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Merge pull request #24764 from deivid-rodriguez/review_debugging_guide

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Review the `byebug` debugging guide [ci skip]
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guides/source/debugging_rails_applications.md
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@ -255,7 +255,8 @@ is your best companion.
The debugger can also help you if you want to learn about the Rails source code 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 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 into the underlying Rails code. use this guide to learn how to move from the code you have written into the
underlying Rails code.
### Setup ### Setup
@ -315,13 +316,11 @@ For example:
=> Rails 5.0.0 application starting in development on http://0.0.0.0:3000 => Rails 5.0.0 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options => Run `rails server -h` for more startup options
Puma starting in single mode... Puma starting in single mode...
* Version 3.0.2 (ruby 2.3.0-p0), codename: Plethora of Penguin Pinatas * Version 3.4.0 (ruby 2.3.1-p112), codename: Owl Bowl Brawl
* Min threads: 5, max threads: 5 * Min threads: 5, max threads: 5
* Environment: development * Environment: development
* Listening on tcp://localhost:3000 * Listening on tcp://localhost:3000
Use Ctrl-C to stop Use Ctrl-C to stop
Started GET "/" for 127.0.0.1 at 2014-04-11 13:11:48 +0200 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" ActiveRecord::SchemaMigration Load (0.2ms) SELECT "schema_migrations".* FROM "schema_migrations"
Processing by ArticlesController#index as HTML Processing by ArticlesController#index as HTML
@ -337,7 +336,6 @@ Processing by ArticlesController#index as HTML
10: respond_to do |format| 10: respond_to do |format|
11: format.html # index.html.erb 11: format.html # index.html.erb
12: format.json { render json: @articles } 12: format.json { render json: @articles }
(byebug) (byebug)
``` ```
@ -347,11 +345,45 @@ by asking the debugger for help. Type: `help`
``` ```
(byebug) help (byebug) help
h[elp][ <cmd>[ <subcmd>]] 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
help -- prints this help. (byebug)
help <cmd> -- prints help on command <cmd>.
help <cmd> <subcmd> -- prints help on <cmd>'s subcommand <subcmd>.
``` ```
To see the previous ten lines you should type `list-` (or `l-`). To see the previous ten lines you should type `list-` (or `l-`).
@ -370,12 +402,11 @@ To see the previous ten lines you should type `list-` (or `l-`).
8 @articles = Article.find_recent 8 @articles = Article.find_recent
9 9
10 respond_to do |format| 10 respond_to do |format|
``` ```
This way you can move inside the file and see the code above This way you can move inside the file and see the code above the line where you
the line where you added the `byebug` call. Finally, to see where you are in added the `byebug` call. Finally, to see where you are in the code again you can
the code again you can type `list=` type `list=`
``` ```
(byebug) list= (byebug) list=
@ -391,7 +422,6 @@ the code again you can type `list=`
10: respond_to do |format| 10: respond_to do |format|
11: format.html # index.html.erb 11: format.html # index.html.erb
12: format.json { render json: @articles } 12: format.json { render json: @articles }
(byebug) (byebug)
``` ```
@ -413,46 +443,45 @@ then `backtrace` will supply the answer.
``` ```
(byebug) where (byebug) where
--> #0 ArticlesController.index --> #0 ArticlesController.index
at /PathTo/project/test_app/app/controllers/articles_controller.rb:8 at /PathToProject/app/controllers/articles_controller.rb:8
#1 ActionController::ImplicitRender.send_action(method#String, *args#Array) #1 ActionController::BasicImplicitRender.send_action(method#String, *args#Array)
at /PathToGems/actionpack-5.0.0/lib/action_controller/metal/implicit_render.rb:4 at /PathToGems/actionpack-5.0.0/lib/action_controller/metal/basic_implicit_render.rb:4
#2 AbstractController::Base.process_action(action#NilClass, *args#Array) #2 AbstractController::Base.process_action(action#NilClass, *args#Array)
at /PathToGems/actionpack-5.0.0/lib/abstract_controller/base.rb:189 at /PathToGems/actionpack-5.0.0/lib/abstract_controller/base.rb:181
#3 ActionController::Rendering.process_action(action#NilClass, *args#NilClass) #3 ActionController::Rendering.process_action(action, *args)
at /PathToGems/actionpack-5.0.0/lib/action_controller/metal/rendering.rb:10 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 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 the specified frame number. If you do that, `byebug` will display your new
context. context.
