Due to the different procedures between Myers and Histogram in identifying the changed lines of code, they possibly generated different diff results. Our manual comparison found that their differences were the number of the changes, the order of the changed lines, or even the detected added and deleted code. They certainly affect the readability of the diff outputs, in other words, the quality of the diff results produced by the two diff algorithms were different.
Importantly, our results provide evidence that Histogram frequently produced better diff results compared to Myers in extracting the differences in source code. In this paper, we present a description of the impact of different diff s on the results of a study. In the example shown in Fig. Nevertheless, there are several differences in the identified changed lines shown in both diff outputs. The first difference is the number of the changed lines.
From Fig. There are 11 changed lines discovered by the Myers , while the Histogram found 13 lines. In a study that aims to collect metrics from the code changes, considering different diff algorithms is important since it has an impact on the number of changes.
In software quality analysis, one key factor of process metrics used to measure the changes is the number of modified lines NLA and NLD. For example, a work undertaken by Gousios et al.
This quantity of the changed lines was then used to calculate the commit size of all affected files. Based on our metrics comparison, we found that 1. Another study related to metrics analysis was conducted by Rausch et al. The authors investigated the complexity of changes that can impact software quality. The study also found that the high mean values of the number of modified files correlates to the failed builds. Based on the result from our metrics analysis, we found 0. Therefore, if Histogram is applied in this study, this will influence around 0.
The second difference is the position of the changed lines. Figure 15 shows that the two diff algorithms detect the deleted lines differently.
Related to SZZ application, both diff algorithms produce different deleted lines that are considered as the candidate of bug-introducing changes. Thus, the identified bug-related lines might be invalid due to different diff algorithms application that can lead to the failure of bug-introducing changes identification.
A study undertaken by da Costa et al. The study on 10 Apache projects analyzed the validity of bug-introducing changes. The validation process of bug-related lines used by the authors is similar to our study.
It compares the release dates of the earliest affected software versions of a bug with the dates of the introduction of the candidates of bug-related lines. However, in our study, we enhanced the process to validate the other three parameters, that is, the bug-introducing commits that initially adds the valid bug-related lines, files containing valid bug-related lines, and bug-fixing commits that relates to valid bug-introducing commits.
We found 2. The similarity of this study to ours is investigating the changing impact due to the modification of SZZ algorithm. However, the study focus on the usability of the changing SZZ in the academic paper over time while our study analyze the impact of different diff algorithms application in the SZZ to study results. Without considering the version of SZZ used in previous studies collected by Rodriguez-Perez et al. Thus, if the Histogram is applied in those prior studies, it might affect the results of studies.
Our investigations on metrics and SZZ application provide evidences that different diff algorithms application in git command can have an impact on a study result. It is also acknowledged that the Histogram algorithm is substantially better than the Myers to produce the changed lines of code.
Thus, we recommend to use the Histogram in git diff command to extract the changes from source code. Threats to the construct validity appear in the mapping study and the SZZ application. In our mapping study, we selected only the papers that specifically mention the git commands. As a result, papers that had used git commands but do not mention it in the full text had been ignored, which can cause selection bias. Since different diff algorithms produce different results, we consider that papers should mention algorithm names of diff if the authors intentionally chose them.
In the SZZ application, we used a small number of keywords to detect commit messages that describe fixing bugs. This limited our ability to extract all potential candidate bug-fixing commits. Even so, the commits that should not be identified as bug-fixing commits were also possible to be collected as long as they included the keywords in their log messages.
However, since our focus is to investigate the level of differences of the diff lists produced by Myers and Histogram , the impact of the incorrect commits to the study result is small. Another threat to the construct validity is the definition of better for the diff algorithm. We consider good quality of the algorithm based on our two criteria, while many could have been considered.
Different software engineering tasks may have different requirements for diff analysis. However, since our focus is expecting to recover the changing operations from the diff outputs, the impact of this issue is not significant. Threats to the external validity emerge regarding the repository used in our experiments. Although we analyzed 24 OSS Java projects mined from Git repositories, we cannot generalize our study results to other open source projects nor industry.
To reduce the threats to reliability , we make our dataset publicly available. We provided lists of our collected files identified by the Myers and Histogram algorithms which were used in the three empirical analyses see on GitHub Footnote To understand the impact of using different diff algorithms, Myers and Histogram , we first clarified applications of diff by conducting a systematic mapping of papers published between and We then empirically analyzed the impact in three major applications: i code churn metrics, ii SZZ algorithm, and iii patches extraction.
Our quantitative analyses has shown that the different diff algorithms can report different amount of changed lines, identify different change locations. Our qualitative investigation revealed that Histogram is better for describing code changes.
Since diff is the fundamental tool for various software engineering tasks, considering limitations and advantages of algorithms is important. Currently we recommend using the Histogram algorithm when analyzing code changes. ACM, New York, pp — Article Google Scholar. Dotzler G, Philippsen M Move-optimized source code tree differencing. In: 15th working conference on reverse engineering, pp — Kamei Y, Shihab E Defect prediction: accomplishments and future challenges.
