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Diffstat (limited to 'guides/source/debugging_rails_applications.md')
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1 files changed, 248 insertions, 208 deletions
diff --git a/guides/source/debugging_rails_applications.md b/guides/source/debugging_rails_applications.md index a9715fb837..f0d0f9753a 100644 --- a/guides/source/debugging_rails_applications.md +++ b/guides/source/debugging_rails_applications.md @@ -17,7 +17,7 @@ After reading this guide, you will know: View Helpers for Debugging -------------------------- -One common task is to inspect the contents of a variable. In Rails, you can do this with three methods: +One common task is to inspect the contents of a variable. Rails provides three different ways to do this: * `debug` * `to_yaml` @@ -54,7 +54,7 @@ Title: Rails debugging guide ### `to_yaml` -Displaying an instance variable, or any other object or method, in YAML format can be achieved this way: +Alternatively, calling `to_yaml` on any object converts it to YAML. You can pass this converted object into the `simple_format` helper method to format the output. This is how `debug` does its magic. ```html+erb <%= simple_format @article.to_yaml %> @@ -64,9 +64,7 @@ Displaying an instance variable, or any other object or method, in YAML format c </p> ``` -The `to_yaml` method converts the method to YAML format leaving it more readable, and then the `simple_format` helper is used to render each line as in the console. This is how `debug` method does its magic. - -As a result of this, you will have something like this in your view: +The above code will render something like this: ```yaml --- !ruby/object Article @@ -94,7 +92,7 @@ Another useful method for displaying object values is `inspect`, especially when </p> ``` -Will be rendered as follows: +Will render: ``` [1, 2, 3, 4, 5] @@ -109,36 +107,41 @@ It can also be useful to save information to log files at runtime. Rails maintai ### What is the Logger? -Rails makes use of the `ActiveSupport::Logger` class to write log information. You can also substitute another logger such as `Log4r` if you wish. +Rails makes use of the `ActiveSupport::Logger` class to write log information. Other loggers, such as `Log4r`, may also be substituted. -You can specify an alternative logger in your `environment.rb` or any environment file: +You can specify an alternative logger in `config/application.rb` or any other environment file, for example: ```ruby -Rails.logger = Logger.new(STDOUT) -Rails.logger = Log4r::Logger.new("Application Log") +config.logger = Logger.new(STDOUT) +config.logger = Log4r::Logger.new("Application Log") ``` Or in the `Initializer` section, add _any_ of the following ```ruby -config.logger = Logger.new(STDOUT) -config.logger = Log4r::Logger.new("Application Log") +Rails.logger = Logger.new(STDOUT) +Rails.logger = Log4r::Logger.new("Application Log") ``` TIP: By default, each log is created under `Rails.root/log/` and the log file is named after the environment in which the application is running. ### Log Levels -When something is logged it's printed into the corresponding log if the log level of the message is equal or higher than the configured log level. If you want to know the current log level you can call the `Rails.logger.level` method. +When something is logged, it's printed into the corresponding log if the log +level of the message is equal to or higher than the configured log level. If you +want to know the current log level, you can call the `Rails.logger.level` +method. -The available log levels are: `:debug`, `:info`, `:warn`, `:error`, `:fatal`, and `:unknown`, corresponding to the log level numbers from 0 up to 5 respectively. To change the default log level, use +The available log levels are: `:debug`, `:info`, `:warn`, `:error`, `:fatal`, +and `:unknown`, corresponding to the log level numbers from 0 up to 5, +respectively. To change the default log level, use ```ruby config.log_level = :warn # In any environment initializer, or Rails.logger.level = 0 # at any time ``` -This is useful when you want to log under development or staging, but you don't want to flood your production log with unnecessary information. +This is useful when you want to log under development or staging without flooding your production log with unnecessary information. TIP: The default Rails log level is `debug` in all environments. @@ -202,7 +205,7 @@ Adding extra logging like this makes it easy to search for unexpected or unusual When running multi-user, multi-account applications, it's often useful to be able to filter the logs using some custom rules. `TaggedLogging` -in Active Support helps in doing exactly that by stamping log lines with subdomains, request ids, and anything else to aid debugging such applications. +in Active Support helps you do exactly that by stamping log lines with subdomains, request ids, and anything else to aid debugging such applications. ```ruby logger = ActiveSupport::TaggedLogging.new(Logger.new(STDOUT)) @@ -212,34 +215,33 @@ logger.tagged("BCX") { logger.tagged("Jason") { logger.info "Stuff" } } # Logs " ``` ### Impact of Logs on Performance -Logging will always have a small impact on performance of your rails app, - particularly when logging to disk. However, there are a few subtleties: +Logging will always have a small impact on the performance of your Rails app, + particularly when logging to disk. Additionally, there are a few subtleties: Using the `:debug` level will have a greater performance penalty than `:fatal`, as a far greater number of strings are being evaluated and written to the log output (e.g. disk). -Another potential pitfall is that if you have many calls to `Logger` like this - in your code: +Another potential pitfall is too many calls to `Logger` in your code: ```ruby logger.debug "Person attributes hash: #{@person.attributes.inspect}" ``` -In the above example, There will be a performance impact even if the allowed +In the above example, there will be a performance impact even if the allowed output level doesn't include debug. The reason is that Ruby has to evaluate these strings, which includes instantiating the somewhat heavy `String` object -and interpolating the variables, and which takes time. +and interpolating the variables. Therefore, it's recommended to pass blocks to the logger methods, as these are -only evaluated if the output level is the same or included in the allowed level +only evaluated if the output level is the same as — or included in — the allowed level (i.e. lazy loading). The same code rewritten would be: ```ruby logger.debug {"Person attributes hash: #{@person.attributes.inspect}"} ``` -The contents of the block, and therefore the string interpolation, is only -evaluated if debug is enabled. This performance savings is only really +The contents of the block, and therefore the string interpolation, are only +evaluated if debug is enabled. This performance savings are only really noticeable with large amounts of logging, but it's a good practice to employ. Debugging with the `byebug` gem @@ -253,8 +255,8 @@ is your best companion. The debugger can also help you if you want to learn about the Rails source code but don't know where to start. Just debug any request to your application and -use this guide to learn how to move from the code you have written deeper into -Rails code. +use this guide to learn how to move from the code you have written into the +underlying Rails code. ### Setup @@ -285,7 +287,7 @@ As soon as your application calls the `byebug` method, the debugger will be started in a debugger shell inside the terminal window where you launched your application server, and you will be placed at the debugger's prompt `(byebug)`. Before the prompt, the code around the line that is about to be run will be -displayed and the current line will be marked by '=>'. Like this: +displayed and the current line will be marked by '=>', like this: ``` [1, 10] in /PathTo/project/app/controllers/articles_controller.rb @@ -310,16 +312,15 @@ processing the entire request. For example: ```bash -=> Booting WEBrick +=> Booting Puma => Rails 5.0.0 application starting in development on http://0.0.0.0:3000 => Run `rails server -h` for more startup options -=> Notice: server is listening on all interfaces (0.0.0.0). Consider using 127.0.0.1 (--binding option) -=> Ctrl-C to shutdown server -[2014-04-11 13:11:47] INFO WEBrick 1.3.1 -[2014-04-11 13:11:47] INFO ruby 2.1.1 (2014-02-24) [i686-linux] -[2014-04-11 13:11:47] INFO WEBrick::HTTPServer#start: pid=6370 port=3000 - - +Puma starting in single mode... +* Version 3.4.0 (ruby 2.3.1-p112), codename: Owl Bowl Brawl +* Min threads: 5, max threads: 5 +* Environment: development +* Listening on tcp://localhost:3000 +Use Ctrl-C to stop Started GET "/" for 127.0.0.1 at 2014-04-11 13:11:48 +0200 ActiveRecord::SchemaMigration Load (0.2ms) SELECT "schema_migrations".