bazel-diff is a command line tool for Bazel projects that allows users to determine the exact affected set of impacted targets between two Git revisions. Using this set, users can test or build the exact modified set of targets.
bazel-diff offers several key advantages over rolling your own target diffing solution
bazel-diffis designed for very large Bazel projects. We use Java Protobuf'sparseDelimitedFrommethod alongside Bazel Query'sstreamed_protooutput option. These two together allow you to parse Gigabyte or larger protobuf messages. We have tested it with projects containing tens of thousands of targets.- We avoid usage of large command line query lists when interacting with Bazel, issue here. When you interact with Bazel with thousands of query parameters you can reach an upper maximum limit, seeing this error:
bash: /usr/local/bin/bazel: Argument list too long
bazel-diff is smart enough to prevent these errors
bazel-diffhas been tested with file renames, deletions, and modifications. Works onbzlfiles,WORKSPACEfiles,BUILDfiles and regular files
Track the feature request for target diffing in Bazel here
This approach was inspired by the following BazelConf talk by Benjamin Peterson.
There are simpler and faster ways to approximate the affected set of targets. However an incorrect solution can result in a system you can't trust, because tests could be broken at a commit where you didn't select to run them. Then you can't rely on green-to-red (or red-to-green) transitions and lose much of the value from your CI system as breakages can be discovered later on unrelated commits.
- Git
- Bazel 3.3.0 or higher
- Java 8 JDK or higher (Bazel requires this)
To start using bazel-diff immediately, simply clone down the repo and then run the example shell script:
git clone https://github.com/Tinder/bazel-diff.git
cd bazel-diff
./bazel-diff-example.sh WORKSPACE_PATH BAZEL_PATH START_GIT_REVISION END_GIT_REVISION
Here is a breakdown of those arguments:
WORKSPACE_PATH: Path to directory containing yourWORKSPACEfile in your Bazel project.- Note: Your project must use Git for
bazel-diffto work!
- Note: Your project must use Git for
BAZEL_PATH: Path to your Bazel executableSTART_GIT_REVISION: Starting Git Branch or SHA for your desired commit rangeEND_GIT_REVISION: Final Git Branch or SHA for your desired commit range
You can see the example shell script in action below:
Open bazel-diff-example.sh to see how this is implemented. This is purely an example use-case, but it is a great starting point to using bazel-diff.
bazel-diff works as follows
-
The
modified-filepathscommand is used to fetch the modified filepaths between two Git revisions, we write this list of modified 8000 filepaths to a file. -
The previous revision is checked out, then we run
generate-hashes. This gives us the hashmap representation for the entire Bazel graph, then we write this JSON to a file. We do not passmodified-filepathshere since it is the starting revision. -
Next we checkout the initial revision, then we run
generate-hasheswith the file output ofmodified-filepathsand write that JSON to a file. Now we have our final hashmap representation for the Bazel graph. -
We run
bazel-diffon the starting and final JSON hash filepaths to get our impacted set of targets. This impacted set of targets is written to a file. You can also pass the-tflag to only return tests
bazel-diff Command
Usage: bazel-diff [-hV] [-aq=<avoidQuery>] -b=<bazelPath>
[-co=<bazelCommandOptions>] [-fh=<finalHashesJSONPath>]
[-o=<outputPath>] [-sh=<startingHashesJSONPath>]
[-so=<bazelStartupOptions>] -w=<workspacePath> [COMMAND]
Writes to a file the impacted targets between two Bazel graph JSON files
-aq, --avoid-query=<avoidQuery>
A Bazel query string, any targets that pass this query will
be removed from the returned set of targets
-b, --bazelPath=<bazelPath>
Path to Bazel binary
-co, --bazelCommandOptions=<bazelCommandOptions>
Additional space separated Bazel command options used when
invoking Bazel
-fh, --finalHashes=<finalHashesJSONPath>
The path to the JSON file of target hashes for the final
revision. Run 'generate-hashes' to get this value.
-h, --help Show this help message and exit.
-o, --output=<outputPath>
Filepath to write the impacted Bazel targets to, newline
separated
-sh, --startingHashes=<startingHashesJSONPath>
The path to the JSON file of target hashes for the initial
revision. Run 'generate-hashes' to get this value.
-so, --bazelStartupOptions=<bazelStartupOptions>
Additional space separated Bazel client startup options used
when invoking Bazel
-V, --version Print version information and exit.