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Rodriguez-Perez G, Robles G, Gonzalez-Barahona JM Reproducibility and credibility in empirical software engineering: a case study based on a systematic literature review of the use of the szz algorithm. Viera A, Garrett J Understanding interobserver agreement: the kappa statistic. Fam Med 37 5 — Google Scholar. Journal of Systems and Software 86 10 — Download references. You can also search for this author in PubMed Google Scholar. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Reprints and Permissions. Nugroho, Y. How different are different diff algorithms in Git?. Empir Software Eng 25, — Download citation. Published : 11 September Issue Date : January Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative.
Skip to main content. Search SpringerLink Search. How different are different diff algorithms in Git? Download PDF. Abstract Automatic identification of the differences between two versions of a file is a common and basic task in several applications of mining code repositories. Introduction The diff utility calculates and displays the differences between two files, and is typically used to investigate the changes between two versions of the same file. In sum, the contributions of this work are: A systematic survey of studies that use diff ; An analysis of metrics collected from diff outputs produced by Myers and Histogram ; An analysis of Myers and Histogram outputs in identifying potential bug-introducing changes; A manual comparison between Myers and Histogram to investigate their output quality.
Source Code Differencing Existing differencing techniques use similarities in names and structure to match code elements at a particular granularity, such as text-based and abstract-syntax-tree-based AST. Diff Algorithms in Git Diff is an automatic comparison program used to find the disagreements between the older and the newer version of the same file in a storage including insertions, deletions, document renaming, document movements etc.
Myers Myers algorithm was developed by Myers A set of changes from an older file into a newer file. Full size image. How Myers identifies the diff.
How Histogram identifies the diff. Diff outputs produced by Myers and Histogram. Which diff algorithm is used? What kind of software artifact is analyzed, code or other documents? What are purposes of using diff? Where does the data source come from, OSS or industry?
Procedure Figure 5 illustrates an overview of our systematic mapping procedure, which is divided into an initial stage and an advanced stage. Design of the survey procedure. Table 1 List of surveyed SE journals and conferences Full size table. Number of collected papers from each source. Table 2 Inclusive and exclusive criteria Full size table. In the Before Commit area, select the actions you want PhpStorm to perform before committing the selected files to the local repository.
Reformat code : perform code formatting according to the Project Code Style settings. Rearrange code : rearrange your code according to the arrangement rules preferences. Optimize imports : remove redundant import statements. Analyze code : analyze modified files before committing them. Click Choose profile to select an inspection profile from which the IDE will run inspections.
Cleanup : batch-apply quick-fixes from code cleanup inspections. Click Choose profile to select a profile from which the IDE will run inspections. Update copyright : add or update a copyright notice according to the selected copyright profile - scope combination. In the After Commit area, you can select the server access configuration or a server group to use for uploading the committed files to a local or remote host, a mounted disk, or a directory.
See Deploy your application for details. Run tool : select the external tool that you want PhpStorm to launch after the selected changes have been committed. You can select a tool from the list, or click the Browse button and configure an external tool in the External Tools dialog that opens. To add a server configuration to the list, click and fill in the required fields in the Add Server dialog that opens. Always use selected server or group of servers : always upload files to the selected server or a server group.
You will be able to review the current commit as well as all other commits before they are pushed to the remote.
Sometimes when you make changes that are related to a specific task, you also apply other unrelated code modifications that affect the same file. Including all such changes into one commit may not be a good option, since it would be more difficult to review, revert , cherry-pick them, and so on. Select the checkbox next to each chunk of modified or newly added code that you want to commit, and leave other changes unselected:. Click Commit. Unselected changes will stay in the current changelist, so that you can commit them separately.
When you make a change to a file in the editor, click the corresponding change marker in the gutter. In the toolbar that appears, select the target changelist for the modified code chunk or create a new changelist :. You can also use git apply yourcoworkers. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.
Post as a guest Name. Email Required, but never shown. The Overflow Blog. Does ES6 make JavaScript frameworks obsolete? Podcast Do polyglots have an edge when it comes to mastering programming Featured on Meta. Now live: A fully responsive profile. Visit chat. Linked Related Hot Network Questions. Question feed. We then need to save the changes to a file which can be used as below. Drupal developers will want to apply Git patches frequently to update changes or to fix bugs.
Developers will create a patch file which can be used by other developers according to their need. To apply a git patch to the current branch use the following command. After applying a patch, you can see the modification in the status.
There might be a situation when the developer does not have write access to the project but still wants to suggest a change or fix a bug. The best way to go around that is to create a patch file. And because patches are additions to the code, testing and reviewing them is easy. This brief guide aims at helping Drupal developers get more familiar with git diff and git apply commands to be able to efficiently create and apply git patches as needed.
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