README.md

Case 1

About the case

genrule is a generic Bazel rule that lets you execute shell commands.

The given example shows how to create a simple genrule that prints "Hello, World!" to a file.

It also shows how to consume a file produced by another target.

bazel build //workshop/case1:hello
cat bazel-bin/workshop/case1/hello.txt

bazel build //workshop/case1:hello_replaced
cat bazel-bin/workshop/case1/replaced.txt

Things to try out

Change one of the targets

Does all or only some of the targets rebuild? Try changing different targets, and run bazel build //workshop/case1:hello_replaced to see what happens.

Does the tests fail if you change the genrule to produce a file with a different content?

Try changing a file and run bazel test //workshop/case1:all

Additional things to try out

Query the build graph

One of Bazels strengths is the query language on the build graph.

To see dependencies for the hello_replaced target, run: bazel query 'deps(//workshop/case1:hello_replaced)'

To see which targets depend on the hello target, run: bazel query 'rdeps(//..., //workshop/case1:hello)'

Inspect the bazel output tree

In the root of the repository, you should notice 4 bazel- directories:

<workspace-name>/                         <== The workspace root
  bazel-bazel_workshop => <..._main>      <== Symlink to execRoot
  bazel-out => <...bazel-out>             <== Convenience symlink to outputPath
  bazel-bin => <...bin>                   <== Convenience symlink to most recent written bin dir $(BINDIR)
  bazel-testlogs => <...testlogs>         <== Convenience symlink to the test logs directory

Bazel uses the execRoot to store build outputs in the tree. When you run an action, the default is that Bazel creates a sandboxed environment for the action to run in. Then the output of the action is stored in the execRoot, according to the directory layout.

You can inspect the bazel-out directory to see the outputs of the build actions, including runfiles.

Read more about the Bazel output tree.