``` ```
(byebug) frame 2 (byebug) frame 2
[184, 193] in /PathToGems/actionpack-5.0.0/lib/abstract_controller/base.rb [176, 185] in /PathToGems/actionpack-5.0.0/lib/abstract_controller/base.rb
184: # is the intended way to override action dispatching. 176: # is the intended way to override action dispatching.
185: # 177: #
186: # Notice that the first argument is the method to be dispatched 178: # Notice that the first argument is the method to be dispatched
187: # which is *not* necessarily the same as the action name. 179: # which is *not* necessarily the same as the action name.
188: def process_action(method_name, *args) 180: def process_action(method_name, *args)
=> 189: send_action(method_name, *args) => 181: send_action(method_name, *args)
190: end 182: end
191: 183:
192: # Actually call the method associated with the action. Override 184: # Actually call the method associated with the action. Override
193: # this method if you wish to change how action methods are called, 185: # this method if you wish to change how action methods are called,
(byebug) (byebug)
``` ```
The available variables are the same as if you were running the code line by The available variables are the same as if you were running the code line by
line. After all, that's what debugging is. line. After all, that's what debugging is.
You can also use `up [n]` (`u` for abbreviated) and `down [n]` commands in order You can also use `up [n]` and `down [n]` commands in order to change the context
to change the context _n_ frames up or down the stack respectively. _n_ defaults _n_ frames up or down the stack respectively. _n_ defaults to one. Up in this
to one. Up in this case is towards higher-numbered stack frames, and down is case is towards higher-numbered stack frames, and down is towards lower-numbered
towards lower-numbered stack frames. stack frames.
### Threads ### Threads
@ -461,11 +490,11 @@ the `thread` command (or the abbreviated `th`). This command has a handful of
options: options:
* `thread`: shows the current thread. * `thread`: shows the current thread.
* `thread list`: is used to list all threads and their statuses. The plus + * `thread list`: is used to list all threads and their statuses. The current
character and the number indicates the current thread of execution. thread is marked with a plus (+) sign.
* `thread stop _n_`: stop thread _n_. * `thread stop n`: stops thread _n_.
* `thread resume _n_`: resumes thread _n_. * `thread resume n`: resumes thread _n_.
* `thread switch _n_`: switches the current thread context to _n_. * `thread switch n`: switches the current thread context to _n_.
This command is very helpful when you are debugging concurrent threads and need This command is very helpful when you are debugging concurrent threads and need
to verify that there are no race conditions in your code. to verify that there are no race conditions in your code.
@ -492,9 +521,9 @@ current context:
12: format.json { render json: @articles } 12: format.json { render json: @articles }
(byebug) instance_variables (byebug) instance_variables
[:@_action_has_layout, :@_routes, :@_headers, :@_status, :@_request, [:@_action_has_layout, :@_routes, :@_request, :@_response, :@_lookup_context,
:@_response, :@_prefixes, :@_lookup_context, :@_action_name, :@_action_name, :@_response_body, :@marked_for_same_origin_verification,
:@_response_body, :@marked_for_same_origin_verification, :@_config] :@_config]
``` ```
As you may have figured out, all of the variables that you can access from a As you may have figured out, all of the variables that you can access from a
@ -504,6 +533,7 @@ command later in this guide).
``` ```
(byebug) next (byebug) next
[5, 14] in /PathTo/project/app/controllers/articles_controller.rb [5, 14] in /PathTo/project/app/controllers/articles_controller.rb
5 # GET /articles.json 5 # GET /articles.json
6 def index 6 def index
@ -523,29 +553,35 @@ And then ask again for the instance_variables:
``` ```
(byebug) instance_variables (byebug) instance_variables
[:@_action_has_layout, :@_routes, :@_headers, :@_status, :@_request, [:@_action_has_layout, :@_routes, :@_request, :@_response, :@_lookup_context,
:@_response, :@_prefixes, :@_lookup_context, :@_action_name, :@_action_name, :@_response_body, :@marked_for_same_origin_verification,
:@_response_body, :@marked_for_same_origin_verification, :@_config, :@_config, :@articles]
:@articles]
``` ```
Now `@articles` is included in the instance variables, because the line defining it Now `@articles` is included in the instance variables, because the line defining
was executed. it was executed.
TIP: You can also step into **irb** mode with the command `irb` (of course!). TIP: You can also step into **irb** mode with the command `irb` (of course!).
This will start an irb session within the context you invoked it. But This will start an irb session within the context you invoked it.
be warned: this is an experimental feature.
The `var` method is the most convenient way to show variables and their values. The `var` method is the most convenient way to show variables and their values.
