prepare for breaking change in rules_nodejs

[alexeagle]

bazel-contrib/rules_nodejs#2125 is going to turn off the patching of the require() function by default. The reason is that it breaks compatibility with many node programs. However rules_sass depends on this, and also has at least conceptual sharing with google3 which uses the patched require() as well.

This change is a no-op for rules_nodejs 2.x where the default is true, but is required with rules_nodejs 3.0 where it will be false.

[nex3]

Can we avoid using the patched require()? We don't use Node at all in google3, so compatibility with that shouldn't be an issue.

[alexeagle]

Sure, you could do that. In code I own I'm mostly removing the need for patching it.

Generally the purpose of that patching in google3 was to make all programs inherently "runfiles-aware", that is, to provide the "unionfs" view of the filesystem as if the input tree and the output tree were overlaid. To remove the need for patching, you'll have to find places where you rely on this, and instead either

• explicitly use a Runfiles helper library to resolve paths, or
• make the program run exclusively using files in the input tree or exclusively using files in the output tree, with an appropriate current working directory.

[alexeagle]

I'm guessing your team doesn't have much time to spend on OSS so I'd suggest accepting this PR to preserve the status quo, then remove the need for the patches when you find time.

[nex3]

Can you file an issue with details on how to fix this going forward?

[alexeagle]

Thanks, I appreciate you merging it!

I'm not sure exactly where the fix belongs, mostly because the symptom I observed was that the sass compiler was just hanging. I probably could have connected a remote debugger to it so I could see the stack - but maybe it would have been hard to decipher since it's produced from the dart2js codegen.

You can repro just by flipping the flag

diff --git a/sass/BUILD b/sass/BUILD
index 567828a..d46ce02 100644
--- a/sass/BUILD
+++ b/sass/BUILD
@@ -20,6 +20,6 @@ nodejs_binary(
     # rules_nodejs 3.0 will flip the default for this flag which breaks rules_sass users
     templated_args = [
         "--nobazel_node_patches",
-        "--bazel_patch_module_resolver",
+        "--nobazel_patch_module_resolver",
     ],
 )

and then bazel test //...
Then I see these hanging:

    SassCompiler examples/hello_world/main-sourcemap-embed-sources.css; 9s worker
    SassCompiler examples/hello_world/main-no-sourcemap.css; 9s worker
    SassCompiler examples/imports_css/main.css; 9s worker
    SassCompiler examples/hello_world/main.css; 9s worker

[nex3]

What does the patch do specifically?

[alexeagle]

I think it's just this: https://github.com/bazelbuild/rules_nodejs/blob/stable/internal/node/require_patch.js