Extracting fixed issues

A common use case when creating a release is to create a release note, containing among other things, the bugs fixed in the release. A good practice is to write in the commit message if a bug is fixed by the commit. A better practice is to have a standard way of doing it, for example, a line with the string "Fixes-bug: " followed by the bug identifier in the last part of the commit message. This makes it easy to compile a list of bugs fixed for a release note. The JGit project is a good example of this; their bug identifier in the commit messages is a simple "Bug: " string followed by the bug ID.

This recipe will show you how to limit the output of git log to list just the commits since the last release (tag), which contains a bug fix.

Getting ready

Clone the JGit repository using the following command lines:

$ git clone https://git.eclipse.org/r/jgit/jgit
$ cd jgit

If you want the exact same output as in this example, reset your master branch to the following commit, b14a93971837610156e815ae2eee3baaa5b7a44b:

$ git checkout master && git reset --hard b14a939

How to do it...

You are now ready to look through the commit log for commit messages that describe the bugs fixed. First, let's limit the log to only look through the history since the last tag (release). To find the last tag, we can use git describe:

$ git describe 
v3.1.0.201310021548-r-96-gb14a939 

The preceding output tells us three things:

• The last tag was v3.1.0.201310021548-r
• The number of commits since the tag were 96
• The current commit in abbreviated form is b14a939

Now, the log can be parsed from HEAD to v3.1.0.201310021548-r. But just running git log 3.1.0.201310021548-r..HEAD will give us all the 96 commits, and we just want the commits with commit messages that contain "Bug: xxxxxx" for our release note. The xxxxxx is an identifier for the bug, for example, a number. We can use the --grep option with git log for this purpose: git log --grep "Bug: ". This will give us all the commits with "Bug: " in the commit message; all we need now is just to format it to something we can use for our release note.

Let's say we want the release note format to look like the following template:

Commit-id: Commit subject
Fixes-bug: xxx

Our command line so far is as follows:

$ git log --grep "Bug: " v3.1.0.201310021548-r..HEAD

This gives us all the bug fix commits, but we can format this to a format that is easily parsed with the --pretty option. First, we will print the abbreviated commit ID %h, followed by a separator of our choice |, then the commit subject %s, (first line of the commit message), followed by a new line %n, and the body, %b:

--pretty="%h|%s%n%b"

The output of course needs to be parsed, but that's easy with regular Linux tools such as grep and sed:

First, we just want the lines that contain "|" or "Bug: ":

grep -E "\||Bug: "

Then, we replace these with sed:

sed -e 's/|/: /' -e 's/Bug:/Fixes-bug:/'

The entire command put together gives:

\$ git log --grep "Bug: " v3.1.0.201310021548-r..HEAD --pretty="%h|%s%n%b" 
| grep -E "\||Bug: " | sed -e 's/|/: /' -e 's/Bug:/Fixes-bug:/'

The previous set of commands gives the following output:

f86a488: Implement rebase.autostash 
Fixes-bug: 422951 
7026658: CLI status should support --porcelain 
Fixes-bug: 419968 
e0502eb: More helpful InvalidPathException messages (include reason) 
Fixes-bug: 413915 
f4dae20: Fix IgnoreRule#isMatch returning wrong result due to missing reset 
Fixes-bug: 423039 
7dc8a4f: Fix exception on conflicts with recursive merge 
Fixes-bug: 419641 
99608f0: Fix broken symbolic links on Cygwin. 
Fixes-bug: 419494 
...

Now, we can extract the bug information from the bug tracker and put the preceding code in the release note as well, if necessary.

How it works...

First, we limit the git log command to only show the range of commits we are interested in, then we further limit the output by filtering the "Bug: " string in the commit message. We pretty print the string so we can easily format it to a style we need for the release note and finally find and replace with grep and sed to completely match the style of the release note.

There's more...

If we just wanted to extract the bug IDs from the commit messages and didn't care about the commit IDs, we could have just used grep after the git log command, still limiting the log to the last tag:

$ git log v3.1.0.201310021548-r..HEAD | grep "Bug: "

If we just want the commit IDs and their subjects but not the actual bug IDs, we can use the --oneline feature of git log combined with the --grep option:

$ git log --grep "Bug: " --oneline v3.1.0.201310021548-r..HEAD