Let's have `byebug` help us with it. Let's have `byebug` help us with it.
``` ```
(byebug) help var (byebug) help var
v[ar] cl[ass] show class variables of self
v[ar] const <object> show constants of object [v]ar <subcommand>
v[ar] g[lobal] show global variables
v[ar] i[nstance] <object> show instance variables of object Shows variables and its values
v[ar] l[ocal] show local variables
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 This is a great way to inspect the values of the current context variables. For
@ -563,16 +599,17 @@ You can also inspect for an object method this way:
@_start_transaction_state = {} @_start_transaction_state = {}
@aggregation_cache = {} @aggregation_cache = {}
@association_cache = {} @association_cache = {}
@attributes = {"id"=>nil, "created_at"=>nil, "updated_at"=>nil} @attributes = #<ActiveRecord::AttributeSet:0x007fd0682a9b18 @attributes={"id"=>#<ActiveRecord::Attribute::FromDatabase:0x007fd0682a9a00 @name="id", @value_be...
@attributes_cache = {} @destroyed = false
@changed_attributes = nil @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 You can also use `display` to start watching variables. This is a good way of
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
tracking the values of a variable while the execution goes on. tracking the values of a variable while the execution goes on.
``` ```
@ -581,7 +618,7 @@ tracking the values of a variable while the execution goes on.
``` ```
The variables inside the displayed list will be printed with their values after 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 you move in the stack. To stop displaying a variable use `undisplay n` where
_n_ is the variable number (1 in the last example). _n_ is the variable number (1 in the last example).
### Step by Step ### Step by Step
@ -591,32 +628,23 @@ available variables. But let's continue and move on with the application
execution. execution.
Use `step` (abbreviated `s`) to continue running your program until the next Use `step` (abbreviated `s`) to continue running your program until the next
logical stopping point and return control to the debugger. 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
You may also use `next` which is similar to step, but function or method calls single step, `next` moves to the next line without descending inside methods.
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.
For example, consider the following situation: For example, consider the following situation:
```ruby ```
Started GET "/" for 127.0.0.1 at 2014-04-11 13:39:23 +0200 Started GET "/" for 127.0.0.1 at 2014-04-11 13:39:23 +0200
Processing by ArticlesController#index as HTML Processing by ArticlesController#index as HTML
[1, 8] in /home/davidr/Proyectos/test_app/app/models/article.rb [1, 6] in /PathToProject/app/models/article.rb
1: class Article < ApplicationRecord 1: class Article < ApplicationRecord
2: 2: def self.find_recent(limit = 10)
3: def self.find_recent(limit = 10) 3: byebug
4: byebug => 4: where('created_at > ?', 1.week.ago).limit(limit)
=> 5: where('created_at > ?', 1.week.ago).limit(limit) 5: end
6: end 6: end
7:
8: end
(byebug) (byebug)
``` ```
@ -628,11 +656,7 @@ method.
``` ```
(byebug) next (byebug) next
[4, 13] in /PathToProject/app/controllers/articles_controller.rb
Next advances to the next line (line 6: `end`), which returns to the next line
of the caller method:
[4, 13] in /PathTo/project/test_app/app/controllers/articles_controller.rb
4: # GET /articles 4: # GET /articles
5: # GET /articles.json 5: # GET /articles.json
6: def index 6: def index
@ -653,23 +677,24 @@ Ruby instruction to be executed -- in this case, Active Support's `week` method.
``` ```
(byebug) step (byebug) step
[50, 59] in /PathToGems/activesupport-5.0.0/lib/active_support/core_ext/numeric/time.rb [49, 58] in /PathToGems/activesupport-5.0.0/lib/active_support/core_ext/numeric/time.rb
50: ActiveSupport::Duration.new(self * 24.hours, [[:days, self]]) 49:
51: end 50: # Returns a Duration instance matching the number of weeks provided.
52: alias :day :days 51: #
53: 52: # 2.weeks # => 14 days
54: def weeks 53: def weeks
=> 55: ActiveSupport::Duration.new(self * 7.days, [[:days, self * 7]]) => 54: ActiveSupport::Duration.new(self * 7.days, [[:days, self * 7]])
56: end 55: end
57: alias :week :weeks 56: alias :week :weeks
58: 57:
59: def fortnights 58: # Returns a Duration instance matching the number of fortnights provided.
(byebug) (byebug)
``` ```
This is one of the best ways to find bugs in your code. 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 ### Breakpoints
A breakpoint makes your application stop whenever a certain point in the program A breakpoint makes your application stop whenever a certain point in the program
@ -678,19 +703,18 @@ is reached. The debugger shell is invoked in that line.
