kotovalexarian-likes-github
/
rails--rails
mirror of https://github.com/rails/rails.git
1
0
Fork 0
Code Releases Activity

Merge pull request #24764 from deivid-rodriguez/review_debugging_guide 

Review the `byebug` debugging guide [ci skip]
This commit is contained in:
Vipul A M 2016-04-28 18:32:37 +05:30
parent afc4976cc7 7fb381d247
commit 895add262f
1 changed files with 185 additions and 140 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

325
guides/source/debugging_rails_applications.md
View File

@ -255,7 +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 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
@ -315,13 +316,11 @@ For example:
=> Rails 5.0.0 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
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
* 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
@ -337,7 +336,6 @@ Processing by ArticlesController#index as HTML
10: respond_to do |format|
11: format.html # index.html.erb
12: format.json { render json: @articles }
(byebug)
```
@ -347,11 +345,45 @@ by asking the debugger for help. Type: `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.
help <cmd> -- prints help on command <cmd>.
help <cmd> <subcmd> -- prints help on <cmd>'s subcommand <subcmd>.
(byebug)
```
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
9
10 respond_to do |format|
```
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=`
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=
@ -391,7 +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)
```
@ -413,46 +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
@ -461,11 +490,11 @@ 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 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 when you are debugging concurrent threads and need
to verify that there are no race conditions in your code.
@ -492,9 +521,9 @@ current context:
12: format.json { render json: @articles }
(byebug) instance_variables
[:@_action_has_layout, :@_routes, :@_headers, :@_status, :@_request,
:@_response, :@_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
@ -504,6 +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
@ -523,29 +553,35 @@ And then ask again for the instance_variables:
```
(byebug) instance_variables
[:@_action_has_layout, :@_routes, :@_headers, :@_status, :@_request,
:@_response, :@_prefixes, :@_lookup_context, :@_action_name,
:@_response_body, :@marked_for_same_origin_verification, :@_config,
:@articles]
[:@_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 will start an irb session 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 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
@ -563,16 +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.
```
@ -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
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).
### Step by Step
@ -591,32 +628,23 @@ 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, 6] in /PathToProject/app/models/article.rb
1: class Article < ApplicationRecord
2:
3: def self.find_recent(limit = 10)
4: byebug
=> 5: where('created_at > ?', 1.week.ago).limit(limit)
6: end
7:
8: end
2: def self.find_recent(limit = 10)
3: byebug
=> 4: where('created_at > ?', 1.week.ago).limit(limit)
5: end
6: end
(byebug)
```
@ -628,11 +656,7 @@ method.
```
(byebug) next
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, 13] in /PathToProject/app/controllers/articles_controller.rb
4: # GET /articles
5: # GET /articles.json
6: def index
@ -653,23 +677,24 @@ 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.
TIP: You can also use `step n` or `next n` to move forward `n` steps at once.
### Breakpoints
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`).
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
@ -703,20 +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
Succesfully 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.
@ -728,10 +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
@ -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
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
@ -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:
* `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.
```
(byebug) help set
You can see the full list by using `help set`. Use `help set _subcommand_` to
learn about a particular `set` command.
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.
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.
The debugger reads these global settings when it starts. For example:
```bash
set forcestep
set callstyle short
set listsize 25
```