Show a better error when MODULE.bazel is missing
Previously, Bazel would error out with this message if it couldn't find
a MODULE.bazel (e.g. in the root module):
```
ERROR: unknown error during computation of main repo mapping
```
Closes
@@ -293,7 +293,7 @@ public class ModuleFileFunction implements SkyFunction {
try {
return FileSystemUtils.readWithKnownFileSize(path, path.getFileSize());
} catch (IOException e) {
- throw new ModuleFileFunctionException(e);
+ throw errorf(Code.MODULE_NOT_FOUND, "MODULE.bazel expected but not found at %s", path);
}
}