You can add breakpoints dynamically with the command `break` (or just `b`). You can add breakpoints dynamically with the command `break` (or just `b`).
There are 3 possible ways of adding breakpoints manually: There are 3 possible ways of adding breakpoints manually:
* `break line`: set breakpoint in the _line_ in the current source file. * `break n`: set breakpoint in line number _n_ in the current source file.
* `break file:line [if expression]`: set breakpoint in the _line_ number inside * `break file:n [if expression]`: set breakpoint in line number _n_ inside
the _file_. If an _expression_ is given it must evaluated to _true_ to fire up file named _file_. If an _expression_ is given it must evaluated to _true_ to
the debugger. fire up the debugger.
* `break class(.|\#)method [if expression]`: set breakpoint in _method_ (. and * `break class(.|\#)method [if expression]`: set breakpoint in _method_ (. and
\# for class and instance method respectively) defined in _class_. The \# 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 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 4: # GET /articles
5: # GET /articles.json 5: # GET /articles.json
6: def index 6: def index
@ -703,20 +727,20 @@ For example, in the previous situation
13: end 13: end
(byebug) break 11 (byebug) break 11
Created breakpoint 1 at /PathTo/project/app/controllers/articles_controller.rb:11 Succesfully created breakpoint with id 1
``` ```
Use `info breakpoints _n_` or `info break _n_` to list breakpoints. If you Use `info breakpoints` to list breakpoints. If you supply a number, it lists
supply a number, it lists that breakpoint. Otherwise it lists all breakpoints. that breakpoint. Otherwise it lists all breakpoints.
``` ```
(byebug) info breakpoints (byebug) info breakpoints
Num Enb What 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 number _n_. If no number is specified, it deletes all breakpoints that are
currently active. currently active.
@ -728,10 +752,11 @@ No breakpoints.
You can also enable or disable breakpoints: You can also enable or disable breakpoints:
* `enable breakpoints`: allow a _breakpoints_ list or all of them if no list is * `enable breakpoints [n [m [...]]]`: allows a specific breakpoint list or all
specified, to stop your program. This is the default state when you create a breakpoints to stop your program. This is the default state when you create a
breakpoint. 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 ### Catching Exceptions
@ -746,24 +771,22 @@ To list all active catchpoints use `catch`.
There are two ways to resume execution of an application that is stopped in the There are two ways to resume execution of an application that is stopped in the
debugger: debugger:
* `continue [line-specification]` \(or `c`): resume program execution, at the * `continue [n]`: resumes program execution at the address where your script last
address where your script last stopped; any breakpoints set at that address are stopped; any breakpoints set at that address are bypassed. The optional argument
bypassed. The optional argument line-specification allows you to specify a line `n` allows you to specify a line number to set a one-time breakpoint which is
number to set a one-time breakpoint which is deleted when that breakpoint is deleted when that breakpoint is reached.
reached. * `finish [n]`: execute until the selected stack frame returns. If no frame
* `finish [frame-number]` \(or `fin`): execute until the selected stack frame number is given, the application will run until the currently selected frame
returns. If no frame number is given, the application will run until the returns. The currently selected frame starts out the most-recent frame or 0 if
currently selected frame returns. The currently selected frame starts out the no frame positioning (e.g up, down or frame) has been performed. If a frame
most-recent frame or 0 if no frame positioning (e.g up, down or frame) has been number is given it will run until the specified frame returns.
performed. If a frame number is given it will run until the specified frame
returns.
### Editing ### Editing
Two commands allow you to open code from the debugger into an editor: 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 * `edit [file:n]`: edit file named _file_ using the editor specified by the
environment variable. A specific _line_ can also be given. EDITOR environment variable. A specific line _n_ can also be given.
### Quitting ### Quitting
@ -777,21 +800,43 @@ will be stopped and you will have to start it again.
`byebug` has a few available options to tweak its behavior: `byebug` has a few available options to tweak its behavior:
* `set autoreload`: Reload source code when changed (defaults: true). ```
* `set autolist`: Execute `list` command on every breakpoint (defaults: true). (byebug) help set
* `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 the full list by using `help set`. Use `help set _subcommand_` to set <setting> <value>
learn about a particular `set` command.
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.
You can see these environment settings with the "show" 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. 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: The debugger reads these global settings when it starts. For example:
```bash ```bash
set forcestep set callstyle short
set listsize 25 set listsize 25
``` ```