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# and 75 frames (use `bt' command for all frames)
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Stop by #0 BP - Method @post.save at /Users/st0012/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/suppressor.rb:43
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```
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#### The catch command
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**Stop when an exception is raised - e.g. `catch ActiveRecord::RecordInvalid`**
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```rb
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[20, 29] in ~/projects/rails-guide-example/app/controllers/posts_controller.rb
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20| end
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21|
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22| # POST /posts or /posts.json
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23| def create
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24| @post = Post.new(post_params)
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=> 25| debugger
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26|
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27| respond_to do |format|
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28| if @post.save!
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29| format.html { redirect_to @post, notice: "Post was successfully created." }
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=>#0 PostsController#create at ~/projects/rails-guide-example/app/controllers/posts_controller.rb:25
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#1 ActionController::BasicImplicitRender#send_action(method="create", args=[]) at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/actionpack-7.0.0.alpha2/lib/action_controller/metal/basic_implicit_render.rb:6
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# and 72 frames (use `bt' command for all frames)
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(rdbg) catch ActiveRecord::RecordInvalid # command
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#1 BP - Catch "ActiveRecord::RecordInvalid"
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```
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```rb
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(rdbg) c # continue command
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[75, 84] in ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/validations.rb
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75| def default_validation_context
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76| new_record? ? :create : :update
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77| end
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78|
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79| def raise_validation_error
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=> 80| raise(RecordInvalid.new(self))
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81| end
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82|
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83| def perform_validations(options = {})
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84| options[:validate] == false || valid?(options[:context])
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=>#0 ActiveRecord::Validations#raise_validation_error at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/validations.rb:80
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#1 ActiveRecord::Validations#save!(options={}) at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/validations.rb:53
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# and 88 frames (use `bt' command for all frames)
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Stop by #1 BP - Catch "ActiveRecord::RecordInvalid"
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```
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#### The watch command
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**Stop when the instance variable is changed - e.g. `watch @_response_body`**
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```rb
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[20, 29] in ~/projects/rails-guide-example/app/controllers/posts_controller.rb
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20| end
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21|
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22| # POST /posts or /posts.json
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23| def create
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24| @post = Post.new(post_params)
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=> 25| debugger
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26|
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27| respond_to do |format|
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28| if @post.save!
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29| format.html { redirect_to @post, notice: "Post was successfully created." }
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=>#0 PostsController#create at ~/projects/rails-guide-example/app/controllers/posts_controller.rb:25
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#1 ActionController::BasicImplicitRender#send_action(method="create", args=[]) at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/actionpack-7.0.0.alpha2/lib/action_controller/metal/basic_implicit_render.rb:6
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# and 72 frames (use `bt' command for all frames)
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(rdbg) watch @_response_body # command
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#0 BP - Watch #<PostsController:0x00007fce69ca5320> @_response_body =
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```
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```rb
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(rdbg) c # continue command
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[173, 182] in ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/actionpack-7.0.0.alpha2/lib/action_controller/metal.rb
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173| body = [body] unless body.nil? || body.respond_to?(:each)
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174| response.reset_body!
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175| return unless body
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176| response.body = body
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177| super
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=> 178| end
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179|
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180| # Tests if render or redirect has already happened.
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181| def performed?
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182| response_body || response.committed?
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=>#0 ActionController::Metal#response_body=(body=["<html><body>You are being <a href=\"ht...) at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/actionpack-7.0.0.alpha2/lib/action_controller/metal.rb:178 #=> ["<html><body>You are being <a href=\"ht...
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#1 ActionController::Redirecting#redirect_to(options=#<Post id: 13, title: "qweqwe", content:..., response_options={:allow_other_host=>false}) at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/actionpack-7.0.0.alpha2/lib/action_controller/metal/redirecting.rb:74
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# and 82 frames (use `bt' command for all frames)
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Stop by #0 BP - Watch #<PostsController:0x00007fce69ca5320> @_response_body = -> ["<html><body>You are being <a href=\"http://localhost:3000/posts/13\">redirected</a>.</body></html>"]
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(rdbg)
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```
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#### Breakpoint options
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In addition to different types of breakpoints, you can also specify options to achieve more advanced debugging workflow. Currently, the debugger supports 4 options:
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- `do: <cmd or expr>` - when the breakpoint is triggered, execute the given command/expression and continue the program:
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- `break Foo#bar do: bt` - when `Foo#bar` is called, print the stack frames
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- `pre: <cmd or expr>` - when the breakpoint is triggered, execute the given command/expression before stopping:
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- `break Foo#bar pre: info` - when `Foo#bar` is called, print its surrounding variables before stopping.
