Bazel：使genrule输出可用于其他规则

Question

I need the outputs of a genrule to be available next to another rule. (ie a py_binary ).

Suppose we have these files:

# root/gen/BUILD:
genrule(
  name = "gen",
  outs = ["a.txt", "a2.txt"],
  cmd = "cd $(RULEDIR) && echo salam > a.txt && echo hello > a2.txt",
)

# root/BUILD:
py_binary(
  name = "use",
  srcs = ["use.py"],
  data = ["gen:a.txt", "gen:a2.txt"],
)

# use.py:
f = open("a.txt", "r")
f2 = open("a2.txt", "r")
print(f.read())
print(f2.read())

At a glance:

project
├── root
│   ├── BUILD
│   ├── gen
│   │   └── BUILD  << This can generate required 'a.txt' and 'a2.txt' 
|   |                 files.
│   └── use.py  << This script needs to access a.txt file as './a.txt',
|                  but with 'bazel run root:use' it should access files
|                  like 'root/gen/a.txt'.
└── WORKSPACE

When I run bazel run :use , it doesn't find the file:

FileNotFoundError: [Errno 2] No such file or directory: 'a.txt'

It needs to have a.txt and a2.txt files nearby , but they are in bazel-bin/gen directory.

Answer 1

You could set output_to_bindir in your genrule so that the output files will be written into the bazel-bin directory instead of the bazel-genfiles directory and then reference them in use.py using their relative path in the workspace, eg:

# root/gen/BUILD
genrule(
  name = "gen",
  ...
  output_to_bindir = True,
)

# use.py:
f = open("root/gen/a.txt", "r")
f2 = open("root/gen/a2.txt", "r")
print(f.read())
print(f2.read())

This should allow the application to load the files when running through bazel run .

Answer 2

If you cannot modify the code in the py_binary, you could write a genrule that creates a link to the other file, eg:

genrule(
  name = "link_a.txt",
  srcs = ["//gen/a.txt"]
  outs = ["a.txt"],
  cmd = "ln $< $@"
)

genrule(
  name = "link_a2.txt",
  srcs = ["//gen/a2.txt"]
  outs = ["a2.txt"],
  cmd = "ln $< $@"
)

( $< is a shortcut for "the path to the input file if there is only one", and similarly $@ is a shortcut for "the path to the output file if there is only one")

It's also possible to wrap the genrule in a reusable macro, or do fancier things in Starlark, if needed.