coala Tutorial

Welcome to this little tutorial. It is meant to be a gentle introduction to the usage of coala.

Prerequisites

In order to complete this tutorial you will need coala installed. (Installation is actually not required but it’s more convenient and recommended.)

Get Some Code

In order to perform a static code analysis on your code you will need some code to check. If you do not have own code you want to check, you can retrieve our tutorial samples:

git clone https://github.com/coala-analyzer/coala-tutorial.git

Please note that the commands given in this tutorial are intended for use with this sample code and may need minor adjustments.

Let’s Start!

There are two options how to let coala know what kind of analysis it should perform on which code.

Command Line Interface

In order to specify the files to analyze, you can use the --files argument of coala like demonstrated below. For all file paths, you can specify (recursive) globs.

Because analysis routines can do many various things we named them Bears. Thus you can specify the kind of analysis with the --bears argument.

Please type the following commands into the console:

cd coala-tutorial
coala --files=src/\*.c --bears=SpaceConsistencyBear --save

coala will now ask you for missing values that are needed to perform the analysis, which in this case is only the use_spaces setting. We recommend setting it to true.

coala will now check the code and, in case you use the tutorial code, yield two results. In the case of the SpaceConsistencyBear you will see trailing whitespace errors on your console.

Feel free to experiment a bit. You’ve successfully analysed some code! But don’t stop reading - you don’t have to enter all those values again!

Configuration Files

coala supports a very simple configuration file. If you’ve executed the instructions from the CLI section above, coala will already have such a file readily prepared for you. Go, take a look at it:

cat .coafile

This should yield something like this:

[Default]
bears = SpaceConsistencyBear
files = src/*.c
use_spaces = yeah

If you now invoke coala it will parse this .coafile from your current directory. This makes it easy to specify once for your project what is checked with which bears and make it available to all contributors.

Feel free to play around with this file. You can either edit it manually or add/edit settings via coala --save ... invocations. If you want coala to save settings every time, you can add save = True manually into your .coafile.

Sections

Thats all nice and well but we also have a Makefile for our project we want to check. So let us introduce another feature of our configuration syntax: sections.

The line [Default] specifies that everything below will belong to the Default section. If nothing is specified, a setting will implicitly belong to this section.

Let’s check the line lengths of our Makefile:

coala -S Makefiles.bears=LineLengthBear Makefiles.files=Makefile --save

As you can see, the -S (or --settings) option allows to specify arbitrary settings. Settings can be directly stored into a section with the section.setting syntax.

By default the LineLengthBear checks whether each line contains 80 chars or less in a line. To change this value, use the max_line_length inside the .coafile.

coala will now yield any result you didn’t correct last time plus a new one for the Makefile. This time coala (or better, the LineLengthBear) doesn’t know how to fix the issue but still tries to provide as much helpful information as possible and provides you the option to directly open the file in an editor of your choice.

Note

If your editor is already open this may not work, because the other process will shortly communicate with the existent process and return immediately. coala handles this for some editors automatically, if your’s does not work yet - please file a bug so we can include it!

If you changed one file in multiple results, coala will merge the changes if this is possible.

coala should have appended something like this to your .coafile:

[Makefiles]
bears = LineLengthBear
files = Makefile

As you see, sections provide a way to have different configurations for possibly different languages in one file. They are executed sequentially.

Auto-applying results

Often you don’t want to look at trivial results like spacing issues. For that purpose coala includes a special setting called default_actions that allows you to set the action for a bear that shall be automatically applied on run.

Let’s automatically fix python code. Take a look at our sample python code:

$ cat src/add.py

"""
This is a simple library that provide a function that can add numbers.

Cheers!
"""



def add(a,b):
    return a+b;

import sys

That looks horrible, doesn’t it? Let’s fix it!

$ coala -S python.bears=PEP8Bear python.files=\*\*/\*.py \
python.default_actions=PEP8Bear:ApplyPatchAction --save
# other output ...
Executing section python...
[INFO][11:03:37] Applied 'ApplyPatchAction' for 'PEP8Bear'.
[INFO][11:03:37] Applied 'ApplyPatchAction' for 'PEP8Bear'.

coala would now fix all spacing issues and without bothering you again.

Currently following actions are available:

  • ApplyPatchAction: Applies a given patch (if existent).
  • ShowPatchAction: Just displays a given patch (if existent) without doing something.

For debugging purposes:

  • PrintDebugMessageAction: Prints a debug message for the appearing result.