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- `if: <expr>` - the breakpoint only stops if the result of `<expr`> is true:
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- `break Post#save if: params[:debug]` - stops at `Post#save` if `params[:debug]` is also true
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- `path: <path_regexp>` - the breakpoint only stops if the event that triggers it (e.g. a method call) happens from the given path:
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- `break Post#save if: app/services/a_service` - stops at `Post#save` if the method call happens at a method matches Ruby regexp `/app\/services\/a_service/`.
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Please also note that the first 3 options: `do:`, `pre:` and `if:` are also available for the debug statements we mentioned earlier. For example:
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```rb
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[2, 11] in ~/projects/rails-guide-example/app/controllers/posts_controller.rb
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2| before_action :set_post, only: %i[ show edit update destroy ]
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3|
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4| # GET /posts or /posts.json
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5| def index
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6| @posts = Post.all
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=> 7| debugger(do: "info")
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8| end
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9|
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10| # GET /posts/1 or /posts/1.json
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11| def show
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=>#0 PostsController#index at ~/projects/rails-guide-example/app/controllers/posts_controller.rb:7
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#1 ActionController::BasicImplicitRender#send_action(method="index", args=[]) at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/actionpack-7.0.0.alpha2/lib/action_controller/metal/basic_implicit_render.rb:6
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# and 72 frames (use `bt' command for all frames)
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(rdbg:binding.break) info
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%self = #<PostsController:0x00000000017480>
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@_action_has_layout = true
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@_action_name = "index"
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@_config = {}
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@_lookup_context = #<ActionView::LookupContext:0x00007fce3ad336b8 @details_key=nil, @digest_cache=...
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@_request = #<ActionDispatch::Request GET "http://localhost:3000/posts" for 127.0.0.1>
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@_response = #<ActionDispatch::Response:0x00007fce3ad397e8 @mon_data=#<Monitor:0x00007fce3ad396a8>...
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@_response_body = nil
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@_routes = nil
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@marked_for_same_origin_verification = true
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@posts = #<ActiveRecord::Relation [#<Post id: 2, title: "qweqwe", content: "qweqwe", created_at: "...
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@rendered_format = nil
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```
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#### Program your debugging workflow
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With those options, you can script your debugging workflow in one line like:
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```rb
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def create
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debugger(do: "catch ActiveRecord::RecordInvalid do: bt 10")
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# ...
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end
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```
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And then the debugger will run the scripted command and insert the catch breakpoint
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```rb
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(rdbg:binding.break) catch ActiveRecord::RecordInvalid do: bt 10
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#0 BP - Catch "ActiveRecord::RecordInvalid"
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[75, 84] in ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/validations.rb
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75| def default_validation_context
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76| new_record? ? :create : :update
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77| end
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78|
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79| def raise_validation_error
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=> 80| raise(RecordInvalid.new(self))
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81| end
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82|
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83| def perform_validations(options = {})
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84| options[:validate] == false || valid?(options[:context])
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=>#0 ActiveRecord::Validations#raise_validation_error at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/validations.rb:80
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#1 ActiveRecord::Validations#save!(options={}) at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/validations.rb:53
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# and 88 frames (use `bt' command for all frames)
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```
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Once the catch breakpoint is triggered, it'll print the stack frames
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```rb
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Stop by #0 BP - Catch "ActiveRecord::RecordInvalid"
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(rdbg:catch) bt 10
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=>#0 ActiveRecord::Validations#raise_validation_error at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/validations.rb:80
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#1 ActiveRecord::Validations#save!(options={}) at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/validations.rb:53
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#2 block in save! at ~/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-7.0.0.alpha2/lib/active_record/transactions.rb:302
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```
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This technique can save you from repeated manual input and make the debugging experience smoother.
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You can find more commands and configuration options from its [documentation](https://github.com/ruby/debug).
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#### Autoloading Caveat
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