* FROM "schema_migrations" Processing by ArticlesController#index as HTML @@ -335,34 +336,57 @@ Processing by ArticlesController#index as HTML 10: respond_to do |format| 11: format.html # index.html.erb 12: format.json { render json: @articles } - (byebug) ``` -Now it's time to explore and dig into your application. A good place to start is +Now it's time to explore your application. A good place to start is by asking the debugger for help. Type: `help` ``` (byebug) help -byebug 2.7.0 - -Type 'help <command-name>' for help on a specific command + break -- Sets breakpoints in the source code + catch -- Handles exception catchpoints + condition -- Sets conditions on breakpoints + continue -- Runs until program ends, hits a breakpoint or reaches a line + debug -- Spawns a subdebugger + delete -- Deletes breakpoints + disable -- Disables breakpoints or displays + display -- Evaluates expressions every time the debugger stops + down -- Moves to a lower frame in the stack trace + edit -- Edits source files + enable -- Enables breakpoints or displays + finish -- Runs the program until frame returns + frame -- Moves to a frame in the call stack + help -- Helps you using byebug + history -- Shows byebug's history of commands + info -- Shows several informations about the program being debugged + interrupt -- Interrupts the program + irb -- Starts an IRB session + kill -- Sends a signal to the current process + list -- Lists lines of source code + method -- Shows methods of an object, class or module + next -- Runs one or more lines of code + pry -- Starts a Pry session + quit -- Exits byebug + restart -- Restarts the debugged program + save -- Saves current byebug session to a file + set -- Modifies byebug settings + show -- Shows byebug settings + source -- Restores a previously saved byebug session + step -- Steps into blocks or methods one or more times + thread -- Commands to manipulate threads + tracevar -- Enables tracing of a global variable + undisplay -- Stops displaying all or some expressions when program stops + untracevar -- Stops tracing a global variable + up -- Moves to a higher frame in the stack trace + var -- Shows variables and its values + where -- Displays the backtrace -Available commands: -backtrace delete enable help list pry next restart source up -break disable eval info method ps save step var -catch display exit interrupt next putl set thread -condition down finish irb p quit show trace -continue edit frame kill pp reload skip undisplay +(byebug) ``` -TIP: To view the help menu for any command use `help <command-name>` at the -debugger prompt. For example: _`help list`_. You can abbreviate any debugging -command by supplying just enough letters to distinguish them from other -commands, so you can also use `l` for the `list` command, for example. - -To see the previous ten lines you should type `list-` (or `l-`) +To see the previous ten lines you should type `list-` (or `l-`). ``` (byebug) l- @@ -378,12 +402,11 @@ To see the previous ten lines you should type `list-` (or `l-`) 8 @articles = Article.find_recent 9 10 respond_to do |format| - ``` -This way you can move inside the file, being able to see the code above and over -the line where you added the `byebug` call. Finally, to see where you are in -the code again you can type `list=` +This way you can move inside the file and see the code above the line where you +added the `byebug` call. Finally, to see where you are in the code again you can +type `list=` ``` (byebug) list= @@ -399,7 +422,6 @@ the code again you can type `list=` 10: respond_to do |format| 11: format.html # index.html.erb 12: format.json { render json: @articles } - (byebug) ``` @@ -411,8 +433,7 @@ contexts as you go through the different parts of the stack. The debugger creates a context when a stopping point or an event is reached. The context has information about the suspended program which enables the debugger to inspect the frame stack, evaluate variables from the perspective of the -debugged program, and contains information about the place where the debugged -program is stopped. +debugged program, and know the place where the debugged program is stopped. At any time you can call the `backtrace` command (or its alias `where`) to print the backtrace of the application. This can be very helpful to know how you got @@ -422,46 +443,45 @@ then `backtrace` will supply the answer. ``` (byebug) where --> #0 ArticlesController.index - at /PathTo/project/test_app/app/controllers/articles_controller.rb:8 - #1 ActionController::ImplicitRender.send_action(method#String, *args#Array) - at /PathToGems/actionpack-5.0.0/lib/action_controller/metal/implicit_render.rb:4 + at /PathToProject/app/controllers/articles_controller.rb:8 + #1 ActionController::BasicImplicitRender.send_action(method#String, *args#Array) + at /PathToGems/actionpack-5.0.0/lib/action_controller/metal/basic_implicit_render.rb:4 #2 AbstractController::Base.process_action(action#NilClass, *args#Array) - at /PathToGems/actionpack-5.0.0/lib/abstract_controller/base.rb:189 - #3 ActionController::Rendering.process_action(action#NilClass, *args#NilClass) - at /PathToGems/actionpack-5.0.0/lib/action_controller/metal/rendering.rb:10 + at /PathToGems/actionpack-5.0.0/lib/abstract_controller/base.rb:181 + #3 ActionController::Rendering.process_action(action, *args) + at /PathToGems/actionpack-5.0.0/lib/action_controller/metal/rendering.rb:30 ... ``` The current frame is marked with `-->`. You can move anywhere you want in this -trace (thus changing the context) by using the `frame _n_` command, where _n_ is +trace (thus changing the context) by using the `frame n` command, where _n_ is the specified frame number. If you do that, `byebug` will display your new context. ``` (byebug) frame 2 -[184, 193] in /PathToGems/actionpack-5.0.0/lib/abstract_controller/base.rb - 184: # is the intended way to override action dispatching. - 185: # - 186: # Notice that the first argument is the method to be dispatched - 187: # which is *not* necessarily the same as the action name. - 188: def process_action(method_name, *args) -=> 189: send_action(method_name, *args) - 190: end - 191: - 192: # Actually call the method associated with the action. Override - 193: # this method if you wish to change how action methods are called, - +[176, 185] in /PathToGems/actionpack-5.0.0/lib/abstract_controller/base.rb + 176: # is the intended way to override action dispatching. + 177: # + 178: # Notice that the first argument is the method to be dispatched + 179: # which is *not* necessarily the same as the action name. + 180: def process_action(method_name, *args) +=> 181: send_action(method_name, *args) + 182: end + 183: + 184: # Actually call the method associated with the action. Override + 185: # this method if you wish to change how action methods are called, (byebug) ``` The available variables are the same as if you were running the code line by line. After all, that's what debugging is. -You can also use `up [n]` (`u` for abbreviated) and `down [n]` commands in order -to change the context _n_ frames up or down the stack respectively. _n_ defaults -to one. Up in this case is towards higher-numbered stack frames, and down is -towards lower-numbered stack frames. +You can also use `up [n]` and `down [n]` commands in order to change the context +_n_ frames up or down the stack respectively. _n_ defaults to one. Up in this +case is towards higher-numbered stack frames, and down is towards lower-numbered +stack frames. ### Threads @@ -469,16 +489,15 @@ The debugger can list, stop, resume and switch between running threads by using the `thread` command (or the abbreviated `th`). This command has a handful of options: -* `thread` shows the current thread. -* `thread list` is used to list all threads and their statuses. The plus + -character and the number indicates the current thread of execution. -* `thread stop _n_` stop thread _n_. -* `thread resume _n_` resumes thread _n_. -* `thread switch _n_` switches the current thread context to _n_. +* `thread`: shows the current thread. +* `thread list`: is used to list all threads and their statuses. The current +thread is marked with a plus (+) sign. +* `thread stop n`: stops thread _n_. +* `thread resume n`: resumes thread _n_. +* `thread switch n`: switches the current thread context to _n_. -This command is very helpful, among other occasions, when you are debugging -concurrent threads and need to verify that there are no race conditions in your -code. +This command is very helpful when you are debugging concurrent threads and need +to verify that there are no race conditions in your code. ### Inspecting Variables @@ -502,9 +521,9 @@ current context: 12: format.json { render json: @articles } (byebug) instance_variables -[:@_action_has_layout, :@_routes, :@_headers, :@_status, :@_request, - :@_response, :@_env, :@_prefixes, :@_lookup_context, :@_action_name, - :@_response_body, :@marked_for_same_origin_verification, :@_config] +[:@_action_has_layout, :@_routes, :@_request, :@_response, :@_lookup_context, + :@_action_name, :@_response_body, :@marked_for_same_origin_verification, + :@_config] ``` As you may have figured out, all of the variables that you can access from a @@ -514,6 +533,7 @@ command later in this guide). ``` (byebug) next + [5, 14] in /PathTo/project/app/controllers/articles_controller.rb 5 # GET /articles.json 6 def index @@ -532,31 +552,40 @@ command later in this guide). And then ask again for the instance_variables: ``` -(byebug) instance_variables.include? "@articles" -true +(byebug) instance_variables +[:@_action_has_layout, :@_routes, :@_request, :@_response, :@_lookup_context, + :@_action_name, :@_response_body, :@marked_for_same_origin_verification, + :@_config, :@articles] ``` -Now `@articles` is included in the instance variables, because the line defining it -was executed. +Now `@articles` is included in the instance variables, because the line defining +it was executed. TIP: You can also step into **irb** mode with the command `irb` (of course!). -This way an irb session will be started within the context you invoked it. But -be warned: this is an experimental feature. +This will start an irb session within the context you invoked it. The `var` method is the most convenient way to show variables and their values. -Let's let `byebug` help us with it. +Let's have `byebug` help us with it. ``` (byebug) help var -v[ar] cl[ass] show class variables of self -v[ar] const <object> show constants of object -v[ar] g[lobal] show global variables -v[ar] i[nstance] <object> show instance variables of object -v[ar] l[ocal] show local variables + + [v]ar <subcommand> + + Shows variables and its values + + + var all -- Shows local, global and instance variables of self. + var args -- Information about arguments of the current scope + var const -- Shows constants of an object. + var global -- Shows global variables. + var instance -- Shows instance variables of self or a specific object. + var local -- Shows local variables in current scope. + ``` This is a great way to inspect the values of the current context variables. For -example, to check that we have no local variables currently defined. +example, to check that we have no local variables currently defined: ``` (byebug) var local @@ -570,16 +599,17 @@ You can also inspect for an object method this way: @_start_transaction_state = {} @aggregation_cache = {} @association_cache = {} -@attributes = {"id"=>nil, "created_at"=>nil, "updated_at"=>nil} -@attributes_cache = {} -@changed_attributes = nil -... +@attributes = #<ActiveRecord::AttributeSet:0x007fd0682a9b18 @attributes={"id"=>#<ActiveRecord::Attribute::FromDatabase:0x007fd0682a9a00 @name="id", @value_be... +@destroyed = false +@destroyed_by_association = nil +@marked_for_destruction = false +@new_record = true +@readonly = false +@transaction_state = nil +@txn = nil ``` -TIP: The commands `p` (print) and `pp` (pretty print) can be used to evaluate -Ruby expressions and display the value of variables to the console. - -You can use also `display` to start watching variables. This is a good way of +You can also use `display` to start watching variables. This is a good way of tracking the values of a variable while the execution goes on. ``` @@ -587,56 +617,46 @@ tracking the values of a variable while the execution goes on. 1: @articles = nil ``` -The variables inside the displaying list will be printed with their values after -you move in the stack. To stop displaying a variable use `undisplay _n_` where +The variables inside the displayed list will be printed with their values after +you move in the stack. To stop displaying a variable use `undisplay n` where _n_ is the variable number (1 in the last example). ### Step by Step Now you should know where you are in the running trace and be able to print the -available variables. But lets continue and move on with the application +available variables. But let's continue and move on with the application execution. Use `step` (abbreviated `s`) to continue running your program until the next -logical stopping point and return control to the debugger. - -You may also use `next` which is