-w, --workspacePath=<workspacePath>
Path to Bazel workspace directory.
modified-filepaths Command
Usage: bazel-diff modified-filepaths [-hV] -b=<bazelPath>
[-co=<bazelCommandOptions>]
[-so=<bazelStartupOptions>]
-w=<workspacePath> <startingGitRevision>
<endingGitRevision> <outputPath>
Writes to the file the modified filepaths between two revisions.
<startingGitRevision> The starting Git revision, e.g. "HEAD^"
<endingGitRevision> The final Git revision, e.g. "HEAD"
<outputPath> Path that the list of modified files will be
written to
-b, --bazelPath=<bazelPath>
Path to Bazel binary
-co, --bazelCommandOptions=<bazelCommandOptions>
Additional space separated Bazel command options
used when invoking Bazel
-h, --help Show this help message and exit.
-so, --bazelStartupOptions=<bazelStartupOptions>
Additional space separated Bazel client startup
options used when invoking Bazel
-V, --version Print version information and exit.
-w, --workspacePath=<workspacePath>
Path to Bazel workspace directory.
generate-hashes Command
Usage: bazel-diff generate-hashes [-hV] -b=<bazelPath>
[-co=<bazelCommandOptions>]
[-m=<modifiedFilepaths>]
[-so=<bazelStartupOptions>]
-w=<workspacePath> <outputPath>
Writes to a file the SHA256 hashes for each Bazel Target in the provided
workspace.
<outputPath> The filepath to write the resulting JSON of dictionary
target => SHA-256 values
-b, --bazelPath=<bazelPath>
Path to Bazel binary
-co, --bazelCommandOptions=<bazelCommandOptions>
Additional space separated Bazel command options used when
invoking Bazel
-h, --help Show this help message and exit.
-m, --modifiedFilepaths=<modifiedFilepaths>
The path to a file containing the list of modified
filepaths in the workspace, you can use the
'modified-filepaths' command to get this list
-so, --bazelStartupOptions=<bazelStartupOptions>
Additional space separated Bazel client startup options
used when invoking Bazel
-V, --version Print version information and exit.
-w, --workspacePath=<workspacePath>
Path to Bazel workspace directory.
Add to your WORKSPACE file:
load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_jar")
http_jar(
name = "bazel_diff",
urls = [
"https://github.com/Tinder/bazel-diff/releases/download/2.1.4/bazel-diff_deploy.jar",
],
sha256 = "6c2a6e16db10db79837a74bfaa2a101461cd0330598fb1dc54778a86057eb131",
)and then in your root BUILD.bazel file:
load("@rules_java//java:defs.bzl", "java_binary")
java_binary(
name = "bazel-diff",
main_class = "com.bazel_diff.BazelDiff",
runtime_deps = ["@bazel_diff//jar"],
)now run the tool with
bazel run //:bazel-diff
Note, in releases prior to 2.0.0 the value for the
main_classattribute is justBazelDiff
curl -LO bazel-diff.jar GITHUB_RELEASE_JAR_URL
java -jar bazel-diff.jar -h
After cloning down the repo, you are good to go, Bazel will handle the rest
To run the project
bazel run :bazel-diff -- bazel-diff -h
To run bazel-diff with debug logging, run your commands with the verbose config like so:
bazel run :bazel-diff --config=verbose -- bazel-diff -h
bazel build //src/main/java/com/bazel_diff:bazel-diff_deploy.jar
java -jar bazel-bin/src/main/java/com/bazel_diff/bazel-diff_deploy.jar # This JAR can be run anywhere
Add the following to your WORKSPACE file to add the external repositories, replacing the RELEASE_ARCHIVE_URL with the archive url of the bazel-diff release you wish to depend on:
load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
http_archive(
name = "bazel_diff",
urls = [
"RELEASE_ARCHIVE_URL",
],
sha256 = "UPDATE_ME",
strip_prefix = "UPDATE_ME"
)
load("@bazel_diff//:repositories.bzl", "bazel_diff_dependencies")
bazel_diff_dependencies()
load("@rules_jvm_external//:defs.bzl", "maven_install")
load("@bazel_diff//:artifacts.bzl", "BAZEL_DIFF_MAVEN_ARTIFACTS")
maven_install(
name = "bazel_diff_maven",
artifacts = BAZEL_DIFF_MAVEN_ARTIFACTS,
repositories = [
"http://uk.maven.org/maven2",
"https://jcenter.bintray.com/",
],
)Now you can simply run bazel-diff from your project:
bazel run @bazel_diff//:bazel-diff -- bazel-diff -h
To run the tests simply run
bazel test //test/...
We use SemVer for versioning. For the versions available, see the tags on this repository.
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