Locating A Bug by Binary Search of Revisions

Bad News: A New Failure Case

We find a bug when searching \w{4}\s+\w{4}\s+\w{4}.

icgrep-build/icgrep '\w{4}\s+\w{4}\s+\w{4}' QA/testfiles/simple1
in this simple test file
provide fodder for some simple

• Create a test case that forces failure. Revision 5164

• Try to find a previous revision that did not have the bug.

Check out and build revision 5020.

build5020/icgrep '\w{4}\s+\w{4}\s+\w{4}' QA/testfiles/simple1
in this simple test file
provide fodder for some simple

Check out and build revision 4820.

build4820/icgrep '\w{4}\s+\w{4}\s+\w{4}' QA/testfiles/simple1
in this simple test file

Success!

r4974 might have been OK.

build4974/icgrep '\w{4}\s+\w{4}\s+\w{4}' QA/testfiles/simple1
in this simple test file
provide fodder for some simple

Nope!

• We continue to perform binary search to find the exact revision at which the bug was introduced.

. . .

Revision 4840

build4840/icgrep '\w{4}\s+\w{4}\s+\w{4}' QA/testfiles/simple1
in this simple test file

Revision 4841

build4841/icgrep '\w{4}\s+\w{4}\s+\w{4}' QA/testfiles/simple1
in this simple test file
provide fodder for some simple

We found the revision - now let's locate and fix the bug. The fix

Automation

git-bisect is a tool that can automate this process based on git repositories.

But there may be problems in successfully building older revisions, if there are environmental changes that affect the build process (e.g., updates to tools or changes to external libraries.)