similar to step, but function or method calls -that appear within the line of code are executed without stopping. - -TIP: You can also use `step n` or `next n` to move forwards `n` steps at once. - -The difference between `next` and `step` is that `step` stops at the next line -of code executed, doing just a single step, while `next` moves to the next line -without descending inside methods. +logical stopping point and return control to the debugger. `next` is similar to +`step`, but while `step` stops at the next line of code executed, doing just a +single step, `next` moves to the next line without descending inside methods. For example, consider the following situation: -```ruby +``` Started GET "/" for 127.0.0.1 at 2014-04-11 13:39:23 +0200 Processing by ArticlesController#index as HTML -[1, 8] in /home/davidr/Proyectos/test_app/app/models/article.rb - 1: class Article < ActiveRecord::Base - 2: - 3: def self.find_recent(limit = 10) - 4: byebug -=> 5: where('created_at > ?', 1.week.ago).limit(limit) - 6: end - 7: - 8: end +[1, 6] in /PathToProject/app/models/article.rb + 1: class Article < ApplicationRecord + 2: def self.find_recent(limit = 10) + 3: byebug +=> 4: where('created_at > ?', 1.week.ago).limit(limit) + 5: end + 6: end (byebug) ``` -If we use `next`, we want go deep inside method calls. Instead, byebug will go -to the next line within the same context. In this case, this is the last line of -the method, so `byebug` will jump to next next line of the previous frame. +If we use `next`, we won't go deep inside method calls. Instead, `byebug` will +go to the next line within the same context. In this case, it is the last line +of the current method, so `byebug` will return to the next line of the caller +method. ``` (byebug) next -Next went up a frame because previous frame finished - -[4, 13] in /PathTo/project/test_app/app/controllers/articles_controller.rb +[4, 13] in /PathToProject/app/controllers/articles_controller.rb 4: # GET /articles 5: # GET /articles.json 6: def index @@ -651,29 +671,29 @@ Next went up a frame because previous frame finished (byebug) ``` -If we use `step` in the same situation, we will literally go the next ruby -instruction to be executed. In this case, the activesupport's `week` method. +If we use `step` in the same situation, `byebug` will literally go to the next +Ruby instruction to be executed -- in this case, Active Support's `week` method. ``` (byebug) step -[50, 59] in /PathToGems/activesupport-5.0.0/lib/active_support/core_ext/numeric/time.rb - 50: ActiveSupport::Duration.new(self * 24.hours, [[:days, self]]) - 51: end - 52: alias :day :days - 53: - 54: def weeks -=> 55: ActiveSupport::Duration.new(self * 7.days, [[:days, self * 7]]) - 56: end - 57: alias :week :weeks - 58: - 59: def fortnights - +[49, 58] in /PathToGems/activesupport-5.0.0/lib/active_support/core_ext/numeric/time.rb + 49: + 50: # Returns a Duration instance matching the number of weeks provided. + 51: # + 52: # 2.weeks # => 14 days + 53: def weeks +=> 54: ActiveSupport::Duration.new(self * 7.days, [[:days, self * 7]]) + 55: end + 56: alias :week :weeks + 57: + 58: # Returns a Duration instance matching the number of fortnights provided. (byebug) ``` -This is one of the best ways to find bugs in your code, or perhaps in Ruby on -Rails. +This is one of the best ways to find bugs in your code. + +TIP: You can also use `step n` or `next n` to move forward `n` steps at once. ### Breakpoints @@ -683,19 +703,18 @@ is reached. The debugger shell is invoked in that line. You can add breakpoints dynamically with the command `break` (or just `b`). There are 3 possible ways of adding breakpoints manually: -* `break line`: set breakpoint in the _line_ in the current source file. -* `break file:line [if expression]`: set breakpoint in the _line_ number inside -the _file_. If an _expression_ is given it must evaluated to _true_ to fire up -the debugger. +* `break n`: set breakpoint in line number _n_ in the current source file. +* `break file:n [if expression]`: set breakpoint in line number _n_ inside +file named _file_. If an _expression_ is given it must evaluated to _true_ to +fire up the debugger. * `break class(.