Including arbitrary files into cc_library rule in bazel

Update 2023-08-17: This is now a feature in bazel, see https://github.com/bazelbuild/bazel/issues/18766 for details. It is available starting bazel version 6.3.0. Use additional_compiler_input parameter to cc_library and other C++ rules to provide arbitrary files.

Adapted from the bazel-discuss mailing list.

I have a cc_library.

I want to set “-fsanitize-ignorelist” to point to a file in my repo.

E.g., I have:

foo.cc
BUILD.bazel
ignorelist.txt

and in BUILD.bazel:

cc_library(
  name = "foo",
  copts = ["-fsanitize-ignorelist=" <TODO what goes here?>],
  srcs = ["foo.cpp"],
)

I’ve tried setting ignorelist.txt as a data dependency, and then referring to it with $(location), but that doesn’t work. I get: clang: error: no such file or directory: ‘bazel-out/k8-fastbuild/ignorelist.txt’

I suspect the issue is that a data dependency is not available in the sandbox used for compilation.

As seen at: As can be seen from documentation for data = ...:

“…Files needed by this rule at runtime. "

So, indeed, the targets mentioned in data are not available in the sandbox at compile time.

What I did was to rename the file such that its name ends with “.h”. It can then be used in the hdrs, and $location will work, and it will be available during compilation.

Like so:

cc_library(
  name = "foo",
  copts = ["-fsanitize-ignorelist=\"$(location ignorelist.txt.h)\""],
  srcs = [ "foo.cpp" ],
  hdrs = [ "ignorelist.txt.h" ], # <-- the .h is the trick
)

As you can see, the original file ignorelist.txt is renamed to ignorelist.txt.h

This makes it possible to mention the file in the hdrs = [...] section. This works because hdrs do not get added into the produced command line for compiling the cc_library, but they do have to be present in the sandbox. As a result the behavior is as expected, and the the file’s extension .h allows it to appear in hdrs. A drawback is that your non-header file now has an extension .h but I found it not to be a very confusing point.

Trying this with srcs or deps instead would not work.

• Anything mentioned in srcs will end up in the compiler’s command line;
• Anything in deps needs to have a CcInfo provider (which our file doesn’t have), and also ends up in the compiler’s command line.

Happy to learn about a canonical way to do this. This feels like a hack, but on the other hand seems to be the only way to achieve the needed result. Perhaps it is worth reporting as a feature request?