Setting Inheritance

All settings in the default section are implicitly inherited to all other sections (if they do not override their values). We can use that to save a few lines!

Lets add the following section to our .coafile:

[TODOS]
bears = KeywordBear

And execute coala with the -s argument which is the same as --save. I recommend setting case insensitive keywords to TODO, FIXME and case sensitive keywords empty.

After the results we’ve already seen, we’ll see a new informational one which informs us that we have a TODO in our code.

Did you note that we didn’t specify which files to check this time? This is because all settings, including files = src/*.c, from the Default section are already available in every other section implicitly. Thus the default section is a good point to set things like logging and output settings or specifying a default set of files to check.

Ignoring Issues

There are several ways to ignore certain issues, so you aren’t lost if any routines yield false positives.

Ignoring Files

coala lets you ignore whole files through the ignore setting:

files = **/*.h
ignore = **/resources.h

This configuration would include all header (.h) files but leaves out resource headers.

Ignoring code Inside Files

Sometimes you need finer-graded ignores. Imagine you have a LineLengthBear that shall not run on some code segments, because you can’t wrap them:

code = "that's checked normally"

# Ignore LineLengthBear
unwrappable_string = "some string that is long and would exceed the limit"

You can also skip an area:

# Start ignoring LineLengthBear
unwrappable_string_2 = unwrappable_string + "yeah it goes even further..."
another_unwrappable_string = unwrappable_string + unwrappable_string_2
# Stop ignoring

You can also conditionally combine ignore rules! Bear names will be split by comma and spaces, invalid bear names like and will be ignored.

Also note that in the bear names delimited by commas and spaces, you may specify glob wildcards that match several bears:

# Start ignoring Line*, Py*
unwrappable_string_2 = unwrappable_string + "yeah it goes even further..."
another_unwrappable_string = unwrappable_string + unwrappable_string_2
# Stop ignoring

In the above example all bears matching the glob Line* and Py* will be ignored. You may also specify more complex globs here such as # Start ignoring (Line*|P[yx]*) which will ignore all bears start with Line, Py, and Px.

# Ignore LineLengthBear and SpaceConsistencyBear
    variable = "Why the heck are spaces used instead of tabs..." + "so_long"

If you put an all instead of the bear names directly after the ignore/ignoring keyword, the results of all bears affecting those lines will be ignored.

Enabling/Disabling Sections

Now that we have sections we need some way to control, which sections are executed. coala provides two ways to do that:

Manual Enabling/Disabling

If you add the line TODOS.enabled=False to some arbitrary place to your .coafile or just enabled=False into the TODOS section, coala will not show the TODOs on every run.

Especially for those bears yielding informational messages which you might want to see from time to time this is a good way to silence them.

Specifying Targets

If you provide positional arguments, like coala Makefiles, coala will execute exclusively those sections that are specified. This will not get stored in your .coafile and will take precedence over all enabled settings. You can specify several targets seperated by a space.

What was that TODO again?

Show bears’ information

To get help on using a bear or to get a description of the bear, use the --show-bears argument:

coala --bears=SpaceConsistencyBear --show-bears

This will display a large amount of information regarding the bears that have been specified (in the .coafile of in the CLI arguments). It shows:

  • A description of what the bear does
  • The sections which uses it
  • The settings it uses (optional and required)

Integrating coala into Your Project

It’s easy to add coala to your project in a way that does not force your developers even to install coala using git submodules. This also has the advantage that all your developers are using exactly the same version of coala. You can try it out in the coala-tutorial repository:

git submodule add https://github.com/coala-analyzer/coala.git
git commit -m 'Add coala submodule'
git add .coafile
git commit -m 'Add .coafile'

You can now use coala/coala as if it were the installed binary. Here’s the instructions for your developers:

git submodule init
git submodule update
coala/coala

Continuing the Journey

If you want to know about more options, take a look at our help with coala -h. If you liked or disliked this tutorial, feel free to drop us a note at our bug tracker (github) or mailing list (https://groups.google.com/forum/#!forum/coala-devel).

If you need more flexibility, know that coala is extensible in many ways due to its modular design:

  • If you want to write your own bears, take a look at sources lying in bears and coalib/bearlib.
  • If you want to add custom actions for results, take a look at the code in coalib/results/results_actions.
  • If you want to have some custom outputs (e.g. HTML pages, a GUI or voice interaction) take a look at modules lying in coalib/output.

Happy coding!