|\#)method [if expression]`: set breakpoint in _method_ (. and \# for class and instance method respectively) defined in _class_. The -_expression_ works the same way as with file:line. - +_expression_ works the same way as with file:n. For example, in the previous situation ``` -[4, 13] in /PathTo/project/app/controllers/articles_controller.rb +[4, 13] in /PathToProject/app/controllers/articles_controller.rb 4: # GET /articles 5: # GET /articles.json 6: def index @@ -708,20 +727,20 @@ For example, in the previous situation 13: end (byebug) break 11 -Created breakpoint 1 at /PathTo/project/app/controllers/articles_controller.rb:11 +Successfully created breakpoint with id 1 ``` -Use `info breakpoints _n_` or `info break _n_` to list breakpoints. If you -supply a number, it lists that breakpoint. Otherwise it lists all breakpoints. +Use `info breakpoints` to list breakpoints. If you supply a number, it lists +that breakpoint. Otherwise it lists all breakpoints. ``` (byebug) info breakpoints Num Enb What -1 y at /PathTo/project/app/controllers/articles_controller.rb:11 +1 y at /PathToProject/app/controllers/articles_controller.rb:11 ``` -To delete breakpoints: use the command `delete _n_` to remove the breakpoint +To delete breakpoints: use the command `delete n` to remove the breakpoint number _n_. If no number is specified, it deletes all breakpoints that are currently active. @@ -733,10 +752,11 @@ No breakpoints. You can also enable or disable breakpoints: -* `enable breakpoints`: allow a _breakpoints_ list or all of them if no list is -specified, to stop your program. This is the default state when you create a +* `enable breakpoints [n [m [...]]]`: allows a specific breakpoint list or all +breakpoints to stop your program. This is the default state when you create a breakpoint. -* `disable breakpoints`: the _breakpoints_ will have no effect on your program. +* `disable breakpoints [n [m [...]]]`: make certain (or all) breakpoints have +no effect on your program. ### Catching Exceptions @@ -751,52 +771,72 @@ To list all active catchpoints use `catch`. There are two ways to resume execution of an application that is stopped in the debugger: -* `continue` [line-specification] \(or `c`): resume program execution, at the -address where your script last stopped; any breakpoints set at that address are -bypassed. The optional argument line-specification allows you to specify a line -number to set a one-time breakpoint which is deleted when that breakpoint is -reached. -* `finish` [frame-number] \(or `fin`): execute until the selected stack frame -returns. If no frame number is given, the application will run until the -currently selected frame returns. The currently selected frame starts out the -most-recent frame or 0 if no frame positioning (e.g up, down or frame) has been -performed. If a frame number is given it will run until the specified frame -returns. +* `continue [n]`: resumes program execution at the address where your script last +stopped; any breakpoints set at that address are bypassed. The optional argument +`n` allows you to specify a line number to set a one-time breakpoint which is +deleted when that breakpoint is reached. +* `finish [n]`: execute until the selected stack frame returns. If no frame +number is given, the application will run until the currently selected frame +returns. The currently selected frame starts out the most-recent frame or 0 if +no frame positioning (e.g up, down or frame) has been performed. If a frame +number is given it will run until the specified frame returns. ### Editing Two commands allow you to open code from the debugger into an editor: -* `edit [file:line]`: edit _file_ using the editor specified by the EDITOR -environment variable. A specific _line_ can also be given. +* `edit [file:n]`: edit file named _file_ using the editor specified by the +EDITOR environment variable. A specific line _n_ can also be given. ### Quitting -To exit the debugger, use the `quit` command (abbreviated `q`), or its alias -`exit`. +To exit the debugger, use the `quit` command (abbreviated to `q`). Or, type `q!` +to bypass the `Really quit? (y/n)` prompt and exit unconditionally. A simple quit tries to terminate all threads in effect. Therefore your server will be stopped and you will have to start it again. ### Settings -`byebug` has a few available options to tweak its behaviour: +`byebug` has a few available options to tweak its behavior: + +``` +(byebug) help set + + set <setting> <value> + + Modifies byebug settings + + Boolean values take "on", "off", "true", "false", "1" or "0". If you + don't specify a value, the boolean setting will be enabled. Conversely, + you can use "set no<setting>" to disable them. -* `set autoreload`: Reload source code when changed (defaults: true). -* `set autolist`: Execute `list` command on every breakpoint (defaults: true). -* `set listsize _n_`: Set number of source lines to list by default to _n_ -(defaults: 10) -* `set forcestep`: Make sure the `next` and `step` commands always move to a new -line. + You can see these environment settings with the "show" command. -You can see the full list by using `help set`. Use `help set _subcommand_` to -learn about a particular `set` command. + List of supported settings: + + autosave -- Automatically save command history record on exit + autolist -- Invoke list command on every stop + width -- Number of characters per line in byebug's output + autoirb -- Invoke IRB on every stop + basename -- <file>:<line> information after every stop uses short paths + linetrace -- Enable line execution tracing + autopry -- Invoke Pry on every stop + stack_on_error -- Display stack trace when `eval` raises an exception + fullpath -- Display full file names in backtraces + histfile -- File where cmd history is saved to. Default: ./.byebug_history + listsize -- Set number of source lines to list by default + post_mortem -- Enable/disable post-mortem mode + callstyle -- Set how you want method call parameters to be displayed + histsize -- Maximum number of commands that can be stored in byebug history + savefile -- File where settings are saved to. Default: ~/.byebug_save +``` TIP: You can save these settings in an `.byebugrc` file in your home directory. The debugger reads these global settings when it starts. For example: ```bash -set forcestep +set callstyle short set listsize 25 ``` @@ -809,7 +849,7 @@ controller. The console would be rendered next to your HTML content. ### Console -Inside any controller action or view, you can then invoke the console by +Inside any controller action or view, you can invoke the console by calling the `console` method. For example, in a controller: @@ -835,7 +875,7 @@ This will render a console inside your view. You don't need to care about the location of the `console` call; it won't be rendered on the spot of its invocation but next to your HTML content. -The console executes pure Ruby code. You can define and instantiate +The console executes pure Ruby code: You can define and instantiate custom classes, create new models and inspect variables. NOTE: Only one console can be rendered per request. Otherwise `web-console` @@ -860,7 +900,7 @@ to use it in production. Debugging Memory Leaks ---------------------- -A Ruby application (on Rails or not), can leak memory - either in the Ruby code +A Ruby application (on Rails or not), can leak memory — either in the Ruby code or at the C code level. In this section, you will learn how to find and fix such leaks by using tool @@ -868,8 +908,8 @@ such as Valgrind. ### Valgrind -[Valgrind](http://valgrind.org/) is a Linux-only application for detecting -C-based memory leaks and race conditions. +[Valgrind](http://valgrind.org/) is an application for detecting C-based memory +leaks and race conditions. There are Valgrind tools that can automatically detect many memory management and threading bugs, and profile your programs in detail. For example, if a C @@ -891,7 +931,7 @@ footnotes that give request information and link back to your source via TextMate. * [Query Trace](https://github.com/ruckus/active-record-query-trace/tree/master) Adds query origin tracing to your logs. -* [Query Reviewer](https://github.com/nesquena/query_reviewer) This rails plugin +* [Query Reviewer](https://github.com/nesquena/query_reviewer) This Rails plugin not only runs "EXPLAIN" before each of your select queries in development, but provides a small DIV in the rendered output of each page with the summary of warnings for each query that it analyzed. @@ -903,7 +943,7 @@ standard Rails error page with a new one containing more contextual information, like source code and variable inspection. * [RailsPanel](https://github.com/dejan/rails_panel) Chrome extension for Rails development that will end your tailing of development.log. Have all information -about your Rails app requests in the browser - in the Developer Tools panel. +about your Rails app requests in the browser — in the Developer Tools panel. Provides insight to db/rendering/total times, parameter list, rendered views and more. |